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Sample records for highly enantioselective conjugate

  1. Highly enantioselective rhodium-catalyzed conjugate addition of arylboronic acids to enones at room temperature

    NARCIS (Netherlands)

    Martina, SLX; Minnaard, AJ; Hessen, B; Feringa, BL; Martina, Sébastien L.X.; Feringa, Bernard

    2005-01-01

    The rhodium-phosphoramidite-catalyzed asymmetric conjugate addition of arylboronic acids to enones proceeds at room temperature using [Rh(OH)(cod)](2) or [RhCl(cod)](2)/KOH as stable and readily available catalyst precursors. (c) 2005 Published by Elsevier Ltd.

  2. Palladium-catalyzed enantioselective conjugate addition of arylboronic acids

    NARCIS (Netherlands)

    Gini, F; Hessen, B; Minnaard, AJ

    2005-01-01

    The first asymmetric palladium-catalyzed conjugate addition of arylboronic acids to alpha,beta-unsaturated aldehydes, ketones, and esters is described. For cyclic substrates, excellent chemo-, regio-, and enantioselectivities are achieved when a Pd(O2CCF3)(2)/DuPHOS catalyst is applied.

  3. Conjugate addition–enantioselective protonation reactions

    Science.gov (United States)

    Phelan, James P

    2016-01-01

    Summary The addition of nucleophiles to electron-deficient alkenes represents one of the more general and commonly used strategies for the convergent assembly of more complex structures from simple precursors. In this review the addition of diverse protic and organometallic nucleophiles to electron-deficient alkenes followed by enantioselective protonation is summarized. Reactions are first categorized by the type of electron-deficient alkene and then are further classified according to whether catalysis is achieved with chiral Lewis acids, organocatalysts, or transition metals. PMID:27559372

  4. Conjugate addition–enantioselective protonation reactions

    Directory of Open Access Journals (Sweden)

    James P. Phelan

    2016-06-01

    Full Text Available The addition of nucleophiles to electron-deficient alkenes represents one of the more general and commonly used strategies for the convergent assembly of more complex structures from simple precursors. In this review the addition of diverse protic and organometallic nucleophiles to electron-deficient alkenes followed by enantioselective protonation is summarized. Reactions are first categorized by the type of electron-deficient alkene and then are further classified according to whether catalysis is achieved with chiral Lewis acids, organocatalysts, or transition metals.

  5. Pentanidium-catalyzed enantioselective phase-transfer conjugate addition reactions

    KAUST Repository

    Ma, Ting

    2011-03-09

    A new chiral entity, pentanidium, has been shown to be an excellent chiral phase-transfer catalyst. The enantioselective Michael addition reactions of tert-butyl glycinate-benzophenone Schiff base with various α,β- unsaturated acceptors provide adducts with high enantioselectivities. A successful gram-scale experiment at a low catalyst loading of 0.05 mol % indicates the potential for practical applications of this methodology. Phosphoglycine ester analogues can also be utilized as the Michael donor, affording enantioenriched α-aminophosphonic acid derivatives and phosphonic analogues of (S)-proline. © 2011 American Chemical Society.

  6. Catalytic enantioselective 1,6-conjugate additions of propargyl and allyl groups

    Science.gov (United States)

    Meng, Fanke; Li, Xiben; Torker, Sebastian; Shi, Ying; Shen, Xiao; Hoveyda, Amir H.

    2016-09-01

    Conjugate (or 1,4-) additions of carbanionic species to α,β-unsaturated carbonyl compounds are vital to research in organic and medicinal chemistry, and there are several chiral catalysts that facilitate the catalytic enantioselective additions of nucleophiles to enoates. Nonetheless, catalytic enantioselective 1,6-conjugate additions are uncommon, and ones that incorporate readily functionalizable moieties, such as propargyl or allyl groups, into acyclic α,β,γ,δ-doubly unsaturated acceptors are unknown. Chemical transformations that could generate a new bond at the C6 position of a dienoate are particularly desirable because the resulting products could then be subjected to further modifications. However, such reactions, especially when dienoates contain two equally substituted olefins, are scarce and are confined to reactions promoted by a phosphine-copper catalyst (with an alkyl Grignard reagent, dialkylzinc or trialkylaluminium compounds), a diene-iridium catalyst (with arylboroxines), or a bisphosphine-cobalt catalyst (with monosilyl-acetylenes). 1,6-Conjugate additions are otherwise limited to substrates where there is full substitution at the C4 position. It is unclear why certain catalysts favour bond formation at C6, and—although there are a small number of catalytic enantioselective conjugate allyl additions—related 1,6-additions and processes involving a propargyl unit are non-existent. Here we show that an easily accessible organocopper catalyst can promote 1,6-conjugate additions of propargyl and 2-boryl-substituted allyl groups to acyclic dienoates with high selectivity. A commercially available allenyl-boron compound or a monosubstituted allene may be used. Products can be obtained in up to 83 per cent yield, >98:2 diastereomeric ratio (for allyl additions) and 99:1 enantiomeric ratio. We elucidate the mechanistic details, including the origins of high site selectivity (1,6- versus 1,4-) and enantioselectivity as a function of the catalyst

  7. Bioinspired total synthesis of katsumadain A by organocatalytic enantioselective 1,4-conjugate addition

    Directory of Open Access Journals (Sweden)

    Yongguang Wang

    2013-08-01

    Full Text Available Katsumadain A, a naturally occurring influenza virus neuraminidase (NA inhibitor, was synthesized by using a bioinspired, organocatalytic enantioselective 1,4-conjugate addition of styryl-2-pyranone with cinnamaldehyde, followed by a tandem Horner–Wadsworth–Emmons/oxa Michael addition.

  8. Enantioselective Conjugate Addition of Diethylzinc to Chalcones Catalysed by Chiral Ni(II) Aminoalcohol Complexes

    NARCIS (Netherlands)

    Vries, André H.M. de; Jansen, Johan F.G.A.; Feringa, Bernard

    1994-01-01

    Conjugate addition of diethylzinc to chalcones is catalysed by complexes prepared in situ from Ni(acac)2 and cis-exo-N,N-dialkyl-3-aminoisoborneols or (+)-cis-endo-N,N-dimethyl-3-aminoborneol ((+)-DAB) (13b). The products are obtained with enantioselectivities up to 84 %. When scalemic (-)-cis-exo-N

  9. ENANTIOSELECTIVE CONJUGATE ADDITION OF DIETHYLZINC TO CHALCONES CATALYZED BY CHIRAL NI(II) AMINOALCOHOL COMPLEXES

    NARCIS (Netherlands)

    DEVRIES, AHM; JANSEN, JFGA; FERINGA, BL

    1994-01-01

    Conjugate addition of diethylzinc to chalcones is catalysed by complexes prepared in situ from Ni(acac)(2) and cis-exo-N,N-dialkyl-3-aminoisoborneols or (+)-cis-endo-N,N-dimethyl-3-aminoborneol ((+)- DAB) (13b). The products are obtained with enantioselectivities up to 84 %. When scalemic (-)-cis-ex

  10. Enantioselective conjugate addition of phenylboronic acid to enones catalysed by a chiral tropos/atropos rhodium complex at the coalescence temperature.

    Science.gov (United States)

    Monti, Chiara; Gennari, Cesare; Piarulli, Umberto

    2005-11-14

    A highly enantioselective rhodium-catalysed conjugate addition of phenylboronic acid to cyclic enones has been achieved using a dynamic library of chiral phosphorus ligands; the tropos/atropos nature of the ligands in the rhodium complex has been characterised via 31P-NMR.

  11. Heterogeneous versus homogeneous copper(II) catalysis in enantioselective conjugate-addition reactions of boron in water.

    Science.gov (United States)

    Kitanosono, Taku; Xu, Pengyu; Kobayashi, Shū

    2014-01-01

    We have developed Cu(II)-catalyzed enantioselective conjugate-addition reactions of boron to α,β-unsaturated carbonyl compounds and α,β,γ,δ-unsaturated carbonyl compounds in water. In contrast to the previously reported Cu(I) catalysis that required organic solvents, chiral Cu(II) catalysis was found to proceed efficiently in water. Three catalyst systems have been exploited: cat. 1: Cu(OH)2 with chiral ligand L1; cat. 2: Cu(OH)2 and acetic acid with ligand L1; and cat. 3: Cu(OAc)2 with ligand L1. Whereas cat. 1 is a heterogeneous system, cat. 2 and cat. 3 are homogeneous systems. We tested 27 α,β-unsaturated carbonyl compounds and an α,β-unsaturated nitrile compound, including acyclic and cyclic α,β-unsaturated ketones, acyclic and cyclic β,β-disubstituted enones, acyclic and cyclic α,β-unsaturated esters (including their β,β-disubstituted forms), and acyclic α,β-unsaturated amides (including their β,β-disubstituted forms). We found that cat. 2 and cat. 3 showed high yields and enantioselectivities for almost all substrates. Notably, no catalysts that can tolerate all of these substrates with high yields and high enantioselectivities have been reported for the conjugate addition of boron. Heterogeneous cat. 1 also gave high yields and enantioselectivities with some substrates and also gave the highest TOF (43,200 h(-1) ) for an asymmetric conjugate-addition reaction of boron. In addition, the catalyst systems were also applicable to the conjugate addition of boron to α,β,γ,δ-unsaturated carbonyl compounds, although such reactions have previously been very limited in the literature, even in organic solvents. 1,4-Addition products were obtained in high yields and enantioselectivities in the reactions of acyclic α,β,γ,δ-unsaturated carbonyl compounds with diboron 2 by using cat. 1, cat. 2, or cat. 3. On the other hand, in the reactions of cyclic α,β,γ,δ-unsaturated carbonyl compounds with compound 2, whereas 1,4-addition products

  12. Enantioselective Conjugate Addition of Grignard Reagents to Enones Catalyzed by Chiral Zinc(II) Complexes

    NARCIS (Netherlands)

    Jansen, Johan F.G.A.; Feringa, Bernard

    1990-01-01

    Various chiral zinc(II) complexes catalyze the asymmetric 1,4-addition of Grignard reagents to α,β-unsaturated ketones with high chemoselectivities (yields of 1,4-adducts, 83-99%), high regioselectivities (1,4/1,2 ratios up to 499) and modest enantioselectivities (ee up to 33%). A study of several f

  13. Enantioselective conjugate additions of α-amino radicals via cooperative photoredox and Lewis acid catalysis.

    Science.gov (United States)

    Ruiz Espelt, Laura; McPherson, Iain S; Wiensch, Eric M; Yoon, Tehshik P

    2015-02-25

    We report the highly enantioselective addition of photogenerated α-amino radicals to Michael acceptors. This method features a dual-catalyst protocol that combines transition metal photoredox catalysis with chiral Lewis acid catalysis. The combination of these two powerful modes of catalysis provides an effective, general strategy to generate and control the reactivity of photogenerated reactive intermediates.

  14. DNA-Accelerated Copper Catalysis of Friedel-Crafts Conjugate Addition/Enantioselective Protonation Reactions in Water

    NARCIS (Netherlands)

    García-Fernández, Almudena; Megens, Rik P.; Villarino, Lara; Roelfes, Gerard

    2016-01-01

    DNA-induced rate acceleration has been identified as one of the key elements for the success of the DNA-based catalysis concept. Here we report on a novel DNA-based catalytic Friedel-Crafts conjugate addition/enantioselective protonation reaction in water, which represents the first example of a

  15. Heterogeneous and homogeneous chiral Cu(II) catalysis in water: enantioselective boron conjugate additions to dienones and dienoesters.

    Science.gov (United States)

    Kitanosono, Taku; Xu, Pengyu; Kobayashi, Shū

    2013-09-25

    It was proved that a judicious choice of counteranion played a prominent role in Cu(II) catalysis for enantioselective boron conjugate additions in water; the use of Cu(OH)2 renders heterogeneous catalysis, whereas Cu(OAc)2 renders homogeneous catalysis; cyclic dienones underwent a remarkable switch of regioselectivity between 1,4- and 1,6-modes of the additions through these catalyses.

  16. Rh-catalyzed enantioselective conjugate addition of arylboronic acids with a dynamic library of chiral tropos phosphorus ligands.

    Science.gov (United States)

    Monti, Chiara; Gennari, Cesare; Piarulli, Umberto

    2007-01-01

    A library of 19 chiral tropos phosphorus ligands, based on a free-to-rotate (tropos) biphenol unit and a chiral P-bonded alcohol (11 phosphites, 1-P(O)(2)O to 11-P(O)(2)O) or secondary amine (8 phosphoramidites, 12-P(O)(2)N to 19-P(O)(2)N), were screened, individually and in combinations of two, in the rhodium-catalyzed asymmetric conjugate addition of arylboronic acids to enones and enoates. High enantioselectivities (up to 99 % ee) and excellent yields were obtained in the addition to either cyclic or acyclic substrates. The flexible biphenolic P ligands outperformed the analogous rigid binaphtholic P ligands. Variable-temperature (31)P NMR studies revealed that the biphenolic ligands are tropos even at low temperature. Only below 190 K was a coalescence observed; upon further cooling, two atropisomers were detected. The Rh homocomplexes ([Rh(L(a))(2)](+)) were also studied: in general, a single doublet (P-Rh coupling) was observed in the case of the biphenolic phosphite ligands, over the temperature range 380-230 K, demonstrating their tropos nature in the rhodium complexes even at low temperatures. On the other hand, the phosphoramidites showed different behaviors depending on the structure of the ligand and on the nature of the rhodium source. The spectrum at 230 K of the mixture of [Rh(acac)(eth)(2)] (eth=C(2)H(4)) with phosphite 6-P(O)(2)O and phosphoramidite 19-P(O)(2)N (the most enantioselective ligand combination in the conjugate addition reaction) revealed the presence of four homocomplexes (total approximately 40 %: [Rh{6-P(O)(2)O}(2)], [Rh{(aR)-19-P(O)(2)N}(2)], [Rh{(aS)-19-P(O)(2)N}(2)], [Rh{(aR)-19-P(O)(2)N}{(aS)-19-P(O)(2)N}]) and one heterocomplex, [Rh{6-P(O)(2)O}{(aR)-19-P(O)(2)N}] (approximately 60 %) In the heterocomplex, the biphenol-derived phosphite is free to rotate (tropos) while the biphenol-derived phosphoramidite shows a temperature-dependent tropos/atropos behavior (coalescence temperature=310 K).

  17. NHC-Catalyzed/Titanium(IV);#8722;Mediated Highly Diastereo- and Enantioselective Dimerization of Enals

    Energy Technology Data Exchange (ETDEWEB)

    Cohen, Daniel T.; Cardinal-David, Benoit; Roberts, John M.; Sarjeant, Amy A.; Scheidt, Karl A. (NWU)

    2012-05-09

    An NHC-catalyzed, diastereo- and enantioselective dimerization of enals has been developed. The use of Ti(Oi-Pr){sub 4} is a key element for the reactivity and selectivity of this process. The cyclopentenes are obtained with high levels of diastereo- and enantioselectivity and their synthetic utility is demonstrated by functionalization of the product alkene.

  18. Highly E-Selective and Enantioselective Michael Addition to Electron-Deficient Internal Alkynes Under Chiral Iminophosphorane Catalysis.

    Science.gov (United States)

    Uraguchi, Daisuke; Yamada, Kohei; Ooi, Takashi

    2015-08-17

    A highly E-selective and enantioselective conjugate addition of 2-benzyloxythiazol-5(4H)-ones to β-substituted alkynyl N-acyl pyrazoles is achieved under the catalysis of a P-spiro chiral iminophosphorane. Simultaneous control of the newly generated central chirality and olefin geometry is possible with a wide array of the alkynyl Michael acceptors possessing different aromatic and aliphatic β-substituents, as well as the various α-amino acid-derived thiazolone nucleophiles. This protocol provides access to structurally diverse, optically active α-amino acids bearing a geometrically defined trisubstituted olefinic component at the α-position.

  19. Highly enantioselective [4 + 2] cyclization of chloroaldehydes and 1-azadienes catalyzed by N-heterocyclic carbenes.

    Science.gov (United States)

    Jian, Teng-Yue; Sun, Li-Hui; Ye, Song

    2012-11-14

    Highly functionalized dihydropyridinones were synthesized via the N-heterocyclic carbene-catalyzed enantioselective [4 + 2] annulation of α-chloroaldehydes and azadienes. Hydrogenation of the resulted dihydropyridinones afforded the corresponding piperidinones with high enantiopurity.

  20. Synthesis of Metal-Organic Zeolites with Homochirality and High Porosity for Enantioselective Separation.

    Science.gov (United States)

    Xu, Zhong-Xuan; Liu, Liyang; Zhang, Jian

    2016-07-01

    Using lactic acid derivatives as chiral ligands, a pair of unprecedented homochiral metal-organic zeolites have been synthesized that feature zeotype CAN topology and have high porosity for enantioselective separation of racemates.

  1. Highly enantioselective synthesis of non-natural aliphatic α-amino acids via asymmetric hydrogenation.

    Science.gov (United States)

    Ji, Jianjian; Chen, Caiyou; Cai, Jiayu; Wang, Xinrui; Zhang, Kai; Shi, Liyang; Lv, Hui; Zhang, Xumu

    2015-07-28

    By employing a rhodium-Duanphos complex as the catalyst, β-alkyl (Z)-N-acetyldehydroamino esters were smoothly hydrogenated in a highly efficient and enantioselective way. Excellent enantioselectivities together with excellent yields were achieved for a series of substrates. An efficient approach for the synthesis of the intermediate of the orally administered anti-diabetic drugs Alogliptin and Linagliptin in the DPP-4 inhibitor class was also developed.

  2. Metal-conjugated affinity labels: A new concept to create enantioselective artificial metalloenzymes

    KAUST Repository

    Reiner, Thomas

    2013-02-20

    How to train a protein: Metal-conjugated affinity labels were used to selectively position catalytically active metal centers in the binding pocket of proteases. The resulting artificial metalloenzymes achieve up to 82% e.r. in the hydrogenation of ketones. The modular setup enables a rapid generation of artificial metalloenzyme libraries, which can be adapted to a broad range of catalytic conditions. 2013 The Authors.

  3. Highly enantio- and diastereoselective one-pot reactions in aqueous media : Combined asymmetric Rh-catalyzed conjugate addition/metal-mediated allylation

    NARCIS (Netherlands)

    Kallstrom, Sara; Jagt, Richard B. C.; Sillanpaa, Reijo; Feringa, Ben L.; Minnaard, Adriaan J.; Leino, Reko; Källström, Sara; Sillanpää, Reijo

    2006-01-01

    1,3-Disubstituted, enantiopure cyclohexanols have been prepared in very high diastereoselectivities and good yields by a concise one-pot method combining the enantioselective rhodium-catalyzed conjugate addition of arylboronic acids with indium-mediated allylation into a highly efficient one-pot rea

  4. Diastereo- and enantioselective three-component coupling approach to highly substituted pyrrolidines.

    Science.gov (United States)

    Chaulagain, Mani Raj; Felten, Albert E; Gilbert, Kevin; Aron, Zachary D

    2013-09-20

    The enantioselective synthesis of substituted pyrrolidines through a mild Lewis-acid catalyzed three-component coupling reaction between picolinaldehyde, amino acids, and activated olefins is reported. The reaction uses low catalyst loadings of commercially available chiral diamines and copper triflate proposed to self-assemble in conjunction with the chelating aldehydes, 4-substituted-2-picolinaldehydes or 4-methylthiazole-2-carboxaldehyde, to generate a catalyst complex. A model is provided to explain how this complex directs enantioselectivity. This work represents a significant advance in the ease, scope, and cost of producing highly substituted, enantioenriched pyrrolidines.

  5. Using heteroaryl-lithium reagents as hydroxycarbonyl anion equivalents in conjugate addition reactions with (S,S)-(+)-pseudoephedrine as chiral auxiliary; enantioselective synthesis of 3-substituted pyrrolidines.

    Science.gov (United States)

    Alonso, Beatriz; Ocejo, Marta; Carrillo, Luisa; Vicario, Jose L; Reyes, Efraim; Uria, Uxue

    2013-01-18

    We have developed an efficient protocol for carrying out the stereocontrolled formal conjugate addition of hydroxycarbonyl anion equivalents to α,β-unsaturated carboxylic acid derivatives using (S,S)-(+)-pseudoephedrine as chiral auxiliary, making use of the synthetic equivalence between the heteroaryl moieties and the carboxylate group. This protocol has been applied as key step in the enantioselective synthesis of 3-substituted pyrrolidines in which, after removing the chiral auxiliary, the heteroaryl moiety is converted into a carboxylate group followed by reduction and double nucleophilic displacement. Alternatively, the access to the same type of heterocyclic scaffold but with opposite absolute configuration has also been accomplished by making use of the regio- and diastereoselective conjugate addition of organolithium reagents to α,β,γ,δ-unsaturated amides derived from the same chiral auxiliary followed by chiral auxiliary removal, ozonolysis, and reductive amination/intramolecular nucleophilic displacement sequence.

  6. Highly enantioselective proton-initiated polycyclization of polyenes.

    Science.gov (United States)

    Surendra, Karavadhi; Corey, E J

    2012-07-25

    This report describes the synthesis of a range of chiral polycyclic molecules (tricyclic to pentacyclic) from achiral polyene precursors by enantioselective proton-initiated polycyclization promoted by the 1:1 complex of o,o'-dichloro-BINOL and SbCl(5). Excellent yields (ca. 90% per ring formed) and enantioselectivety (20:1 to 50:1) were obtained. The process is practical as well as efficient, because the chiral ligand is both readily prepared from R,R- or S,S-BINOL and easily recovered from the reaction mixture by extraction.

  7. Novel chiral thioureas for highly enantioselective Michael reactions of malonates to nitroalkenes

    Institute of Scientific and Technical Information of China (English)

    Li Jun Yan; Quan Zhong Liu; Xue Lian Wang

    2009-01-01

    Highly efficient Michael addition reactions of malonates to nitroalkenes catalyzed by novel chiral thioureas derived from optically pure BINOL and amino acids are reported. Various trans-nitroalkenes reacted with malonates affording the desired products in up to 95% yield with excellent enantioselectivities (up to 97% ee).

  8. Diversity-Oriented Enantioselective Synthesis of Highly Functionalized Cyclic and Bicyclic Alcohols

    NARCIS (Netherlands)

    Mao, Bin; Fananas Mastral, Martin; Lutz, Martin; Feringa, Ben L.

    2013-01-01

    The copper-catalyzed hetero-allylic asymmetric alkylation (h-AAA) of functionalized Grignard reagents that contain alkene or alkyne moieties has been achieved with excellent regio-and enantioselectivity. The corresponding alkylation products were further transformed into a variety of highly function

  9. The first chiral diene-based metal-organic frameworks for highly enantioselective carbon-carbon bond formation reactions

    Energy Technology Data Exchange (ETDEWEB)

    Sawano, Takahiro; Ji, Pengfei; McIsaac, Alexandra R.; Lin, Zekai; Abney, Carter W.; Lin, Wenbin [UC

    2016-02-01

    We have designed the first chiral diene-based metal–organic framework (MOF), E₂-MOF, and postsynthetically metalated E₂-MOF with Rh(I) complexes to afford highly active and enantioselective single-site solid catalysts for C–C bond formation reactions. Treatment of E₂-MOF with [RhCl(C₂H₄)₂]₂ led to a highly enantioselective catalyst for 1,4-additions of arylboronic acids to α,β-unsaturated ketones, whereas treatment of E₂-MOF with Rh(acac)(C₂H₄)₂ afforded a highly efficient catalyst for the asymmetric 1,2-additions of arylboronic acids to aldimines. Interestingly, E₂-MOF·Rh(acac) showed higher activity and enantioselectivity than the homogeneous control catalyst, likely due to the formation of a true single-site catalyst in the MOF. E₂-MOF·Rh(acac) was also successfully recycled and reused at least seven times without loss of yield and enantioselectivity.

  10. Investigation of retention and chiral recognition mechanism using quantitative structure-enantioselectivity retention relationship in high performance liquid chromatography

    Institute of Scientific and Technical Information of China (English)

    CHEN, Hui; LU, Xian-Yu; GAO, Ru-Yu; HUANG, Jun-Min; YANG, Hua-Zheng; WANG, Qin-Sun

    2000-01-01

    The enantiomers of a series of fourteen O-ethyl O-(substituted) phenyl N-isopropyl-phosphoroamidothioates have been separated by high performance liquid chromatography (HPLC) on the Pirkde-type chiral stationary phase. Seven molecular descriptors were lculated and four .significant descriptors were chosen to correlate against the experimental Ink′ values in order to form thequantitative structure-enantioselectivity retention relationships (QSERRs). Through the QSERRs, the retention and enantioselectivity meehanism were examined.

  11. L-prolinol as a highly enantioselective catalyst for Michael addition of cyclohexanone to nitroolefins.

    Science.gov (United States)

    Chua, Pei Juan; Tan, Bin; Zeng, Xiaofei; Zhong, Guofu

    2009-07-15

    Though many chiral amines such as l-proline and its derivatives have proven to be versatile catalysts in many reactions, L-prolinol was seldom used as organocatalyst for reactions. Herein, we report the first L-prolinol catalyzed asymmetric Michael addition of cyclohexanone to nitroolefins in the presence of benzoic acid to afford Michael adducts with high diastereoselectivities (87:13->99:1) and enantioselectivities (82-96%).

  12. Highly enantioselective sec-alkyl sulfatase activity of Sulfolobus acidocaldarius DSM 639.

    Science.gov (United States)

    Wallner, Sabine R; Nestl, Bettina M; Faber, Kurt

    2004-12-23

    [reaction: see text] rac-sec-Alkyl sulfate esters 1a-4a were resolved in high enantioselectivities with E-values up to >200 using whole cells of aerobically grown Sulfolobus acidocaldarius DSM 639. The stereochemical course of this biohydrolysis was shown to proceed with strict inversion of configuration; thus, the preferred (R)-enantiomers were converted into the corresponding (S)-sec-alcohols to furnish a homochiral product mixture.

  13. Phase conjugation of high energy lasers.

    Energy Technology Data Exchange (ETDEWEB)

    Bliss, David E; Valley, Michael T.; Atherton, Briggs W.; Bigman, Verle Howard; Boye, Lydia Ann; Broyles, Robin Scott; Kimmel, Mark W.; Law, Ryan J.; Yoder, James R.

    2013-01-01

    In this report we explore claims that phase conjugation of high energy lasers by stimulated Brillouin scattering (SBS) can compensate optical aberrations associated with severely distorted laser amplifier media and aberrations induced by the atmosphere. The SBS media tested was a gas cell pressurized up to 300 psi with SF6 or Xe or both. The laser was a 10 Hz, 3J, Q-switched Nd:YAG with 25 ns wide pulses. Atmospheric aberrations were created with space heaters, helium jets and phase plates designed with a Kolmogorov turbulence spectrum characterized by a Fried parameter, ro , ranging from 0.6 6.0 mm. Phase conjugate tests in the laboratory were conducted without amplification. For the strongest aberrations, D/ro ~ 20, created by combining the space heaters with the phase plate, the Strehl ratio was degraded by a factor of ~50. Phase conjugation in SF6 restored the peak focusable intensity to about 30% of the original laser. Phase conjugate tests at the outdoor laser range were conducted with laser amplifiers providing gain in combination with the SBS cell. A large 600,000 BTU kerosene space heater was used to create turbulence along the beam path. An atmospheric structure factor of Cn2 = 5x10-13 m2/3 caused the illumination beam to expand to a diameter 250mm and overfill the receiver. The phase conjugate amplified return could successfully be targeted back onto glints 5mm in diameter. Use of a lenslet arrays to lower the peak focusable intensity in the SBS cell failed to produce a useful phase conjugate beam; The Strehl ratio was degraded with multiple random lobes instead of a single focus. I will review literature results which show how multiple beams can be coherently combined by SBS when a confocal reflecting geometry is used to focus the laser in the SBS cell.

  14. Zirconium(IV)- and hafnium(IV)-catalyzed highly enantioselective epoxidation of homoallylic and bishomoallylic alcohols.

    Science.gov (United States)

    Li, Zhi; Yamamoto, Hisashi

    2010-06-16

    In this report, zirconium(IV)- and hafnium(IV)-bishydroxamic acid complexes were utilized in the highly enantioselective epoxidation of homoallylic alcohols and bishomoallylic alcohols, which used to be quite difficult substrates for other types of asymmetric epoxidation reactions. The performance of the catalyst was improved by adding polar additive and molecular sieves. For homoallylic alcohols, the reaction could provide epoxy alcohols in up to 83% yield and up to 98% ee, while, for bishomoallylic alcohols, up to 79% yield and 99% ee of epoxy alcohols rather than cyclized tetrahydrofuran compounds could be obtained in most cases.

  15. Zirconium(IV) and Hafnium(IV)-Catalyzed Highly Enantioselective Epoxidation of Homoallylic and Bishomoallylic Alcohols

    Science.gov (United States)

    Li, Zhi; Yamamoto, Hisashi

    2010-01-01

    In this report, zirconium(IV) and hafnium(IV)-bishydroxamic acid complexes were utilized in the highly enantioselective epoxidation of homoallylic alcohols and bishomoallylic alcohols, which used to be quite difficult substrates for other types of asymmetric epoxidation reactions. The performance of the catalyst was improved by adding polar additive and molecular sieves. For homoallylic alcohols, the reaction could provide epoxy alcohols in up to 81% yield and up to 98% ee, while for bishomoallylic alcohols, up to 75% yield and 99% ee of epoxy alcohols rather than cyclize compounds could be obtained in most cases. PMID:20481541

  16. Catalyst self-adaptation in conjugate addition to nitroalkenes and nitroacrylates: instant chirality control in diphenylmethane-based phosphoramidite ligands.

    Science.gov (United States)

    Wakabayashi, Kazuki; Aikawa, Kohsuke; Kawauchi, Susumu; Mikami, Koichi

    2008-04-16

    The tropos diphenylmethane-based phosphoramidite ligand (A) provides high catalytic activity and enantioselectivity in the Cu catalysis of conjugate addition to nitroalkenes and nitroacrylate, by virtue of instant chirality control in A.

  17. Enantioselective Conjugate Addition of Diethylzinc to Chalcone Catalyzed by Ni(acac)2 and Chiralβ-Amino Alcohols

    Institute of Scientific and Technical Information of China (English)

    EnantioselectiveConjugateAdditionofDiethylzinctoChalconeCatalyzedbyNi(acac)2andChiral/I-AminoAlcohols; 王恒山; 达朝山; 辛卓群; 粟武; 肖亦男; 刘大学; 王锐

    2003-01-01

    Enantioselectivge conjugate addition of diethyzinc to chalcone was carried out in the presenee of Ni (acac)2 complexed with five pyrrolidfumyimethanois derived from L-proline. (S)-N-Benzyl-2-(l-hydroxy.l-methylethyl) pyrrolidlne was found to be the best ngnd in asymmetric conjugate addition among the five ligands. The products were obtained with up to 70% ee.The configuration of the product was determined jointly by the substituents on the carbon of the hydroxy group and the nitrogen atom.

  18. Synergistic chiral iminium and palladium catalysis: Highly regio- and enantioselective [3 + 2] annulation reaction of 2-vinylcyclopropanes with enals

    Science.gov (United States)

    Zhu, Haipan; Du, Peile; Li, Jianjun; Liao, Ziyang; Liu, Guohua

    2016-01-01

    Summary A cooperative catalytic strategy of chiral iminium catalysis by regioselective activation of the C=C bond in enals and a transition metal promoting to open the 2-vinylcyclopropanes for highly regio- and enantioselective [3 + 2] cycloaddition reaction of 2-vinylcyclopropanes with α,β-unsaturated aldehydes has been developed. PMID:27559383

  19. Highly enantioselective asymmetric autocatalysis using chiral ruthenium complex-ion-exchanged synthetic hectorite as a chiral initiator.

    Science.gov (United States)

    Kawasaki, Tsuneomi; Omine, Toshiki; Suzuki, Kenta; Sato, Hisako; Yamagishi, Akihiko; Soai, Kenso

    2009-03-21

    The synthetic hectorite containing intercalated chiral Delta- and Lambda-tris(1,10-phenanthroline)ruthenium(II) ions acts as a heterogeneous chiral catalyst in the enantioselective addition of diisopropylzinc to pyrimidine-5-carbaldehyde to afford, in combination with asymmetric autocatalytic amplification of enantiomeric excess, 5-pyrimidyl alkanol with high enantiomeric excess.

  20. A highly enantioselective phase-transfer catalyzed epoxidation of enones with a mild oxidant, trichloroisocyanuric acid.

    Science.gov (United States)

    Ye, Jinxing; Wang, Yongcan; Liu, Renhua; Zhang, Guofu; Zhang, Qing; Chen, Jiping; Liang, Xinmiao

    2003-11-07

    The enantioselective epoxidation can be carried out using trichloroisocyanuric acid (TCCA) as oxidant in the presence of chiral quaternary ammonium salt as a phase-transfer catalyst; treatment of chalcone derivatives with TCCA under mild conditions afforded the corresponding epoxy ketones in good yields with moderate to excellent enantioselectivities of up to 96%.

  1. Robust, Chiral, and Porous BINAP-Based Metal–Organic Frameworks for Highly Enantioselective Cyclization Reactions

    Energy Technology Data Exchange (ETDEWEB)

    Sawano, Takahiro; Thacker, Nathan C.; Lin, Zekai; McIsaac, Alexandra R.; Lin, Wenbin (UC)

    2016-05-06

    We report here the design of BINAP-based metal–organic frameworks and their postsynthetic metalation with Rh complexes to afford highly active and enantioselective single-site solid catalysts for the asymmetric cyclization reactions of 1,6-enynes. Robust, chiral, and porous Zr-MOFs of UiO topology, BINAP-MOF (I) or BINAP-dMOF (II), were prepared using purely BINAP-derived dicarboxylate linkers or by mixing BINAP-derived linkers with unfunctionalized dicarboxylate linkers, respectively. Upon metalation with Rh(nbd)2BF4 and [Rh(nbd)Cl]2/AgSbF6, the MOF precatalysts I·Rh(BF4) and I·Rh(SbF6) efficiently catalyzed highly enantioselective (up to 99% ee) reductive cyclization and Alder-ene cycloisomerization of 1,6-enynes, respectively. I·Rh catalysts afforded cyclization products at comparable enantiomeric excesses (ee’s) and 4–7 times higher catalytic activity than the homogeneous controls, likely a result of catalytic site isolation in the MOF which prevents bimolecular catalyst deactivation pathways. However, I·Rh is inactive in the more sterically encumbered Pauson–Khand reactions between 1,6-enynes and carbon monoxide. In contrast, with a more open structure, Rh-functionalized BINAP-dMOF, II·Rh, effectively catalyzed Pauson–Khand cyclization reactions between 1,6-enynes and carbon monoxide at 10 times higher activity than the homogeneous control. II·Rh was readily recovered and used three times in Pauson–Khand cyclization reactions without deterioration of yields or ee’s. Our work has expanded the scope of MOF-catalyzed asymmetric reactions and showed that the mixed linker strategy can effectively enlarge the open space around the catalytic active site to accommodate highly sterically demanding polycyclic metallocycle transition states/intermediates in asymmetric intramolecular cyclization reactions.

  2. Exogenous-Base-Free Palladacycle-Catalyzed Highly Enantioselective Arylation of Imines with Arylboroxines.

    Science.gov (United States)

    Schrapel, Carmen; Peters, René

    2015-08-24

    Enantiomerically pure benzylic amines are important for the development of new drugs. A readily accessible planar-chiral ferrocene-derived palladacycle is shown to be a highly efficient catalyst for the formation of N-substituted benzylic stereocenters; this catalyst accelerates the 1,2-addition of arylboroxines to aromatic and aliphatic imines with exceptional levels of enantioselectivity. Using aldimines an exogenous base was not necessary for the activation of the boroxines, when acetate was used as an anionic ligand. Common problems such as aryl-aryl homocouplings and imine hydrolysis were fully overcome, the latter even in the absence of molecular sieves. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  3. Correction: A highly enantioselective Biginelli reaction using self-assembled methanoproline-thiourea organocatalysts: asymmetric synthesis of 6-isopropyl-3,4-dihydropyrimidines.

    Science.gov (United States)

    Hang, Zhijun; Zhu, Jun; Lian, Xiang; Xu, Peng; Yu, Han; Han, Sheng

    2016-02-07

    Correction for 'A highly enantioselective Biginelli reaction using self-assembled methanoproline-thiourea organocatalysts: asymmetric synthesis of 6-isopropyl-3,4-dihydropyrimidines' by Zhijun Hang et al., Chem. Commun., 2016, 52, 80-83.

  4. Polymer enzyme conjugates as chiral ligands for sharpless dihydroxylation of alkenes in organic solvents.

    Science.gov (United States)

    Konieczny, Stefan; Leurs, Melanie; Tiller, Joerg C

    2015-01-02

    Conjugates of enzymes and poly(2-methyloxazoline) were used as organosoluble amphiphilic polymer nanocontainers for dissolving osmate, thereby converting the enzymes into organosoluble artificial metalloenzymes. These were shown to catalyze the dihydroxylation of different alkenes with high enantioselectivity. The highest selectivities, found for osmate complexed with laccase polymer-enzyme conjugates (PECs), even exceed those of classical Sharpless catalysts.

  5. Highly enantioselective transfer hydrogenation of ketones with chiral (NH)2 P2 macrocyclic iron(II) complexes.

    Science.gov (United States)

    Bigler, Raphael; Huber, Raffael; Mezzetti, Antonio

    2015-04-20

    Bis(isonitrile) iron(II) complexes bearing a C2 -symmetric diamino (NH)2 P2 macrocyclic ligand efficiently catalyze the hydrogenation of polar bonds of a broad scope of substrates (ketones, enones, and imines) in high yield (up to 99.5 %), excellent enantioselectivity (up to 99 % ee), and with low catalyst loading (generally 0.1 mol %). The catalyst can be easily tuned by modifying the substituents of the isonitrile ligand.

  6. Enantioselective and diastereoselective separation of synthetic pyrethroid insecticides on a novel chiral stationary phase by high-performance liquid chromatography.

    Science.gov (United States)

    Tan, Xulin; Hou, Shicong; Wang, Min

    2007-07-01

    A novel chiral packing material for high-performance liquid chromatography (HPLC) was prepared by connecting (R)-1-phenyl-2-(4-methylphenyl) ethylamine (PTE) amide derivative of (S)-isoleucine to aminopropyl silica gel through 2-amino-3,5-dinitro-1-carboxamido-benzene unit. This chiral stationary phase was applied to the enantioselective and diastereoselective separation of five pyrethroid insecticides by HPLC under normal phase condition. To achieve satisfactory baseline separation an optimization of the variables of mobile phase composition was required. The two enantiomers of fenpropathrin and four stereoisomers of fenvalerate were baseline separated using hexane-1,2-dichloroethane-2-propanol as mobile phase. The results show that the enantioselectivity of CSP is better than Pirkle type 1-A column for these compounds. Only partial separations for the cypermethrin and cyfluthrin stereoisomers were observed. Seven peaks and eight peaks were observed for cypermethrin and cyfluthrin, respectively. The elution orders were assigned by using different stereoisomer-enriched products.

  7. Enantioselective high-performance liquid chromatographic determination of nicardipine in human plasma.

    Science.gov (United States)

    Uno, T; Ohkubo, T; Sugawara, K

    1997-09-26

    A sensitive method for the enantioselective high-performance liquid chromatography (HPLC) determination of nicardipine in human plasma is described. (+)-Nicardipine, (-)-nicardipine and (+)-barnidipine as an internal standard are detected by an ultraviolet detector at 254 nm. Racemic nicardipine in human plasma was extracted by a rapid and simple procedure based on C18 bonded-phase extraction. The extraction samples were purified and concentrated on a pre-column using a C1 stationary phase and the enantiomers of nicardipine are quantitatively separated by HPLC on a Sumichiral OA-4500 column, containing a chemically modified Pirkle-type stationary phase. Determination of (+)- and (-)-nicardipine was possible in a concentration range of 5-100 ng ml(-1) and the limit of detection in plasma was 2.5 ng ml(-1). The recoveries of (+)- and (-)-nicardipine added to plasma were 91.4-98.4% and 93.3-96.7%, respectively, with coefficients of variation of less than 9.0 and 9.4% respectively. The method was applied to low level monitoring of (+)- and (-)-nicardipine in plasma from healthy volunteers.

  8. Catalytic Enantioselective Olefin Metathesis in Natural Product Synthesis. Chiral Metal-Based Complexes that Deliver High Enantioselectivity and More

    Science.gov (United States)

    Malcolmson, Steven J.; Meek, Simon J.; Zhugralin, Adil R.

    2012-01-01

    Chiral olefin metathesis catalysts enable chemists to access enantiomerically enriched small molecules with high efficiency; synthesis schemes involving such complexes can be substantially more concise than those that would involve enantiomerically pure substrates and achiral Mo alkylidenes or Ru-based carbenes. The scope of research towards design and development of chiral catalysts is not limited to discovery of complexes that are merely the chiral versions of the related achiral variants. A chiral olefin metathesis catalyst, in addition to furnishing products of high enantiomeric purity, can offer levels of efficiency, product selectivity and/or olefin stereoselectivity that are unavailable through the achiral variants. Such positive attributes of chiral catalysts (whether utilized in racemic or enantiomerically enriched form) should be considered as general, applicable to other classes of transformations. PMID:19967680

  9. Development, optimization and validation of a sub-minute analytical enantioselective high performance liquid chromatographic separation for a folic acid precursor in normal phase mode.

    Science.gov (United States)

    Frühauf, Doris; Juza, Markus

    2012-12-21

    A sub-minute enantioselective normal phase high performance liquid chromatographic (HPLC) method for the analysis of a chiral precursor molecule employed frequently in folic acid syntheses was developed, optimized and successfully validated according to ICH-guidelines. It could be shown that ultra-high performance chromatography (UHPLC) can give significant advantages compared to traditional HPLC not only in reversed phase HPLC, but also for enantioselective separations in normal phase mode. Novel 3 μm-particle sizes allow developing analytical chromatographic methods completely resolving two enantiomers in the shortest time possible while preserving high efficiency and low detection limits. By offering increased resolution, sensitivity and speed, enantioselective UHPLC (eUHPLC) improves sample throughput, productivity and provides considerably faster access to information on enantiomeric purity also under non-aqueous conditions.

  10. Lipase immobilized on HOOC-MCF: A highly enantioselective catalyst for transesterification resolution of (R,S)-1-phenylethanol

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    Pseudomonas cepacia lipase (PSL) immobilized on the carboxyl-functionalized meso-cellular foams (HOOC-MCF) was used for the transesterification resolution of (R,S)-1-phenylethanol in organic solvent. The results showed that the ee value of (S)-1-phenylethanol and (R)-1-phenylethyl acetate reached 99% with 50% conversion of 1-phenylethanol using toluene as solvent.Furthermore, it was found that PSL/HOOC-MCF exhibited high enantioselectivity in organic solvent with log P ≤ 2 such as toluene and hexane.

  11. Highly diastereoselective and enantioselective olefin cyclopropanation using engineered myoglobin-based catalysts.

    Science.gov (United States)

    Bordeaux, Melanie; Tyagi, Vikas; Fasan, Rudi

    2015-02-01

    Using rational design, an engineered myoglobin-based catalyst capable of catalyzing the cyclopropanation of aryl-substituted olefins with catalytic proficiency (up to 46,800 turnovers) and excellent diastereo- and enantioselectivity (98-99.9%) was developed. This transformation could be carried out in the presence of up to 20 g L(-1) olefin substrate with no loss in diastereo- and/or enantioselectivity. Mutagenesis and mechanistic studies support a cyclopropanation mechanism mediated by an electrophilic, heme-bound carbene species and a model is provided to rationalize the stereopreference of the protein catalyst. This work shows that myoglobin constitutes a promising and robust scaffold for the development of biocatalysts with carbene-transfer reactivity.

  12. Highly enantioselective esterification of racemic ibuprofen in a packed bed reactor using immobilised Rhizomucor miehei lipase.

    Science.gov (United States)

    Sánchez; Valero; Lafuente; Solà

    2000-07-01

    A systematic study of the enantioselective resolution of ibuprofen by commercial Rhizomucor miehei lipase (Lipozyme(R) IM20) has been carried out using isooctane as solvent and butanol as esterificating agent. The main variables controlling the process (temperature, ibuprofen concentration, ratio butanol:ibuprofen) have been studied using an orthogonal full factorial experimental design, in which the selected objective function was enantioselectivity. This strategy has resulted in a polynomial function that describes the process. By optimizing this function, optimal conditions for carrying out the esterification of racemic ibuprofen have been determined. Under these conditions, enantiomeric excess and total conversion values were 93.8% and 49.9%, respectively, and the enantioselectivity was 113 after 112 h of reaction. These conditions have been considered in the design of a continuous reactor to scale up the process. The esterification of ibuprofen was properly described by pseudo first-order kinetics. Thus, a packed bed reactor operating as a plug-flow reactor (PFR) is the most appropriate in terms of minimizing the residence time compared with a continuous stirred tank reactor (CSTR) to achieve the same final conversion. This reactor shows a similar behavior in terms of enantioselectivity, enantiomeric excess, and conversion when compared with batch reactors. A residence-time distribution (RTD) shows that the flow model is essentially a plug flow with a slight nonsymmetrical axial dispersion (Peclet number = 43), which was also corroborated by the model of CSTR in series. The stability of the system (up to 100 h) and the possibility of reutilization of the enzyme (up to four times) lead to consider this reactor as a suitable configuration for scale up of the process.

  13. High-throughput Screening of the Enantioselectivity of Hyperthermophilic Mutant Esterases from Archaeon Aeropyrum pernix K1 for Resolution of (R,S)-2-Octanol Acetate

    Institute of Scientific and Technical Information of China (English)

    ZHANG Gui-rong; GAO Ren-jun; ZHANG Ai-jun; RAO Lang; CAO Shu-gui

    2007-01-01

    To identify the desired hyperthermophilic variants within a mutant esterase library for the resolution of (R,S)-2-octanol acetate, a simple, reliable, and versatile method was developed in this study. We built a screening strategy including two steps, first we selected agar plate with substrate to screen the enzymatic activity; secondly we used a pH indicator to screen the enantioselectivity. This method could rapidly detect favorable mutants with high activity and enantioselectivity. A total of 96.2% of tedious screening work can be precluded using this screening strategy. It is an effective screening for alkyl ester and can be applied to relative screening researches. The four improved mutants were screened from the mutant esterase library. Their enantioselectivities, activities, and structures were investigated at different temperatures.

  14. Highly Catalytic Enantioselective Addition of Diethyl Zinc to Aldehydes and Chalcone in the Presence of Chiral Ligands

    Institute of Scientific and Technical Information of China (English)

    WANG; Rui

    2001-01-01

    Catalytic asymmetric carbon-carbon bond formation is one of the most important reactions and have attracted much attention to develop more efficient enantioselective C-C formation methods in organic synthesis. In this field, asymmetric addition of diethylzinc to aldehydes[1] and conjugate addition to enones[2] have drawn special interests and have been greatly developed. Regardless of it, much spaces in these areas still exist, so it needs more extensive and intensive researches for the purpose of as follows: (1) attaching ligands to a polymer for the easy separation of the catalysts so as to be able to allow very efficient recovery and reuse of the catalysts, and the possibility of carrying out the desired transfomation in continuous mode in a flow reactor, etc., (2) searching for novel chiral catalysts with such features as more suitable for more extensive substrates varieties, and more convenient and economical as well as possessing applicable prospect, and so on. Here we report some works in these areas done in our laboratory.  ……

  15. Highly Catalytic Enantioselective Addition of Diethyl Zinc to Aldehydes and Chalcone in the Presence of Chiral Ligands

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    @@ Catalytic asymmetric carbon-carbon bond formation is one of the most important reactions and have attracted much attention to develop more efficient enantioselective C-C formation methods in organic synthesis. In this field, asymmetric addition of diethylzinc to aldehydes[1] and conjugate addition to enones[2] have drawn special interests and have been greatly developed. Regardless of it, much spaces in these areas still exist, so it needs more extensive and intensive researches for the purpose of as follows: (1) attaching ligands to a polymer for the easy separation of the catalysts so as to be able to allow very efficient recovery and reuse of the catalysts, and the possibility of carrying out the desired transfomation in continuous mode in a flow reactor, etc., (2) searching for novel chiral catalysts with such features as more suitable for more extensive substrates varieties, and more convenient and economical as well as possessing applicable prospect, and so on. Here we report some works in these areas done in our laboratory.

  16. Highly Enantioselective Fluorescent Recognition of Both Unfunctionalized and Functionalized Chiral Amines by a Facile Amide Formation from a Perfluoroalkyl Ketone.

    Science.gov (United States)

    Wang, Chao; Anbaei, Parastoo; Pu, Lin

    2016-05-17

    The H8 BINOL-based perfluoroalkyl ketone (S)-2 is found to exhibit highly enantioselective fluorescent enhancements toward both unfunctionalized and functionalized chiral amines. It greatly expands the substrate scope of the corresponding BINOL-based sensor. A dramatic solvent effect was observed for the reaction of the amines with compound (S)-2. In DMF, cleavage of the perfluoroalkyl group of compound (S)-2 to form amides was observed but not in other solvents, such as methylene chloride, chloroform, THF, hexane, and perfluorohexane. Thus, the addition of another solvent, such as THF, can effectively quench the reaction of compound (S)-2 with amines in DMF to allow stable fluorescent measurement. This is the first example that the formation of strong amide bonds under very mild conditions is used for the enantioselective recognition of chiral amines. The mechanism of the reaction of compound (S)-2 with chiral amines is investigated by using various analytical methods including mass spectrometry as well as NMR and UV/Vis absorption spectroscopy.

  17. Highly efficient catalytic enantioselective Mannich reaction of malonates with N-tert-butoxycarbonyl imines by using Yb(OTf)3/pybox catalysts at room temperature.

    Science.gov (United States)

    Karimi, Babak; Jafari, Ehsan; Enders, Dieter

    2013-07-29

    Go Mannich! A highly efficient and enantioselective method for the direct asymmetric reaction of dibenzyl malonate with N-tert-butoxycarbonyl aldimines in the presence of Yb(OTf)3 and iPr-pybox complexes is described (see scheme; pybox = pyridine bisoxazoline).

  18. Bromoporphyrins as versatile synthons for modular construction of chiral porphyrins: cobalt-catalyzed highly enantioselective and diastereoselective cyclopropanation.

    Science.gov (United States)

    Chen, Ying; Fields, Kimberly B; Zhang, X Peter

    2004-11-17

    5,10-Bis(2',6'-dibromophenyl)porphyrins bearing various substituents at the 10 and 20 positions were demonstrated to be versatile synthons for modular construction of chiral porphyrins via palladium-catalyzed amidation reactions with chiral amides. The quadruple carbon-nitrogen bond formation reactions were accomplished in high yields with different chiral amide building blocks under mild conditions, forming a family of D2-symmetric chiral porphyrins. Cobalt(II) complexes of these chiral porphyrins were prepared in high yields and shown to be active catalysts for highly enantioselective and diastereoselective cyclopropanation under a practical one-pot protocol (alkenes as limiting reagents and no slow addition of diazo reagents).

  19. Determination of levamisole and tetramisole in seized cocaine samples by enantioselective high-performance liquid chromatography and circular dichroism detection.

    Science.gov (United States)

    Bertucci, Carlo; Tedesco, Daniele; Fabini, Edoardo; Di Pietra, Anna Maria; Rossi, Francesca; Garagnani, Marco; Del Borrello, Elia; Andrisano, Vincenza

    2014-10-10

    Levamisole, an anthelmintic drug, has been increasingly employed as an adulterant of illicit street cocaine over the last decade; recently, the use of tetramisole, the racemic mixture of levamisole and its enantiomer dexamisole, was also occasionally observed. A new enantioselective high-performance liquid chromatography (HPLC) method, performed on cellulose tris(3,5-dimethylphenylcarbamate) chiral stationary phases in normal-phase mode, was validated to determine the enantiomeric composition of tetramisole enantiomers in seized cocaine samples. Furthermore, the hyphenation of the validated HPLC method with a circular dichroism (CD) detection system allowed the direct determination of elution order and a selective monitoring of levamisole and dexamisole in the presence of possible interferences. The method was applied to the identification and quantitation of the two enantiomers of tetramisole in seized street cocaine samples.

  20. Rhodium-Catalyzed Asymmetric Conjugate Additions of Boronic Acids Using Monodentate Phosphoramidite Ligands

    NARCIS (Netherlands)

    -G Boiteau, J.; Imbos, R.; J. Minnaard, A.; Feringa, B.L.

    2003-01-01

    Monodentate phosphoramidites have been used for the first time as chiral ligands in the Rh-catalyzed enantioselective conjugate addition of arylboronic acids to enones, unsaturated esters, lactones, and nitro alkenes. High reaction rates and ee’s up to 89% have been obtained.

  1. Exploring the origin of high optical absorption in conjugated polymers

    KAUST Repository

    Vezie, Michelle S.

    2016-05-16

    The specific optical absorption of an organic semiconductor is critical to the performance of organic optoelectronic devices. For example, higher light-harvesting efficiency can lead to higher photocurrent in solar cells that are limited by sub-optimal electrical transport. Here, we compare over 40 conjugated polymers, and find that many different chemical structures share an apparent maximum in their extinction coefficients. However, a diketopyrrolopyrrole-thienothiophene copolymer shows remarkably high optical absorption at relatively low photon energies. By investigating its backbone structure and conformation with measurements and quantum chemical calculations, we find that the high optical absorption can be explained by the high persistence length of the polymer. Accordingly, we demonstrate high absorption in other polymers with high theoretical persistence length. Visible light harvesting may be enhanced in other conjugated polymers through judicious design of the structure.

  2. Design of highly active binary catalyst systems for CO2/epoxide copolymerization: polymer selectivity, enantioselectivity, and stereochemistry control.

    Science.gov (United States)

    Lu, Xiao-Bing; Shi, Lei; Wang, Yi-Ming; Zhang, Rong; Zhang, Ying-Ju; Peng, Xiao-Jun; Zhang, Zhi-Chao; Li, Bo

    2006-02-01

    Asymmetric, regio- and stereoselective alternating copolymerization of CO(2) and racemic aliphatic epoxides proceeds effectively under mild temperature and pressure by using a binary catalyst system of a chiral tetradentate Schiff base cobalt complex [SalenCo(III)X] as the electrophile in conjunction with an ionic organic ammonium salt or a sterically hindered strong organic base as the nucleophile. The substituent groups on the aromatic rings, chiral diamine backbone, and axial X group of the electrophile, as well as the nucleophilicity, leaving ability, and coordination ability of the nucleophile, all significantly affect the catalyst activity, polymer selectivity, enantioselectivity, and stereochemistry. A bulky chiral cyclohexenediimine backbone complex [SalcyCo(III)X] with an axial X group of poor leaving ability as the electrophile, combined with a bulky nuclephile with poor leaving ability and low coordination ability, is an ideal binary catalyst system for the copolymerization of CO(2) and a racemic aliphatic epoxide to selectively produce polycarbonates with relatively high enantioselectivity, >95% head-to-tail connectivity, and >99% carbonate linkages. A fast copolymerization of CO(2) and epoxides was observed when the concentration of the electrophile or/and the nucleophile was increased, and the number of polycarbonate chains was proportional to the concentration of the nucleophile. Electrospray ionization mass spectrometry, in combination with a kinetic study, showed that the copolymerization involved the coordination activation of the monomer by the electrophile and polymer chain growth predominately occurring in the nucleophile. Both the enantiomorphic site effect resulting from the chiral electrophile and the polymer chain end effect mainly from the bulky nucleophile cooperatively control the stereochemistry of the CO(2)/epoxide copolymerization.

  3. (+)-camphor-derived tri- and tetradentate amino alcohols; synthesis and application as ligands in the nickel catalyzed enantioselective conjugate addition of diethylzinc

    NARCIS (Netherlands)

    Vries, André H.M. de; Imbos, Rosalinde; Feringa, Bernard

    1997-01-01

    Several novel tri- and tetradentate amino alcohol ligands, all derived from (+)-camphor, have been synthesized by using specific N-alkylation procedures. The amino alcohols were employed as chiral ligands in the nickel catalyzed conjugate additions of diethylzine to chalcone and cyclohexenone as

  4. (+)-camphor-derived tri- and tetradentate amino alcohols; synthesis and application as ligands in the nickel catalyzed enantioselective conjugate addition of diethylzinc

    NARCIS (Netherlands)

    Vries, André H.M. de; Imbos, Rosalinde; Feringa, Bernard

    1997-01-01

    Several novel tri- and tetradentate amino alcohol ligands, all derived from (+)-camphor, have been synthesized by using specific N-alkylation procedures. The amino alcohols were employed as chiral ligands in the nickel catalyzed conjugate additions of diethylzine to chalcone and cyclohexenone as mod

  5. Organocatalytic Enantioselective Henry Reactions

    Directory of Open Access Journals (Sweden)

    Raquel P. Herrera

    2011-05-01

    Full Text Available A large number of interesting organocatalytic enantioselective protocols have been explored and successfully applied in the last decade. Among them, the Henry (nitroaldol reaction represents a powerful carbon-carbon bond-forming procedure for the preparation of valuable synthetic intermediates, such as enantioenriched nitro alcohols, which can be further transformed in a number of important nitrogen and oxygen-containing compounds. This area of research is still in expansion and a more complex version of this useful process has recently emerged, the domino Michael/Henry protocol, affording highly functionalized cycles with multiple stereogenic centers.

  6. Organocatalytic tandem Michael addition reactions: A powerful access to the enantioselective synthesis of functionalized chromenes, thiochromenes and 1,2-dihydroquinolines

    Directory of Open Access Journals (Sweden)

    Chittaranjan Bhanja

    2012-10-01

    Full Text Available Enantioselective organocatalysis has become a field of central importance within asymmetric chemical synthesis and appears to be efficient approach toward the construction of complex chiral molecules from simple achiral materials in one-pot transformations under mild conditions with high stereocontrol. This review addresses the most significant synthetic methods reported on chiral-amine-catalyzed tandem Michael conjugate addition of heteroatom-centered nucleophiles to α,β-unsaturated compounds followed by cyclization reactions for the enantioselective construction of functionalized chiral chromenes, thiochromenes and 1,2-dihydroquinolines in optically enriched forms found in a myriad of bioactive natural products and synthetic compounds.

  7. Sequential rhodium/palladium catalysis: enantioselective formation of dihydroquinolinones in the presence of achiral and chiral ligands.

    Science.gov (United States)

    Zhang, Lei; Qureshi, Zafar; Sonaglia, Lorenzo; Lautens, Mark

    2014-12-08

    Compatible combinations of achiral and chiral ligands can be used in rhodium/palladium catalysis to achieve highly enantioselective domino reactions. The difference in rates of catalysis and minimal effects of ligand interference confer control in the domino sequence. The "all-in-one" 1,4-conjugate arylation and C-N cross-coupling through sequential Rh/Pd catalysis provides access to enantioenriched dihydroquinolinone building blocks.

  8. Discovery of an Escherichia coli Esterase with High Activity and Enantioselectivity toward 1,2-O-Isopropylideneglycerol Esters▿†

    Science.gov (United States)

    Godinho, Luis F.; Reis, Carlos R.; Tepper, Pieter G.; Poelarends, Gerrit J.; Quax, Wim J.

    2011-01-01

    Escherichia coli has been widely used as an expression host for the identification of desired biocatalysts through screening or selection assays. We have previously used E. coli in growth selection and screening assays for identification of Bacillus subtilis lipase variants (located in the periplasm) with improved activity and enantioselectivity toward 1,2-O-isopropylideneglycerol (IPG) esters. In the course of these studies, we discovered that E. coli itself exhibits significant cytoplasmic esterase activity toward IPG esters. In order to identify the enzyme (or enzymes) responsible for this esterase activity, we analyzed eight E. coli knockout strains, in which single esterase genes were deleted, for their ability to hydrolyze IPG butyrate. This approach led to the identification of esterase YbfF as the major E. coli enzyme responsible for the hydrolytic activity toward IPG esters. The gene coding for YbfF was cloned and overexpressed in E. coli, and the corresponding protein was purified and characterized for its biocatalytic performance. YbfF displays a high level of activity toward IPG butyrate and IPG caprylate and prefers the R-enantiomer of these substrates, producing the S-enantiomer of the IPG product with high enantiomeric excess (72 to 94% ee). The enantioselectivity of YbfF for IPG caprylate (E = 40) could be significantly enhanced when using dimethylformamide (DMF) or dimethyl sulfoxide (DMSO) as cosolvents in kinetic resolution experiments. The enzyme also shows high enantioselectivity toward 1-phenylethyl acetate (E ≥ 200), giving the chiral product (R)-1-phenylethanol with >99% ee. The high activity and enantioselectivity of YbfF make it an attractive enzyme for organic synthesis. PMID:21764964

  9. A highly enantioselective and regioselective organocatalytic direct Mannich reaction of methyl alkyl ketones with cyclic imines benzo[e][1,2,3]oxathiazine 2,2-dioxides.

    Science.gov (United States)

    Wang, You-Qing; Cui, Xiao-Yu; Ren, Yuan-Yuan; Zhang, Yongna

    2014-12-07

    A highly enantioselective direct Mannich reaction of methyl alkyl ketones with cyclic imines benzo[e][1,2,3]oxathiazine 2,2-dioxides, catalyzed by the combination of cinchona alkaloid derived primary amine and TFA, is disclosed. For unsymmetrical methyl alkyl ketones, it is favoured that specific regioselective addition to the imine substrates occurs at the less-substituted methyl group by steric control.

  10. Enantioselective Vinylogous Organocascade Reactions.

    Science.gov (United States)

    Hepburn, Hamish B; Dell'Amico, Luca; Melchiorre, Paolo

    2016-08-01

    Cascade reactions are powerful tools for rapidly assembling complex molecular architectures from readily available starting materials in a single synthetic operation. Their marriage with asymmetric organocatalysis has led to the development of novel techniques, which are now recognized as reliable strategies for the one-pot enantioselective synthesis of stereochemically dense molecules. In recent years, even more complex synthetic challenges have been addressed by applying the principle of vinylogy to the realm of organocascade catalysis. The key to the success of vinylogous organocascade reactions is the unique ability of the chiral organocatalyst to transfer reactivity to a distal position without losing control on the stereo-determining events. This approach has greatly expanded the synthetic horizons of the field by providing the possibility of forging multiple stereocenters in remote positions from the catalyst's point of action with high selectivity, while simultaneously constructing multiple new bonds. This article critically describes the developments achieved in the field of enantioselective vinylogous organocascade reactions, charting the ideas, the conceptual advances, and the milestone reactions that have been essential for reaching highly practical levels of synthetic efficiency.

  11. High enantioselective Novozym 435-catalyzed esterification of (R,S)-flurbiprofen monitored with a chiral stationary phase.

    Science.gov (United States)

    Siódmiak, Tomasz; Mangelings, Debby; Vander Heyden, Yvan; Ziegler-Borowska, Marta; Marszałł, Michał Piotr

    2015-03-01

    Lipases form Candida rugosa and Candida antarctica were tested for their application in the enzymatic kinetic resolution of (R,S)-flurbiprofen by enantioselective esterification. Successful chromatographic separation with well-resolved peaks of (R)- and (S)-flurbiprofen and their esters was achieved in one run on chiral stationary phases by high-performance liquid chromatography (HPLC). In this study screening of enzymes was performed, and Novozym 435 was selected as an optimal catalyst for obtaining products with high enantiopurity. Additionally, the influence of organic solvents (dichloromethane, dichloroethane, dichloropropane, and methyl tert-butyl ether), primary alcohols (methanol, ethanol, n-propanol, and n-butanol), reaction time, and temperature on the enantiomeric ratio and conversion was tested. The high values of enantiomeric ratio (E in the range of 51.3-90.5) of the esterification of (R,S)-flurbiprofen were obtained for all tested alcohols using Novozym 435, which have a great significance in the field of biotechnological synthesis of drugs. The optimal temperature range for the performed reactions was from 37 to 45 °C. As a result of the optimization, (R)-flurbiprofen methyl ester was obtained with a high optical purity, eep = 96.3 %, after 96 h of incubation. The enantiomeric ratio of the reaction was E = 90.5 and conversion was C = 35.7 %.

  12. Tsukamurella sp. E105 as a new biocatalyst for highly enantioselective hydrolysis of ethyl 2-(2-oxopyrrolidin-1-yl) butyrate.

    Science.gov (United States)

    He, Junyao; Yuan, Shuai; Wang, Pu; Wang, Nengqiang

    2012-09-01

    A new bacterial strain, E105, has been introduced as a biocatalyst for the enantioselective hydrolysis of ethyl (R,S)-2-(2-oxopyrrolidin-1-yl) butyrate, (R,S)-1, to (S)-2-(2-oxopyrrolidin-1-yl) butyric acid, (S)-2. This strain was isolated from 60 soil samples using (R,S)-1 as the sole carbon source. The isolate was identified as Tsukamurella tyrosinosolvens E105, based on its morphological characteristics, physiological tests, and 16S rDNA sequence analysis. The process of cell growth and hydrolase production for this strain was then investigated. The hydrolase activity reached its maximum after cultivation at 200 rpm and 30 °C for 36 h. Furthermore, the performance of the enantioselective hydrolysis of (R,S)-1 was studied. The optimal reaction temperature, initial pH, substrate concentration, and concentration of suspended cells were 30 °C, 6.8, 10 and 30 g/l (DCW), respectively. Under these conditions, a high conversion (>45 %) of the product (S)-2 with an excellent enantiomeric excess (ee) (>99 %), and a satisfied enantiomeric ratio (E) (>600) as well were obtained. This study showed that the bacterial isolate T. tyrosinosolvens E105 displayed a high enantioselectivity towards the hydrolysis of racemic ethyl 2-(2-oxopyrrolidin-1-yl) butyrate.

  13. Highly enantioselective cross-aldol reactions of acetaldehyde mediated by a dual catalytic system operating under site isolation.

    Science.gov (United States)

    Fan, Xinyuan; Rodríguez-Escrich, Carles; Wang, Shoulei; Sayalero, Sonia; Pericàs, Miquel A

    2014-10-06

    Polystyrene-supported (PS) diarylprolinol catalysts 1 a (Ar = phenyl) and 1 b (Ar = 3,5-bis(trifluoromethyl)phenyl) have been developed. Operating under site-isolation conditions, PS-1 a/1 b worked compatibly with PS-bound sulfonic acid catalyst 2 to promote deoligomerization of paraldehyde and subsequent cross-aldol reactions of the resulting acetaldehyde in one pot, affording aldol products in high yields with excellent enantioselectivities. The effect of water on the performance of the catalytic system has been studied and its optimal amount (0.5 equiv) has been determined. The dual catalytic system (1/2) allows repeated recycling and reuse (10 cycles). The potential of this methodology is demonstrated by a two-step synthesis of a phenoperidine analogue (68% overall yield; 98% ee) and by the preparation of highly enantioenriched 1,3-diols 4 and 3-methylamino-1-arylpropanols 5, key intermediates in the synthesis of a variety of druglike structures. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  14. Direct enantioselective access to 4-substituted tetrahydroquinolines by catalytic asymmetric transfer hydrogenation of quinolines.

    Science.gov (United States)

    Rueping, Magnus; Theissmann, Thomas; Stoeckel, Mirjam; Antonchick, Andrey P

    2011-10-07

    A convenient protocol for the enantioselective synthesis of 4-substituted tetrahydroquinolines has been developed. Chiral BINOL phosphoric acids promote the reduction of a wide range of 4-substituted quinolines with Hantzsch esters with good to high levels of enantioselectivity.

  15. Rigid, Conjugated Macrocycles for High Performance Organic Photodetectors.

    Science.gov (United States)

    Zhang, Boyuan; Trinh, M Tuan; Fowler, Brandon; Ball, Melissa; Xu, Qizhi; Ng, Fay; Steigerwald, Michael L; Zhu, X-Y; Nuckolls, Colin; Zhong, Yu

    2016-12-21

    Organic photodetectors (OPDs) are attractive for their high optical absorption coefficient, broad wavelength tunability, and compatibility with lightweight and flexible devices. Here we describe a new molecular design that enables high performance organic photodetectors. We use a rigid, conjugated macrocycle as the electron acceptor in devices to obtain high photocurrent and low dark current. We make a direct comparison between the devices made with the macrocyclic acceptor and an acyclic control molecule; we find that the superior performance of the macrocycle originates from its rigid, conjugated, and cyclic structure. The macrocycle's rigid structure reduces the number of charged defects originating from deformed sp(2) carbons and covalent defects from photo/thermoactivation. With this molecular design, we are able to suppress dark current density while retaining high responsivity in an ultrasensitive nonfullerene OPD. Importantly, we achieve a detectivity of ∼10(14) Jones at near zero bias voltage. This is without the need for extra carrier blocking layers commonly employed in fullerene-based devices. Our devices are comparable to the best fullerene-based photodetectors, and the sensitivity at low working voltages (<0.1 V) is a record for nonfullerene OPDs.

  16. Highly sensitive biosensors based on water-soluble conjugated polymers

    Institute of Scientific and Technical Information of China (English)

    XU Hui; WU Haiping; FAN Chunhai; LI Wenxin; ZHANG Zhizhou; HE Lin

    2004-01-01

    Conjugated, conductive polymers are a kind of important organic macromolecules, which has found applications in a variety of areas. The application of conjugated polymers in developing fluorescent biosensors represents the merge of polymer sciences and biological sciences. Conjugated polymers are very good light harvesters as well as fluorescent polymers, and they are also "molecular wires". Through elaborate designs, these important features, i.e. efficient light harvesting and electron/energy transfer, can be used as signal amplification in fluorescent biosensors. This might significantly improve the sensitivity of conjugated polymer-based biosensors. In this article, we reviewed the application of conjugated polymers, via either electron transfer or energy transfer, to detections of gene targets, antibodies or enzymes. We also reviewed recent efforts in conjugated polymer-based solid-state sensor designs as well as chip-based multiple target detection. Possible directions in this conjugated polymer-based biosensor area are also discussed.

  17. Chiral enantioresolution of cathinone derivatives present in "legal highs", and enantioselectivity evaluation on cytotoxicity of 3,4-methylenedioxypyrovalerone (MDPV).

    Science.gov (United States)

    Silva, Bárbara; Fernandes, Carla; Tiritan, Maria Elizabeth; Pinto, Madalena M M; Valente, Maria João; Carvalho, Márcia; de Pinho, Paula Guedes; Remião, Fernando

    Recently, great interest has been focused on synthetic cathinones since their consumption has increased exponentially. All synthetic cathinones exist as chiral molecules; the biological and/or toxicological properties of cathinones generally differ according to the enantiomers in human body. In this study, a chiral liquid chromatography method was developed to separate and determine the enantiomeric ratio of synthetic cathinones present in "legal highs" acquired in old smart shops or over the Internet. All the synthetic cathinones were efficiently enantio-separated with α and Rs ranging from 1.24 to 3.62 and from 1.24 to 10.52, respectively, using polysaccharide-based chiral stationary phases. All synthetic cathinones, with the exception of 4-methylethcathinone (4-MEC), were present in the commercialized "legal highs" in an enantiomeric proportion of 50:50. One of the studied chiral compounds was 3,4-methylenedioxypyrovalerone (MDPV), one of the most consumed cathinone derivative worldwide. Our research group has recently reported its hepatotoxicity in the racemic form. Thus, the analytical enantioresolution of the MDPV was scaled up to multi-milligram using a semi-preparative amylose tris-3,5-dimethylphenylcarbamate column (20 cm × 7.0 mm ID, 7 µm particle size). Both enantiomers were isolated with high enantiomeric purity (enantiomeric excess > 99 %). The toxicity of S-(-)-MDPV and R-(+)-MDPV was evaluated, for the first time, using primary cultures of rat hepatocytes. It was also possible to verify that MDPV enantiomers showed hepatotoxicity in a concentration-dependent manner, but displayed no enantioselective toxicity in this cell culture model.

  18. Highly efficient enantioselective epoxidation of α,β-enones catalyzed by cheap chiral lanthanum and gadolinium alkoxides

    NARCIS (Netherlands)

    Chen, Ruifang; Qian, Changtao; Vries, Johannes G. de

    2001-01-01

    (S)-6,6'-Dibromo-BINOL and (S)-6,6'-diphenyl-BINOL have been developed as efficient chiral ligands applicable to lanthanoid catalyzed asymmetric epoxidation of α,β-unsaturated ketones in the presence of cumene hydroperoxide. Excellent chemical yield and enantioselectivity have been achieved for seve

  19. Separation of polyamines, conjugated to DNA, by reversed-phase high-performance liquid chromatography.

    Science.gov (United States)

    Mateos, J L; Reyes, A; Vicente, C; Legaz, M E

    2000-02-18

    Genomic DNA was isolated from the lichen Evernia prunastri in order to analyze by high-performance liquid chromatography the occurrence of polyamines conjugated to the macromolecule. The acid-insoluble (PH) fraction of this DNA contained mainly conjugated spermidine, although small amounts of free putrescine and spermidine were also present. The PH fraction of DNA also contained conjugated evernic acid, the main phenol produced by this lichen species. Conjugation of polyamines to calf thymus DNA was carried out under in vitro conditions. Conjugation was to spermidine and mainly to spermine and produced DNA compactation. Evernic acid enhanced the action of polyamines in order to produce DNA aggregation.

  20. Racemic but tropos (chirally flexible) BIPHEP ligands for Rh(I)-complexes: highly enantioselective ene-type cyclization of 1,6-enynes.

    Science.gov (United States)

    Mikami, Koichi; Kataoka, Shohei; Yusa, Yukinori; Aikawa, Kohsuke

    2004-10-14

    [reaction: see text] The tropos (chirally flexible) or atropos (chirally rigid) nature of BIPHEP-Rh complexes at room temperature critically depends on the amines complexed. The aliphatic DPEN complex is atropos, whereas the aromatic DABN complex is tropos. BIPHEP-Rh chirality can thus be controlled by DABN at room temperature. The amine-free BIPHEP-Rh complex is tropos. At 5 degrees C, even amine-free BIPHEP-Rh complexes are atropos and hence can be used as enantiopure catalysts to give high enantioselectivity in ene-type cyclization of 1,6-enynes.

  1. Highly enantioselective hydrogenation of N-aryl imines derived from acetophenones by using Ru-pybox complexes under hydrogenation or transfer hydrogenation conditions in isopropanol.

    Science.gov (United States)

    Menéndez-Pedregal, Estefanía; Vaquero, Mónica; Lastra, Elena; Gamasa, Pilar; Pizzano, Antonio

    2015-01-07

    The asymmetric reduction of N-aryl imines derived from acetophenones by using Ru complexes bearing both a pybox (2,6-bis(oxazoline)pyridine) and a monodentate phosphite ligand has been described. The catalysts show good activity with a diverse range of substrates, and deliver the amine products in very high levels of enantioselectivity (up to 99 %) under both hydrogenation and transfer hydrogenation conditions in isopropanol. From deuteration studies, a very different labeling is observed under hydrogenation and transfer hydrogenation conditions, which demonstrates the different nature of the hydrogen source in both reactions.

  2. CATALYTIC ENANTIOSELECTIVE ALLYLIC OXIDATION

    NARCIS (Netherlands)

    Rispens, Minze T.; Zondervan, Charon; Feringa, Bernard

    1995-01-01

    Several chiral Cu(II)-complexes of cyclic amino acids catalyse the enantioselective allylic oxidation of cyclohexene to cyclohexenyl esters. Cyclohexenyl propionate was obtained in 86% yield with e.e.'s up to 61%.

  3. Highly enantioselective Michael addition of cyclohexanone to nitroolefins catalyzed by pyrrolidine-based bifunctional benzoylthiourea in water.

    Science.gov (United States)

    Wang, Zhen-Yu; Ban, Shu-Rong; Yang, Meng-Chen; Li, Qing-Shan

    2016-11-01

    Organocatalysis and aqueous reactions are identified as the focus of the greening of chemistry. Combining these two strategies effectively remains an interesting challenge in organic synthesis. Herein, we used pyrrolidine-based benzoylthiourea 1c to catalyze the asymmetric Michael addition of cyclohexanone to various nitroolefins in water to afford the corresponding compounds in moderate to good yields, and with excellent diastereoselectivities (up to >99:1 dr) and enantioselectivities (up to 99% ee).

  4. Highly enantioselective oxazaborolidine-catalyzed reduction of 1,3-dicarbonyl compounds: role of the additive diethylaniline.

    Science.gov (United States)

    Chein, Rong-Jie; Yeung, Ying-Yeung; Corey, E J

    2009-04-02

    The oxazaborolidine-catalyzed reduction of 2,2-disubstituted cycloalkan-1,3-diones or hindered 2,2-disubstituted cyclic ketones using catecholborane as reductant proceeds with greater enantioselectivity when N,N-diethylaniline is added. It has now been shown that the effect of this additive is to catalyze the conversion of a harmful minor impurity in catalyst preparations to the active catalyst.

  5. High enantioselectivity in the asymmetric hydrogenation of ketones by a supported Pt nanocatalyst on a mesoporous modified MCM-41 support

    Institute of Scientific and Technical Information of China (English)

    Susmit Basu

    2015-01-01

    Catalysts containing metal nanotubes were prepared by the adsorption of platinum metal nano‐tubes onto functionalized and modified silica surfaces (MCM‐41 and fumed silica). (3‐Chloropro‐pyl)trimethoxysilane and cinchonidine were used for functionalization and modification, respec‐tively. Potassium chloroplatinate was used as the metal precursor to impregnate platinum metal nanotubes on the pretreated functionalized and modified silica surfaces. The solid catalysts were characterized by ESEM, TEM, EDAX, and XPS. The MCM‐41 supported platinum nanotube catalyst showed>98%to~100%enantioselectivity towards the hydrogenation of a range of pharmaceuti‐cally important chemicals such as methyl pyruvate, ethyl pyruvate, and acetophenone with nearly full conversion.

  6. Enantioselective olefin metathesis with cyclometalated ruthenium complexes.

    Science.gov (United States)

    Hartung, John; Dornan, Peter K; Grubbs, Robert H

    2014-09-17

    The success of enantioselective olefin metathesis relies on the design of enantioenriched alkylidene complexes capable of transferring stereochemical information from the catalyst structure to the reactants. Cyclometalation of the NHC ligand has proven to be a successful strategy to incorporate stereogenic atoms into the catalyst structure. Enantioenriched complexes incorporating this design element catalyze highly Z- and enantioselective asymmetric ring opening/cross metathesis (AROCM) of norbornenes and cyclobutenes, and the difference in ring strain between these two substrates leads to different propagating species in the catalytic cycle. Asymmetric ring closing metathesis (ARCM) of a challenging class of prochiral trienes has also been achieved. The extent of reversibility and effect of reaction setup was also explored. Finally, promising levels of enantioselectivity in an unprecedented Z-selective asymmetric cross metathesis (ACM) of a prochiral 1,4-diene was demonstrated.

  7. Enantioselective Olefin Metathesis with Cyclometalated Ruthenium Complexes

    Science.gov (United States)

    2015-01-01

    The success of enantioselective olefin metathesis relies on the design of enantioenriched alkylidene complexes capable of transferring stereochemical information from the catalyst structure to the reactants. Cyclometalation of the NHC ligand has proven to be a successful strategy to incorporate stereogenic atoms into the catalyst structure. Enantioenriched complexes incorporating this design element catalyze highly Z- and enantioselective asymmetric ring opening/cross metathesis (AROCM) of norbornenes and cyclobutenes, and the difference in ring strain between these two substrates leads to different propagating species in the catalytic cycle. Asymmetric ring closing metathesis (ARCM) of a challenging class of prochiral trienes has also been achieved. The extent of reversibility and effect of reaction setup was also explored. Finally, promising levels of enantioselectivity in an unprecedented Z-selective asymmetric cross metathesis (ACM) of a prochiral 1,4-diene was demonstrated. PMID:25137310

  8. Enantioselective, iridium-catalyzed monoallylation of ammonia.

    Science.gov (United States)

    Pouy, Mark J; Stanley, Levi M; Hartwig, John F

    2009-08-19

    Highly enantioselective, iridium-catalyzed monoallylations of ammonia are reported. These reactions occur with electron-neutral, -rich, and -poor cinnamyl carbonates, alkyl and trityloxy-substituted allylic carbonates, and dienyl carbonates in moderate to good yields and excellent enantioselectivities. This process is enabled by the use of an iridium catalyst that does not require a Lewis acid for activation and that is stable toward a large excess of ammonia. This selective formation of primary allylic amines allows for one-pot syntheses of heterodiallylamines and allylic amides that are not otherwise accessible via iridium-catalyzed allylic amination without the use of blocking groups and protective group manipulations.

  9. High-conjugation-efficiency aqueous CdSe quantum dots.

    Science.gov (United States)

    Au, Giang H T; Shih, Wan Y; Shih, Wei-Heng

    2013-11-12

    Quantum dots (QDs) are photoluminescent nanoparticles that can be directly or indirectly coupled with a receptor such as an antibody to specifically image a target biomolecule such as an antigen. Recent studies have shown that QDs can be directly made at room temperature and in an aqueous environment (AQDs) with 3-mercaptopropionic acid (MPA) as the capping ligand without solvent and ligand exchange typically required by QDs made by the organic solvent routes (OQDs). In this study, we have synthesized CdSe AQDs and compared their conjugation efficiency and imaging efficacy with commercial carboxylated OQDs in HT29 colon cancer cells using a primary antibody-biotinylated secondary antibody-streptavidin (SA) sandwich. We showed that the best imaging condition for AQDs occurred when one AQD was bound with 3 ± 0.3 SA with a nominal SA/AQD ratio of 4 corresponding to an SA conjugation efficiency of 75 ± 7.5%. In comparison, for commercial CdSe-ZnS OQDs to achieve 2.7 ± 0.4 bound SAs per OQD for comparable imaging efficacy a nominal SA/OQD ratio of 80 was needed corresponding to an SA conjugation efficiency of 3.4 ± 0.5% for CdSe-ZnS OQDs. The more than 10 times better SA conjugation efficiency of the CdSe AQDs as compared to that of the CdSe-ZnS OQDs was attributed to more capping molecules on the AQD surface as a result of the direct aqueous synthesis. More capping molecules on the AQD surface also allowed the SA-AQD conjugate to be stable in cell culture medium for more than three days without losing their staining capability in a flowing cell culture medium. In contrast, SA-OQD conjugates aggregated in cell culture medium and in phosphate buffer saline solution over time.

  10. Isoindolinones as Michael Donors under Phase Transfer Catalysis: Enantioselective Synthesis of Phthalimidines Containing a Tetrasubstituted Carbon Stereocenter

    Directory of Open Access Journals (Sweden)

    Francesco Scorzelli

    2015-05-01

    Full Text Available Readily available chiral ammonium salts derived from cinchona alkaloids have proven to be effective phase transfer catalysts in the asymmetric Michael reaction of 3-substituted isoindolinones. This protocol provides a convenient method for the construction of valuable asymmetric 3,3-disubstituted isoindolinones in high yields and  moderate to good enantioselectivity. Diastereoselectivity was also investigated in the construction of contiguous tertiary and quaternary stereocenters. The use of acrolein as Michael acceptor led to an interesting tricyclic derivative, a pyrroloisoindolinone analogue, via a tandem conjugated addition/cyclization reaction.

  11. Narrow Gap, High Mobility, and Stable Pi Conjugated Polymers

    Science.gov (United States)

    2012-09-20

    Transmissive Switching in a Pseuodo Three-Electrode Electrochromic Device ” 14 7. Mortimer, R.J., Graham, K.R., Grenier, C.R.G., Reynolds, J.R. ACS Appl...applications and other devices of interest to the Air Force with a special focus on photodetectors (especially in the near infrared), solar cells, and...supercapacitors. Capitalizing on our history of developing variable gap conjugated polymers for a variety of applications (e.g. electrochromism and

  12. Enantioselective Organocatalytic α-Fluorination of Cyclic Ketones

    OpenAIRE

    Kwiatkowski, Piotr; Beeson, Teresa D.; Conrad, Jay C.; MacMillan, David W. C.

    2011-01-01

    The first highly enantioselective α-fluorination of ketones using organocatalysis has been accomplished. The long-standing problem of enantioselective ketone α-fluorination via enamine activation has been overcome via high-throughput evaluation of a new library of amine catalysts. The optimal system, a primary amine functionalized Cinchona alkaloid, allows the direct and asymmetric α-fluorination of a variety of carbo- and heterocyclic substrates. Furthermore, this protocol also provides dias...

  13. Enantioselective Hydroaminomethylation of Olefins Enabled by Rh/Brønsted Acid Relay Catalysis.

    Science.gov (United States)

    Meng, Jing; Li, Xing-Han; Han, Zhi-Yong

    2017-03-03

    Herein, by employing a rhodium catalyst with a commercial ligand and a phosphoric acid catalyst, highly chemo-, regio-, and enantioselective hydroaminomethylation of olefins is realized through a relay catalytic hydroformylation/dynamic kinetic reductive amination process. The method features mild conditions (1 bar of syngas, room temperature in most cases), high yields (up to 99%), and high enantioselectivities (up to >99.5:0.5 er). Besides styrenes, acrylamides also provided the products with high yields and enantioselectivities. Aliphatic alkenes and vinyl esters are also applicable for the current method, albeit lower yields and enantioselectivities were obtained.

  14. Palladium-Catalyzed Asymmetric Conjugate Addition of Arylboronic Acids to Five-, Six-, and Seven-Membered β-Substituted Cyclic Enones: Enantioselective Construction of All-Carbon Quaternary Stereocenters

    KAUST Repository

    Kikushima, Kotaro

    2011-05-11

    The first enantioselective Pd-catalyzed construction of all-carbon quaternary stereocenters via 1,4-addition of arylboronic acids to β-substituted cyclic enones is reported. Reaction of a wide range of arylboronic acids and cyclic enones using a catalyst prepared from Pd(OCOCF(3))(2) and a chiral pyridinooxazoline ligand yields enantioenriched products bearing benzylic stereocenters. Notably, this transformation is tolerant to air and moisture, providing a practical and operationally simple method of synthesizing enantioenriched all-carbon quaternary stereocenters.

  15. Enantioselective Degradation of Triadimefon in Green-house Soil

    Directory of Open Access Journals (Sweden)

    Liu Hong Cheng

    2015-09-01

    Full Text Available To study enantioselctive degradation of triadimefon, the enantioselective degradation of triadimefon in greenhouse soil and normal soil were investigated in detail. The enantiomers of triadimefon were separated by Chiralpak AD column and determined by Liquid Chromatography Via Tandem Mass Spectrometry (LC-MS/MS. The degradation exhibited some enantioselective, resulting in a concentration order of R-(- tridimefon>S-(+ triadimefon and the degradation of triadimefon in greenhouse soils with high content of organic matter was faster than normal soil.

  16. Albumin–Polymer–Drug Conjugates: Long Circulating, High Payload Drug Delivery Vehicles

    DEFF Research Database (Denmark)

    Smith, Anton Allen Abbotsford; Zuwala, Kaja; Pilgrim, Oliver;

    2016-01-01

    a marginal increase in the circulation lifetime of the drugs. We combine the benefits of the two platforms and at the same time overcome their respective limitations. Specifically, we develop the synthesis of albumin–polymer–drug conjugates to obtain long circulating, high payload drug delivery vehicles....... In vivo data validate that albumin endows the conjugate with a blood residence time similar to that of the protein and well exceeding that of the polymer. Therapeutic activity of the conjugates is validated using prodrugs of panobinostat, an HIV latency reversal agent, in which case the conjugates matched......Albumin is an exquisite tool of nature used in biomedicine to achieve long blood residence time for drugs, but the payload it can carry is typically limited to one molecule per protein. In contrast, synthetic macromolecular prodrugs contain multiple copies of drugs per polymer chain but offer only...

  17. Albumin–Polymer–Drug Conjugates: Long Circulating, High Payload Drug Delivery Vehicles

    DEFF Research Database (Denmark)

    Smith, Anton Allen Abbotsford; Zuwala, Kaja; Pilgram, Oliver

    2016-01-01

    Albumin is an exquisite tool of nature used in biomedicine to achieve long blood residence time for drugs, but the payload it can carry is typically limited to one molecule per protein. In contrast, synthetic macromolecular prodrugs contain multiple copies of drugs per polymer chain but offer only...... a marginal increase in the circulation lifetime of the drugs. We combine the benefits of the two platforms and at the same time overcome their respective limitations. Specifically, we develop the synthesis of albumin–polymer–drug conjugates to obtain long circulating, high payload drug delivery vehicles....... In vivo data validate that albumin endows the conjugate with a blood residence time similar to that of the protein and well exceeding that of the polymer. Therapeutic activity of the conjugates is validated using prodrugs of panobinostat, an HIV latency reversal agent, in which case the conjugates matched...

  18. Asymmetric NHC-catalyzed aza-Diels-Alder reactions: Highly enantioselective route to α-amino acid derivatives and DFT calculations

    KAUST Repository

    Yang, Limin

    2014-08-01

    A facile N-heterocyclic carbene catalytic enantioselective aza-Diels-Alder reaction of oxodiazenes with α-chloroaldehydes as dienophile precursors is reported, with excellent enantioselectivity (ee > 99%) and excellent yield (up to 93%). DFT study showed that cis-TSa, formed from a top face approach of oxodiazene to cis-IIa, is the most favorable transition state and is consistent with the experimental observations. © 2014 American Chemical Society.

  19. High Relaxivity Gadolinium Hydroxypyridonate-Viral Capsid Conjugates: Nano-sized MRI Contrast Agents

    Energy Technology Data Exchange (ETDEWEB)

    Meux, Susan C.; Datta, Ankona; Hooker, Jacob M.; Botta, Mauro; Francis, Matthew B.; Aime, Silvio; Raymond, Kenneth N.

    2007-08-29

    High relaxivity macromolecular contrast agents based on the conjugation of gadolinium chelates to the interior and exterior surfaces of MS2 viral capsids are assessed. The proton nuclear magnetic relaxation dispersion (NMRD) profiles of the conjugates show up to a five-fold increase in relaxivity, leading to a peak relaxivity (per Gd{sup 3+} ion) of 41.6 mM{sup -1}s{sup -1} at 30 MHz for the internally modified capsids. Modification of the exterior was achieved through conjugation to flexible lysines, while internal modification was accomplished by conjugation to relatively rigid tyrosines. Higher relaxivities were obtained for the internally modified capsids, showing that (1) there is facile diffusion of water to the interior of capsids and (2) the rigidity of the linker attaching the complex to the macromolecule is important for obtaining high relaxivity enhancements. The viral capsid conjugated gadolinium hydroxypyridonate complexes appear to possess two inner-sphere water molecules (q = 2) and the NMRD fittings highlight the differences in the local motion for the internal ({tau}{sub RI} = 440 ps) and external ({tau}{sub RI} = 310 ps) conjugates. These results indicate that there are significant advantages of using the internal surface of the capsids for contrast agent attachment, leaving the exterior surface available for the installation of tissue targeting groups.

  20. Highly Enantioselective Construction of Tertiary Thioethers and Alcohols via Phosphine-Catalyzed Asymmetric γ-Addition reactions of 5H-Thiazol-4-ones and 5H-Oxazol-4-ones: Scope and Mechanistic Understandings

    KAUST Repository

    Wang, Tianli

    2015-06-02

    Phosphine-catalyzed highly enantioselective γ-additions of 5H-thiazol-4-ones and 5H-oxazol-4-ones to allenoates have been developed for the first time. With the employment of amino-acid derived bifunctional phosphines, a wide range of substituted 5H-thiazol-4-one and 5H-oxazol-4-one derivatives bearing heteroarom (S or O)-containing tertiary chiral centers were constructed in high yields and excellent enantioselectivities. The reported method provides a facile access to enantioenriched tertiary thioether/alcohols. The mechanism of γ-addition reaction was investigated by performing DFT calculations, and the hydrogen bonding interactions between the Brønsted acid moiety of the phosphine catalysts and the “C=O” unit of donor molecules were shown to be crucial in asymmetric induction.

  1. Enantioselective Michael Addition of Water

    NARCIS (Netherlands)

    Chen, B.S.; Resch, V.; Otten, L.G.; Hanefeld, U.

    2014-01-01

    The enantioselective Michael addition using water as both nucleophile and solvent has to date proved beyond the ability of synthetic chemists. Herein, the direct, enantioselective Michael addition of water in water to prepare important β-hydroxy carbonyl compounds using whole cells of Rhodococcus st

  2. Lewis base activation of Lewis acids: catalytic, enantioselective vinylogous aldol addition reactions.

    Science.gov (United States)

    Denmark, Scott E; Heemstra, John R

    2007-07-20

    The generality of Lewis base catalyzed, Lewis acid mediated, enantioselective vinylogous aldol addition reactions has been investigated. The combination of silicon tetrachloride and chiral phosphoramides is a competent catalyst for highly selective additions of a variety of alpha,beta-unsaturated ketone-, 1,3-diketone-, and alpha,beta-unsaturated amide-derived dienolates to aldehydes. These reactions provided high levels of gamma-site selectivity for a variety of substitution patterns on the dienyl unit. Both ketone- and morpholine amide-derived dienol ethers afforded high enantio- and diastereoselectivity in the addition to conjugated aldehydes. Although alpha,beta-unsaturated ketone-derived dienolate did not react with aliphatic aldehydes, alpha,beta-unsaturated amide-derived dienolates underwent addition at reasonable rates affording high yields of vinylogous aldol product. The enantioselectivities achieved with the morpholine derived-dienolate in the addition to aliphatic aldehydes was the highest afforded to date with the silicon tetrachloride-chiral phosphoramide system. Furthermore, the ability to cleanly convert the morpholine amide to a methyl ketone was demonstrated.

  3. Molecular design toward highly efficient photovoltaic polymers based on two-dimensional conjugated benzodithiophene.

    Science.gov (United States)

    Ye, Long; Zhang, Shaoqing; Huo, Lijun; Zhang, Maojie; Hou, Jianhui

    2014-05-20

    As researchers continue to develop new organic materials for solar cells, benzo[1,2-b:4,5-b']dithiophene (BDT)-based polymers have come to the fore. To improve the photovoltaic properties of BDT-based polymers, researchers have developed and applied various strategies leading to the successful molecular design of highly efficient photovoltaic polymers. Novel polymer materials composed of two-dimensional conjugated BDT (2D-conjugated BDT) have boosted the power conversion efficiency of polymer solar cells (PSCs) to levels that exceed 9%. In this Account, we summarize recent progress related to the design and synthesis of 2D-conjugated BDT-based polymers and discuss their applications in highly efficient photovoltaic devices. We introduce the basic considerations for the construction of 2D-conjugated BDT-based polymers and systematic molecular design guidelines. For example, simply modifying an alkoxyl-substituted BDT to form an alkylthienyl-substituted BDT can improve the polymer hole mobilities substantially with little effect on their molecular energy level. Secondly, the addition of a variety of chemical moieties to the polymer can produce a 2D-conjugated BDT unit with more functions. For example, the introduction of a conjugated side chain with electron deficient groups (such as para-alkyl-phenyl, meta-alkoxyl-phenyl, and 2-alkyl-3-fluoro-thienyl) allowed us to modulate the molecular energy levels of 2D-conjugated BDT-based polymers. Through the rational design of BDT analogues such as dithienobenzodithiophene (DTBDT) or the insertion of larger π bridges, we can tune the backbone conformations of these polymers and modulate their photovoltaic properties. We also discuss the influence of 2D-conjugated BDT on polymer morphology and the blends of these polymers with phenyl-C61 (or C71)-butyric acid methyl ester (PCBM). Finally, we summarize the various applications of the 2D-conjugated BDT-based polymers in highly efficient PSC devices. Overall, this Account

  4. High-Field-Effect Mobility of Low-Crystallinity Conjugated Polymers with Localized Aggregates.

    Science.gov (United States)

    Son, Sung Y; Kim, Yebyeol; Lee, Junwoo; Lee, Gang-Young; Park, Won-Tae; Noh, Yong-Young; Park, Chan E; Park, Taiho

    2016-07-01

    Charge carriers typically move faster in crystalline regions than in amorphous regions in conjugated polymers because polymer chains adopt a regular arrangement resulting in a high degree of π-π stacking in crystalline regions. In contrast, the random polymer chain orientation in amorphous regions hinders connectivity between conjugated backbones; thus, it hinders charge carrier delocalization. Various studies have attempted to enhance charge carrier transport by increasing crystallinity. However, these approaches are inevitably limited by the semicrystalline nature of conjugated polymers. Moreover, high-crystallinity conjugated polymers have proven inadequate for soft electronics applications because of their poor mechanical resilience. Increasing the polymer chain connectivity by forming localized aggregates via π-orbital overlap among several conjugated backbones in amorphous regions provides a more effective approach to efficient charge carrier transport. A simple strategy relying on the density of random copolymer alkyl side chains was developed to generate these localized aggregates. In this strategy, steric hindrance caused by these side chains was modulated to change their density. Interestingly, a random polymer exhibiting low alkyl side chain density and crystallinity displayed greatly enhanced field-effect mobility (1.37 cm(2)/(V·s)) compared with highly crystalline poly(3-hexylthiophene).

  5. A Porphyrin-Based Conjugated Polymer for Highly Efficient In Vitro and In Vivo Photothermal Therapy.

    Science.gov (United States)

    Guo, Bing; Feng, Guangxue; Manghnani, Purnima Naresh; Cai, Xiaolei; Liu, Jie; Wu, Wenbo; Xu, Shidang; Cheng, Xiamin; Teh, Cathleen; Liu, Bin

    2016-12-01

    Conjugated polymers have been increasingly studied for photothermal therapy (PTT) because of their merits including large absorption coefficient, facile tuning of exciton energy dissipation through nonradiative decay, and good therapeutic efficacy. The high photothermal conversion efficiency (PCE) is the key to realize efficient PTT. Herein, a donor-acceptor (D-A) structured porphyrin-containing conjugated polymer (PorCP) is reported for efficient PTT in vitro and in vivo. The D-A structure introduces intramolecular charge transfer along the backbone, resulting in redshifted Q band, broadened absorption, and increased extinction coefficient as compared to the state-of-art porphyrin-based photothermal reagent. Through nanoencapsulation, the dense packing of a large number of PorCP molecules in a single nanoparticle (NP) leads to favorable nonradiative decay, good photostability, and high extinction coefficient of 4.23 × 10(4) m(-1) cm(-1) at 800 nm based on porphyrin molar concentration and the highest PCE of 63.8% among conjugated polymer NPs. With the aid of coloaded fluorescent conjugated polymer, the cellular uptake and distribution of the PorCP in vitro can be clearly visualized, which also shows effective photothermal tumor ablation in vitro and in vivo. This research indicates a new design route of conjugated polymer-based photothermal therapeutic materials for potential personalized theranostic nanomedicine.

  6. N-(4-(4-(2,3-Dichloro- or 2-methoxyphenyl)piperazin-1-yl)-butyl)-heterobiarylcarboxamides with Functionalized Linking Chains as High Affinity and Enantioselective D3 Receptor Antagonistsγ

    Science.gov (United States)

    Newman, Amy Hauck; Grundt, Peter; Cyriac, George; Deschamps, Jeffrey R.; Taylor, Michelle; Kumar, Rakesh; Ho, David; Luedtke, Robert R.

    2009-01-01

    In the present report, the D3 receptor pharmacophore is modified in the 2,3-diCl-and 2-OCH3-phenyl piperazine class of compounds with the goal to improve D3 receptor affinity and selectivity. This extension of structure-activity relationships (SAR) has resulted in the identification of the first enantioselective D3 antagonists (R- and S-22) to be reported, wherein enantioselectivity is more pronounced at D3 than at D2, and that a binding region on the second extracellular loop (E2) may play a role in both enantioselectivity and D3 receptor selectivity. Moreover, we have discovered some of the most D3-selective compounds reported to date that show high affinity (Ki =1 nM) for D3 and ∼400-fold selectivity over the D2 receptor subtype. Several of these analogues showed exquisite selectivity for D3 receptors over >60 other receptors further underscoring their value as in vivo research tools. These lead compounds also have appropriate physical characteristics for in vivo exploration and therefore will be useful in determining how intrinsic activity at D3 receptors tested in vitro is related to behaviors in animal models of addiction and other neuropsychiatric disorders. PMID:19331412

  7. Palladium-Catalyzed, Enantioselective Heine Reaction.

    Science.gov (United States)

    Punk, Molly; Merkley, Charlotte; Kennedy, Katlyn; Morgan, Jeremy B

    2016-07-01

    Aziridines are important synthetic intermediates for the generation of nitrogen-containing molecules. N-Acylaziridines undergo rearrangement by ring expansion to produce oxazolines, a process known as the Heine reaction. The first catalytic, enantioselective Heine reaction is reported for meso-N-acylaziridines where a palladium(II)-diphosphine complex is employed. The highly enantioenriched oxazoline products are valuable organic synthons and potential ligands for transition-metal catalysis.

  8. Highly efficient heterogeneous procedure for the conjugate addition of amines to electron deficient alkenes

    Institute of Scientific and Technical Information of China (English)

    LIANG XueZheng; QUAN NanNan; WANG Jian; YANG JianGuo

    2009-01-01

    The novel efficient procedure has been developed for the conjugate addition of amines to electron deficient alkenes.K2CO3 supported on different carriers have been synthesized for the conjugate addition of amines and alkenes.After optimizing the reaction conditions,K2CO3/MgO was chosen as the most efficient catalyst for the reactions.The results showed that the catalyst was very efficient for the conjugate addition of amines to electron deficient alkenes with the excellent yields in several minutes.Operational simplicity,without need of any solvent,low cost of the catalyst used,high yields,reusability,excellent chemoselectivity,and applicability to large-scale reactions are the key features of this methodology.

  9. Highly efficient heterogeneous procedure for the conjugate addition of amines to electron deficient alkenes

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    The novel efficient procedure has been developed for the conjugate addition of amines to electron deficient alkenes. K2CO3 supported on different carriers have been synthesized for the conjugate addition of amines and alkenes. After optimizing the reaction conditions, K2CO3/MgO was chosen as the most efficient catalyst for the reactions. The results showed that the catalyst was very efficient for the conjugate addition of amines to electron deficient alkenes with the excellent yields in several minutes. Operational simplicity, without need of any solvent, low cost of the catalyst used, high yields, reusability, excellent chemoselectivity, and applicability to large-scale reactions are the key features of this methodology.

  10. Design of a high-quality optical conjugate structure in optical tweezers.

    Science.gov (United States)

    Hu, Chunguang; An, Ran; Zhang, Chengwei; Lei, Hai; Hu, Xiaodong; Li, Hongbin; Hu, Xiaotang

    2015-02-20

    We propose an approach to realize a high-quality optical conjugate of a piezo-driven mirror (PM) in optical tweezers. Misalignments between the optical beam and the steering center of the PM are analyzed mathematically. The decentrations in different directions cause different changes, either a position change of the conjugate plane or a spot variation of the beam during PM steering. On the other hand, these misalignment-introduced problems provide the information to check the assembling errors. Thus a wanted conjugate plane of the PM can be effectively and precisely achieved according to the detection signals. This approach is also available to deal with multifactor coupling error. At the end, the procedure for error analysis is given by testing homebuilt optical tweezers.

  11. Redox-active conjugated microporous polymers: a new organic platform for highly efficient energy storage.

    Science.gov (United States)

    Xu, Fei; Chen, Xiong; Tang, Zhiwei; Wu, Dingcai; Fu, Ruowen; Jiang, Donglin

    2014-05-14

    Conjugated microporous polymers are developed as a new platform for lithium-battery energy storage, which features a near-unity coulombic efficiency, high capacity and cycle stability. The polymers exhibit synergistic structural effects on facilitating charge dynamics by virtue of their built-in redox skeletons, open nanopores and large surface areas.

  12. Highly conjugated water soluble CdSe quantum dots to multiwalled carbon nanotubes

    Institute of Scientific and Technical Information of China (English)

    Gui Zheng Zou

    2009-01-01

    Highly conjugated multiwalled carbon nanotube-quantum dot heterojunctions were synthesized by ethylene carbodiimide coupling procedure. The functional multiwalled carbon nanotube with carboxylic groups on sidewall could react with the amino group of L-cysteine capped CdSe quantum dots and then resulted in nanotube-quantum dot heterojunctions. Scanning electron microscopy was used to characterize the heterojunctions.

  13. Site-specific conjugation of an antibody-binding protein catalyzed by horseradish peroxidase creates a multivalent protein conjugate with high affinity to IgG.

    Science.gov (United States)

    Minamihata, Kosuke; Goto, Masahiro; Kamiya, Noriho

    2015-01-01

    Cross-linking proteins offers an approach to enhance the distinct function of proteins due to the multivalent effect. In this study, we demonstrated the preparation of a multivalent antibody-binding protein possessing high affinity to IgG by conjugating a number of antibody-binding proteins using the horseradish peroxidase (HRP)-mediated protein conjugation method. By introducing a peptide tag containing a tyrosine (Y-tag) to the C-terminus of the model protein, a chimera protein of protein G and protein A (pG2 pA), the Tyr residue in the Y-tag was efficiently recognized by HRP and cross-linked with each other to yield a pG2 pA conjugate, composed of mainly two to three units of pG2 pA. The cross-linking occurred site specifically at the Tyr residue in the Y-tag and introduction of the Y-tag showed no effect on the function of pG2 pA. The affinity of the Y-tagged pG2 pA conjugate against IgG clearly increased because of the multivalent effect, demonstrating the benefit of this protein cross-linking reaction, which yields functional protein oligomers. Such multivalent protein conjugates created by this reaction should have potential to be used in ELISA and Western blotting applications in which highly sensitive detection of target molecules is desired.

  14. Enantioselective addition of diphenyl phosphonate to ketimines derived from isatins catalyzed by binaphthyl-modified organocatalysts

    Science.gov (United States)

    Jang, Hee Seung; Kim, Yubin

    2016-01-01

    Summary Chiral binaphthyl-modified squaramide-catalyzed enantioselective addition of diphenyl phosphonate to ketimines derived from isatins has been achieved. This method affords practical and efficient access to chiral 3-amino-3-phosphonyl-substituted oxindole derivatives in high yields with excellent enantioselectivities (up to 99% ee). PMID:27559405

  15. Enantioselective carbenoid insertion into C(sp3)–H bonds

    Science.gov (United States)

    Santiago, J V

    2016-01-01

    Summary The enantioselective carbenoid insertion into C(sp3)–H bonds is an important tool for the synthesis of complex molecules due to the high control of enantioselectivity in the formation of stereogenic centers. This paper presents a brief review of the early issues, related mechanistic studies and recent applications on this chemistry area. PMID:27340479

  16. Enantioselective addition of diphenyl phosphonate to ketimines derived from isatins catalyzed by binaphthyl-modified organocatalysts

    Directory of Open Access Journals (Sweden)

    Hee Seung Jang

    2016-07-01

    Full Text Available Chiral binaphthyl-modified squaramide-catalyzed enantioselective addition of diphenyl phosphonate to ketimines derived from isatins has been achieved. This method affords practical and efficient access to chiral 3-amino-3-phosphonyl-substituted oxindole derivatives in high yields with excellent enantioselectivities (up to 99% ee.

  17. Enantioselective synthesis of pyrazolone α-aminonitrile derivatives via an organocatalytic Strecker reaction.

    Science.gov (United States)

    Mahajan, Suruchi; Chauhan, Pankaj; Kaya, Uğur; Deckers, Kristina; Rissanen, Kari; Enders, Dieter

    2017-06-21

    A new organocatalytic enantioselective Strecker reaction of pyrazolone-derived ketimine electrophiles has been developed. Using pseudo-enantiomeric squaramide catalysts the nucleophilic 1,2-addition of trimethylsilyl cyanide to the ketimines efficiently provides a direct entry to both enantiomers of pyrazolone α-aminonitrile derivatives at will in good yields and high enantioselectivities for a wide variety of substrates.

  18. Organocatalytic Enantioselective Synthesis of 1,4-Dioxanes and Other Oxa-Heterocycles by Oxetane Desymmetrization.

    Science.gov (United States)

    Yang, Wen; Sun, Jianwei

    2016-01-26

    A new asymmetric synthesis of chiral 1,4-dioxanes and other oxa-heterocycles has been developed by means of organocatalytic enantioselective desymmetrization of oxetanes. This mild process proceeds with exceedingly high efficiency and enantioselectivity to establish the quaternary stereocenters. This method complements the existing, yet limited, strategies for the synthesis of these oxa-heterocycles.

  19. Catalytic, Enantioselective 1,3-Dipolar Cycloadditions of Nitrile Imines with Methyleneindolinones

    Science.gov (United States)

    Gerten, Anthony L.; Slade, Michael C.; Pugh, Kelsie M.

    2013-01-01

    Catalytic, enantioselective 1,3-dipolar cycloadditions of nitrile imines with methyleneindolinones are reported. The spiro[pyrazolin[3,3′-oxindole] products are formed in good yields (up to 98%) and high enantioselectivity (up to 99% ee). PMID:24132663

  20. Enantioselective Pinacol Coupling of Aromatic Aldehydes Induced by Chiral Titanium Complexes

    Institute of Scientific and Technical Information of China (English)

    Qing Fang CHENG; Xing You XU; Ming Yan WANG; Jun CHEN; Wei Xing MA; Xu Jie YANG

    2006-01-01

    Asymmetric pinacol coupling of aromatic aldehydes with TiCl4-Zn in the presence of enantiopure squaric acid amidoalcohols afforded 1, 2-diols in excellent yields with high dldiastereoselectivities and enantioselectivities in the range of 46-89% ee. Some factors influencing dl-diastereoselectivity and enantioselectivity were discussed.

  1. Enhancement of the enantioselectivity of carboxylesterase A by structure-based mutagenesis

    NARCIS (Netherlands)

    Godinho, Luis F.; Reis, Carlos R.; Rozeboom, Henriette J.; Dekker, Frank J.; Dijkstra, Bauke W.; Poelarends, Gerrit J.; Quax, Wim J.

    2012-01-01

    Previously studied Bacillus subtilis carboxylesterases (CesA and CesB) have potential for the kinetic resolution of racemic esters of 1,2-O-isopropylideneglycerol (IPG). CesA exhibits high activity but low enantioselectivity towards IPG-butyrate and IPG-caprylate, while the more enantioselective Ces

  2. Gold(I)-Catalyzed Dearomative Rautenstrauch Rearrangement: Enantioselective Access to Cyclopenta[b]indoles

    Science.gov (United States)

    Zi, Weiwei; Wu, Hongmiao; Toste, F. Dean

    2016-01-01

    A highly enantioselective dearomative Rautenstrauch rearrangement catalyzed by cationic (S)-DTBM-Segphosgold(I) is reported. This reaction provides a straightforward method to prepare enantioenriched cyclopenta[b]indoles. These studies show vast difference in enantioselectivity in the reactions of propargyl acetates and propargyl acetals in the chiral ligand-controlled Rautenstrauch reaction. PMID:25710515

  3. Controlling Enantioselectivity in Additions to Cyclic Oxocarbenium Ions via Transition Metal Catalysis.

    Science.gov (United States)

    Watson, Mary P; Maity, Prantik

    2012-01-01

    Controlling enantioselectivity in additions to oxocarbenium ions remains a challenge in asymmetric catalysis. By catalytically generating a chiral organometallic intermediate, a copper acetylide, we have developed a novel approach for additions of carbon nucleophiles to cyclic oxocarbenium ions in high enantioselectivities and yields.

  4. Photo- and biophysical studies of lectin-conjugated fluorescent nanoparticles: reduced sensitivity in high density assays.

    Science.gov (United States)

    Wang, Yaqi; Gildersleeve, Jeffrey C; Basu, Amit; Zimmt, Matthew B

    2010-11-18

    Lectin-conjugated, fluorescent silica nanoparticles (fNP) have been developed for carbohydrate-based histopathology evaluations of epithelial tissue biopsies. The fNP platform was selected for its enhanced emissive brightness compared to direct dye labeling. Carbohydrate microarray studies were performed to compare the carbohydrate selectivity of the mannose-recognizing lectin Concanavalin A (ConA) before and after conjugation to fluorescent silica nanoparticles (ConA-fNP). These studies revealed surprisingly low emission intensities upon staining with ConA-fNP compared to those with biotin-ConA/Cy3-streptavidin staining. A series of photophysical and biophysical characterizations of the fNP and ConA-fNP conjugates were performed to probe the low sensitivity from fNP in the microarray assays. Up to 1200 fluorescein (FL) and 80 tetramethylrhodamine (TR) dye molecules were incorporated into 46 nm diameter fNP, yielding emissive brightness values 400 and 35 times larger than the individual dye molecules, respectively. ConA lectin conjugated to carboxylic acid surface-modified nanoparticles covers 15-30% of the fNP surface. The CD spectra and mannose substrate selectivity of ConA conjugated to the fNP differed slightly compared to that of soluble ConA. Although, the high emissive brightness of fNP enhances detection sensitivity for samples with low analyte densities, large fNP diameters limit fNP recruitment and binding to samples with high analyte densities. The high analyte density and nearly two-dimensional target format of carbohydrate microarrays make probe size a critical parameter. In this application, fNP labels afford minimal sensitivity advantage compared to direct dye labeling.

  5. Flexible C2-symmetric bis-sulfoxides as ligands in enantioselective 1,4-addition of boronic acids to electron-deficient alkenes.

    Science.gov (United States)

    Khiar, Noureddine; Salvador, Álvaro; Valdivia, Victoria; Chelouan, Ahmed; Alcudia, Ana; Álvarez, Eleuterio; Fernández, Inmaculada

    2013-07-05

    The application of acyclic C2-symmetric chelating bis-sulfoxide ligands in the Rh(I)-catalyzed enantioselective 1,4-addition of boronic acids to electron-deficient alkenes is reported. Among the acyclic ethane-bridged bis-sulfoxides tested, the ligand Ferbisox (11), bearing ferrocenyl moieties as substituents at the sulfinyl sulfurs, has exhibited the best results in terms of chemical yield (up to 96%) and enantioselectivity (up to 97% ee). The conjugate addition takes place smoothly in toluene at room temperature in short reaction times (typically 2 h). The reaction scope, including the use of different boronic acids, five-, six-, and seven-membered cyclic enones, an unsaturated lactone, and the most challenging acyclic ketones, is reported. An X-ray diffraction study of the [Ferbisox·RhCl]2 precatalyst clearly exhibits a dimeric structure with an S coordination of the sulfoxide to rhodium. On the basis of the X-ray data and on structural studies conducted in solution by (1)H NMR, a model explaining the high enantioselection observed is proposed.

  6. Effective and novel enantioselective preparation of pyranopyrazoles and pyranocoumarins that is catalyzed by a quinine-derived primary amine.

    Science.gov (United States)

    Yang, Sai; Shen, Liu-lan; Kim, Yoon-Jung; Jeong, Jin-Hyun

    2016-01-14

    In this study, we executed an effective and novel enantioselective Michael/cyclodehydration sequential reaction between pyrazolin-5-one (or 4-hydroxy-2-pyrone) and chalcones that is catalyzed by a quinine-derived primary amine L7 in the presence of Boc-D-Phg-OH. Chiral pyranopyrazoles and pyranocoumarins were obtained in excellent enantioselectivities (up to 93%) with moderate yields and moderate enantioselectivities with high yields (up to 84%).

  7. Chiral Lewis base-assisted Brønsted acid (LBBA)-catalyzed enantioselective cyclization of 2-geranylphenols.

    Science.gov (United States)

    Sakakura, Akira; Sakuma, Masayuki; Ishihara, Kazuaki

    2011-06-17

    Chiral Lewis base-assisted Brønsted acids (Chiral LBBAs) have been designed as new organocatalysts for biomimetic enantioselective cyclization. A salt of a chiral phosphonous acid diester with FSO(3)H catalyzes the enantioselective cyclization of 2-geranylphenols to give the desired trans-fused cyclized products with high diastereo- and enantioselectivities (up to 98:2 dr and 93% ee). © 2011 American Chemical Society

  8. Development of Enantioselective Fluorescent Sensors for Chiral Recognition

    Institute of Scientific and Technical Information of China (English)

    Lin Pu

    2004-01-01

    Novel chiral compounds have been synthesized for the enantioselective fluorescent recognition of alpha-hydroxycarboxylic acids and amino acids. By introducing dendritic branches to the chiral receptor units, the fluorescence signals of the receptors are significantly amplified because of the light-harvesting effect of the dendritic structure. This has greatly increased the sensitivity of the sensors in the fluorescent recognition. Highly enantioselective fluorescent responses have also been achieved. These sensors are potentially useful for the high throughput screening of chiral catalysts for asymmetric synthesis.

  9. Biotin-conjugated fusogenic liposomes for high-quality cell purification.

    Science.gov (United States)

    Hersch, Nils; Wolters, Benjamin; Ungvari, Zoltan; Gautam, Tripti; Deshpande, Dhruva; Merkel, Rudolf; Csiszar, Anna; Hoffmann, Bernd; Csiszár, Agnes

    2016-01-01

    Purification of defined cell populations from mixed primary cell sources is essential for many biomedical and biotechnological applications but often very difficult to accomplish due to missing specific surface markers. In this study, we developed a new approach for efficient cell population separation based on the specific membrane fusion characteristics of distinct cell types upon treatment with fusogenic liposomes. When such liposomes are conjugated with biotin, specific cell populations can be efficiently surface functionalized by biotin after liposomal treatment while other populations remain unlabeled. Due to the high affinity of biotin for avidin-like proteins, biotin functionalized cells are ideal targets for conjugation of e.g. avidin tagged magnetic beads, fluorophores or antibodies with bioanalytical relevance. Here, based on the differential biotinylation of distinct cell populations high quality separation of cardiac fibroblasts from myocytes, and cerebromicrovascular endothelial cells from fibroblasts was successfully established.

  10. Isothiourea-catalysed enantioselective pyrrolizine synthesis: synthetic and computational studies.

    Science.gov (United States)

    Stark, Daniel G; Williamson, Patrick; Gayner, Emma R; Musolino, Stefania F; Kerr, Ryan W F; Taylor, James E; Slawin, Alexandra M Z; O'Riordan, Timothy J C; Macgregor, Stuart A; Smith, Andrew D

    2016-10-14

    The catalytic enantioselective synthesis of a range of cis-pyrrolizine carboxylate derivatives with outstanding stereocontrol (14 examples, >95 : 5 dr, >98 : 2 er) through an isothiourea-catalyzed intramolecular Michael addition-lactonisation and ring-opening approach from the corresponding enone acid is reported. An optimised and straightforward three-step synthetic route to the enone acid starting materials from readily available pyrrole-2-carboxaldehydes is delineated, with benzotetramisole (5 mol%) proving the optimal catalyst for the enantioselective process. Ring-opening of the pyrrolizine dihydropyranone products with either MeOH or a range of amines leads to the desired products in excellent yield and enantioselectivity. Computation has been used to probe the factors leading to high stereocontrol, with the formation of the observed cis-steroisomer predicted to be kinetically and thermodynamically favoured.

  11. Developing conjugated polymers with high electron affinity by replacing a C-C unit with a B←N unit.

    Science.gov (United States)

    Dou, Chuandong; Ding, Zicheng; Zhang, Zijian; Xie, Zhiyuan; Liu, Jun; Wang, Lixiang

    2015-03-16

    The key parameters of conjugated polymers are lowest unoccupied molecular orbital (LUMO) and highest occupied molecular orbital (HOMO) energy levels. Few approaches can simultaneously lower LUMO and HOMO energy levels of conjugated polymers to a large extent (>0.5 eV). Disclosed herein is a novel strategy to decrease both LUMO and HOMO energy levels of conjugated polymers by about 0.6 eV through replacement of a C-C unit by a B←N unit. The replacement makes the resulting polymer transform from an electron donor into an electron acceptor, and is proven by fluorescence quenching experiments and the photovoltaic response. This work not only provides an effective approach to tune the LUMO/HOMO energy levels of conjugated polymers, but also uses organic boron chemistry as a new toolbox to develop conjugated polymers with high electron affinity for polymer optoelectronic devices.

  12. Biphasic enantioselective olefin epoxidation using Tropos dibenzoazepinium catalysts.

    Science.gov (United States)

    Vachon, Jérôme; Pérollier, Céline; Monchaud, David; Marsol, Claire; Ditrich, Klaus; Lacour, Jérôme

    2005-07-22

    Several novel chiral iminium TRISPHAT [tris(tetrachlorobenzenediolato)phosphate(V)] salts combining a diphenylazepinium core, chiral exocyclic appendages, and lipophilic counterions have been prepared and tested in biphasic enantioselective olefin epoxidation conditions. Interestingly, the iminium salts derived from commercially available (S)- or (R)-1,2,2-trimethylpropylamine can display efficiency similar to those made from L-acetonamine. Variable-temperature NMR spectroscopy (VT-NMR) and circular dichroism (CD) experiments were performed in search of a correlation between good enantioselectivity in the products and high diastereomeric control of the biphenyl axial chirality of the catalysts.

  13. Improvement of the analysis of dansylated derivatives of polyamines and their conjugates by high-performance liquid chromatography.

    Science.gov (United States)

    Fontaniella, B; Mateos, J L; Vicente, C; Legaz, M E

    2001-06-15

    The paper described a method for improving the hydrolysis of conjugated polyamines in PH fraction, isolated from the lichen Evernia prunastri, as well as the optimization of dansylation procedure of these polyamines on the basis of the pH value to which derivatization is achieved. Dansylated polyamines have been later separated by high-performance liquid chromatography (HPLC) using a gradient elution. Hydrolysis of conjugates requires acid treatment at room temperature rather than at 110 degrees C, as usually described. Dansylation is improved at high pH values, whereas removal of phenolics (mainly evernic acid), from the conjugates requires low pH values.

  14. Enantioselective synthesis of helical polydiacetylene by application of linearly polarized light and magnetic field.

    Science.gov (United States)

    Xu, Yangyang; Yang, Guang; Xia, Hongyan; Zou, Gang; Zhang, Qijin; Gao, Jiangang

    2014-09-23

    Magnetic optical activity, which can occur in all media and is induced by longitudinal magnetic field, causes the difference in absorption coefficients of left and right circularly polarized light and has the potential for magnetically induced enantioselectivity in chemical reactions. Compared with the well-established technique with circularly polarized light, there are few reports on the production of helical conjugated polymers in a photochemical reaction based on above magnetochiral anisotropy mechanism. Herein, we demonstrate experimentally that the enantioselective polymerization of diacetylene derivative can be achieved in the liquid crystal phase by application of linearly polarized light under a parallel or antiparallel magnetic field. The screw direction of predominant helical polydiacetylene chain can be rigorously controlled with the relative orientation of linearly polarized light and the magnetic field. Moreover, the prepared helical polydiacetylene assemblies can serve as a direct visual probe for the enantioselective recognition of D- or L-lysine.

  15. High-mobility n-type conjugated polymers based on electron-deficient tetraazabenzodifluoranthene diimide for organic electronics.

    Science.gov (United States)

    Li, Haiyan; Kim, Felix Sunjoo; Ren, Guoqiang; Jenekhe, Samson A

    2013-10-09

    High-mobility p-type and ambipolar conjugated polymers have been widely reported. However, high-mobility n-type conjugated polymers are still rare. Herein we present poly(tetraazabenzodifluoranthene diimide)s, PBFI-T and PBFI-BT, which exhibit a novel two-dimensional (2D) π-conjugation along the main chain and in the lateral direction, leading to high-mobility unipolar n-channel transport in field-effect transistors. The n-type polymers exhibit electron mobilities of up to 0.30 cm(2)/(V s), which is among the highest values for unipolar n-type conjugated polymers. Complementary inverters incorporating n-channel PBFI-T transistors produced nearly perfect switching characteristics with a high gain of 107.

  16. Reverse Polarization of a High-Energy Exciton in Conjugated Polymers

    Institute of Scientific and Technical Information of China (English)

    李晓雪; 董宪峰; 高琨; 解士杰

    2011-01-01

    Polarization of a high-energy exciton in conjugated polymers is investigated theoretically by using an extended one-dimensional tight-binding Su-Schrieffer-Heeger(SSH)model.Under an external electric field,the reverse polarization of a high-energy exciton is obtained and the corresponding physical mechanism is analyzed.A critical field Ec is obtained,over which the polarization of the high-energy exciton will switch from negative to positive.In addition,by taking into account the effect of the non-degenerate confinement,we find that it is possible to realize reverse polarization through high energy photoexcitation in non-degenerate polymers.%Polarization of a high-energy exciton in conjugated polymers is investigated theoretically by using an extended one-dimensional tight-binding Su-Schrieffer-Heeger (SSH) model. Under an external electric field, the reverse polarization of a high-energy exciton is obtained and the corresponding physical mechanism is analyzed. A critical Held Ec is obtained, over which the polarization of the high-energy exciton will switch from negative to positive. In addition, by taking into account the effect of the non-degenerate confinement, we find that it is possible to realize reverse polarization through high energy photoexcitation in non-degenerate polymers.

  17. Enantioselective synthesis of α-oxy amides via Umpolung amide synthesis.

    Science.gov (United States)

    Leighty, Matthew W; Shen, Bo; Johnston, Jeffrey N

    2012-09-19

    α-Oxy amides are prepared through enantioselective synthesis using a sequence beginning with a Henry addition of bromonitromethane to aldehydes and finishing with Umpolung Amide Synthesis (UmAS). Key to high enantioselection is the finding that ortho-iodo benzoic acid salts of the chiral copper(II) bis(oxazoline) catalyst deliver both diastereomers of the Henry adduct with high enantiomeric excess, homochiral at the oxygen-bearing carbon. Overall, this approach to α-oxy amides provides an innovative complement to alternatives that focus almost entirely on the enantioselective synthesis of α-oxy carboxylic acids.

  18. Catalytic Enantioselective Electrophilic Aminations of Acyclic α-Alkyl β-Carbonyl Nucleophilies.

    Science.gov (United States)

    Liu, Xiaofeng; Sun, Bingfeng; Deng, Li

    2009-06-01

    Highly enantioselective aminations of acyclic α-alkyl β-keto thioesters and trifluoroethyl α-methyl α-cyanoacetate (12) with as low as 0.05 mol % of a bifunctional cinchona alkaloid catalyst were established. This ability to afford highly enantioselectivity for the amination of α-alkyl β-carbonyl compounds renders the 6'-OH cinchona alkaloid-catalyzed amination applicable for the enantioselective synthesis of acyclic chiral compounds bearing N-substituted quaternary stereocenters. The synthetic application of this reaction is illustrated in a concise asymmetric synthesis of α-methylserine, a key intermediate previously utilized in the total synthesis of a small molecule immunomodulator, conagenin.

  19. Highly enantioselective aza-Diels-Alder reaction of 1-azadienes with enecarbamates catalyzed by chiral phosphoric acids.

    Science.gov (United States)

    He, Long; Laurent, Gregory; Retailleau, Pascal; Folléas, Benoît; Brayer, Jean-Louis; Masson, Géraldine

    2013-10-11

    On demand: A highly enantio- and diastereoselective synthesis of 6-amino- trisubstituted tetrahydropyridine compounds has been developed through the inverse-electron-demand aza-Diels-Alder reaction of N-aryl α,β-unsaturated ketimines with enecarbamates (E)-1. Chiral phosphoric acid catalysts achieve simultaneous activation of both the 1-azadiene and dienophile partners.

  20. Ionic liquid-supported (ILS) (S)-pyrrolidine sulfonamide, a recyclable organocatalyst for the highly enantioselective Michael addition to nitroolefins.

    Science.gov (United States)

    Ni, Bukuo; Zhang, Qianying; Dhungana, Kritanjali; Headley, Allan D

    2009-02-19

    A new class of ionic liquid supported (ILS) (S)-pyrrolidine sulfonamide organocatalyst has been developed and shown to be a very effective catalyst for the asymmetric Michael addition reactions of ketones and aldehyde to nitroolefins with high enantio- and diastereoselectivities. This ILS organocatalyst is also easily recycled and could be reused at least five times without significant loss of its ability to affect the outcome of the asymmetric reactions.

  1. Highly Efficient Conjugate Addition of Amines to Electron Deficient Alkenes Catalyzed by KF Supported on Metal Oxides

    Institute of Scientific and Technical Information of China (English)

    LIANG, Xuezheng; ZHANG, Jinga; BAO, Shaohua; YANG, Jianguo

    2009-01-01

    A novel efficient procedure has been developed for the conjugate addition of amines to electron deficient al- kenes. A series of KF supported on different carders have been synthesized for the conjugate addition amines to al- kenes. After optimizing the reaction conditions, KF/MgO was chosen as the most efficient catalyst for the reactions. The results showed that the catalyst was very efficient for the conjugate addition of amines to electron deficient al- kenes with excellent yields in several minutes. Operational simplicity, no need of any solvent, low cost of the cata- lyst used, high yields, reusability, excellent chemoselectivity and wide applicability are the key features of this methodology.

  2. Rh-Catalyzed Chemo- and Enantioselective Hydrogenation of Allylic Hydrazones.

    Science.gov (United States)

    Hu, Qiupeng; Hu, Yanhua; Liu, Yang; Zhang, Zhenfeng; Liu, Yangang; Zhang, Wanbin

    2017-01-23

    A highly efficient P-stereogenic diphosphine-rhodium complex was applied to the chemo- and enantioselective hydrogenation of allylic hydrazones for the synthesis of chiral allylic hydrazines in 89-96 % yields and with 82-99 % ee values. This methodology was successfully applied to the preparation of versatile chiral allylic amine derivatives.

  3. Copper-Catalyzed Enantioselective Allyl-Allyl Cross-Coupling

    NARCIS (Netherlands)

    Hornillos, Valentin; Perez, Manuel; Fananas-Mastral, Martin; Feringa, Ben L.

    2013-01-01

    A Cu(I)-phosphoramidite-based catalytic system that allows asymmetric allyl-allyl cross-coupling with high enantioselectivity is reported. This transformation tolerates a large variety of functionalized substrates. The versatility of this new reaction is illustrated in the catalytic asymmetric

  4. Guanidine-catalyzed enantioselective desymmetrization of meso-aziridines

    KAUST Repository

    Zhang, Yan

    2011-01-01

    An amino-indanol derived chiral guanidine was developed as an efficient Brønsted base catalyst for the desymmetrization of meso-aziridines with both thiols and carbamodithioic acids as nucleophiles, which provided 1,2-difunctionalized ring-opened products in high yields and enantioselectivities. © The Royal Society of Chemistry.

  5. Enantioselective Enzymes by Computational Design and In Silico Screening

    NARCIS (Netherlands)

    Wijma, Hein J; Floor, Robert J; Bjelic, Sinisa; Marrink, Siewert J; Baker, David; Janssen, Dick B

    2015-01-01

    Computational enzyme design holds great promise for providing new biocatalysts for synthetic chemistry. A strategy to design small mutant libraries of complementary enantioselective epoxide hydrolase variants for the production of highly enantioenriched (S,S)-diols and (R,R)-diols is developed. Key

  6. Catalytic enantioselective cyclization and C3-fluorination of polyenes.

    Science.gov (United States)

    Cochrane, Nikki A; Nguyen, Ha; Gagne, Michel R

    2013-01-16

    (Xylyl-phanephos)Pt(2+) in combination with XeF(2) mediates the consecutive diastereoselective cation-olefin cyclization/fluorination of polyene substrates. Isolated yields were typically in the 60-69% range while enantioselectivities reached as high as 87%. The data are consistent with a stereoretentive fluorination of a P(2)Pt-alkyl cation intermediate.

  7. Enantioselective determination of chiral toxaphene congeners in laying hens and eggs using multidimensional high-resolution gas chromatography.

    Science.gov (United States)

    Hamed, Sobhy; Leupold, Guenter; Ismail, Ahmed; Parlar, Harun

    2005-09-07

    A total of 22 chiral toxaphene congeners were analyzed in organ tissues and eggs of laying hens after they had been fed with food spiked with technical toxaphene. For the analysis, multidimensional high-resolution gas chromatography using a chiral column coated with randomly silylated heptakis(O-tert-butyldimethylsilyl)-beta-cyclodextrin, electron capture detection, and valveless "live column switching" technique was applied. The analytical results were additionally confirmed with mass spectral data, recorded in electron-capture negative ionization mode with selected-ion monitoring mass spectrometry. During both the feeding period of the laying hens with toxaphene-contaminated food (38 weeks, accumulation phase) and the following subsiding period without toxaphenes (another 14 weeks, decontamination phase), organs (liver, kidney, skin/fat), blood, meat, and eggs of the hens served as model matrices for toxaphene uptake. The enantiomeric ratios (ERs) of congeners 26, 31, 32, 40, 41, 42(a+b), 44, 50, and 62--known as the most important components of technical toxaphene occurring in the environment--could be analytically determined. Significant differences were observed with respect to their initial racemic ratios. On the basis of their chemical structures, the metabolic pathways of some congeners could be explained. Astonishingly, some of the toxaphenes applied as racemates could merely be found as single enantiomers at the end of the feeding program, for example, congener 32 in blood and meat samples or congener 44, especially in organ tissues, which showed ERs of zero or infinity. The findings of this study impressively emphasize that it is essential to isolate and analyze individual toxaphene enantiomers in food and biota tissues to be capable of evaluating their toxicity and metabolization more specifically.

  8. Tropos or atropos nature of rhodium complexes bearing a tetrakis(phosphanyl)terphenyl ligand: highly enantioselective catalysis of ene-type cyclization.

    Science.gov (United States)

    Mikami, Koichi; Kataoka, Shohei; Aikawa, Kohsuke

    2005-12-22

    [reaction and structure: see text] Not only axial but also helical chirality of tropos TETRAPHOS-Rh complexes can be controlled by chiral diamines. The flexibility of the TETRAPHOS-Rh complex is increased by association of DABN. In contrast, the diamine-free complex is chirally more stable than the BIPHEP counterpart. The higher levels of enantioselectivity in ene-type cyclization of 1,6-enynes can thus be achieved even at room temperature by the diamine-free TETRAPHOS-Rh complex.

  9. Enantioselective Synthesis of cis-Decalins Using Organocatalysis and Sulfonyl Nazarov Reagents

    Directory of Open Access Journals (Sweden)

    Javier Peña

    2015-04-01

    Full Text Available The first organocatalytic synthesis of cis-decalins using sulfonyl Nazarov reagents is reported. The Jørgensen’s catalyst directs this highly enantioselective synthesis using different cyclohexenal derivatives.

  10. Bipolar and Unipolar Silylene-Diphenylene σ-π Conjugated Polymer Route for Highly Efficient Electrophosphorescence

    Science.gov (United States)

    Chang, Yao-Tang; Sharma, Sunil; Hung, Miao-Ken; Lee, Yu-Hsuan; Chen, Show-An

    2016-12-01

    σ-π conjugated polymer strategy is proposed for designing electroluminescent host polymers with silylene-diphenylene as the backbone repeat unit giving a high triplet energy (ET = 2.67 eV). By incorporation of high ET (3.0 eV) electron (oxadiazole, OXD) and hole (triphenyl amine, TPA) transport moieties, or TPA alone (in this case, the main chain acts as electron transport channel) as side arms on the silylene, the high ET bipolar and unipolar polymers are formed, allowing a use of iridium green phosphor (Ir(ppy)2(acac), Ir-G) (ET = 2.40 eV) as the dopant. The matching of energy levels of the dopant with the hosts, leading to charge trapping into it; and singlets and triplets of the exciplex and excimer can be harvested via energy transfer to the dopant. Using these host-guest systems as the emitting layer, chlorinated indium-tin-oxide (Cl-ITO) as the anode, and benzimidazole derivative (TPBI) as the electron transport layer, this two-layer device gives the high luminance efficiency 80.1 cd/A and external quantum efficiency 21.2%, which is the best among the report values for polymer light emitting diode (PLED) in the literatures. This example manifests that σ-π conjugated polymer strategy is a promising route for designing polymer host for efficient electrophosphorescence.

  11. CONJUGATE MODEL FOR HEAT AND MASS TRANSFER OF POROUS WALL IN THE HIGH TEMPERATURE GAS FLOW

    Institute of Scientific and Technical Information of China (English)

    A.F. Polyakov; D.L.Reviznikov; 沈青; 魏叔如

    2001-01-01

    Heat and mass transfer of a porous permeable wall in a high temperature gas dynamical flow is considered. Numerical simulation is conducted on the ground of the conjugate mathematical model which includes filtration and heat transfer equations in a porous body and boundary layer equations on its surface. Such an approach enables one to take into account complex interaction between heat and mass transfer in the gasdynamical flow and in the structure subjected to this flow.The main attention is given to the impact of the intraporous heat transfer intensity on the transpiration cooling efficiency.

  12. High-field mobility in an assembly of conjugated polymer segments

    Science.gov (United States)

    Bussac, M. N.; Zuppiroli, L.

    1996-08-01

    We present a calculation of the hopping rate between the finite chains of a conjugated polymer. It is based on the optimization of the semiclassical hopping rates with respect to the possible widths and possible positions of the large polaron during the jump. For sufficient long chains and high enough fields, we arrive at an expression for the mobility which resembles a Fowler-Nordheim dependence with the field F, namely, exp-(F0/F). In this regime the mobility is weakly temperature dependent.

  13. Co(salen)-mediated enantioselective radiofluorination of epoxides. Synthesis and biological evaluation of both enantiomers of [18F]FMISO

    DEFF Research Database (Denmark)

    Revunov, Evgeny V.

    -fluoride) in a combination with chiral base ((-)tetramisole), chiral Lewis acid ((R,R)-Co(salen)) and hexafluoroisopropanol, providing the corresponding (S)-[18F]fluorohydrines enantioselectively (20-46% enantiomeric excess) with high yields (78-93 % radiochemical yield). The enantioselective Co(salen)-mediated no...

  14. Enantioselective aldol reaction between isatins and cyclohexanone catalyzed by amino acid sulphonamides.

    Science.gov (United States)

    Wang, Jun; Liu, Qi; Hao, Qing; Sun, Yanhua; Luo, Yiming; Yang, Hua

    2015-04-01

    Sulphonamides derived from primary α-amino acid were successfully applied to catalyze the aldol reaction between isatin and cyclohexanone under neat conditions. More interestingly, molecular sieves, as privileged additives, were found to play a vital role in achieving high enantioselectivity. Consequently, high yields (up to 99%) along with good enantioselectivities (up to 92% ee) and diastereoselectivities (up to 95:5 dr) were obtained. In addition, this reaction was also conveniently scaled up, demonstrating the applicability of this protocol.

  15. Highly enantioselective (-)-sparteine-mediated lateral metalation-functionalization of remote silyl protected ortho-ethyl N,N-dialkyl aryl O-carbamates.

    Science.gov (United States)

    Fässler, Jürg; McCubbin, J Adam; Roglans, Anna; Kimachi, Tetsutaro; Hollett, Joshua W; Kunz, Roland W; Tinkl, Michael; Zhang, Yousheng; Wang, Ruiyao; Campbell, Michael; Snieckus, Victor

    2015-04-03

    We report the enantioselective, lateral deprotonation of ortho-protected or functionalized tertiary N,N-dialkyl aryl O-carbamates 5-7 (Scheme 2 ) and meta-protected carbamates 14, 15, and 20 (Schemes 5 and 7 ) by s-BuLi/(-)-sparteine and subsequent quench with a variety of electrophiles to give products 11-13 and 16, 17, and 21 in yields up to 96% and enantiomeric ratios up to 99:1. The influence of organolithium reagents, ratio of organolithium/(-)-sparteine pair versus N,N-dialkyl aryl O-carbamate starting materials, temperature, solvents, electrophiles, substituents located ortho or meta to the O-carbamate moiety, and O-carbamate N-substituents was investigated. The identical absolute configuration of the stereogenic center of the major enantiomers of the products, as established by single-crystal X-ray analysis for substrates (S)-11c, (S)-19, and (S)-21a, provides evidence for a consistent stereochemical course in the enantioselective deprotonation. Mechanistic investigations, including an estimate of the configurational stability of the benzyllithium species 9 (starting from 12e; Scheme 8 ) and 23 (starting from 17e; Scheme 9 ), both derived by tin-lithium exchange, and 24 (starting from 20; Scheme 9 ) are reported. The experimental results, together with semiempirical molecular orbital calculations (PM3/SMD), are consistent with a process in which enantioinduction occurs in the deprotonation step (Scheme 11 ).

  16. Electropolymerized Star-Shaped Benzotrithiophenes Yield π-Conjugated Hierarchical Networks with High Areal Capacitance

    KAUST Repository

    Ringk, Andreas

    2016-03-30

    High-surface-area π-conjugated polymeric networks have the potential to lend outstanding capacitance to supercapacitors because of the pronounced faradaic processes that take place across the dense intimate interface between active material and electrolytes. In this report, we describe how benzo[1,2-b:3,4-b’:5,6-b’’]trithiophene (BTT) and tris-EDOT-benzo[1,2-b:3,4-b’:5,6-b’’]trithiophene (TEBTT) can serve as 2D (trivalent) building blocks in the development of electropolymerized hierarchical π-conjugated frameworks with particularly high areal capacitance. In comparing electropolymerized networks of BTT, TEBTT, and their copolymers with EDOT, we show that P(TEBTT/EDOT)-based frameworks can achieve higher areal capacitance (e.g., as high as 443.8 mF cm-2 at 1 mA cm-2) than those achieved by their respective homopolymers (PTEBTT and PEDOT) in the same experimental conditions of electrodeposition (PTEBTT: 271.1 mF cm-2 (at 1 mA cm-2) and PEDOT: 12.1 mF cm-2 (at 1 mA cm-2)). For example, P(TEBTT/EDOT)-based frameworks synthesized in a 1:1 monomer-to-comonomer ratio show a ca. 35x capacitance improvement over PEDOT. The high areal capacitance measured for P(TEBTT/EDOT) copolymers can be explained by the open, highly porous hierarchical morphologies formed during the electropolymerization step. With >70% capacitance retention over 1,000 cycles (up to 89% achieved), both PTEBTT- and P(TEBTT/EDOT)-based frameworks are resilient to repeated electrochemical cycling and can be considered promising systems for high life cycle capacitive electrode applications.

  17. Enantioselective Brønsted acid catalyzed transfer hydrogenation: organocatalytic reduction of imines.

    Science.gov (United States)

    Rueping, Magnus; Sugiono, Erli; Azap, Cengiz; Theissmann, Thomas; Bolte, Michael

    2005-08-18

    The first enantioselective Brønsted acid catalyzed reduction of imines has been developed. This new organocatalytic transfer hydrogenation of ketimines with Hantzsch dihydropyridine as the hydrogen source offers a mild method to various chiral amines with high enantioselectivity. The stereochemistry of the chiral amines can be rationalized by a stereochemical model derived from an X-ray crystal structure of a chiral BINOL phosphate catalyst. [reaction: see text

  18. Enantioselective palladium-catalyzed dearomative cyclization for the efficient synthesis of terpenes and steroids.

    Science.gov (United States)

    Du, Kang; Guo, Pan; Chen, Yuan; Cao, Zhen; Wang, Zheng; Tang, Wenjun

    2015-03-02

    A novel enantioselective palladium-catalyzed dearomative cyclization has been developed for the efficient construction of a series of chiral phenanthrenone derivatives bearing an all-carbon quaternary center. The effectiveness of this method in the synthesis of terpenes and steroids was demonstrated by a highly efficient synthesis of a kaurene intermediate, the facile construction of the skeleton of the anabolic steroid boldenone, and the enantioselective total synthesis of the antimicrobial diterpene natural product (-)-totaradiol.

  19. Asymmetric allylation of α-ketoester-derived N-benzoylhydrazones promoted by chiral sulfoxides/N-oxides Lewis bases: highly enantioselective synthesis of quaternary α-substituted α-allyl-α-amino acids.

    Science.gov (United States)

    Reyes-Rangel, Gloria; Bandala, Yamir; García-Flores, Fred; Juaristi, Eusebio

    2013-09-01

    Chiral sulfoxides/N-oxides (R)-1 and (R,R)-2 are effective chiral promoters in the enantioselective allylation of α-keto ester N-benzoylhydrazone derivatives 3a-g to generate the corresponding N-benzoylhydrazine derivatives 4a-g, with enantiomeric excesses as high as 98%. Representative hydrazine derivatives 4a-b were subsequently treated with SmI2, and the resulting amino esters 5a-b with LiOH to obtain quaternary α-substituted α-allyl α-amino acids 6a-b, whose absolute configuration was assigned as (S), with fundament on chemical correlation and electronic circular dichroism (ECD) data. © 2013 Wiley Periodicals, Inc.

  20. Diketopyrrolopyrrole-diketopyrrolopyrrole-based conjugated copolymer for high-mobility organic field-effect transistors

    KAUST Repository

    Kanimozhi, Catherine K.

    2012-10-10

    In this communication, we report the synthesis of a novel diketopyrrolopyrrole-diketopyrrolopyrrole (DPP-DPP)-based conjugated copolymer and its application in high-mobility organic field-effect transistors. Copolymerization of DPP with DPP yields a copolymer with exceptional properties such as extended absorption characteristics (up to ∼1100 nm) and field-effect electron mobility values of >1 cm 2 V -1 s -1. The synthesis of this novel DPP-DPP copolymer in combination with the demonstration of transistors with extremely high electron mobility makes this work an important step toward a new family of DPP-DPP copolymers for application in the general area of organic optoelectronics. © 2012 American Chemical Society.

  1. Enantioselective Transport by a Steroidal Guanidinium Receptor

    NARCIS (Netherlands)

    Baragaña, Beatriz; Blackburn, Adrian G.; Breccia, Perla; Davis, Anthony P.; Mendoza, Javier de; Padrón-Carrillo, José M.; Prados, Pilar; Riedner, Jens; Vries, Johannes G. de

    2002-01-01

    The cationic steroidal receptors 9 and 11 have been synthesized from cholic acid 3. Receptor 9 extracts N-acetyl-α-amino acids from aqueous media into chloroform with enantioselectivities (L:D) of 7-10:1. The lipophilic variant 11 has been employed for the enantioselective transport of N-acetylpheny

  2. Enantioselective Epoxide Polymerization Using a Bimetallic Cobalt Catalyst

    KAUST Repository

    Thomas, Renee M.

    2010-11-24

    A highly active enantiopure bimetallic cobalt complex was explored for the enantioselective polymerization of a variety of monosubstituted epoxides. The polymerizations were optimized for high rates and stereoselectivity, with s-factors (kfast/kslow) for most epoxides exceeding 50 and some exceeding 300, well above the threshold for preparative utility of enantiopure epoxides and isotactic polyethers. Values for mm triads of the resulting polymers are typically greater than 95%, with some even surpassing 98%. In addition, the use of a racemic catalyst allowed the preparation of isotactic polyethers in quantitative yields. The thermal properties of these isotactic polyethers are presented, with many polymers exhibiting high T m values. This is the first report of the rapid synthesis of a broad range of highly isotactic polyethers via the enantioselective polymerization of racemic epoxides. © 2010 American Chemical Society.

  3. Catalytic enantioselective construction of quaternary stereocenters: assembly of key building blocks for the synthesis of biologically active molecules.

    Science.gov (United States)

    Liu, Yiyang; Han, Seo-Jung; Liu, Wen-Bo; Stoltz, Brian M

    2015-03-17

    The ever-present demand for drugs with better efficacy and fewer side effects continually motivates scientists to explore the vast chemical space. Traditionally, medicinal chemists have focused much attention on achiral or so-called "flat" molecules. More recently, attention has shifted toward molecules with stereogenic centers since their three-dimensional structures represent a much larger fraction of the chemical space and have a number of superior properties compared with flat aromatic compounds. Quaternary stereocenters, in particular, add greatly to the three-dimensionality and novelty of the molecule. Nevertheless, synthetic challenges in building quaternary stereocenters have largely prevented their implementation in drug discovery. The lack of effective and broadly general methods for enantioselective formation of quaternary stereocenters in simple molecular scaffolds has prompted us to investigate new chemistry and develop innovative tools and solutions. In this Account, we describe three approaches to constructing quaternary stereocenters: nucleophilic substitution of 3-halooxindoles, conjugate addition of boronic acids to cyclic enones, and allylic alkylation of enolates. In the first approach, malonic ester nucleophiles attack electrophilic 3-halooxindoles, mediated by a copper(II)-bisoxazoline catalyst. A variety of oxindoles containing a benzylic quaternary stereocenter can be accessed through this method. However, it is only applicable to the specialized 3,3-disubstituted oxindole system. To access benzylic quaternary stereocenters in a more general context, we turned our attention to the enantioselective conjugate addition of carbon nucleophiles to α,β-unsaturated carbonyl acceptors. We discovered that in the presence of catalytic palladium-pyridinooxazoline complex, arylboronic acids add smoothly to β-substituted cyclic enones to furnish ketones with a β-benzylic quaternary stereocenter in high yields and enantioselectivities. The reaction is

  4. Time evolution of high-altitude plasma bubbles imaged at geomagnetic conjugate points

    Directory of Open Access Journals (Sweden)

    K. Shiokawa

    2004-09-01

    Full Text Available Temporal and spatial evolution of two high-altitude plasma bubbles (evening and midnight was observed on 4 April 2002, at geomagnetic conjugate points at Sata, Japan (magnetic latitude 24° N, and Darwin, Australia (magnetic latitude 22° S, using two 630-nm airglow imagers. The apex height of the bubbles reached ~1500km. The upward velocity of the evolution was faster in the evening (~170m/s at 20:00-21:00 LT than around midnight (~28m/s at 23:00-00:00 LT. Bifurcating features of the bubbles into a smaller scale size of ~50km were clearly seen for both the evening and midnight bubbles, showing fairly good conjugacy between the Northern and Southern Hemispheres.

  5. Naphthodipyrrolidone (NDP) Based Conjugated Polymers with High Electron Mobility and Ambipolar Transport Properties

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Haichang; Zhang, Shuo; Mao, Yifan; Liu, Kewei; Chen, Yu-Ming; Jiang, Zhang; Strzalka, Joseph; Yang, Wenjun; Wang, Chien-Lung; Zhu, Yu

    2017-06-07

    Two novel donor-acceptor pi-conjugated polymers based on naphthodipyrrolidone (NDP) were synthesized and characterized. The polymers possess low band gaps and suitable molecular orbital levels as ambipolar semiconductors. The thin film organic field effect transistor of NDP polymers exhibited ambipolar transport properties with a high electron mobility up to 0.67 cm(2) V-1 s(-1). The grazing-incidence wide-angle X-ray scattering (GIWAXS) studies demonstrated that the polymer molecules pack into a long-range-ordered lamellar structure with isotropically oriented crystalline domains. Thermal annealing promoted edge-on lamellar stacking as evidenced by the increased diffraction intensity along the out-of-plane direction. The polymer with NDP and bithiophene units achieved the best edge-on lamellar stacking after thermal annealing, which yielded the best electron transport performance in this work.

  6. Enhancement of the enantioselectivity of carboxylesterase A by structure-based mutagenesis.

    Science.gov (United States)

    Godinho, Luis F; Reis, Carlos R; Rozeboom, Henriëtte J; Dekker, Frank J; Dijkstra, Bauke W; Poelarends, Gerrit J; Quax, Wim J

    2012-03-31

    Previously studied Bacillus subtilis carboxylesterases (CesA and CesB) have potential for the kinetic resolution of racemic esters of 1,2-O-isopropylideneglycerol (IPG). CesA exhibits high activity but low enantioselectivity towards IPG-butyrate and IPG-caprylate, while the more enantioselective CesB does not process IPG-butyrate and exhibits several-fold lower activity than CesA towards IPG-caprylate. A sequence and structure comparison allowed us to identify active site residues that may cause the difference in (enantio)selectivities of CesA and CesB towards these IPG esters. This structure-based approach led to the identification of two active site residues in CesA (F166 and F182), as promising candidates for mutagenesis in order to enhance its enantioselectivity. Mutagenesis of positions 166 and 182 in CesA yielded novel variants with enhanced enantioselectivity and without significant loss of catalytic activity. For IPG-butyrate, a CesA double mutant F166V/F182C (ER=13) was generated showing a ∼13-fold increased enantioselectivity as compared to wild-type CesA (E=1). For IPG-caprylate, we designed a CesA double mutant F166V/F182Y (ER=9) displaying a ∼5-fold increased enantioselectivity as compared to the wild-type enzyme (ER=2). These findings, combined with the results of molecular docking experiments, demonstrate the importance of residues at positions 166 and 182 for the enantioselectivity of CesA, and may contribute to the development of efficient biocatalysts.

  7. The origin of enantioselectivity in the l-threonine-derived phosphine-sulfonamide catalyzed aza-Morita-Baylis-Hillman reaction: Effects of the intramolecular hydrogen bonding

    KAUST Repository

    Lee, Richmond

    2013-01-01

    l-Threonine-derived phosphine-sulfonamide 4 was identified as the most efficient catalyst to promote enantioselective aza-Morita-Baylis-Hillman (MBH) reactions, affording the desired aza-MBH adducts with excellent enantioselectivities. Density functional theory (DFT) studies were carried out to elucidate the origin of the observed enantioselectivity. The importance of the intramolecular N-H⋯O hydrogen-bonding interaction between the sulfonamide and enolate groups was identified to be crucial in inducing a high degree of stereochemical control in both the enolate addition to imine and the subsequent proton transfer step, affording aza-MBH reactions with excellent enantioselectivity. © 2013 The Royal Society of Chemistry.

  8. Polarization and dissociation of a high energy photon-excited state in conjugated polymers

    Energy Technology Data Exchange (ETDEWEB)

    Li, Xiao-xue, E-mail: sps_lixx@ujn.edu.cn

    2015-02-20

    We use the tight-binding Su–Schrieffer–Heeger model for the one-dimensional conjugated polymers to explore the static polarization behavior of a high energy photon-excited state under the electric field. An obvious reverse polarization is obtained although the electric field is weak. With the increase of field strength, the degree of polarization increases first and then decreases. When the electric field is strong enough, the excited state is dissociated into the polaron pair. In addition, the effects of electron–electron interaction and interchain coupling are also discussed. The results indicate that the electron–electron interaction could weaken the reverse polarization of the high energy photon-excited state, which tends to be dissociated into a high-energy exciton and a pair of solitons with the including of interchain coupling. - Highlights: • We explore the polarization of a high energy photon-excited state in polymers. • An obvious reverse polarization under the moderate electric field is obtained. • High energy photon-excited state is dissociated into polaron pair at strong field. • Increasing electron–electron interaction will weaken the reverse polarization. • Interchain coupling induces dissociation into high-energy exciton and solitons.

  9. Bio-degradable highly fluorescent conjugated polymer nanoparticles for bio-medical imaging applications.

    Science.gov (United States)

    Repenko, Tatjana; Rix, Anne; Ludwanowski, Simon; Go, Dennis; Kiessling, Fabian; Lederle, Wiltrud; Kuehne, Alexander J C

    2017-09-07

    Conjugated polymer nanoparticles exhibit strong fluorescence and have been applied for biological fluorescence imaging in cell culture and in small animals. However, conjugated polymer particles are hydrophobic and often chemically inert materials with diameters ranging from below 50 nm to several microns. As such, conjugated polymer nanoparticles cannot be excreted through the renal system. This drawback has prevented their application for clinical bio-medical imaging. Here, we present fully conjugated polymer nanoparticles based on imidazole units. These nanoparticles can be bio-degraded by activated macrophages. Reactive oxygen species induce scission of the conjugated polymer backbone at the imidazole unit, leading to complete decomposition of the particles into soluble low molecular weight fragments. Furthermore, the nanoparticles can be surface functionalized for directed targeting. The approach opens a wide range of opportunities for conjugated polymer particles in the fields of medical imaging, drug-delivery, and theranostics.Conjugated polymer nanoparticles have been applied for biological fluorescence imaging in cell culture and in small animals, but cannot readily be excreted through the renal system. Here the authors show fully conjugated polymer nanoparticles based on imidazole units that can be bio-degraded by activated macrophages.

  10. Enantioselective Hydrolysis of Amino Acid Esters Promoted by Bis(β-cyclodextrin) Copper Complexes.

    Science.gov (United States)

    Xue, Shan-Shan; Zhao, Meng; Ke, Zhuo-Feng; Cheng, Bei-Chen; Su, Hua; Cao, Qian; Cao, Zhen-Kun; Wang, Jun; Ji, Liang-Nian; Mao, Zong-Wan

    2016-02-26

    It is challenging to create artificial catalysts that approach enzymes with regard to catalytic efficiency and selectivity. The enantioselective catalysis ranks the privileged characteristic of enzymatic transformations. Here, we report two pyridine-linked bis(β-cyclodextrin) (bisCD) copper(II) complexes that enantioselectively hydrolyse chiral esters. Hydrolytic kinetic resolution of three pairs of amino acid ester enantiomers (S1-S3) at neutral pH indicated that the "back-to-back" bisCD complex CuL(1) favoured higher catalytic efficiency and more pronounced enantioselectivity than the "face-to-face" complex CuL(2). The best enantioselectivity was observed for N-Boc-phenylalanine 4-nitrophenyl ester (S2) enantiomers promoted by CuL(1), which exhibited an enantiomer selectivity of 15.7. We observed preferential hydrolysis of L-S2 by CuL(1), even in racemic S2, through chiral high-performance liquid chromatography (HPLC). We demonstrated that the enantioselective hydrolysis was related to the cooperative roles of the intramolecular flanking chiral CD cavities with the coordinated copper ion, according to the results of electrospray ionization mass spectrometry (ESI-MS), inhibition experiments, rotating-frame nuclear Overhauser effect spectroscopy (ROESY), and theoretical calculations. Although the catalytic parameters lag behind the level of enzymatic transformation, this study confirms the cooperative effect of the first and second coordination spheres of artificial catalysts in enantioselectivity and provides hints that may guide future explorations of enzyme mimics.

  11. Enantioselective Hydrolysis of Amino Acid Esters Promoted by Bis(β-cyclodextrin) Copper Complexes

    Science.gov (United States)

    Xue, Shan-Shan; Zhao, Meng; Ke, Zhuo-Feng; Cheng, Bei-Chen; Su, Hua; Cao, Qian; Cao, Zhen-Kun; Wang, Jun; Ji, Liang-Nian; Mao, Zong-Wan

    2016-02-01

    It is challenging to create artificial catalysts that approach enzymes with regard to catalytic efficiency and selectivity. The enantioselective catalysis ranks the privileged characteristic of enzymatic transformations. Here, we report two pyridine-linked bis(β-cyclodextrin) (bisCD) copper(II) complexes that enantioselectively hydrolyse chiral esters. Hydrolytic kinetic resolution of three pairs of amino acid ester enantiomers (S1–S3) at neutral pH indicated that the “back-to-back” bisCD complex CuL1 favoured higher catalytic efficiency and more pronounced enantioselectivity than the “face-to-face” complex CuL2. The best enantioselectivity was observed for N-Boc-phenylalanine 4-nitrophenyl ester (S2) enantiomers promoted by CuL1, which exhibited an enantiomer selectivity of 15.7. We observed preferential hydrolysis of L-S2 by CuL1, even in racemic S2, through chiral high-performance liquid chromatography (HPLC). We demonstrated that the enantioselective hydrolysis was related to the cooperative roles of the intramolecular flanking chiral CD cavities with the coordinated copper ion, according to the results of electrospray ionization mass spectrometry (ESI-MS), inhibition experiments, rotating-frame nuclear Overhauser effect spectroscopy (ROESY), and theoretical calculations. Although the catalytic parameters lag behind the level of enzymatic transformation, this study confirms the cooperative effect of the first and second coordination spheres of artificial catalysts in enantioselectivity and provides hints that may guide future explorations of enzyme mimics.

  12. Identification of highly reactive cysteine residues at less exposed positions in the Fab constant region for site-specific conjugation.

    Science.gov (United States)

    Shiraishi, Yasuhisa; Muramoto, Takashige; Nagatomo, Kazutaka; Shinmi, Daisuke; Honma, Emiko; Masuda, Kazuhiro; Yamasaki, Motoo

    2015-06-17

    Engineered cysteine residues are currently used for the site-specific conjugation of antibody-drug conjugates (ADC). In general, positions on the protein surface have been selected for substituting a cysteine as a conjugation site; however, less exposed positions (with less than 20% of accessible surface area [ASA]) have not yet been evaluated. In this study, we engineered original cysteine positional variants of a Fab fragment, with less than 20% of ASA, and evaluated their thiol reactivities through conjugation with various kinds of payloads. As a result, we have identified three original cysteine positional variants (heavy chain: Hc-A140C, light chain: Lc-Q124C and Lc-L201C), which exhibited similar monomer content, thermal stability, and antigen binding affinity in comparison to the wild-type Fab. In addition, the presence of cysteine in these positions made it possible for the Fab variants to react with variable-sized molecules with high efficiency. The favorable physical properties of the cysteine positional variants selected in our study suggest that less exposed positions, with less than 20% of ASA, provide an alternative for creating conjugation sites.

  13. Enantioselective biotransformations of nitriles in organic synthesis.

    Science.gov (United States)

    Wang, Mei-Xiang

    2015-03-17

    The hydration and hydrolysis of nitriles are valuable synthetic methods used to prepare carboxamides and carboxylic acids. However, chemical hydration and hydrolysis of nitriles involve harsh reaction conditions, have low selectivity, and generate large amounts of waste. Therefore, researchers have confined the scope of these reactions to simple nitrile substrates. However, biological transformations of nitriles are highly efficient, chemoselective, and environmentally benign, which has led synthetic organic chemists and biotechologists to study these reactions in detail over the last two decades. In nature, biological systems degrade nitriles via two distinct pathways: nitrilases catalyze the direct hydrolysis of nitriles to afford carboxylic acids with release of ammonia, and nitrile hydratases catalyze the conversion of nitriles into carboxamides, which then furnish carboxylic acids via hydrolysis in the presence of amidases. Researchers have subsequently developed biocatalytic methods into useful industrial processes for the manufacture of commodity chemicals, including acrylamide. Since the late 1990s, research by my group and others has led to enormous progress in the understanding and application of enantioselective biotransformations of nitriles in organic synthesis. In this Account, I summarize the important advances in enantioselective biotransformations of nitriles and amides, with a primary focus on research from my laboratory. I describe microbial whole-cell-catalyzed kinetic resolution of various functionalized nitriles, amino- and hydroxynitriles, and nitriles that contain small rings and the desymmetrization of prochiral and meso dinitriles and diamides. I also demonstrate how we can apply the biocatalytic protocol to synthesize natural products and bioactive compounds. These nitrile biotransformations offer an attractive and unique protocol for the enantioselective synthesis of polyfunctionalized organic compounds that are not readily obtainable by

  14. Determination of conjugated bile acids in human bile and duodenal fluid by reverse-phase high-performance liquid chromatography.

    Science.gov (United States)

    Bloch, C A; Watkins, J B

    1978-05-01

    A simple mehtod using reverse-phase liquid chromatography is presented for resolution and quantitation of the major conjugated bile acids of man, including the glycine and taurine conjugates of the dihydroxy bile acids, chenodeoxycholic and deoxycholic acid. Using modern, high-performance chromatographic equipment, analysis time is less than 30 minutes. The quantitative range of the method, with detection by refractive index, is 0.05 to 0.1 mumol of bile acid and the limit of detection for an injection sample is 0.01 mumol. This provides a sensitivity sufficient for analysis of dilute duodenal and gallbladder bile with minimal sample preparation.

  15. Development of catalysts and ligands for enantioselective gold catalysis.

    Science.gov (United States)

    Wang, Yi-Ming; Lackner, Aaron D; Toste, F Dean

    2014-03-18

    During the past decade, the use of Au(I) complexes for the catalytic activation of C-C π-bonds has been investigated intensely. Over this time period, the development of homogeneous gold catalysis has been extraordinarily rapid and has yielded a host of mild and selective methods for the formation of carbon-carbon and carbon-heteroatom bonds. The facile formation of new bonds facilitated by gold naturally led to efforts toward rendering these transformations enantioselective. In this Account, we survey the development of catalysts and ligands for enantioselective gold catalysis by our research group as well as related work by others. We also discuss some of our strategies to address the challenges of enantioselective gold(I) catalysis. Early on, our work with enantioselective gold-catalyzed transformations focused on bis(phosphinegold) complexes derived from axially chiral scaffolds. Although these complexes were highly successful in some reactions like cyclopropanation, the careful choice of the weakly coordinating ligand (or counterion) was necessary to obtain high levels of enantioselectivity for the case of allene hydroamination. These counterion effects led us to use the anion itself as a source of chirality, which was successful in the case of allene hydroalkoxylation. In general, these tactics enhance the steric influence around the reactive gold center beyond the two-coordinate ligand environment. The use of binuclear complexes allowed us to use the second gold center and its associated ligand (or counterion) to exert a further steric influence. In a similar vein, we employed a chiral anion (in place of or in addition to a chiral ligand) to move the chiral information closer to the reactive center. In order to expand the scope of reactions amenable to enantioselective gold catalysis to cycloadditions and other carbocyclization processes, we also developed a new class of mononuclear phosphite and phosphoramidite ligands to supplement the previously widely

  16. Conjugation of anti-dihydrodiol epoxides of benzo[a]pyrene, chrysene, benzo[c]phenanthrene and dibenz[a,h]anthracene with glutathione catalyzed by cytosol and by the Mu-class glutathione transferase HTP II from rat liver.

    Science.gov (United States)

    Funk, M; Gath, I; Seidel, A; Oesch, F; Platt, K L

    1995-03-30

    The (+/-)-anti-dihydrodiol epoxides (DE) of benzo[a]pyrene (BP), chrysene (Chr), benzo[c]phenanthrene (BcPh) and dibenz[a,h]anthracene (DBA) were incubated in the presence of glutathione (GSH) with hepatic cytosol from untreated and Aroclor 1254 pretreated rats and with the Mu-class glutathione transferase (GST) HTP II from rat liver. The diastereoisomeric GSH conjugates formed were separated, identified and quantified by HPLC employing synthetic reference compounds. All (+/-)-anti-dihydrodiol epoxides investigated in this study were proven to be substrates of the cytosolic GSTs. The highly mutagenic and carcinogenic (+)-anti-DE with R,S,S,R absolute configuration was preferentially conjugated in the case of BP and Chr. Aroclor 1254 pretreatment increased the turnover 2-3-fold and changed the enantioselectivity. The previously purified GST HTP II exhibited a high degree of enantioselectivity (> or = 95%) towards the R,S,S,R-configurated enantiomer in the case of the bay-region (+/-)-anti-BPDE, (+/-)-anti-ChrDE and (+/-)-anti-DBADE, whereas in the case of fjord-region (+/-)-anti-BcPhDE both enantiomers were good substrates. The contribution of HTP II to the enzymatic activity of the cytosolic GST pool was estimated to be in the range of 11-32%. In agreement with previous results, the observed enantioselectivity of the purified enzyme seems to be of minor significance considering the total GST pool in the liver.

  17. Unsymmetrical triphenylamine-oligothiophene hybrid conjugated systems as donor materials for high-voltage solution-processed organic solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Ripaud, Emilie; Rousseau, Theodulf; Leriche, Philippe; Roncali, Jean [Group Linear Conjugated Systems, CNRS Moltech-Anjou, University of Angers, 2Bd Lavoisier, 49045 Angers (France)

    2011-07-15

    The synthesis of unsymmetrical triphenylamine-oligothiophene hybrid conjugated systems bearing dicyanovinyl electron acceptor end-groups is presented. When used as molecular donor materials in solution-processed bulk heteroj-unction solar cells, these compounds lead to efficient devices with very high open-circuit voltages. (Copyright copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  18. Biochemical and structural characterization of recombinant short-chain NAD(H)-dependent dehydrogenase/reductase from Sulfolobus acidocaldarius highly enantioselective on diaryl diketone benzil.

    Science.gov (United States)

    Pennacchio, Angela; Sannino, Vincenzo; Sorrentino, Giosuè; Rossi, Mosè; Raia, Carlo A; Esposito, Luciana

    2013-05-01

    The gene encoding a novel alcohol dehydrogenase that belongs to the short-chain dehydrogenases/reductases superfamily was identified in the aerobic thermoacidophilic crenarchaeon Sulfolobus acidocaldarius strain DSM 639. The saadh2 gene was heterologously overexpressed in Escherichia coli, and the resulting protein (SaADH2) was purified to homogeneity and both biochemically and structurally characterized. The crystal structure of the SaADH2 NADH-bound form reveals that the enzyme is a tetramer consisting of identical 27,024-Da subunits, each composed of 255 amino acids. The enzyme has remarkable thermophilicity and thermal stability, displaying activity at temperatures up to 80 °C and a 30-min half-inactivation temperature of ∼88 °C. It also shows good tolerance to common organic solvents and a strict requirement for NAD(H) as the coenzyme. SaADH2 displays a preference for the reduction of alicyclic, bicyclic and aromatic ketones and α-ketoesters, but is poorly active on aliphatic, cyclic and aromatic alcohols, showing no activity on aldehydes. Interestingly, the enzyme catalyses the asymmetric reduction of benzil to (R)-benzoin with both excellent conversion (98 %) and optical purity (98 %) by way of an efficient in situ NADH-recycling system involving a second thermophilic ADH. The crystal structure of the binary complex SaADH2-NADH, determined at 1.75 Å resolution, reveals details of the active site providing hints on the structural basis of the enzyme enantioselectivity.

  19. Enantioselectivity of Photochemical Reactions within Polymer Microcapsules

    Institute of Scientific and Technical Information of China (English)

    MA,Lei; WU,Li-Zhu; ZHANG,Li-Ping; TUNG,Chen-Ho

    2003-01-01

    Polymer microcapsule was employed as a reaction medium to achieve enantioselectivity in photochemical reduction of phenyl cyclohexyl ketone and photoelectrocyclization of tropolone methyl ether unader the influence of various chiral inductors. In all cases,low but evident enantioselectivity was observed. The poor enantioselectivity is probably due to the facts that not all the capsules include simultaneously both the chiral inductor and the reactant molecules, and the wall of the microcapsule is not rigid enough tohold the reactant and the chiral inductor moleculesin close contact.

  20. Enantioselective Nanoporous Carbon Based on Chiral Ionic Liquids.

    Science.gov (United States)

    Fuchs, Ido; Fechler, Nina; Antonietti, Markus; Mastai, Yitzhak

    2016-01-04

    One of the greatest challenges in modern chemical processing is to achieve enantiospecific control in chemical reactions using chiral media such as chiral mesoporous materials. Herein, we describe a novel and effective synthetic pathway for the preparation of enantioselective nanoporous carbon, based on chiral ionic liquids (CILs). CILs of phenylalanine (CIL(Phe)) are used as precursors for the carbonization of chiral mesoporous carbon. We employ circular dichroism spectroscopy, isothermal titration calorimetry (ITC), and chronoamperometry in order to demonstrate the chiral nature of the mesoporous carbon. The approach presented in this paper is highly significant for the development of a new type of chiral porous materials for enantioselective chemistry. In addition, it contributes significantly to our understanding of the structure and nature of chiral nanoporous materials and surfaces. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  1. Enantioselective synthesis of R-(-)-Ligularenolide and the progesterone receptor ligang R-(-)-PF1092C starting from S-(+)-Carvone.

    NARCIS (Netherlands)

    Jenniskens, L.H.D.; Groot, de Æ.

    1998-01-01

    A new enantioselective synthesis of eremophilane sesquiterpenes was developed starting from S-(+)-carvone 3, using a conjugate addition-annelation sequence. The synthesis of R-(−)-ligularenolide 1 was accomplished in a staightforward manner with the annelation of the lactone as the last step. For th

  2. SHORT COMMUNICATION FACILE ENANTIOSELECTIVE ...

    African Journals Online (AJOL)

    Enantiomeric excess was assayed using optical rotation measurements. The ... gases there is need to extend this work to other reducing agents. A promising alternative .... This lowers the entropy of the reaction and is responsible for the high.

  3. Enantioselective Synthesis of 2,2-Disubstituted Terminal Epoxides via Catalytic Asymmetric Corey-Chaykovsky Epoxidation of Ketones

    Directory of Open Access Journals (Sweden)

    Shigeki Matsunaga

    2012-02-01

    Full Text Available Catalytic asymmetric Corey-Chaykovsky epoxidation of various ketones with dimethyloxosulfonium methylide using a heterobimetallic La-Li3-BINOL complex (LLB is described. The reaction proceeded smoothly at room temperature in the presence of achiral phosphine oxide additives, and 2,2-disubstituted terminal epoxides were obtained in high enantioselectivity (97%–91% ee and yield ( > 99%–88% from a broad range of methyl ketones with 1–5 mol% catalyst loading. Enantioselectivity was strongly dependent on the steric hindrance, and other ketones, such as ethyl ketones and propyl ketones resulted in slightly lower enantioselectivity (88%–67% ee.

  4. Enantioselective α-Hydroxylation by Modified Salen-Zirconium(IV)-Catalyzed Oxidation of β-Keto Esters.

    Science.gov (United States)

    Yang, Fan; Zhao, Jingnan; Tang, Xiaofei; Zhou, Guangli; Song, Wangze; Meng, Qingwei

    2017-02-03

    The highly enantioselective α-hydroxylation of β-keto esters using cumene hydroperoxide (CHP) as the oxidant was realized by a chiral (1S,2S)-cyclohexanediamine backbone salen-zirconium(IV) complex as the catalyst. A variety of corresponding chiral α-hydroxy β-keto esters were obtained in excellent yields (up to 99%) and enantioselectivities (up to 98% ee). The zirconium-catalyzed enantioselective α-hydroxylation of β-keto esters was scalable, and the zirconium catalyst was recyclable. The reaction can be performed in gram scale, and corresponding chiral products were acquired in 95% yield and 99% ee.

  5. Analysis of high performance conjugate heat transfer with the OpenPALM coupler

    Science.gov (United States)

    Duchaine, Florent; Jauré, Stéphan; Poitou, Damien; Quémerais, Eric; Staffelbach, Gabriel; Morel, Thierry; Gicquel, Laurent

    2015-01-01

    In many communities such as climate science or industrial design, to solve complex coupled problems with high fidelity external coupling of legacy solvers puts a lot of pressure on the tool used for the coupling. The precision of such predictions not only largely depends on simulation resolutions and the use of huge meshes but also on high performance computing to reduce restitution times. In this context, the current work aims at studying the scalability of code coupling on high performance computing architectures for a conjugate heat transfer problem. The flow solver is a Large Eddy Simulation code that has been already ported on massively parallel architectures. The conduction solver is based on the same data structure and thus shares the flow solver scalability properties. Accurately coupling solvers on massively parallel architectures while maintaining their scalability is challenging. It requires exchanging and treating information based on two different computational grids that are partitioned differently on a different number of cores. Such transfers have to be thought to maintain code scalabilities while maintaining numerical accuracy. This raises communication and high performance computing issues: transferring data from a distributed interface to another distributed interface in a parallel way and on a very large number of processors is not straightforward and solutions are not clear. Performance tests have been carried out up to 12 288 cores on the CURIE supercomputer (TGCC/CEA). Results show a good behavior of the coupled model when increasing the number of cores thanks to the fully distributed exchange process implemented in the coupler. Advanced analyses are carried out to draw new paths for future developments for coupled simulations: i.e. optimization of the data transfer protocols through asynchronous communications or coupling-aware preprocessing of the coupled models (mesh partitioning phase).

  6. Conjugation with Acridines Turns Nuclear Localization Sequence into Highly Active Antimicrobial Peptide

    Directory of Open Access Journals (Sweden)

    Zhang Wei

    2015-12-01

    Full Text Available The emergence of multidrug-resistant bacteria creates an urgent need for alternative antibiotics with new mechanisms of action. In this study, we synthesized a novel type of antimicrobial agent, Acr3-NLS, by conjugating hydrophobic acridines to the N-terminus of a nuclear localization sequence (NLS, a short cationic peptide. To further improve the antimicrobial activity of our agent, dimeric (Acr3-NLS2 was simultaneously synthesized by joining two monomeric Acr3-NLS together via a disulfide linker. Our results show that Acr3-NLS and especially (Acr3-NLS2 display significant antimicrobial activity against gram-negative and gram-positive bacteria compared to that of the NLS. Subsequently, the results derived from the study on the mechanism of action demonstrate that Acr3-NLS and (Acr3-NLS2 can kill bacteria by membrane disruption and DNA binding. The double targets–cell membrane and intracellular DNA–will reduce the risk of bacteria developing resistance to Acr3-NLS and (Acr3-NLS2. Overall, this study provides a novel strategy to design highly effective antimicrobial agents with a dual mode of action for infection treatment.

  7. Preparation and characterization of aqueous dispersions of high amylose starch and conjugated linoleic acid complex.

    Science.gov (United States)

    Seo, Tae-Rang; Kim, Hee-Young; Lim, Seung-Taik

    2016-11-15

    Crystalline starch-CLA complexes were prepared by blending an alcoholic solution of conjugated linoleic acid (CLA) in an aqueous high-amylose maize starch dispersion. Recovery yield of CLA in the precipitates obtained by centrifuging the dispersion was dependent on reaction conditions such as temperature, time and pH. The CLA recovery reached a maximum when the reaction was performed at 90°C for 6h at neutral pH, with 67.7% of the initial CLA being co-precipitated with starch. The precipitates contained amylose-CLA complex exhibiting a V6I-type crystalline structure under X-ray diffraction analysis and a type II polymorph under DSC analysis. Ultrasonic treatment for the re-dispersed starch-CLA complex in water resulted in the reduction of hydrodynamic diameter of the complex particles to 201.5nm. The dispersion exhibited a zeta potential of -27.0mV and remained stable in an ambient storage without forming precipitates for more than 4weeks. Copyright © 2016 Elsevier Ltd. All rights reserved.

  8. High-frequency conjugative transfer of antibiotic resistance genes to Yersinia pestis in the flea midgut.

    Science.gov (United States)

    Hinnebusch, B Joseph; Rosso, Marie-Laure; Schwan, Tom G; Carniel, Elisabeth

    2002-10-01

    The acquisition of foreign DNA by horizontal transfer from unrelated organisms is a major source of variation leading to new strains of bacterial pathogens. The extent to which this occurs varies widely, due in part to lifestyle factors that determine exposure to potential donors. Yersinia pestis, the plague bacillus, infects normally sterile sites in its mammalian host, but forms dense aggregates in the non-sterile digestive tract of its flea vector to produce a transmissible infection. Here we show that unrelated co-infecting bacteria in the flea midgut are readily incorporated into these aggregates, and that this close physical contact leads to high-frequency conjugative genetic exchange. Transfer of an antibiotic resistance plasmid from an Escherichia coli donor to Y. pestis occurred in the flea midgut at a frequency of 10-3 after only 3 days of co-infection, and after 4 weeks 95% of co-infected fleas contained an average of 103 antibiotic-resistant Y. pestis transconjugants. Thus, transit in its arthropod vector exposes Y. pestis to favourable conditions for efficient genetic exchange with microbial flora of the flea gut. Horizontal gene transfer in the flea may be the source of antibiotic-resistant Y. pestis strains recently isolated from plague patients in Madagascar.

  9. First observations of simultaneous interhemispheric conjugate high-latitude thermospheric winds

    Science.gov (United States)

    Kosch, M. J.; Anderson, C.; Yiu, H.-C. I.; Kellerman, A. C.; Makarevich, R. A.; Aruliah, A.; Conde, M.; Griffin, E.; Davies, T.; McWhirter, I.; Dyson, P. L.

    2010-09-01

    We report the first observations of simultaneous high-latitude interhemispheric F region neutral wind fields by combining the 630 nm optical measurements from two scanning Doppler imagers (SDIs) and three Fabry-Perot interferometers (FPIs) for a period exceeding 5 h. From the Southern Hemisphere, a SDI at Mawson and a FPI at Davis, both in Antarctica, are geomagnetically mapped onto the Northern Hemisphere. These data are combined in the Northern Hemisphere with a SDI at Longyearbyen, Svalbard, and two FPIs near Kiruna in Sweden and Sodankyla in Finland. Geomagnetic conditions were moderate (Kp = 3--3+) and steady although the interplanetary magnetic field Bz component did change polarity several times. There is good agreement between the conjugate 630 nm optical intensities and wind vectors where the two SDIs' fields of view overlap. All wind field vectors are overlaid onto the northern Super Dual Auroral Radar Network ion convection contours. Qualitatively, the agreement between neutral and ion flow is remarkably good throughout the study interval, even down to mesoscale spatial size.

  10. Highly Sensitive Colorimetric Assay for Determining Fe3+ Based on Gold Nanoparticles Conjugated with Glycol Chitosan

    Directory of Open Access Journals (Sweden)

    Kyungmin Kim

    2017-01-01

    Full Text Available A highly sensitive and simple colorimetric assay for the detection of Fe3+ ions was developed using gold nanoparticles (AuNPs conjugated with glycol chitosan (GC. The Fe3+ ion coordinates with the oxygen atoms of GC in a hexadentate manner (O-Fe3+-O, decreasing the interparticle distance and inducing aggregation. Time-of-flight secondary ion mass spectrometry showed that the bound Fe3+ was coordinated to the oxygen atoms of the ethylene glycol in GC, which resulted in a significant color change from light red to dark midnight blue due to aggregation. Using this GC-AuNP probe, the quantitative determination of Fe3+ in biological, environmental, and pharmaceutical samples could be achieved by the naked eye and spectrophotometric methods. Sensitive response and pronounced color change of the GC-AuNPs in the presence of Fe3+ were optimized at pH 6, 70°C, and 300 mM NaCl concentration. The absorption intensity ratio (A700/A510 linearly correlated to the Fe3+ concentration in the linear range of 0–180 μM. The limits of detection were 11.3, 29.2, and 46.0 nM for tap water, pond water, and iron supplement tablets, respectively. Owing to its facile and sensitive nature, this assay method for Fe3+ ions can be applied to the analysis of drinking water and pharmaceutical samples.

  11. Conjugate-SELEX: A High-throughput Screening of Thioaptamer-liposomal Nanoparticle Conjugates for Targeted Intracellular Delivery of Anticancer Drugs.

    Science.gov (United States)

    Mu, Qingshan; Annapragada, Akshaya; Srivastava, Mayank; Li, Xin; Wu, Jean; Thiviyanathan, Varatharasa; Wang, Hongyu; Williams, Alexander; Gorenstein, David; Annapragada, Ananth; Vigneswaran, Nadarajah

    2016-11-01

    Patients with advanced head and neck squamous cell carcinoma receiving chemotherapy have a poor prognosis partly due to normal tissue toxicity; therefore, development of a tumor-targeted drug delivery platform to minimize collateral toxicity is a goal of cancer nanomedicine. Aptamers can achieve this purpose. While conventional Systematic Evolution of Ligands by Exponential Enrichment (SELEX) screens aptamer-only libraries and conjugates them to delivery vehicles after selection, we hypothesized that specific delivery requires screening libraries with aptamer-nanoparticle conjugates. We designed a procedure called, "Conjugate-SELEX", where liposomal nanoparticles (LNP) conjugated with aptamers is screened to identify aptamers that carried attached LNPs to the human head and neck squamous cell carcinoma cell cytosol. Aptamer-LNPs were simultaneously selected for a low affinity to human hepatocytes, minimizing hepatoxicity and LNP clearance. Post-SELEX Next Generation sequencing demonstrated convergence to a family of sequences with one base difference. Affinity pulldown and proteomics analysis identified the uptake-mediating surface receptor as the neuroblast differentiation-associated protein AHNAK (Desmoyokin), a ubiquitous intracellular protein expressed in certain epithelial cell types. Uptake studies with the lead aptamer-conjugates showed enhanced uptake and increased cytotoxicity induced by doxorubicin in cells treated with aptamer-conjugated LNPs over LNP controls. Conjugate-SELEX identifies aptamers capable of targeted cytosolic delivery of attached LNPs payload, while minimizing off-target delivery. The technique lends itself to identification of uptake-mediating surface receptors.

  12. Enantiomerization and enantioselective bioaccumulation of metalaxyl in Tenebrio molitor larvae.

    Science.gov (United States)

    Gao, Yongxin; Wang, Huili; Qin, Fang; Xu, Peng; Lv, Xiaotian; Li, Jianzhong; Guo, Baoyuan

    2014-02-01

    The enantiomerization and enantioselective bioaccumulation of metalaxyl by a single dose of exposure to Tenebrio molitor larvae under laboratory condition were studied by high-performance liquid chromatography tandem mass spectroscopy (HPLC-MS/MS) based on a ChiralcelOD-3R [cellulosetris-tris-(3, 5-dichlorophenyl-carbamate)] column. Exposure of enantiopure R-metalaxyl and S-metalaxyl in Tenebrio molitor larvae exhibited significant enantiomerization, with formation of the R enantiomers from the S enantiomers, and vice versa, which might be attributed to the chiral pesticide catalyzed by a certain enzyme in Tenebrio molitor larvae. Enantiomerization was not observed in wheat bran during the period of 21 d. In addition, bioaccumulation of rac-metalaxyl in Tenebrio molitor larvae was enantioselective with a preferential accumulation of S-metalaxyl. These results showed that enantioselectivity was caused not only by actual degradation and metabolism but also by enantiomerization, which was an important process in the environmental fate and behavior of metalaxyl enantiomers.

  13. Controlled synthesis of conjugated microporous polymer films: versatile platforms for highly sensitive and label-free chemo- and biosensing.

    Science.gov (United States)

    Gu, Cheng; Huang, Ning; Gao, Jia; Xu, Fei; Xu, Yanhong; Jiang, Donglin

    2014-05-05

    Conjugated microporous polymers (CMPs), in which rigid building blocks form robust networks, are usually synthesized as insoluble and unprocessable powders. We developed a methodology using electropolymerization for the synthesis of thin CMP films. The thickness of these films is synthetically controllable, ranging from nanometers to micrometers, and they are obtained on substrates or as freestanding films. The CMP films combine a number of striking physical properties, including high porosity, extended π conjugation, facilitated exciton delocalization, and high-rate electron transfer. We explored the CMP films as versatile platforms for highly sensitive and label-free chemo- and biosensing of electron-rich and electron-poor arenes, metal ions, dopamine, and hypochloroic acid, featuring rapid response, excellent selectivity, and robust reusability.

  14. Two-dimensional charge transport in self-organized, high-mobility conjugated polymers

    DEFF Research Database (Denmark)

    Sirringhaus, H.; Brown, P.J.; Friend, R.H.

    1999-01-01

    Self-organization in many solution-processed, semiconducting conjugated polymers results in complex microstructures, in which ordered microcrystalline domains are embedded in an amorphous matrix(I). This has important consequences for electrical properties of these materials: charge transport...... is usually limited by the most difficult hopping processes and is therefore dominated by the disordered matrix, resulting in low charge-carrier mobilities(2) (less than or equal to 10(-5) cm(2)V(-1)s(-1)). Here we use thin-film, field-effect transistor structures to probe the transport properties...... of the ordered microcrystalline domains in the conjugated polymer poly(3-hexylthiophene), P3HT, Self-organization in P3HT results in a lamella structure with two-dimensional conjugated sheets formed by interchain stacking. We find that, depending on processing conditions, the lamellae can adopt two different...

  15. Enantioselective amine α-functionalization via palladium-catalysed C-H arylation of thioamides

    Science.gov (United States)

    Jain, Pankaj; Verma, Pritha; Xia, Guoqin; Yu, Jin-Quan

    2017-02-01

    Saturated aza-heterocycles are highly privileged building blocks that are commonly encountered in bioactive compounds and approved therapeutic agents. These N-heterocycles are also incorporated as chiral auxiliaries and ligands in asymmetric synthesis. As such, the development of methods to functionalize the α-methylene C-H bonds of these systems enantioselectively is of great importance, especially in drug discovery. Currently, enantioselective lithiation with (-)-sparteine followed by Pd(0) catalysed cross-coupling to prepare α-arylated amines is largely limited to pyrrolidines. Here we report a Pd(II)-catalysed enantioselective α-C-H coupling of a wide range of amines, which include ethyl amines, azetidines, pyrrolidines, piperidines, azepanes, indolines and tetrahydroisoquinolines. Chiral phosphoric acids are demonstrated as effective anionic ligands for the enantioselective coupling of methylene C-H bonds with aryl boronic acids. This catalytic reaction not only affords high enantioselectivities, but also provides exclusive regioselectivity in the presence of two methylene groups in different steric environments.

  16. The Catalytic Enantioselective Total Synthesis of (+)‐Liphagal

    DEFF Research Database (Denmark)

    Day, Joshua J.; McFadden, Ryan M.; Virgil, Scott C.;

    2011-01-01

    Ring a ding: The first catalytic enantioselective total synthesis of the meroterpenoid natural product (+)-liphagal is disclosed. The approach showcases a variety of technology including enantioselective enolate alkylation, a photochemical alkyne-alkene [2+2] reaction, microwaveassisted metal cat...

  17. Photochemical Studies on 5-Methylbicyclo[1.1.1]pentane Derivatives: p-Orbital Overlap Controlled Enantioselectivity

    Institute of Scientific and Technical Information of China (English)

    马满玲; 杨超; 李冰; 邵玉田; 赵国磊; 夏吾炯

    2012-01-01

    The first example of the p-orbital overlap controlled enantioselectivity of Norrish type II photocyclization reaction was described. Irradiation of 5-methyl bicyclo[l. 1.1 ]pentanyl ketone with UV in the solid state as well as in the acetonitrile solution afforded the Norrish/Yang photocyclization compound as the sole product. Solid-state asymmetric photochemical studies using ionic chiral auxiliary technique led to the enantioselectivity as high as 60%. The results were rationalized by Xray single crystal structure.

  18. L-Threonine-derived novel bifunctional phosphine-sulfonamide catalyst-promoted enantioselective aza-morita-Baylis-Hillman reaction

    KAUST Repository

    Zhong, Fangrui

    2011-03-18

    A series of novel bifunctional phosphine-sulfonamide organic catalysts were designed and readily prepared from natural amino acids, and they were utilized to promote enantioselective aza-Morita-Baylis-Hillman (MBH) reactions. l-Threonine-derived phosphine-sulfonamide 9b was found to be the most efficient catalyst, affording the desired aza-MBH adducts in high yields and with excellent enantioselectivities. © 2011 American Chemical Society.

  19. High Turnover of Tissue Factor Enables Efficient Intracellular Delivery of Antibody-Drug Conjugates

    DEFF Research Database (Denmark)

    de Goeij, Bart E.C.G.; Satijn, D.; Freitag, C. M.

    2015-01-01

    , and degradation than EGFR and HER2. By conjugating TF, EGFR, and HER2-specific antibodies with duostatin-3, a toxin that induces potent cytotoxicity upon antibody-mediated internalization but lacks the ability to induce bystander killing, we were able to compare cytotoxicity of ADCs with different tumor...

  20. Conjugate Heat Transfer and Thermal Mechanical Analysis for Liquid Metal Targets for High Power Electron Beams.

    Energy Technology Data Exchange (ETDEWEB)

    Olivas, Eric Richard [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

    2016-02-26

    A conjugate heat transfer and thermal structural analysis was completed, with the objective of determining the following: Lead bismuth eutectic (LBE) peak temperature, free convective velocity patterns in the LBE, peak beam window temperature, and thermal stress/deformation in the window.

  1. Catalytic Enantioselective 1,2-Addition of Terminal 1,3-Diynes to Trifluoromethyl Ketones

    Institute of Scientific and Technical Information of China (English)

    Yan Zheng; Hai Ma; Jun-An Ma

    2016-01-01

    A facile catalytic enantioselective 1,2-addition of diynes to trifluoromethyl ketones was developed.By a combination of Me2Zn,Ti(OPr-i)4,BaF2 and quinine,the reaction of a series of terminal diynes with trifluoromethyl ketones proceeded to afford trifluoromethylated chrial tertiary alcohols with the diyne moiety in good to high yields with moderate to high enantioselectivities.Furthermore,this catalytic asymmetric diyne addition to trifluoromethylketone was applied in the synthesis of the Efavirenz analogue.

  2. Enhanced Molecular Packing of a Conjugated Polymer with High Organic Thermoelectric Power Factor.

    Science.gov (United States)

    Ma, Wei; Shi, Ke; Wu, Yang; Lu, Zuo-Yu; Liu, Han-Yu; Wang, Jie-Yu; Pei, Jian

    2016-09-21

    The detailed relationship between film morphology and the performance of solution processed n-type organic thermoelectric (TE) devices is investigated. It is interesting to find that the better ordered molecular packing of n-type polymer can be achieved by adding a small fraction of dopant molecules, which is not observed before. The better ordered structure will be favorable for the charge carrier mobility. Meanwhile, dopant molecules improve free carrier concentration via doping reaction. As a result, a significantly enhanced electrical conductivity (12 S cm(-1)) and power factor (25.5 μW m(-1) K(-2)) of TE devices are obtained. Furthermore, the phase separation of conjugated polymer/dopants is observed for the first time with resonant soft X-ray scattering. Our results indicate that the miscibility of conjugated polymers and dopants plays an important role on controlling the morphology and doping efficiency of TE devices.

  3. Highly enantio- and diastereoselective reactions of γ-substituted butenolides through direct vinylogous conjugate additions

    KAUST Repository

    Zhang, Wen

    2012-09-05

    The strength of the weak: An L-tert-leucine-derived amine-thiourea catalyst (see scheme, green box) promotes the asymmetric vinylogous conjugate addition reaction between γ-aryl- and alkyl-substituted butenolides with the butenamides and enoates shown. Computational studies show the preference for the observed stereochemistry is a result of favourable weak non-bonding interactions, which stabilize the transition state. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  4. Enantioselectivity in environmental risk assessment of modern chiral pesticides.

    Science.gov (United States)

    Ye, Jing; Zhao, Meirong; Liu, Jing; Liu, Weiping

    2010-07-01

    Chiral pesticides comprise a new and important class of environmental pollutants nowadays. With the development of industry, more and more chiral pesticides will be introduced into the market. But their enantioselective ecotoxicology is not clear. Currently used synthetic pyrethroids, organophosphates, acylanilides, phenoxypropanoic acids and imidazolinones often behave enantioselectively in agriculture use and they always pose unpredictable enantioselective ecological risks on non-target organisms or human. It is necessary to explore the enantioselective toxicology and ecological fate of these chiral pesticides in environmental risk assessment. The enantioselective toxicology and the fate of these currently widely used pesticides have been discussed in this review article.

  5. CARBOXYLESTERASES IN ENANTIOSELECTIVE SYNTHESIS OF ORGANIC COMPOUNDS

    Directory of Open Access Journals (Sweden)

    E. A. Shesterenko

    2013-02-01

    Full Text Available The classification, structure, and mechanism of catalytic action of carboxylesterase of different origin are presented in the review. The prospects of carboxylesterases application for metabolism and both several drugs and prodrugs activation investigation in vitro are shown. The enzyme usage as biocatalyst of stereoselective hydrolysis and synthesis of a wide range of acyclic, carbocyclic and heterocyclic compounds — esters are also urgent. It was established that enantiomers obtainable with the help of carboxylesterase are characterized by high chemical yields and optical purity; immobilization on different supports stabilizes the enzyme and allows the repeated usage of obtained biocatalysts. The own studies conducted and the enzymatic hydrolysis features of news 3-acylhydroxy-1,4-benzodiasepin-2-ones — potential anxiolytic and hypnotic means, with a help of pig liver microsomal fraction carboxylesterase have been established. For the first time the enantioselective hydrolysis of 3-acetoxy-7-bromo-1-methyl-5-phenyl-1,2-dihydro-3H-1,4-benzdiazepine-2-one was accomplished using free and immobilized in phyllophorine and alginate, stabilized by Ca2+ microsomal fraction. The S-enantiomer of substrate was isolated, which suggests the increased specificity of pig liver microsomal fraction carboxylesterase to its R-enantiomer.

  6. Enantioselective Syntheses of (-)- and (+)-Homocitric Acid Lactones.

    Science.gov (United States)

    Rodríguez R, Gastón H.; Biellmann, Jean-François

    1996-03-08

    Highly enantioselective syntheses of enantiomers of homocitric acid lactones (R)-5a and (S)-5b are described. Thermal Diels-Alder cycloadditions of 2a and 2b to 1,3-butadiene produced adducts 3a and 3b, respectively. Oxidative ozonolysis of latter adducts gave products 4a and 4b which after acid treatment afforded a mixture with 5a and 5b as major component. Acid lactones 5a and 5b were converted into their dimethyl esters 6a and 6b which were purified by chromatography. After saponification, the products obtained were crystallized to yield (-)- and (+)-homocitric acid lactones ((R)-5a and (S)-5b). Diastereomeric excess (de) of Diels-Alder adducts 3a and 3b was determined by means of Mosher esters of glycols 8a, 8b, and racemic 8. Diels-Alder cycloaddition products of lactones 2a and 2b to 1,3-butadiene showed a diastereoselectivity of 96%.

  7. Copper-Catalyzed Enantioselective Synthesis of α-Hydroxyamine Using Monodentate Phosphoramidites

    Institute of Scientific and Technical Information of China (English)

    DONG,Lin; CUN,Lin-Feng; GONG,Liu-Zhu; MI,Ai-Qiao; JIANG,Yao-Zhong

    2004-01-01

    @@ Development of new methods for the introduction of a nitrogen atom to a carbonyl group is still the most important synthetic target. Cu-catalyzed addition of organozinc reagents to α,β-unsaturated carbonyl compounds has been the subject of intensive investigation.[1] Moreover, trapping of the intermediate Zn-enolates has been achieved using nitrosobenzene. To demonstrate the feasibility of developing enantioselective variants of these tandem C-C bond formations,α,β-unsaturated substrates a~d was subjected to standard reaction conditions using Feringa's (L1*, L2*) and our own phosphoramidite ligands (L3*, L4*). In this reaction, medium to high levels of enantioselectivities were observed.

  8. Enantioselective Palladium-Catalyzed Carbene Insertion into the N-H Bonds of Aromatic Heterocycles.

    Science.gov (United States)

    Arredondo, Vanessa; Hiew, Stanley C; Gutman, Eugene S; Premachandra, Ilandari Dewage Udara Anulal; Van Vranken, David L

    2017-03-15

    C3-substituted indoles and carbazoles react with α-aryl-α-diazoesters under palladium catalysis to form α-(N-indolyl)-α-arylesters and α-(N-carbazolyl)-α-arylesters. The products result from insertion of a palladium-carbene ligand into the N-H bond of the aromatic N-heterocycles. Enantioselection was achieved using a chiral bis(oxazoline) ligand, in many cases with high enantioselectivity (up to 99 % ee). The method was applied to synthesize the core of a bioactive carbazole derivative in a concise manner.

  9. Mirror symmetry breaking with limited enantioselective autocatalysis and temperature gradients: a stability survey

    CERN Document Server

    Blanco, Celia; Crusats, Joaquim; El-Hachemi, Zoubir; Moyano, Albert; Hochberg, David; 10.1039/C2CP43488A

    2012-01-01

    We analyze limited enantioselective (LES) autocatalysis in a temperature gradient and with internal flow/recycling of hot and cold material. Microreversibility forbids broken mirror symmetry for LES in the presence of a temperature gradient alone. This symmetry can be broken however when the auto-catalysis and limited enantioselective catalysis are each localized within the regions of low and high temperature, respectively. This scheme has been recently proposed as a plausible model for spontaneous emergence of chirality in abyssal hydrothermal vents. Regions in chemical parameter space are mapped out in which the racemic state is unstable and bifurcates to chiral solutions.

  10. Diastereodivergent and Enantioselective [4+2] Annulations of γ-Butenolides with Cyclic 1-Azadienes

    Directory of Open Access Journals (Sweden)

    Chao Li

    2015-07-01

    Full Text Available An asymmetric annulation reaction of γ-butenolides and cyclic 1-azadienes containing a 1,2-benzoisothiazole-1,1-dioxide motif has been studied, proceeding in a tandem Michael addition-aza-Michael addition sequence. Endo-type cycloadducts bearing fused tetracyclic skeletons were isolated in fair yields and with high enantioselectivity (up to >99% ee under the catalysis of modified cinchona alkaloid (DHQD2PHAL. Besides, exo-type diastereomers could be produced using β-isocupreidine (β-ICD as the catalyst, though with moderate enantioselectivity.

  11. Diastereodivergent and Enantioselective [4+2] Annulations of γ-Butenolides with Cyclic 1-Azadienes.

    Science.gov (United States)

    Li, Chao; Jiang, Kun; Chen, Ying-Chun

    2015-07-27

    An asymmetric annulation reaction of γ-butenolides and cyclic 1-azadienes containing a 1,2-benzoisothiazole-1,1-dioxide motif has been studied, proceeding in a tandem Michael addition-aza-Michael addition sequence. Endo-type cycloadducts bearing fused tetracyclic skeletons were isolated in fair yields and with high enantioselectivity (up to >99% ee) under the catalysis of modified cinchona alkaloid (DHQD)2PHAL. Besides, exo-type diastereomers could be produced using β-isocupreidine (β-ICD) as the catalyst, though with moderate enantioselectivity.

  12. Enantioselective Evans-Tishchenko Reduction of b-Hydroxyketone Catalyzed by Lithium Binaphtholate

    Directory of Open Access Journals (Sweden)

    Makoto Nakajima

    2011-06-01

    Full Text Available Lithium diphenylbinaphtholate catalyzed the enantioselective Evans-Tishchenko reduction of achiral b-hydroxyketones to afford monoacyl-protected 1,3-diols with high stereoselectivities. In the reaction of racemic b-hydroxyketones, kinetic optical resolution occurred in a highly stereoselective manner.

  13. Bifunctional Asymmetric Catalysis with Hydrogen Chloride: Enantioselective Ring-Opening of Aziridines Catalyzed by a Phosphinothiourea.

    Science.gov (United States)

    Mita, Tsuyoshi; Jacobsen, Eric N

    2009-06-01

    Ring-opening of aziridines with hydrogen chloride to form β-chloroamine derivatives is catalyzed by a chiral phosphinothiourea derivative in high yields and with high enantioselectivities. On the basis of (31)P NMR studies, activation of HCl appears to proceed via quantitative protonation of the catalyst to afford a phosphonium chloride complex.

  14. Enantioselective Biotransformation of Chiral Persistent Organic Pollutants.

    Science.gov (United States)

    Zhang, Ying; Ye, Jing; Liu, Min

    2017-01-01

    Enantiomers of chiral compounds commonly undergo enantioselective transformation in most biologically mediated processes. As chiral persistent organic pollutants (POPs) are extensively distributed in the environment, differences between enantiomers in biotransformation should be carefully considered to obtain exact enrichment and specific health risks. This review provides an overview of in vivo biotransformation of chiral POPs currently indicated in the Stockholm Convention and their chiral metabolites. Peer-reviewed journal articles focused on the research question were thoroughly searched. A set of inclusion and exclusion criteria were developed to identify relevant studies. We mainly compared the results from different animal models under controlled laboratory conditions to show the difference between enantiomers in terms of distinct transformation potential. Interactions with enzymes involved in enantioselective biotransformation, especially cytochrome P450 (CYP), were discussed. Further research areas regarding this issue were proposed. Limited evidence for a few POPs has been found in 30 studies. Enantioselective biotransformation of α-hexachlorocyclohexane (α-HCH), chlordane, dichlorodiphenyltrichloroethane (DDT), heptachlor, hexabromocyclododecane (HBCD), polychlorinated biphenyls (PCBs), and toxaphene, has been investigated using laboratory mammal, fish, bird, and worm models. Tissue and excreta distributions, as well as bioaccumulation and elimination kinetics after administration of racemate and pure enantiomers, have been analyzed in these studies. Changes in enantiomeric fractions have been considered as an indicator of enantioselective biotransformation of chiral POPs in most studies. Results of different laboratory animal models revealed that chiral POP biotransformation is seriously affected by chirality. Pronounced results of species-, tissue-, gender-, and individual-dependent differences are observed in in vivo biotransformation of chiral POPs

  15. A Click Chemistry Approach towards Flavin-Cyclodextrin Conjugates-Bioinspired Sulfoxidation Catalysts.

    Science.gov (United States)

    Tomanová, Petra; Šturala, Jiří; Buděšínský, Miloš; Cibulka, Radek

    2015-11-04

    A click chemistry approach based on the reaction between alkynylflavins and mono(6-azido-6-deoxy)-β-cyclodextrin has proven to be a useful tool for the synthesis of flavin-cyclodextrin conjugates studied as monooxygenase mimics in enantioselective sulfoxidations.

  16. Influence of biochar on the enantioselective behavior of the chiral fungicide metalaxyl in soil

    Science.gov (United States)

    Gámiz, Beatriz; Pignatello, Joseph J.; Hermosín, María Carmen; Cox, Lucía; Celis, Rafael

    2015-04-01

    Chiral pesticides comprise an emerging and important class of organic pollutants currently, accounting for more than a quarter of used pesticides. Consequently, the contamination problems caused by chiral pesticides are concern matter and factors affecting enantioselective processes of chiral pesticides in soil need to be understood. For example, certain soil management practices, such as the use of organic amendments, can affect the enantioselective behavior of chiral pesticides in soils. Recently, biochar (BC), i.e. organic matter subjected to pyrolysis, has been proposed as organic amendment due to beneficial properties such as its high stability against decay in soil environments and its apparent ability to influence the availability of nutrients. BC is considered to be more biologically inert as compared to otherforms of organic carbon. However, its side-effects on the enantioselectivity of processes affecting the fate of chiral pesticides is unknown. The aim of this study was to assess the effect of biochar (BC) on the enantioselectivity of sorption, degradation, and leaching of the chiral fungicide metalaxyl in an agricultural soil. Amending the soil with BC (2% w/w) resulted in 3 times higher sorption of metalaxyl enantiomers compared to unamended soil, but no enantioselectivity in the process was observed. Moreover, both enantiomers showed some resistance to be desorbed in BC-amended soil compared to unamended soil. Dissipation studies revealed that the degradation of metalaxylwas more enantioselective in the unamended soil than in BC-amended soil. In unamended soil, R-metalaxyl(biologically active) and S- metalaxyl had half-lives (t1/2) of 3 and 34 days, respectively. BC enhanced the persistence of both enantiomers in the soil, with R-metalaxyl being degraded faster (t1/2=43 days) than S-metalaxyl (t1/2= 100 days). The leaching of both S-and R-metalaxyl was almost suppressed after amending the soil with BC; less than 10% of the fungicide applied to soil

  17. Photosensitizer-doped conjugated polymer nanoparticles with high cross-sections for one- and two-photon excitation.

    Science.gov (United States)

    Grimland, Jennifer L; Wu, Changfeng; Ramoutar, Ria R; Brumaghim, Julia L; McNeill, Jason

    2011-04-01

    We report a novel nanoparticle that is promising for photodynamic therapy applications, which consists of a π-conjugated polymer doped with a singlet oxygen photosensitizer. The nanoparticles exhibit highly efficient collection of excitation light due to the large excitation cross-section of the polymer. A quantum efficiency of singlet oxygen production of 0.5 was determined. Extraordinarily large two-photon excitation cross-sections were determined, indicating promise for near infrared multiphoton photodynamic therapy. Gel electrophoresis of DNA after near-UV irradiation in the presence of nanoparticles indicated both purine base and backbone DNA damage.

  18. Multi-Year Radar Observations of Planetary Waves at High Conjugate Latitudes (Invited)

    Science.gov (United States)

    Fritts, D. C.; Iimura, H.; Janches, D.; Mitchell, N. J.; Singer, W.

    2013-12-01

    Meteor radars at nearly conjugate latitudes from ~54o to 68o S and N are enabling multi-year studies of planetary wave (PW) structure and seasonal, interannual, and inter-hemispheric variability. The various PWs exhibit dramatically different seasonal and inter-hemispheric variability, strongly variable amplitude and phase structures with altitude, latitude, and time, and episodic maxima in E-P flux components. This talk will review these features defined with meteor radars at Rothera Station and Ferraz Base (62 and 68 S), on Tierra del Fuego (54 S), and at Juliusruh, Germany and Esrange, Sweden (55 and 68 N).

  19. A broadly applicable NHC-Cu-catalyzed approach for efficient, site-, and enantioselective coupling of readily accessible (pinacolato)alkenylboron compounds to allylic phosphates and applications to natural product synthesis.

    Science.gov (United States)

    Gao, Fang; Carr, James L; Hoveyda, Amir H

    2014-02-05

    A set of protocols for catalytic enantioselective allylic substitution (EAS) reactions that allow for additions of alkenyl units to readily accessible allylic electrophiles is disclosed. Transformations afford 1,4-dienes that contain a tertiary carbon stereogenic site and are promoted by 1.0-5.0 mol % of a copper complex of an N-heterocyclic carbene (NHC). Aryl- as well as alkyl-substituted electrophiles bearing a di- or trisubstituted alkene may be employed. Reactions can involve a variety of robust alkenyl-(pinacolatoboron) [alkenyl-B(pin)] compounds that can be either purchased or prepared by various efficient, site-, and/or stereoselective catalytic reactions, such as cross-metathesis or proto-boryl additions to terminal alkynes. Vinyl-, E-, or Z-disubstituted alkenyl-, 1,1-disubstituted alkenyl-, acyclic, or heterocyclic trisubstituted alkenyl groups may be added in up to >98% yield, >98:2 SN2':SN2, and 99:1 enantiomeric ratio (er). NHC-Cu-catalyzed EAS with alkenyl-B(pin) reagents containing a conjugated carboxylic ester or aldehyde group proceed to provide the desired 1,4-diene products in good yield and with high enantioselectivity despite the presence of a sensitive stereogenic tertiary carbon center that could be considered prone to epimerization. In most instances, the alternative approach of utilizing an alkenylmetal reagent (e.g., an Al-based species) represents an incompatible option. The utility of the approach is illustrated through applications to enantioselective synthesis of natural products such as santolina alcohol, semburin, nyasol, heliespirone A, and heliannuol E.

  20. Asymmetric synthesis of N,O-heterocycles via enantioselective iridium-catalysed intramolecular allylic amidation

    NARCIS (Netherlands)

    Zhao, Depeng; Fananas-Mastral, Martin; Chang, Mu-Chieh; Otten, Edwin; Feringa, Ben L.

    2014-01-01

    Chiral N,O-heterocycles were synthesized in high yields and excellent enantioselectivity up to 97% ee via iridium-catalysed intramolecular allylic substitution with nucleophilic attack by the amide oxygen atom. The resulting benzoxazine derivatives were further transformed into challenging chiral

  1. Stereospecific nickel-catalyzed cross-coupling reactions of alkyl ethers: enantioselective synthesis of diarylethanes.

    Science.gov (United States)

    Taylor, Buck L H; Swift, Elizabeth C; Waetzig, Joshua D; Jarvo, Elizabeth R

    2011-01-26

    Secondary benzylic ethers undergo stereospecific substitution reactions with Grignard reagents in the presence of nickel catalysts. Reactions proceed with inversion of configuration and high stereochemical fidelity. This reaction allows for facile enantioselective synthesis of biologically active diarylethanes from readily available optically enriched carbinols.

  2. Lipase Catalyzed Enantioselective Transesterification of 5-Acyloxy-2(5H)-Furanones

    NARCIS (Netherlands)

    Deen, Hanneke van der; Hof, Robert P.; Oeveren, Arjan van; Kellogg, Richard M.; Feringa, Bernard

    1994-01-01

    Several lipases catalyse the transesterification of gamma-acyloxyfuranones in organic solvents with high enantioselectivities. This method has been used for the kinetic resolution of 5-acetoxy-2(5H)-furanone, 5-acetoxy-4-methyl-2(5H)-furanone and 5-propionyloxy-2(5H)-furanone, in e.e.'s ranging from

  3. Cooperative catalysis by palladium and a chiral phosphoric acid: enantioselective amination of racemic allylic alcohols.

    Science.gov (United States)

    Banerjee, Debasis; Junge, Kathrin; Beller, Matthias

    2014-11-24

    Cooperative catalysis by [Pd(dba)2] and the chiral phosphoric acid BA1 in combination with the phosphoramidite ligand L8 enabled the efficient enantioselective amination of racemic allylic alcohols with a variety of functionalized amines. This catalytic protocol is highly regio- and stereoselective (up to e.r. 96:4) and furnishes valuable chiral amines in almost quantitative yield.

  4. Combining silver- and organocatalysis: an enantioselective sequential catalytic approach towards pyrano-annulated pyrazoles.

    Science.gov (United States)

    Hack, Daniel; Chauhan, Pankaj; Deckers, Kristina; Mizutani, Yusuke; Raabe, Gerhard; Enders, Dieter

    2015-02-11

    A one-pot asymmetric Michael addition/hydroalkoxylation sequence, catalyzed by a sequential catalytic system consisting of a squaramide and a silver salt, provides a new series of chiral pyrano-annulated pyrazole derivatives in excellent yields (up to 95%) and high enantioselectivities (up to 97% ee).

  5. Análise enantiosseletiva de fármacos: contribuições da cromatografia líquida de alta eficiência e eletroforese capilar Enantioselective analysis of drugs: contributions of high-performance liquid chromatography and capillary electrophoresis

    Directory of Open Access Journals (Sweden)

    Pierina Sueli Bonato

    2005-08-01

    Full Text Available The demand for analytical methods suitable for accurate and reproducible determination of drug enantiomers has increased significantly in the last years. High-performance liquid chromatography (HPLC using chiral stationary phases and capillary electrophoresis (CE are the most important techniques used for this purpose. In this paper, the fundamental aspects of chiral separations using both techniques are presented. Some important aspects for the development of enantioselective methods, particularly for the analysis of drugs and metabolites in biological samples, are also discussed.

  6. The Catalytic Enantioselective Total Synthesis of (+)-Liphagal

    KAUST Repository

    Day, Joshua J.

    2011-06-10

    Ring a ding: The meroterpenoid natural product (+)-liphagal has been synthesized enantioselectively in 19 steps from commercially available materials. The trans-homodecalin system was achieved by ring expansion followed by stereoselective hydrogenation. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  7. Directed evolution of an enantioselective lipase

    NARCIS (Netherlands)

    Liebeton, Klaus; Zonta, Albin; Schimossek, Klaus; Nardini, Marco; Lang, Dietmar; Dijkstra, Bauke W.; Reetz, Manfred T.; Jaeger, Karl-Erich

    2000-01-01

    Background: The biocatalytic production of enantiopure compounds is of steadily increasing importance to the chemical and biotechnological industry. In most cases, however, it is impossible to identify an enzyme that possesses the desired enantioselectivity. Therefore, there is a strong need to crea

  8. DNA Duplex Engineering for Enantioselective Fluorescent Sensor.

    Science.gov (United States)

    Hu, Yuehua; Lin, Fan; Wu, Tao; Zhou, Yufeng; Li, Qiusha; Shao, Yong; Xu, Zhiai

    2017-02-21

    The rapid identification of biomacromolecule structure that has a specific association with chiral enantiomers especially from natural sources will be helpful in developing enantioselective sensor and in speeding up drug exploitation. Herein, owing to its existence also in living cells, apurinic/apyrimidinic site (AP site) was first engineered into ds-DNA duplex to explore its competence in enantiomer selectivity. An AP site-specific fluorophore was utilized as an enantioselective discrimination probe to develop a straightforward chiral sensor using natural tetrahydropalmatine (L- and D-THP) as enantiomer representatives. We found that only L-THP can efficiently replace the prebound fluorophore to cause a significant fluorescence increase due to its specific binding with the AP site (two orders magnitude higher in affinity than binding with D-THP). The AP site binding specificity of L-THP over D-THP was assessed via intrinsic fluorescence, isothermal titration calorimetry, and DNA stability. The enantioselective performance can be easily tuned by the sequences near the AP site and the number of AP sites. A single AP site provides a perfect binding pocket to differentiate the chiral atom-induced structure discrepancy. We expect that our work will inspire interest in engineering local structures into a ds-DNA duplex for developing novel enantioselective sensors.

  9. Enantioselective solvent-free Robinson annulation reactions

    Indian Academy of Sciences (India)

    D Rajagopal; R Narayanan; S Swaminathan

    2001-06-01

    The enantioselective cyclization of the prochiral cyclic substrates 1 to 7 and 26, can be carried out in the neat using -proline as catalyst. The substrates 18 to 22 and 27 could not be cyclized with S-proline but could be cyclized with a mixture of -phenylalanine and -camphorsulphonic acid. The enantioselective cyclization of prochiral acyclic triones 45 and 47 and also the racemic tricarbonyl compounds 54 to 57 could also be carried out in the \\text{neat} using -proline as catalyst. The optically active enediones obtained in the above cyclizations could also be obtained directly from 1,3-diones or 2-hydroxymethylene cycloalkanones in a one-pot reaction with methyl vinyl ketone (MVK) and S-proline in the absence of solvents. 13C NMR studies of the one-pot synthesis of S-11 and S-14 reveal that the annulations involve initial formation of an acid-base complex followed by a Michael reaction and then an enantioselective cyclization. Such enantioselective cyclizations probably occur on the surface of -proline crystals.

  10. Changes in free and conjugated polyamines during starvation of sugarcane juices as analyzed by high-performance liquid chromatography.

    Science.gov (United States)

    Rodríguez, C W; de Armas, R; Vicente, C; Legaz, M E

    2000-06-09

    Changes of the polyamines (PAs) titer in high- and mid-molecular-mass carbohydrates (HMMCs and MMMCs, respectively) obtained from sugarcane juices stored for 72 h at pH 5.2 or clarified at pH 8.0 have been studied. Cadaverine (CAD) is the most abundant free (S) PA in the MMMC fraction from juices at pH 5.2, whereas putrescine (PUT) was revealed as the main PA at pH 8.0. A slight increase in the free PUT titer can be noted at pH 5.2 for 72 h of juice starvation. PAs from MMMC were mainly conjugated to acid-insoluble (PH) molecules. Accumulation of PH-PAs with the time of starvation was especially significant for PUT and CAD. However, CAD has also been detected in the acid-soluble (SH) fraction and its concentration increases with the time of starvation at pH 5.2. The accumulation pattern of free and conjugated PAs from HMMCs is similar to that found for MMMCs although some differences can be observed. For instance, the increase in free PUT with the time at pH 8.0 was 2.7-times higher in the HMMC fraction than in the MMMC fraction. Conjugated PAs associated to acid-soluble macromolecules (SH fraction) achieved a level in HMMC fractions higher than that observed in the MMMC fraction. Moreover, the reported increase with time that was observed in PH-CAD from the MMMC fraction was not observed in the HMMC fraction, and, finally, the increase in PH-PUT with the time was lower for the HMMC fraction than for the MMMC fraction.

  11. An erbium(III)-based NIR emitter with a highly conjugated β-diketonate for blue-region sensitization

    Energy Technology Data Exchange (ETDEWEB)

    Martín-Ramos, P., E-mail: pablomartinramos@gmail.com [Advanced Materials Laboratory, ETSIIAA, Universidad de Valladolid, Avenida de Madrid 44, 34004 Palencia (Spain); Department of Physics and MALTA Consolider Team, Universidad de La Laguna, E-38206 San Cristóbal de La Laguna, Santa Cruz de Tenerife (Spain); Martín, I.R.; Lahoz, F. [Department of Physics and MALTA Consolider Team, Universidad de La Laguna, E-38206 San Cristóbal de La Laguna, Santa Cruz de Tenerife (Spain); Hernández-Navarro, S. [Advanced Materials Laboratory, ETSIIAA, Universidad de Valladolid, Avenida de Madrid 44, 34004 Palencia (Spain); Pereira da Silva, P.S. [CEMDRX, Physics Department, Universidade de Coimbra, Rua Larga, P-3004-516 Coimbra (Portugal); Hernández, I. [CITIMAC Dept., Facultad de Ciencias, University of Cantabria, Avenida Los Castros s/n, 39005 Santander (Spain); School of Physics and Astronomy, Queen Mary University of London, Mile End Road, London E1 4NS (United Kingdom); Lavín, V. [Department of Physics and MALTA Consolider Team, Universidad de La Laguna, E-38206 San Cristóbal de La Laguna, Santa Cruz de Tenerife (Spain); Ramos Silva, M. [CEMDRX, Physics Department, Universidade de Coimbra, Rua Larga, P-3004-516 Coimbra (Portugal)

    2015-01-15

    Highlights: • A new highly coordinated Er{sup 3+} complex has been synthesized and its properties studied. • X-ray diffraction shows that complex packs efficiently: no solvent accessible voids. • dnm ligand successfully extends the excitation bands to the blue region up to 550 nm. • Efficient energy transfer by antenna effect results in 1.53 μm emission from Er{sup 3+}. - Abstract: The sensitization of lanthanide complexes in the visible region is of particular interest for practical applications such as labeling, biological analysis and optoelectronics. A visible-light sensitized Er{sup 3+} complex based on the use of a highly conjugated β-diketonate (1,3-di(2-naphthyl)-1,3-propanedione, Hdnm) and 5-nitro-1,10-phenanthroline (5NO{sub 2}phen) as an ancillary ligand, [Er(dnm){sub 3}(5NO{sub 2}phen)], has been synthesized, fully characterized and its photophysical properties have been investigated. Suitably expanded π-conjugation in the complex molecule makes the excitation window red-shifted to the visible region (up to 550 nm). Efficient energy transfer by antenna effect results in 1.53 μm emission from the Er{sup 3+} ion.

  12. Noncovalent Se···O Conformational Locks for Constructing High-Performing Optoelectronic Conjugated Polymers.

    Science.gov (United States)

    Dong, Tao; Lv, Lei; Feng, Linlin; Xia, Yu; Deng, Wei; Ye, Pan; Yang, Bei; Ding, Shang; Facchetti, Antonio; Dong, Huanli; Huang, Hui

    2017-09-01

    Noncovalent conformational locks are broadly employed to construct highly planar π-conjugated semiconductors exhibiting substantial charge transport characteristics. However, current chalcogen-based conformational lock strategies for organic semiconductors are limited to S···X (X = O, N, halide) weak interactions. An easily accessible (minimal synthetic steps) and structurally planar selenophene-based building block, 1,2-diethoxy-1,2-bisselenylvinylene (DESVS), with novel Se···O noncovalent conformational locks is designed and synthesized. DESVS unique properties are supported by density functional theory computed electronic structures, single crystal structures, and experimental lattice cohesion metrics. Based on this building block, a new class of stable, structurally planar, and solution-processable conjugated polymers are synthesized and implemented in organic thin-film transistors (TFT) and organic photovoltaic (OPV) cells. DESVS-based polymers exhibit carrier mobilities in air as high as 1.49 cm(2) V(-1) s(-1) (p-type) and 0.65 cm(2) V(-1) s(-1) (n-type) in TFTs, and power conversion efficiency >5% in OPV cells. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  13. Enantioselective Synthesis of All-Carbon Quaternary Stereogenic Centers via Copper-Catalyzed Asymmetric Allylic Alkylation of (Z)-Allyl Bromides with Organolithium Reagents

    NARCIS (Netherlands)

    Fananas-Mastral, Martin; Vitale, Romina; Perez, Manuel; Feringa, Ben L.

    2015-01-01

    A copper/phosphoramidite catalyzed asymmetric allylic alkylation of Z trisubstituted allyl bromides with organolithium reagents is reported. The reaction affords all-carbon quaternary stereogenic centers in high yields and very good regio- and enantioselectivity. This systematic study illustrates

  14. Elucidating the Role of Conjugated Polyelectrolyte Interlayers for High-Efficiency Organic Photovoltaics.

    Science.gov (United States)

    Lim, Kyung-Geun; Park, Sung Min; Woo, Han Young; Lee, Tae-Woo

    2015-09-21

    Despite the promising function of conjugated polyelectrolytes (CPEs) as an interfacial layer in organic photovoltaics (OPVs), the underlying mechanism of dipole orientation and the electrical characteristics of CPE interlayers remain unclear. Currently, the ionic functionality of CPEs (i.e., whether they are cationic or anionic) is believed to determine the interfacial dipole alignment and the resulting electron or hole extraction properties at the interface between an organic photoactive layer and a metal electrode. In this research, we find that in contrast to this common belief, the photovoltaic efficiency can be improved significantly by both cationic and anionic CPE layers regardless of the ion functionality of the CPE. This improvement occurs because the interfacial dipoles of cationic and anionic CPEs are realigned in the identical direction despite the different ionic functionality. The net dipole is determined not by the intrinsic molecular dipole of the CPE but by the ionic redistribution in the CPE layer and the resulting interfacial dipole at the intimate contact with adjacent layers. We also demonstrated that the energy level alignment and performance parameters of OPVs can be controlled systematically by the electrically poled CPE layers with the oriented interfacial dipoles; the distribution of positive and negative ions in the CPE layer was adjusted by applying an appropriate external electric field, and the energy alignment was reversible by changing the electric field direction. The anionic and cationic CPEs (PSBFP-Na and PAHFP-Br) based on the same π-conjugated backbone of fluorene-phenylene were each used as the electron extraction layer on a photoactive layer. Both anionic and cationic CPE interlayers improved the energy level alignment at the interface between the photoactive layer and the electrode and the resulting performance parameters, which thereby increased the power conversion efficiency to 8.3 %.

  15. Diastereoselective and enantioselective reduction of tetralin-1,4-dione

    Directory of Open Access Journals (Sweden)

    2008-10-01

    Full Text Available BackgroundThe chemistry of tetralin-1,4-dione, the stable tautomer of 1,4-dihydroxynaphthalene, has not been explored previously. It is readily accessible and offers interesting opportunities for synthesis.ResultsThe title reactions were explored. L-Selectride reduced the diketone to give preferentially the cis-diol (d.r. 84 : 16. Red-Al gave preferentially the trans-diol (d.r. 13 : 87. NaBH4, LiAlH4, and BH3 gave lower diastereoselectivities (yields: 76–98%. Fractional crystallization allowed isolation of the cis-diol and the trans-diol (55% and 66% yield, respectively. Borane was used to cleanly give the mono-reduction product. Highly enantioselective CBS reductions afforded the trans-diol (72% yield, 99% ee and the mono-reduction product (81%, 95% ee.ConclusionDiastereoselective and enantioselective reductions of the unexplored tetralin-1,4-dione provides a very convenient entry into a number of synthetically highly attractive 1,4-tetralindiols and 4-hydroxy-1-tetralone.

  16. Quinoxaline-based π-conjugated donor polymer for highly efficient organic thin-film solar cells

    Science.gov (United States)

    Kitazawa, Daisuke; Watanabe, Nobuhiro; Yamamoto, Shuhei; Tsukamoto, Jun

    2009-08-01

    A quinoxaline-based π-conjugated donor polymer, poly[2,7-(9,9-dioctylfluorene)-alt-5,5-(5',8'-di-2-thienyl-2',3'-diphenylquinoxaline)] (N-P7), was synthesized to achieve a high power conversion efficiency (PCE) of bulk heterojunction (BHJ)-based solar cells. The optical band-gap and highest occupied molecular orbital level of N-P7 were 1.95 and -5.37 eV, respectively. BHJ-based solar cells using N-P7 as a donor and phenyl C71 butyric acid methyl ester as an acceptor gave a PCE as high as 5.5% under AM 1.5G 100 mW/cm2 illumination. We also investigated the effects of substituent groups of quinoxaline-based polymers on the morphology of the BHJ layer.

  17. Enantioselective transesterification of glycidol catalysed by a novel lipase expressed from Bacillus subtilis.

    Science.gov (United States)

    Wang, Lei; Tai, Jian-Dong; Wang, Ren; Xun, Er-Na; Wei, Xiao-Fei; Wang, Lei; Wang, Zhi

    2010-05-10

    A novel plasmid (pBSR2) was constructed by incorporating a strong lipase promoter and a terminator into the original pBD64. The lipase gene from Bacillus subtilis strain IFFI10210 was cloned into the plasmid pBSR2 and transformed into B. subtilis A.S.1.1655 to obtain an overexpression strain. The recombinant lipase [BSL2 (B. subtilis lipase 2)] has been expressed from the novel constructed strain and used in kinetic resolution of glycidol through enantioselective transesterification. The effects of reaction conditions on the activity as well as enantioselectivity were investigated. BSL2 showed a satisfying enantioselectivity (E>30) under the optimum conditions [acyl donor: vinyl butyrate; the mole ratio of vinyl butyrate to glycidol was 3:1; organic medium: 1,2-dichloroethane with water activity (a(w))=0.33; temperature 40 degrees C]. The remaining (R)-glycidol with a high enantiomeric purity [ee (enantiomeric excess) >99%] could be obtained when the conversion was approx. 60%. The results clearly show a good potential for industrial application of BSL2 in the resolution of glycidol through enantioselective transesterification.

  18. Enantioselective degradation of metalaxyl in grape, tomato, and rice plants.

    Science.gov (United States)

    Wang, Meiyun; Hua, Xiude; Zhang, Qing; Yang, Yu; Shi, Haiyan; Wang, Minghua

    2015-02-01

    Enantioselective biodegradation of chiral pesticide metalaxyl in grape, tomato, and rice plants under field conditions were studied. Metalaxyl enantiomers were completely separated with a resolution (Rs) of 5.01 by high-performance liquid chromatography (HPLC) based on a cellulose tris (3-chloro-4-methyl phenyl carbamate) chiral column (Lux Cellulose-2). Metalaxyl enantiomers from matrixes were extracted by acetonitrile and purged using Cleanert Alumina-A solid phase extraction (SPE). The linearity, recovery, precision, sensitivity, and matrix effect of the method were assessed. The result showed that significant stereoselectivity occurred in grape, tomato, and rice plants. In grape, (+)-S-metalaxyl with a half-life of 5.5 d degraded faster than (-)-R-metalaxyl with that of 6.9 d, and the enantiomer fraction (EF) value reached 0.37 at 21 d. The same enantioselectivity was observed in tomato, and the half-life was 2.2 d for the S-enantiomer and 3.0 d for the R-enantiomer. The EF values decreased from 0.49 of 0 d to 0.26 of 14 d. On the other hand, a preferential degradation of the R-form was found in rice plants, with an EF value of 0.70 at 14 d, and the corresponding half-life was 2.3 d for the R-form and 2.8 d for the S-form. © 2014 Wiley Periodicals, Inc.

  19. Enantioselective degradation of metalaxyl in cucumber, cabbage, spinach and pakchoi.

    Science.gov (United States)

    Wang, Meiyun; Zhang, Qing; Cong, Lujing; Yin, Wei; Wang, Minghua

    2014-01-01

    The enantioselective degradation behaviors of the acylamino acid fungicide metalaxyl in vegetables (cucumber, cabbage, spinach and pakchoi) under field and greenhouse conditions were elucidated by reversed-phase high-performance liquid chromatography (HPLC). A cellulose tris (3-chloro-4-methyl phenyl carbamate) chiral column (Lux Cellulose-2) was used for the chiral separation of the enantiomers using acetonitrile-0.1% formic acid solution (40:60, v/v) as mobile phase at a flow rate of 1.0 mL min(-1). The two enantiomers could be completely separated with a resolution (Rs) of 5.2. The linearity range, matrix effect, precision and recovery were evaluated. The method was successfully applied for the enantioselective analysis of metalaxyl in cucumber, cabbage, spinach and pakchoi under different conditions. The results showed that R-enantiomer dissipated faster than S-enantiomer in cucumber of greenhouse. Inversely, a preferential degradation of S-form was found in spinach and pakchoi under field and greenhouse conditions. No stereoselective degradation in cabbage was observed. These results can be applied for evaluating the environmental risk and food safety. Copyright © 2013 Elsevier Ltd. All rights reserved.

  20. A general enantioselective route to the chamigrene natural product family

    KAUST Repository

    White, David E.

    2010-06-01

    Described in this report is an enantioselective route toward the chamigrene natural product family. The key disconnections in our synthetic approach include sequential enantioselective decarboxylative allylation and ring-closing olefin metathesis to form the all-carbon quaternary stereocenter and spirocyclic core present in all members of this class of compounds. The generality of this strategy is demonstrated by the first total syntheses of elatol and the proposed structure of laurencenone B, as well as the first enantioselective total syntheses of laurencenone C and α-chamigrene. A brief exploration of the substrate scope of the enantioselective decarboxylative allylation/ring-closing metathesis sequence with fully substituted vinyl chlorides is also presented.

  1. Highly diastereo- and enantioselective allylboration of aldehydes using α-substituted allyl/crotyl pinacol boronic esters via in situ generated borinic esters.

    Science.gov (United States)

    Chen, Jack L-Y; Scott, Helen K; Hesse, Matthew J; Willis, Christine L; Aggarwal, Varinder K

    2013-04-10

    Readily available, α-substituted allyl/crotyl pinacol boronic esters often give low E/Z selectivity (with Z favored) in reactions with aldehydes. We found that addition of nBuLi to the pinacol boronic ester followed by trapping of the alkoxide with TFAA leads to an intermediate allyl borinic ester which undergoes allylboration with very high E selectivity. The substrate scope includes primary to tertiary alkyl α-substituents, crotyl substrates, and the previously unreported β-methallyl pinacol boronic esters. The latter give very high Z selectivity under standard conditions which is completely reversed to high E selectivity under the new conditions. Monitoring the reaction by (11)B NMR confirmed that the reaction proceeds through a borinic ester intermediate.

  2. Enantioselective Effects of Metalaxyl Enantiomers on Breast Cancer Cells Metabolic Profiling Using HPLC-QTOF-Based Metabolomics

    Directory of Open Access Journals (Sweden)

    Ping Zhang

    2017-01-01

    Full Text Available In this study, an integrative high-performance liquid chromatography coupled with quadrupole time-of-flight tandem mass spectrometry (HPLC-QTOF based metabolomics approach was performed to evaluate the enantioselective metabolic perturbations in MCF-7 cells after treatment with R-metalaxyl and S-metalaxyl, respectively. Untargeted metabolomics profile, multivariate pattern recognition, metabolites identification, and pathway analysis were determined after metalaxyl enantiomer exposure. Principal component analysis (PCA and partitial least-squares discriminant analysis (PLS-DA directly reflected the enantioselective metabolic perturbations induced by metalaxyl enantiomers. On the basis of multivariate statistical results, a total of 49 metabolites including carbohydrates, amino acids, nucleotides, fatty acids, organic acids, phospholipids, indoles, derivatives, etc. were found to be the most significantly changed metabolites and metabolic fluctuations caused by the same concentration of R-metalaxyl and S-metalaxyl were enantioselective. Pathway analysis indicated that R-metalaxyl and S-metalaxyl mainly affected the 7 and 10 pathways in MCF-7 cells, respectively, implying the perturbed pathways induced by metalaxyl enantiomers were also enantioselective. Furthermore, the significantly perturbed metabolic pathways were highly related to energy metabolism, amino acid metabolism, lipid metabolism, and antioxidant defense. Such results provide more specific insights into the enantioselective metabolic effects of chiral pesticides in breast cancer progression, reveal the underlying mechanisms, and provide available data for the health risk assessments of chiral environmental pollutants at the molecular level.

  3. Enantioselective Effects of Metalaxyl Enantiomers on Breast Cancer Cells Metabolic Profiling Using HPLC-QTOF-Based Metabolomics.

    Science.gov (United States)

    Zhang, Ping; Zhu, Wentao; Wang, Dezhen; Yan, Jin; Wang, Yao; He, Lin

    2017-01-12

    In this study, an integrative high-performance liquid chromatography coupled with quadrupole time-of-flight tandem mass spectrometry (HPLC-QTOF) based metabolomics approach was performed to evaluate the enantioselective metabolic perturbations in MCF-7 cells after treatment with R-metalaxyl and S-metalaxyl, respectively. Untargeted metabolomics profile, multivariate pattern recognition, metabolites identification, and pathway analysis were determined after metalaxyl enantiomer exposure. Principal component analysis (PCA) and partitial least-squares discriminant analysis (PLS-DA) directly reflected the enantioselective metabolic perturbations induced by metalaxyl enantiomers. On the basis of multivariate statistical results, a total of 49 metabolites including carbohydrates, amino acids, nucleotides, fatty acids, organic acids, phospholipids, indoles, derivatives, etc. were found to be the most significantly changed metabolites and metabolic fluctuations caused by the same concentration of R-metalaxyl and S-metalaxyl were enantioselective. Pathway analysis indicated that R-metalaxyl and S-metalaxyl mainly affected the 7 and 10 pathways in MCF-7 cells, respectively, implying the perturbed pathways induced by metalaxyl enantiomers were also enantioselective. Furthermore, the significantly perturbed metabolic pathways were highly related to energy metabolism, amino acid metabolism, lipid metabolism, and antioxidant defense. Such results provide more specific insights into the enantioselective metabolic effects of chiral pesticides in breast cancer progression, reveal the underlying mechanisms, and provide available data for the health risk assessments of chiral environmental pollutants at the molecular level.

  4. Direct, intermolecular, enantioselective, iridium-catalyzed allylation of carbamates to form carbamate-protected, branched allylic amines.

    Science.gov (United States)

    Weix, Daniel J; Marković, Dean; Ueda, Mitsuhiro; Hartwig, John F

    2009-07-02

    The direct reaction between carbamates and achiral allylic carbonates to form branched, conveniently protected primary allylic amines with high regioselectivity and enantioselectivity is reported. This process occurs without base or with 0.5 equiv K(3)PO(4) in the presence of a metalacyclic iridium catalyst containing a labile ethylene ligand. The reactions of aryl-, heteroaryl-, and alkyl-substituted allylic carbonates with BocNH(2), FmocNH(2), CbzNH(2), TrocNH(2), TeocNH(2), and 2-oxazolidinone occur in good yields, with high selectivity for the branched isomer and high enantioselectivities (98% average ee).

  5. Vancomycin Molecular Interactions: Antibiotic and Enantioselective Mechanisms

    Science.gov (United States)

    Ward, Timothy J.; Gilmore, Aprile; Ward, Karen; Vowell, Courtney

    Medical studies established that vancomycin and other related macrocyclic antibiotics have an enhanced antimicrobial activity when they are associated as dimers. The carbohydrate units attached to the vancomycin basket have an essential role in the dimerization reaction. Covalently synthesized dimers were found active against vancomycin-resistant bacterial strains. A great similarity between antibiotic potential and enantioselectivity was established. A covalent vancomycin dimer was studied in capillary electrophoresis producing excellent chiral separation of dansyl amino acids. Balhimycin is a macrocyclic glycopeptide structurally similar to vancomycin. The small differences are, however, responsible for drastic differences in enantioselectivity in the same experimental conditions. Contributions from studies examining vancomycin's mechanism for antimicrobial activity have substantially aided our understanding of its mechanism in chiral recognition.

  6. Simultaneous generation of ions and high-order harmonics from thin conjugated polymer foil irradiated with ultrahigh contrast laser

    Energy Technology Data Exchange (ETDEWEB)

    Choi, I. W.; Kim, I J.; Pae, K. H.; Nam, K. H.; Lee, C.-L.; Yun, H.; Kim, H. T.; Lee, S. K.; Yu, T. J.; Sung, J. H.; Lee, J. [Advanced Photonics Research Institute, Gwangju Institute of Science and Technology, Gwangju 500-712 (Korea, Republic of); Pirozhkov, A. S.; Ogura, K.; Orimo, S.; Daido, H. [Quantum Beam Science Directorate, Japan Atomic Energy Agency, Kizugawa, Kyoto 619-0215 (Japan)

    2011-10-31

    We report the manufacturing of an (ultra-)thin foil target made of conjugated polymer, poly(9,9'-dioctylfluorene-co-benzothiadiazole) (F8BT), and the simultaneous observation of laser-accelerated ions and second harmonic radiation, when irradiated with ultrahigh-contrast laser pulse at a maximum intensity of 4 x 10{sup 19 }W/cm{sup 2}. Maximum proton energy of 8 MeV is achieved along the target normal direction. Strong second harmonic with over 6% energy ratio compared to fundamental is emitted along the specular direction. Two-dimensional particle-in-cell simulations confirm the simultaneous generation of protons and high-order harmonics, which demonstrates the feasibility of applications requiring particle and radiation sources at once, effectively using the same laser and target.

  7. A Novel Thiophene Derivative-based Conjugated Polymer for Polymer Solar Cells with High Open-circuit Voltage

    Institute of Scientific and Technical Information of China (English)

    谌烈; 沈星星; 陈义旺

    2012-01-01

    A novel D-A alternative conjugated polymer PBDTDMCT containing benzo[1,2-b:4,5-b']dithiophene (BDT) and dimethyl thiophene-3,4-dicarboxylate (DMCT), was designed and synthesized by Stille cross-coupling reaction. The copolymer exhibited excellent solubility and good thermal stability. The optical band gap determined from the onset of absorption of the polymer film was 2.10 eV. By incorporation of the ester groups into the polymer side chain, the HOMO level of polymer PBDTDMT was tuned to be deep-lying (--5.65 eV). Open-circuit voltage of polymer solar cells constructed based on PBDTDMT and [6,6]-phenyl-CTwbutyric acid methyl ester (PCTIBM) can be tuned to achieve values as high as ca. 1.0 V.

  8. Regio-, Diastereo-, and Enantioselective Nitroso-Diels-Alder Reaction of 1,3-Diene-1-carbamates Catalyzed by Chiral Phosphoric Acids.

    Science.gov (United States)

    Pous, Jonathan; Courant, Thibaut; Bernadat, Guillaume; Iorga, Bogdan I; Blanchard, Florent; Masson, Géraldine

    2015-09-23

    Chiral phosphoric acid-catalyzed asymmetric nitroso-Diels-Alder reaction of nitrosoarenes with carbamate-dienes afforded cis-3,6-disubstituted dihydro-1,2-oxazines in high yields with excellent regio-, diastereo-, and enantioselectivities. Interestingly, we observed that the catalyst is able not only to control the enantioselectivity but also to reverse the regioselectivity of the noncatalyzed nitroso-Diels-Alder reaction. The regiochemistry reversal and asynchronous concerted mechanism were confirmed by DFT calculations.

  9. Tungsten-catalyzed regio- and enantioselective aminolysis of trans-2,3-epoxy alcohols: an entry to virtually enantiopure amino alcohols.

    Science.gov (United States)

    Wang, Chuan; Yamamoto, Hisashi

    2014-12-08

    The first catalytic enantioselective aminolysis of trans-2,3-epoxy alcohols has been accomplished. This stereospecific ring-opening process was efficiently promoted by a tungsten/bis(hydroxamic acid) catalytic system, furnishing various anti-3-amino-1,2-diols with excellent regiocontrol and high enantioselectivities (up to 95% ee). Moreover, virtually enantiopure 3-amino-1,2-diols could be obtained by the sequential combination of two reactions that both involve the use of a chiral catalyst.

  10. Highly Enantioselective Organocatalytic Asymmetric Mukaiyama-aldol Reaction of Difluoroenoxysilanes with β,γ-Unsaturated α-Ketoesters%高对映选择性的有机催化的二氟烯醇硅醚与β,γ-不饱和-α-酮酸酯的不对称Mukaiyama-aldol反应

    Institute of Scientific and Technical Information of China (English)

    刘运林; 周剑

    2012-01-01

    We report the first example of catalytic asymmetric reaction of difluoroenoxysilanes 1 and β,γ-unsaturated α-ketoesters 2. In the presence of tertiary amine or tertiary amine-H-bonding donor bifunctional catalysts, it was found that the reaction selectively took place at the ketone moiety of ketoesters 2, and no conjugate reaction happened. Hydronquinine derived urea catalyst 11 was identified as a powerful catalyst for this Mukaiyama-aldol reaction to finnish a-difluoroalkyl substituted tertiary alcohols in good to high yield (44%-81%), with moderate to excellent enantioselectivity (72%-96%). The optimum reaction condition was determined to run the reaction at -40 ℃ using THF as the solvent, in the presence of 10 mol% of chiral catalyst 11. The reaction possibly proceeded via the dual activation of both reaction partners: the tertiary amine moiety of catalyst 11 working as a Lewis base to activate difluoroenoxysilanes 1, while the urea part of the catalyst as a Bronsted acid to activate carbonyl group of ketoesters 2. Different aryl substituted difluoroenoxysilanes 1 and ),-aryl substi- tuted β,γ-unsaturated a-ketoesters 2 all worked well under the established reaction condition, with 15 examples provided. The thus obtained chiral α-difluoroalkyl substituted tertiary alcohols were not only valuable in the medicinal research, but also versatile building blocks for the synthesis of a variety of difluoroalkyl-substituted chiral compounds. For example, the selec- tive reduction of the ketone or ester group of product 3g has been realized by using NaBH4 or Et3SiH as the reducing agents, giving the triol 14 or diol 15 in moderate yield without the loss ofee.%首次研究了二氟烯醇硅醚1与β,γ-不饱和酮酸酯2的反应.发现不论使用叔胺或叔胺-氢键给体双功能催化剂,均专一地发生Mukaiyama-aldol反应生成相应的叔醇3.利用手性氢化奎宁衍生的双功能脲催化剂11高对映选择性地实现了这一反

  11. Organocatalytic cascade aza-Michael/hemiacetal reaction between disubstituted hydrazines and α,β-unsaturated aldehydes: Highly diastereo- and enantioselective synthesis of pyrazolidine derivatives

    Directory of Open Access Journals (Sweden)

    Zhi-Cong Geng

    2012-10-01

    Full Text Available The catalytic synthesis of nitrogen-containing heterocycles is of great importance to medicinal and synthetic chemists, and also a challenge for modern chemical methodology. In this paper, we report the synthesis of pyrazolidine derivatives through a domino aza-Michael/hemiacetal sequence with chiral or achiral secondary amines as organocatalysts. Thus, a series of achiral pyrazolidine derivatives were obtained with good yields (up to 90% and high diastereoselectivities (>20:1 with pyrrolidine as an organocatalyst, and enantioenriched pyrazolidines are also achieved with good results (up to 86% yield, >10/1 regioselectivity, >20:1 dr, 99% ee in the presence of (S-diphenylprolinol trimethylsilyl ether catalyst.

  12. Asymmetric Synthesis of Multisubstituted Dihydrobenzofurans by Intramolecular Conjugate Addition of Short-Lived C-O Axially Chiral Enolates.

    Science.gov (United States)

    Tomohara, Keisuke; Kasamatsu, Koji; Yoshimura, Tomoyuki; Furuta, Takumi; Kawabata, Takeo

    2016-07-01

    Enantioselective intramolecular conjugate addition reactions of short-lived C-O axially chiral enolates have been developed. The reactions proceeded with inversion of the configuration and provided dihydrobenzofurans with contiguous tetra- and trisubstituted carbon centers in up to 96% enantiomeric excess (ee).

  13. Enantioselectivity in the phytotoxicity of herbicide imazethapyr.

    Science.gov (United States)

    Zhou, Qingyan; Xu, Chao; Zhang, Yongsong; Liu, Weiping

    2009-02-25

    Chiral compounds usually behave enantioselectively in phyto-biochemical processes. With the increasing application of chiral herbicides, their enantioselective phytotoxicity to plants merits further study, and little information is available in this area. The purpose of this study was to examine the enantioselective phytotoxicity of the herbicide imazethapyr (IM) on the roots of maize (Zea mays L.) seedlings. Enantiomers of IM were separated by HPLC, and their absolute configurations were confirmed as S-(+)-IM and R-(-)-IM by the octant rule. Plant growth measurements and morphological, microscopic, and ultrastructural observations were conducted after treatment with individual IM enantiomers and the racemate. Observations of root morphology showed that the root diameter significantly increased, whereas the root volume, surface area, and number of root tips decreased significantly. IM enantiomers selectively damaged root hair growth and significantly reduced the sloughing of border cells from the tips. IM also had adverse effects on cell organelles, such as statocytes, mitochondria, dictyosomes, and endoplasmic reticulum in maize roots. Moreover, cell membranes and cell walls were thicker than usual after IM treatment. All of the results showed the same trend that the R-(-)-IM affected the root growth of maize seedlings more severely than the S-(+)-IM. The inhibition abilities of (+/-)-IM was between S-(+)- and R-(-)-IM. The behavior of the active enantiomer, instead of just the racemate, may have more relevance to the herbicidal effects and ecological safety of IM. Therefore, enantiomeric differences should be considered when evaluating the bioavailability of the herbicide IM.

  14. A Tyrosine Aminomutase from Rice (Oryza sativa) Isomerizes (S)-α- to (R)-β-Tyrosine with Unique High Enantioselectivity and Retention of Configuration.

    Science.gov (United States)

    Walter, Tyler; King, Zayna; Walker, Kevin D

    2016-01-12

    A recently discovered 3,5-dihydro-5-methylidene-4H-imidazol-4-one (MIO)-dependent tyrosine aminomutase (OsTAM) from rice [Yan, J., et al. (2015) Plant Cell 27, 1265] converts (S)-α-tyrosine to a mixture of (R)- and (S)-β-tyrosines, with high (94%) enantiomeric excess, which does not change with pH, like it does for two bacterial TAMs. The K(M) of 490 μM and the k(cat) of 0.005 s(-1) are similar for other TAM enzymes. OsTAM is unique and also catalyzes (R)-β- from (S)-α-phenylalanine. OsTAM principally retains the configuration at the reactive C(α) and C(β) centers during catalysis much like the phenylalanine aminomutase on the Taxol biosynthetic pathway in Taxus plants.

  15. Enantioselective determination of metoprolol and its metabolites in human urine high-performance liquid chromatography with fluorescence detection (HPLC-FLD) and tandem mass spectrometry (MS/MS).

    Science.gov (United States)

    Baranowska, Irena; Adolf, Weronika; Magiera, Sylwia

    2015-11-01

    A sensitive, stereoselective assay using solid phase extraction and high-performance liquid chromatography (HPLC) with fluorescence detection (FLD) was developed and validated for the analysis of enantiomers of metoprolol and its metabolites (α-hydroxymetoprolol, O-desmethylmetoprolol). Chiral separation was achieved using a CHIRALCEL OD-RH column, packed with cellulose tris-(3,5-dimethylphenyl-carbamate) stationary phase, employing a mobile phase composed by a mixture of 0.2% diethylamine in water and acetonitrile in gradient elution mode. Linear calibration curves were obtained over the range of 0.025-2.0μg/mL (R(2)>0.994) in urine for both enantiomers of metoprolol and its metabolites with quantitation limit of 0.025μg/mL. Intra and inter-day precision and accuracy were below 15% for both metoprolol and metabolites enantiomers. The recovery of enantiomer of metoprolol and its metabolite was greater than 68.0%, utilizing a SPE procedure. The method was tested with urine quality control samples and human urine fractions after administration of 50mg rac-metoprolol.

  16. Synthesis by High-Efficiency Liquid-Phase (HELP Method of Oligonucleotides Conjugated with High-Molecular Weight Polyethylene Glycols (PEGs

    Directory of Open Access Journals (Sweden)

    Bonora GM

    1998-01-01

    Full Text Available The chemical modification of synthetic oligonucleotides has recently been investigated to improve their pharmacological utilization. In addition to chemical alterations of the backbone and of the heterocyclic bases, their conjugation with amphiphylic moieties, such as the polyethylene glycol has been proposed. The large scale production of these molecules as demanded for commercial purposes is hampered by the heterogeneity of the solid-phase processes and by the low reactivity of high-molecular weight PEGs in solution. A new synthetic procedure based on the recently developed liquid-phase method (HELP, has been set up to overcome these limitations.

  17. Enantioselective Synthesis of N-PMP-1,2-dihydropyridines via Formal [4 + 2] Cycloaddition between Aqueous Glutaraldehyde and Imines.

    Science.gov (United States)

    Ramaraju, Panduga; Mir, Nisar A; Singh, Deepika; Gupta, Vivek K; Kant, Rajni; Kumar, Indresh

    2015-11-20

    A simple and highly practical one-pot formal [4 + 2] cycloaddition approach for the enantioselective synthesis of N-PMP-1,2-dihydropyridines (DHPs) is described. This chemistry involves an amino-catalytic direct Mannich reaction/cyclization followed by IBX-mediated chemo- and regioselective oxidation sequence between readily available aqueous glutaraldehyde and imines under very mild conditions. A series of N-PMP-1,2-DHPs have been prepared in high yields and excellent enantioselectivity. This method also gives access to both enantiomers of 1,2-DHPs in surplus amount by shifting the catalyst configuration.

  18. The substrate binding cavity of particulate methane monooxygenase from Methylosinus trichosporium OB3b expresses high enantioselectivity for n-butane and n-pentane oxidation to 2-alcohol.

    Science.gov (United States)

    Miyaji, Akimitsu; Miyoshi, Teppei; Motokura, Ken; Baba, Toshihide

    2011-11-01

    The particulate methane monooxygenase (pMMO) of Methylosinus trichosporium OB3b oxidized n-butane and n-pentane and mainly produced (R)-2-butanol and (R)-2-pentanol that comprised 78 and 89% of the product, respectively, indicating that the pro-R hydrogen of the 2-position carbon of n-butane and n-pentane is oriented toward a catalytic site within the substrate binding site of pMMO. The protein cavity adjacent to the catalytic center for pMMO has optimum volume for recognizing n-butane and n-pentane for enantioselective hydroxylation.

  19. Chiral separation by enantioselective liquid-liquid extraction

    NARCIS (Netherlands)

    Schuur, B.; Verkuijl, B. J. V.; Minnaard, A. J.; De Vries, J. G.; Heeres, H. J.; Feringa, B. L.

    2011-01-01

    The literature on enantioselective liquid-liquid extraction (ELLE) spans more than half a century of research. Nonetheless, a comprehensive overview has not appeared during the past few decades. Enantioselective liquid-liquid extraction is a technology of interest for a wide range of chemists and ch

  20. Enantioselective N-heterocyclic carbene-catalyzed synthesis of trifluoromethyldihydropyridinones.

    Science.gov (United States)

    Wang, Dong-Ling; Liang, Zhi-Qin; Chen, Kun-Quan; Sun, De-Qun; Ye, Song

    2015-06-05

    The enantioselective N-heterocyclic carbene-catalyzed [4 + 2] cyclocondensation of α-chloroaldehydes and trifluoromethyl N-Boc azadienes was developed, giving the corresponding 3,4-disubstituted-6-trifluoromethyldihydropyridin-2(1H)-ones in good yields with exclusive cis-selectivities and excellent enantioselectivities.

  1. Cost-effectiveness of heptavalent conjugate pneumococcal vaccine (Prevenar) in Germany: considering a high-risk population and herd immunity effects.

    Science.gov (United States)

    Lloyd, Adam; Patel, Nishma; Scott, David A; Runge, Claus; Claes, Christa; Rose, Markus

    2008-02-01

    In Germany, the seven-valent conjugate vaccine Prevenar is recommended for use in children at high risk of pneumococcal disease. Recent data suggest that giving conjugate vaccine to all children may lead to a decline in pneumococcal disease in unvaccinated adults, a phenomenon known as herd immunity. This analysis evaluated the cost and economic consequences in Germany of vaccinating (1) children at high risk, (2) all children when considering only benefits for vaccinated individuals and (3) all children when also considering herd immunity benefits. Costs in the model included vaccination, management of meningitis, bacteraemia, pneumonia and acute otitis media, insurance payments to parents and the costs of care for long-term disabilities. The model estimated that the cost-effectiveness of vaccination would be 38,222 euros per life year gained in children at high risk and 100,636 euros per life year gained in all children when not considering herd immunity. When considering herd immunity effects, the model estimated that offering vaccination for all children would reduce adult deaths by 3,027 per year, and vaccination would be broadly cost neutral. The findings are sensitive to the effect of conjugate vaccine on the rates of pneumonia and invasive disease in the elderly. If the herd immunity effect of conjugate vaccination in Germany is similar to that observed elsewhere, offering vaccine to all children will be more attractive than the current policy of restricting vaccination to children at high risk of pneumococcal disease.

  2. Air-stable π-conjugated amorphous copolymer field-effect transistors with high mobility of 0.3 cm2/Vs

    DEFF Research Database (Denmark)

    Georgakopoulos, S.; Gu, Y.; Nielsen, Martin Meedom

    2012-01-01

    We have fabricated organic bottom-contact top-gate field-effect transistors with an indenofluorene-phenanthrene co-polymer semiconductor, exhibiting ON/OFF ratio of 10(7) and uncommonly high mobility for an amorphous conjugated polymer of up to 0.3 cm(2)/Vs. Lack of crystallinity in this material...

  3. High-Resolution Spectroscopy of Jet-Cooled 1,1 '-Diphenylethylene: Electronically Excited and Ionic States of a Prototypical Cross-Conjugated System

    NARCIS (Netherlands)

    Smolarek, S.; Vdovin, A.; Rijs, A.; van Walree, C. A.; Zgierski, M. Z.; Buma, W. J.

    2011-01-01

    The photophysics of a prototypical cross-conjugated pi-system, 1,1'-diphenylethylene, have been studied using high-resolution resonance enhanced multiphoton ionization excitation spectroscopy and zero kinetic energy photoelectron spectroscopy, in combination with advanced ab initio calculations

  4. High-resolution spectroscopy of jet-cooled 1,1 '-diphenylethylene: electronically excited and ionic states of a prototypical cross-conjugated system

    NARCIS (Netherlands)

    Smolarek, S.; Vdovin, A.; Rijs, A.; van Walree, C.A.; Zgierski, M.Z.; Buma, W.J.

    2011-01-01

    The photophysics of a prototypical cross-conjugated π-system, 1,1′-diphenylethylene, have been studied using high-resolution resonance enhanced multiphoton ionization excitation spectroscopy and zero kinetic energy photoelectron spectroscopy, in combination with advanced ab initio calculations. We f

  5. Enantioselective Benzylic Hydroxylation Catalysed by P450 Monooxygenases: Characterisation of a P450cam Mutant Library and Molecular Modelling.

    Science.gov (United States)

    Eichler, Anja; Gricman, Łukasz; Herter, Susanne; Kelly, Paul P; Turner, Nicholas J; Pleiss, Jürgen; Flitsch, Sabine L

    2016-03-02

    Cytochrome P450 monooxygenases can catalyse the stereoselective C-H activation of a very broad range of substrates. Prediction and control of enantioselectivity of this enzyme class is of great interest for the synthesis of high-value chiral molecules. Here we have used a combination of molecular dynamics simulations and experimental screening to study the enantioselectivity of a library of active-site mutants of chimeric P450cam-RhFRed towards the benzylic hydroxylation of structurally related regioisomers of ethylmethylbenzene. Small variations either in substrate structure or in enzyme active site architecture were shown to lead to dramatic changes in enantioselectivity; this was broadly in agreement with computational predictions. In addition to validating computational approaches, these studies have provided us with a deeper understanding of effects that might control stereoselectivity in these biooxidation reactions.

  6. Enantioselective Synthesis of Antiepileptic Agent, (−-Levetiracetam, through Evans Asymmetric Strategy

    Directory of Open Access Journals (Sweden)

    K. Chandra Babu

    2013-01-01

    Full Text Available A practical and efficient enantioselective synthesis of antiepileptic drug, (−-Levetiracetam, has been described in five steps (33.0% overall yield and high optical purity (99.0% ee, using Evans asymmetric strategy for α-alkylation of carbonyl functionality as the key step. The simplicity of the experimental procedures and high stereochemical outcome make this method synthetically attractive for preparing the target compound on multigram scales.

  7. Enantioselective Synthesis of Antiepileptic Agent, (−)-Levetiracetam, through Evans Asymmetric Strategy

    OpenAIRE

    Chandra Babu, K.; Buchi Reddy, R.; Mukkanti, K.; Suresh, K.; Madhusudhan, G.; Satish Nigam

    2013-01-01

    A practical and efficient enantioselective synthesis of antiepileptic drug, (−)-Levetiracetam, has been described in five steps (33.0% overall yield) and high optical purity (99.0% ee), using Evans asymmetric strategy for α-alkylation of carbonyl functionality as the key step. The simplicity of the experimental procedures and high stereochemical outcome make this method synthetically attractive for preparing the target compound on multigram scales.

  8. Enantioselective redox-relay oxidative heck arylations of acyclic alkenyl alcohols using boronic acids.

    Science.gov (United States)

    Mei, Tian-Sheng; Werner, Erik W; Burckle, Alexander J; Sigman, Matthew S

    2013-05-08

    A general, highly selective asymmetric redox-relay oxidative Heck reaction using achiral or racemic acyclic alkenols and boronic acid derivatives is reported. This reaction delivers remotely functionalized arylated carbonyl products from acyclic alkenol substrates, with excellent enantioselectivity under mild conditions, bearing a range of useful functionality. A preliminary mechanistic investigation suggests that the regioselectivity of the initial migratory insertion is highly dependent on the electronic nature of the boronic acid and more subtle electronic effects of the alkenyl alcohol.

  9. Quantum dot bio-conjugate: as a western blot probe for highly sensitive detection of cellular proteins

    Science.gov (United States)

    Kale, Sonia; Kale, Anup; Gholap, Haribhau; Rana, Abhimanyu; Desai, Rama; Banpurkar, Arun; Ogale, Satishchandra; Shastry, Padma

    2012-03-01

    In the present study, we report a quantum dot (QD)-tailored western blot analysis for a sensitive, rapid and flexible detection of the nuclear and cytoplasmic proteins. Highly luminescent CdTe and (CdTe)ZnS QDs are synthesized by aqueous method. High resolution transmission electron microscopy, Raman spectroscopy, fourier transform infrared spectroscopy, fluorescence spectroscopy and X-ray diffraction are used to characterize the properties of the quantum dots. The QDs are functionalized with antibodies of prostate apoptosis response-4 (Par-4), poly(ADP-ribose) polymerases and β actin to specifically bind with the proteins localized in the nucleus and cytoplasm of the cells, respectively. The QD-conjugated antibodies are used to overcome the limitations of conventional western blot technique. The sensitivity and rapidity of protein detection in QD-based approach is very high, with detection limits up to 10 pg of protein. In addition, these labels provide the capability of enhanced identification and localization of marker proteins in intact cells by confocal laser scanning microscopy.

  10. Unsubstituted Benzodithiophene-Based Conjugated Polymers for High-Performance Organic Field-Effect Transistors and Organic Solar Cells.

    Science.gov (United States)

    Chen, Weichao; Xiao, Manjun; Han, Liangliang; Zhang, Jidong; Jiang, Huanxiang; Gu, Chuantao; Shen, Wenfei; Yang, Renqiang

    2016-08-03

    Unsubstituted benzo[1,2-b:4,5-b']dithiophene (BDT) was used to construct a high-performance conjugated polymer with 5,6-difluoro-4,7-bis[4-(2-octyldodecyl)thiophene-2-yl]benzo[c][1,2,5] thiadiazole (DTFFBT), named PBDT-DTFFBT. The polymer shows the low-lying highest occupied molecular orbital (HOMO) energy level (-5.40 eV) and a broad absorption spectra with strong vibronic absorption peak. Pure polymer films exhibit good crystallinity and edge-on orientation, partially attributed to the BDT units without any side chains, and as a result, the corresponding thin-film transistor showed excellent hole mobility over 1 cm(2) V(-1) s(-1). Interestingly, a well-distributed nanofibrillar polymer aggregation with face-on orientation was obviously formed when blending with PC71BM, which was in favor of the charge transportation. Consequently, the bulk heterojunction polymer solar cells based on the blends showed high power conversion efficiency of 9.29% with large short-current density (14.56 mA cm(-2)) and high fill factor (0.751) without any process additives or thermal annealing.

  11. High operational and environmental stability of high-mobility conjugated polymer field-effect transistors through the use of molecular additives

    Science.gov (United States)

    Nikolka, Mark; Nasrallah, Iyad; Rose, Bradley; Ravva, Mahesh Kumar; Broch, Katharina; Sadhanala, Aditya; Harkin, David; Charmet, Jerome; Hurhangee, Michael; Brown, Adam; Illig, Steffen; Too, Patrick; Jongman, Jan; McCulloch, Iain; Bredas, Jean-Luc; Sirringhaus, Henning

    2017-03-01

    Due to their low-temperature processing properties and inherent mechanical flexibility, conjugated polymer field-effect transistors (FETs) are promising candidates for enabling flexible electronic circuits and displays. Much progress has been made on materials performance; however, there remain significant concerns about operational and environmental stability, particularly in the context of applications that require a very high level of threshold voltage stability, such as active-matrix addressing of organic light-emitting diode displays. Here, we investigate the physical mechanisms behind operational and environmental degradation of high-mobility, p-type polymer FETs and demonstrate an effective route to improve device stability. We show that water incorporated in nanometre-sized voids within the polymer microstructure is the key factor in charge trapping and device degradation. By inserting molecular additives that displace water from these voids, it is possible to increase the stability as well as uniformity to a high level sufficient for demanding industrial applications.

  12. High operational and environmental stability of high-mobility conjugated polymer field-effect transistors through the use of molecular additives

    Science.gov (United States)

    Nikolka, Mark; Nasrallah, Iyad; Rose, Bradley; Ravva, Mahesh Kumar; Broch, Katharina; Sadhanala, Aditya; Harkin, David; Charmet, Jerome; Hurhangee, Michael; Brown, Adam; Illig, Steffen; Too, Patrick; Jongman, Jan; McCulloch, Iain; Bredas, Jean-Luc; Sirringhaus, Henning

    2016-12-01

    Due to their low-temperature processing properties and inherent mechanical flexibility, conjugated polymer field-effect transistors (FETs) are promising candidates for enabling flexible electronic circuits and displays. Much progress has been made on materials performance; however, there remain significant concerns about operational and environmental stability, particularly in the context of applications that require a very high level of threshold voltage stability, such as active-matrix addressing of organic light-emitting diode displays. Here, we investigate the physical mechanisms behind operational and environmental degradation of high-mobility, p-type polymer FETs and demonstrate an effective route to improve device stability. We show that water incorporated in nanometre-sized voids within the polymer microstructure is the key factor in charge trapping and device degradation. By inserting molecular additives that displace water from these voids, it is possible to increase the stability as well as uniformity to a high level sufficient for demanding industrial applications.

  13. High operational and environmental stability of high-mobility conjugated polymer field-effect transistors through the use of molecular additives

    KAUST Repository

    Nikolka, Mark

    2016-12-12

    Due to their low-temperature processing properties and inherent mechanical flexibility, conjugated polymer field-effect transistors (FETs) are promising candidates for enabling flexible electronic circuits and displays. Much progress has been made on materials performance; however, there remain significant concerns about operational and environmental stability, particularly in the context of applications that require a very high level of threshold voltage stability, such as active-matrix addressing of organic light-emitting diode displays. Here, we investigate the physical mechanisms behind operational and environmental degradation of high-mobility, p-type polymer FETs and demonstrate an effective route to improve device stability. We show that water incorporated in nanometre-sized voids within the polymer microstructure is the key factor in charge trapping and device degradation. By inserting molecular additives that displace water from these voids, it is possible to increase the stability as well as uniformity to a high level sufficient for demanding industrial applications.

  14. Catalytic enantioselective addition of Grignard reagents to aromatic silyl ketimines

    Science.gov (United States)

    Rong, Jiawei; Collados, Juan F.; Ortiz, Pablo; Jumde, Ravindra P.; Otten, Edwin; Harutyunyan, Syuzanna R.

    2016-12-01

    α-Chiral amines are of significant importance in medicinal chemistry, asymmetric synthesis and material science, but methods for their efficient synthesis are scarce. In particular, the synthesis of α-chiral amines with the challenging tetrasubstituted carbon stereocentre is a long-standing problem and catalytic asymmetric additions of organometallic reagents to ketimines that would give direct access to these molecules are underdeveloped. Here we report a highly enantioselective catalytic synthesis of N-sulfonyl protected α-chiral silyl amines via the addition of inexpensive, easy to handle and readily available Grignard reagents to silyl ketimines. The key to this success was our ability to suppress any unselective background addition reactions and side reduction pathway, through the identification of an inexpensive, chiral Cu-complex as the catalytically active structure.

  15. Electrical characterization of fluorinated benzothiadiazole based conjugated copolymer – a promising material for high-performance solar cells

    DEFF Research Database (Denmark)

    Toušek, J.; Toušková, J.; Remeš, Z.;

    2015-01-01

    Measurements of electrical conductivity, electron work function, carrier mobility ofholes and the diffusion length of excitons were performed on samples of conjugatedpolymers relevant to polymer solar cells. A state of the art fluorinated benzothiadiazolebased conjugated copolymer (PBDTTHD − DTBTff...

  16. HIGHLY DIASTEREOSELECTIVE MICHAEL REACTION UNDER SOLVENT-FREE CONDITIONS USING MICROWAVES: CONJUGATE ADDITION OF FLAVANONE TO ITS CHALCONE PRECURSOR

    Science.gov (United States)

    Microwave-assisted reaction of 2'-hydroxychalcones in the presence of DBU resulted in the formation of hitherto unknown dimers by conjugate addition of the intermediate cyclic ketone to the starting enone.

  17. Toward High-Performance Organic-Inorganic Hybrid Solar Cells: Bringing Conjugated Polymers and Inorganic Nanocrystals in Close Contact.

    Science.gov (United States)

    He, Ming; Qiu, Feng; Lin, Zhiqun

    2013-06-06

    Organic-inorganic hybrid solar cells composed of conjugated polymers (CPs) and inorganic nanocrystal (NC) semiconductors have garnered considerable attention as a potential alternative to traditional silicon solar cells due to the capacity of producing high-efficiency solar energy in a cost-effective manner. The combination of advantageous characteristics of CPs and NCs enables the construction of nanostructured high-performance, lightweight, flexible, large-area, and low-cost hybrid solar cells. However, it remains a grand challenge to control the film morphology and interfacial structure of such organic/inorganic semiconductor blends on the nanoscale. In this Perspective, we highlight the strategies of implementing close contact between CPs and NCs by tailoring the colloidal synthesis, the coordination reaction, and the chemical modification of CPs. As such, they offer promising opportunities for rationally controlling the phase separation between electron-donating CPs and electron-accepting NCs, increasing the interfacial areas between them, enhancing their electronic interaction, and thus substantially promoting the photovoltaic performance of the resulting organic-inorganic hybrid solar cells.

  18. Reversible holography and optical phase conjugation for image formation/correction using highly efficient organic photorefractive polymers

    Directory of Open Access Journals (Sweden)

    José-Luis Maldonado

    2015-12-01

    Full Text Available In this work, we report the reversible reconstruction of holographic and distorted transmission images through the four wave mixing (FWM technique and optical phase conjugation (OPC, an alternative method to adaptive optics, by using highly efficient Photorefractive (PR polymers fabricated in our laboratories. These PR polymers are based on our synthesized nonlinear chromophore 4-[4-(diethylamino-2 hydroxybenzylideneamino] benzonitrile (Dc. For the PR devices, diffraction efficiencies as high as 90% at 25 wt.% doping level of Dc at an external applied electric field (Eext around 56 V/μm are achieved. The reconstruction implementation is simple, of low cost, all-optical and it is capable of recovering 90% of the original images. The real-time holographic experiments were performed at Eext of just 27 V/μm, which is one of the lowest reported values. Reversible holographic imaging is showed with a rise-time around 0.35 s.

  19. Enantioselective bioaccumulation of diniconazole in Tenebrio molitor larvae.

    Science.gov (United States)

    Liu, Chen; LV, Xiao Tian; Zhu, Wen Xue; QU, Hao Yang; Gao, Yong Xin; Guo, Bao Yuan; Wang, Hui Li

    2013-12-01

    The enantioselective bioaccumulation of diniconazole in Tenebrio molitor Linne larva was investigated with liquid chromatography tandem mass spectrometry based on the ChiralcelOD-3R[cellulose tri-(3,5-dimethylphenyl carbamate)] column. In this study we documented the effects of dietary supplementation with wheat bran contaminated by racemic diniconazole at two dose levels of 20 mg kg(-1) and 2 mg kg(-1) (dry weight) in Tenebrio molitor. The results showed that both doses of diniconazole were taken up by Tenebrio molitor rapidly in the first few days, the concentrations of R-enantiomer and S-enantiomer at high doses reached the highest level of 0.55 mg kg(-1) and 0.48 mg kg(-1) , respectively, on the 1(st) d, and the concentrations of them obtained a maxima of 0.129 mg kg(-1) and 0.128 mg kg(-1) at low dose, respectively, on the 3(rd) d, which means that the concentration of diniconazole was proportional to the time of achieving the highest accumulated level. It afterwards attained equilibrium after a sharp decline at both 20 mg kg(-1) and 2 mg kg(-1) of diniconazole. The determination results from the feces of Tenebrio molitor demonstrated that the extraction recovery (ER) values of the high dose group were higher than that of the low dose group and the values were all above 1; therefore, it could be inferred that enantiomerization existed in Tenebrio molitor. Additionally, the biota accumulation factor was used to evaluate the bioaccumulation of diniconazole enantiomers, showing that the bioaccumulation of diniconazole in Tenebrio molitor was enantioselective with preferential accumulation of S-enantiomer.

  20. Visible-light excitation of iminium ions enables the enantioselective catalytic β-alkylation of enals

    Science.gov (United States)

    Silvi, Mattia; Verrier, Charlie; Rey, Yannick P.; Buzzetti, Luca; Melchiorre, Paolo

    2017-09-01

    Chiral iminium ions—generated upon condensation of α,β-unsaturated aldehydes and amine catalysts—are used extensively by chemists to make chiral molecules in enantioenriched form. In contrast, their potential to absorb light and promote stereocontrolled photochemical processes remains unexplored. This is despite the fact that visible-light absorption by iminium ions is a naturally occurring event that triggers the mechanism of vision in higher organisms. Herein we demonstrate that the direct excitation of chiral iminium ions can unlock unconventional reaction pathways, enabling enantioselective catalytic photochemical β-alkylations of enals that cannot be realized via thermal activation. The chemistry uses readily available alkyl silanes, which are recalcitrant to classical conjugate additions, and occurs under illumination by visible-light-emitting diodes. Crucial to success was the design of a chiral amine catalyst with well-tailored electronic properties that can generate a photo-active iminium ion while providing the source of stereochemical induction. This strategy is expected to offer new opportunities for reaction design in the field of enantioselective catalytic photochemistry.

  1. Bifunctional Enantioselective Ligands of Chiral BINOL Derivatives for Asymmetric Addition of Alkynylzinc to Aldehydes

    Institute of Scientific and Technical Information of China (English)

    ZOU Xiao-Wei; ZHENG Li-Fei; WU Ling-Lin; ZONG Li-Li; CHENG Yi-Xiang

    2008-01-01

    Four analogous binaphthyl compounds (R)-3a-3d containing (R)-3,3'-bis(2-pyridyl) groups were synthesized by the conjugation of (R)-2,2'-dimethoxy-1,1'-binaphthyl-3,3'-diboronic acid [(R)-2] with 2-bromopyridine,2-bromo-5-methylpyridine, 2-chloro-4-fluoropyridine and 2-chloro-3-(trifluoromethyl)pyridine via Pd-catalyzed Suzuki reactions, respectively.The application of the four chiral ligands in combination with Et2Zn and Ti(Oi-Pr)4 to the asymmetric addition of phenylacetylene to various aldehydes has been studied.The results show that (R)-3a and (R)-3b are not good catalysts for the alkynylzinc addition to aldehydes, (R)-3d shows good enantioselectivity only for the alkynylzinc addition to aliphatic aldehydes, and (R)-3c exhibits excellent enantioselectivity for phenylethynylzinc addition to both aromatic and aliphatic aldehydes.All the four chiral ligands produced the opposite configuration of the propargylic alcohols to that of the chiral ligands.

  2. Effect of olive-mill waste addition to agricultural soil on the enantioselective behavior of the chiral fungicide metalaxyl.

    Science.gov (United States)

    Gámiz, Beatriz; Celis, Rafael; Hermosín, M Carmen; Cornejo, Juan

    2013-10-15

    Certain soil management practices can affect the enantioselective behavior of chiral pesticide enantiomers in agricultural soils. In this work, laboratory experiments were conducted to study the effects of olive-mill waste (OMW) addition to a Mediterranean agricultural soil on the enantioselectivity of sorption, degradation, and leaching processes of the chiral fungicide metalaxyl. Sorption-desorption isotherms indicated that the sorption of metalaxyl enantiomers by unamended and OMW-amended soil (2% w/w) was non-enantioselective and that OMW addition had little effect on the extent of sorption of metalaxyl enantiomers by the soil. Soil incubation experiments revealed that the degradation of metalaxyl in unamended soil was highly enantioselective, with R-metalaxyl being degraded faster (t1/2 = 12 days) than S-metalaxyl (t1/2 = 39 days). OMW addition to the soil increased the half-life of the biologically-active R-metalaxyl enantiomer from 12 to 28 days, and decreased the half-life of the non-active S-metalaxyl enantiomer from 39 to 33 days. Consequently, the enantioselectivity of metalaxyl degradation in the soil was greatly reduced upon OMW addition. Column leaching data were consistent with batch sorption and incubation results, showing similar retardation of S- and R-metalaxyl in unamended and OMW-amended soil and enantioselective leaching of the fungicide only in unamended soil. The results have important implications regarding the biological efficacy and environmental impact of the fungicide when applied as a mixture of enantiomers or racemate to OMW-treated soils. Copyright © 2013 Elsevier Ltd. All rights reserved.

  3. Azaisoindigo conjugated polymers for high performance n-type and ambipolar thin film transistor applications

    KAUST Repository

    Yue, Wan

    2016-09-28

    Two new alternating copolymers, PAIIDBT and PAIIDSe have been prepared by incorporating a highly electron deficient azaisoindigo core. The molecular structure and packing of the monomer is determined from the single crystal X-ray diffraction. Both polymers exhibit high EAs and highly planar polymer backbones. When polymers are used as the semiconducting channel for solution-processed thin film transistor application, good properties are observed. A–A type PAIIDBT exhibits unipolar electron mobility as high as 1.0 cm2 V−1 s−1, D–A type PAIIDSe exhibits ambipolar charge transport behavior with predominately electron mobility up to 0.5 cm2 V−1 s−1 and hole mobility to 0.2 cm2 V−1 s−1. The robustness of the extracted mobility values are also commented on in detail. Molecular orientation, thin film morphology and energetic disorder of both polymers are systematically investigated.

  4. Enantioselective Intramolecular Hydroarylation of Alkenes via Directed C-H Bond Activation

    Energy Technology Data Exchange (ETDEWEB)

    Harada, Hitoshi; Thalji, Reema; Bergman, Robert; Ellman, Jonathan

    2008-05-22

    Highly enantioselective catalytic intramolecular ortho-alkylation of aromatic imines containing alkenyl groups tethered at the meta position relative to the imine directing group has been achieved using [RhCl(coe){sub 2}]{sub 2} and chiral phosphoramidite ligands. Cyclization of substrates containing 1,1- and 1,2-disubstituted as well as trisubstituted alkenes were achieved with enantioselectivities >90% ee for each substrate class. Cyclization of substrates with Z-alkene isomers proceeded much more efficiently than substrates with E-alkene isomers. This further enabled the highly stereoselective intramolecular alkylation of certain substrates containing Z/E-alkene mixtures via a Rh-catalyzed alkene isomerization with preferential cyclization of the Z-isomer.

  5. Cellulose Nanocrystals as Chiral Inducers: Enantioselective Catalysis and Transmission Electron Microscopy 3D Characterization.

    Science.gov (United States)

    Kaushik, Madhu; Basu, Kaustuv; Benoit, Charles; Cirtiu, Ciprian M; Vali, Hojatollah; Moores, Audrey

    2015-05-20

    Cellulose nanocrystals (CNCs), derived from cellulose, provide us with an opportunity to devise more sustainable solutions to current technological challenges. Enantioselective catalysis, especially heterogeneous, is the preferred method for the synthesis of pure chiral molecules in the fine chemical industries. Cellulose has been long sought as a chiral inducer in enantioselective catalysis. We report herein an unprecedentedly high enantiomeric excess (ee) for Pd patches deposited onto CNCs used as catalysts for the hydrogenation of prochiral ketones in water at room temperature and 4 bar H2. Our system, where CNCs acted as support and sole chiral source, achieved an ee of 65% with 100% conversions. Cryo-electron microscopy, high-resolution transmission electron microscopy, and tomography were used for the first time to study the 3D structure of a metal functionalized CNC hybrid. It established the presence of sub-nanometer-thick Pd patches at the surface of CNCs and provided insight into the chiral induction mechanism.

  6. Enantioselective Intramolecular Hydroarylation of Alkenes via Directed C-H Bond Activation

    Energy Technology Data Exchange (ETDEWEB)

    Harada, Hitoshi; Thalji, Reema; Bergman, Robert; Ellman, Jonathan

    2008-05-22

    Highly enantioselective catalytic intramolecular ortho-alkylation of aromatic imines containing alkenyl groups tethered at the meta position relative to the imine directing group has been achieved using [RhCl(coe){sub 2}]{sub 2} and chiral phosphoramidite ligands. Cyclization of substrates containing 1,1- and 1,2-disubstituted as well as trisubstituted alkenes were achieved with enantioselectivities >90% ee for each substrate class. Cyclization of substrates with Z-alkene isomers proceeded much more efficiently than substrates with E-alkene isomers. This further enabled the highly stereoselective intramolecular alkylation of certain substrates containing Z/E-alkene mixtures via a Rh-catalyzed alkene isomerization with preferential cyclization of the Z-isomer.

  7. Enantioselective, intermolecular benzylic C-H amination catalysed by an engineered iron-haem enzyme

    Science.gov (United States)

    Prier, Christopher K.; Zhang, Ruijie K.; Buller, Andrew R.; Brinkmann-Chen, Sabine; Arnold, Frances H.

    2017-07-01

    C-H bonds are ubiquitous structural units of organic molecules. Although these bonds are generally considered to be chemically inert, the recent emergence of methods for C-H functionalization promises to transform the way synthetic chemistry is performed. The intermolecular amination of C-H bonds represents a particularly desirable and challenging transformation for which no efficient, highly selective, and renewable catalysts exist. Here we report the directed evolution of an iron-containing enzymatic catalyst—based on a cytochrome P450 monooxygenase—for the highly enantioselective intermolecular amination of benzylic C-H bonds. The biocatalyst is capable of up to 1,300 turnovers, exhibits excellent enantioselectivities, and provides access to valuable benzylic amines. Iron complexes are generally poor catalysts for C-H amination: in this catalyst, the enzyme's protein framework confers activity on an otherwise unreactive iron-haem cofactor.

  8. Enantioselective Synthesis of (−)-Acetylapoaranotin

    Science.gov (United States)

    2017-01-01

    The first enantioselective total synthesis of the epipolythiodiketopiperazine (ETP) natural product (−)-acetylapoaranotin (3) is reported. The concise synthesis was enabled by an eight-step synthesis of a key cyclohexadienol-containing amino ester building block. The absolute stereochemistry of both amino ester building blocks used in the synthesis is set through catalytic asymmetric (1,3)-dipolar cycloaddition reactions. The formal syntheses of (−)-emethallicin E and (−)-haemotocin are also achieved through the preparation of a symmetric cyclohexadienol-containing diketopiperazine. PMID:28349698

  9. Enantioselective cellular uptake of chiral semiconductor nanocrystals

    Science.gov (United States)

    Martynenko, I. V.; Kuznetsova, V. A.; Litvinov, I. K.; Orlova, A. O.; Maslov, V. G.; Fedorov, A. V.; Dubavik, A.; Purcell-Milton, F.; Gun'ko, Yu K.; Baranov, A. V.

    2016-02-01

    The influence of the chirality of semiconductor nanocrystals, CdSe/ZnS quantum dots (QDs) capped with L- and D-cysteine, on the efficiency of their uptake by living Ehrlich Ascite carcinoma cells is studied by spectral- and time-resolved fluorescence microspectroscopy. We report an evident enantioselective process where cellular uptake of the L-Cys QDs is almost twice as effective as that of the D-Cys QDs. This finding paves the way for the creation of novel approaches to control the biological properties and behavior of nanomaterials in living cells.

  10. Catalytic enantioselective synthesis of quaternary carbon stereocentres

    Science.gov (United States)

    Quasdorf, Kyle W.; Overman, Larry E.

    2014-12-01

    Quaternary carbon stereocentres--carbon atoms to which four distinct carbon substituents are attached--are common features of molecules found in nature. However, before recent advances in chemical catalysis, there were few methods of constructing single stereoisomers of this important structural motif. Here we discuss the many catalytic enantioselective reactions developed during the past decade for the synthesis of single stereoisomers of such organic molecules. This progress now makes it possible to incorporate quaternary stereocentres selectively in many organic molecules that are useful in medicine, agriculture and potentially other areas such as flavouring, fragrances and materials.

  11. High-Energy Dissipation Performance in Epoxy Coatings by the Synergistic Effect of Carbon Nanotube/Block Copolymer Conjugates.

    Science.gov (United States)

    Garate, Hernan; Bianchi, Micaela; Pietrasanta, Lía I; Goyanes, Silvia; D'Accorso, Norma B

    2017-01-11

    modified by CNT-BCP conjugates. These findings provide a means to design epoxy-based coatings with high-energy dissipation performance.

  12. Rh(I)-Catalyzed Intermolecular Hydroacylation: Enantioselective Cross-Coupling of Aldehydes and Ketoamides

    Science.gov (United States)

    2015-01-01

    Under Rh(I) catalysis, α-ketoamides undergo intermolecular hydroacylation with aliphatic aldehydes. A newly designed Josiphos ligand enables access to α-acyloxyamides with high atom-economy and enantioselectivity. On the basis of mechanistic and kinetic studies, we propose a pathway in which rhodium plays a dual role in activating the aldehyde for cross-coupling. A stereochemical model is provided to rationalize the sense of enantioinduction observed. PMID:24937681

  13. Lewis base catalyzed enantioselective allylic hydroxylation of Morita-Baylis-Hillman carbonates with water

    KAUST Repository

    Zhu, Bo

    2011-08-19

    A Lewis base catalyzed allylic hydroxylation of Morita-Baylis-Hillman (MBH) carbonates has been developed. Various chiral MBH alcohols can be synthesized in high yields (up to 99%) and excellent enantioselectivities (up to 94% ee). This is the first report using water as a nucleophile in asymmetric organocatalysis. The nucleophilic role of water has been verified using 18O-labeling experiments. © 2011 American Chemical Society.

  14. Biocatalytic route to chiral acyloins: P450-catalyzed regio- and enantioselective α-hydroxylation of ketones.

    Science.gov (United States)

    Agudo, Rubén; Roiban, Gheorghe-Doru; Lonsdale, Richard; Ilie, Adriana; Reetz, Manfred T

    2015-01-16

    P450-BM3 and mutants of this monooxygenase generated by directed evolution are excellent catalysts for the oxidative α-hydroxylation of ketones with formation of chiral acyloins with high regioselectivity (up to 99%) and enantioselectivity (up to 99% ee). This constitutes a new route to a class of chiral compounds that are useful intermediates in the synthesis of many kinds of biologically active compounds.

  15. Enantioselective Intramolecular Aldehyde α-Alkylation with Simple Olefins: Direct Access to Homo-Ene Products

    OpenAIRE

    Comito, Robert J.; Finelli, Fernanda G.; MacMillan, David W. C.

    2013-01-01

    A highly selective method for the synthesis of asymmetrically substituted carbocycles and heterocycles from unactivated aldehyde–olefin precursors has been achieved via enantioselective SOMO-catalysis. Addition of a catalytically generated enamine radical cation across a pendent olefin serves to establish a general asymmetric strategy towards the production of a wide range of formyl-substituted rings with alkene transposition. Conceptually, this novel mechanism allows direct access to “homo-e...

  16. Diastereodivergent and Enantioselective [4+2] Annulations of γ-Butenolides with Cyclic 1-Azadienes

    OpenAIRE

    Chao Li; Kun Jiang; Ying-Chun Chen

    2015-01-01

    An asymmetric annulation reaction of γ-butenolides and cyclic 1-azadienes containing a 1,2-benzoisothiazole-1,1-dioxide motif has been studied, proceeding in a tandem Michael addition-aza-Michael addition sequence. Endo-type cycloadducts bearing fused tetracyclic skeletons were isolated in fair yields and with high enantioselectivity (up to >99% ee) under the catalysis of modified cinchona alkaloid (DHQD)2PHAL. Besides, exo-type diastereomers could be produced using β-isocupreidine (β-ICD...

  17. Enantioselective Synthesis of β-(3-Hydroxypyrazol-1-yl)ketones Using An Organocatalyzed Michael Addition Reaction

    Science.gov (United States)

    Gogoi, Sanjib; Zhao, Cong-Gui; Ding, Derong

    2009-01-01

    β-(3-Hydroxypyrazol-1-yl)ketones have been prepared in high yields and excellent enantioselectivities (94–98% ee) via a Michael addition reaction between 2-pyrazolin-5-ones and aliphatic acyclic α,β-unsaturated ketones using 9-epi-9-amino-9-deoxyquinine as the catalyst. These results account for the first example of an aza-Michael addition of the ambident 2-pyrazolin-5-one anion to a Michael acceptor. PMID:19415906

  18. Lumazine Synthase Protein Nanoparticle-Gd(III)-DOTA Conjugate as a T1 contrast agent for high-field MRI.

    Science.gov (United States)

    Song, YoungKyu; Kang, Young Ji; Jung, Hoesu; Kim, Hansol; Kang, Sebyung; Cho, HyungJoon

    2015-10-23

    With the applications of magnetic resonance imaging (MRI) at higher magnetic fields increasing, there is demand for MRI contrast agents with improved relaxivity at higher magnetic fields. Macromolecule-based contrast agents, such as protein-based ones, are known to yield significantly higher r1 relaxivity at low fields, but tend to lose this merit when used as T1 contrast agents (r1/r2 = 0.5 ~ 1), with their r1 decreasing and r2 increasing as magnetic field strength increases. Here, we developed and characterized an in vivo applicable magnetic resonance (MR) positive contrast agent by conjugating Gd(III)-chelating agent complexes to lumazine synthase isolated from Aquifex aeolicus (AaLS). The r1 relaxivity of Gd(III)-DOTA-AaLS-R108C was 16.49 mM(-1)s(-1) and its r1/r2 ratio was 0.52 at the magnetic field strength of 7 T. The results of 3D MR angiography demonstrated the feasibility of vasculature imaging within 2 h of intravenous injection of the agent and a significant reduction in T1 values were observed in the tumor region 7 h post-injection in the SCC-7 flank tumor model. Our findings suggest that Gd(III)-DOTA-AaLS-R108C could serve as a potential theranostic nanoplatform at high magnetic field strength.

  19. Conjugated Linoleic Acid Supplementation under a High-Fat Diet Modulates Stomach Protein Expression and Intestinal Microbiota in Adult Mice.

    Science.gov (United States)

    Chaplin, Alice; Parra, Pilar; Serra, Francisca; Palou, Andreu

    2015-01-01

    The gastrointestinal tract constitutes a physiological interface integrating nutrient and microbiota-host metabolism. Conjugated linoleic acids (CLA) have been reported to contribute to decreased body weight and fat accretion. The modulation by dietary CLA of stomach proteins related to energy homeostasis or microbiota may be involved, although this has not been previously analysed. This is examined in the present study, which aims to underline the potential mechanisms of CLA which contribute to body weight regulation. Adult mice were fed either a normal fat (NF, 12% kJ content as fat) or a high-fat (HF, 43% kJ content as fat) diet. In the latter case, half of the animals received daily oral supplementation of CLA. Expression and content of stomach proteins and specific bacterial populations from caecum were analysed. CLA supplementation was associated with an increase in stomach protein expression, and exerted a prebiotic action on both Bacteroidetes/Prevotella and Akkermansia muciniphila. However, CLA supplementation was not able to override the negative effects of HF diet on Bifidobacterium spp., which was decreased in both HF and HF+CLA groups. Our data show that CLA are able to modulate stomach protein expression and exert a prebiotic effect on specific gut bacterial species.

  20. Anthracene-containing wide-band-gap conjugated polymers for high-open-circuit-voltage polymer solar cells.

    Science.gov (United States)

    Gong, Xue; Li, Cuihong; Lu, Zhen; Li, Guangwu; Mei, Qiang; Fang, Tao; Bo, Zhishan

    2013-07-25

    The synthesis, characterization, and photophysical and photovoltaic properties of two anthracene-containing wide-band-gap donor and acceptor (D-A) alternating conjugated polymers (P1 and P2) are described. These two polymers absorb in the range of 300-600 nm with a band gap of about 2.12 eV. Polymer solar cells with P1:PC71 BM as the active layer demonstrate a power conversion efficiency (PCE) of 2.23% with a high Voc of 0.96 V, a Jsc of 4.4 mA cm(-2) , and a comparable fill factor (FF) of 0.53 under simulated solar illumination of AM 1.5 G (100 mW cm(-2) ). In addition, P2:PC71 BM blend-based solar cells exhibit a PCE of 1.42% with a comparable Voc of 0.89 V, a Jsc of 3.0 mA cm(-2) , and an FF of 0.53. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  1. A Large-Bandgap Conjugated Polymer for Versatile Photovoltaic Applications with High Performance.

    Science.gov (United States)

    Zhang, Maojie; Guo, Xia; Ma, Wei; Ade, Harald; Hou, Jianhui

    2015-08-19

    A new copolymer PM6 based on fluorothienyl-substituted benzodithiophene is synthesized and characterized. The inverted polymer solar cells based on PM6 exhibit excellent performance with Voc of 0.98 V and power conversion efficiency (PCE) of 9.2% for a thin-film thickness of 75 nm. Furthermore, the single-junction semitransparent device shows a high PCE of 5.7%.

  2. Interfacial Engineering for Highly Efficient-Conjugated Polymer-Based Bulk Heterojunction Photovoltaic Devices

    Energy Technology Data Exchange (ETDEWEB)

    Alex Jen; David Ginger; Christine Luscombe; Hong Ma

    2012-04-02

    The aim of our proposal is to apply interface engineering approach to improve charge extraction, guide active layer morphology, improve materials compatibility, and ultimately allow the fabrication of high efficiency tandem cells. Specifically, we aim at developing: i. Interfacial engineering using small molecule self-assembled monolayers ii. Nanostructure engineering in OPVs using polymer brushes iii. Development of efficient light harvesting and high mobility materials for OPVs iv. Physical characterization of the nanostructured systems using electrostatic force microscopy, and conducting atomic force microscopy v. All-solution processed organic-based tandem cells using interfacial engineering to optimize the recombination layer currents vi. Theoretical modeling of charge transport in the active semiconducting layer The material development effort is guided by advanced computer modeling and surface/ interface engineering tools to allow us to obtain better understanding of the effect of electrode modifications on OPV performance for the investigation of more elaborate device structures. The materials and devices developed within this program represent a major conceptual advancement using an integrated approach combining rational molecular design, material, interface, process, and device engineering to achieve solar cells with high efficiency, stability, and the potential to be used for large-area roll-to-roll printing. This may create significant impact in lowering manufacturing cost of polymer solar cells for promoting clean renewable energy use and preventing the side effects from using fossil fuels to impact environment.

  3. SPINOL-derived phosphoric acids: synthesis and application in enantioselective Friedel-Crafts reaction of indoles with imines.

    Science.gov (United States)

    Xu, Fangxi; Huang, Dan; Han, Chao; Shen, Wei; Lin, Xufeng; Wang, Yanguang

    2010-12-17

    A new class of chiral phosphoric acids with spirobiindane as scaffold were conveniently synthesized from (S)-1,1'-spirobiindane-7,7'-diol ((S)-SPINOL) and employed to catalyze the asymmetric Friedel-Crafts reaction of indoles with imines to afford 3-indolyl methanamines. High yields (68-97%) and excellent enantioselectivities (up to 99% ee) were obtained.

  4. Isonitrile iron(II) complexes with chiral N2P2 macrocycles in the enantioselective transfer hydrogenation of ketones.

    Science.gov (United States)

    Bigler, Raphael; Mezzetti, Antonio

    2014-12-19

    Bis(isonitrile) iron(II) complexes bearing a C2-symmetric N2P2 macrocyclic ligand, which are easily prepared from the corresponding bis(acetonitrile) analogue, catalyze the asymmetric transfer hydrogenation (ATH) of a broad scope of ketones in excellent yields (up to 98%) and with high enantioselectivity (up to 91% ee).

  5. "Fit-for-purpose" development of analytical and (semi)preparative enantioselective high performance liquid and supercritical fluid chromatography for the access to a novel σ1 receptor agonist.

    Science.gov (United States)

    Rossi, Daniela; Marra, Annamaria; Rui, Marta; Brambilla, Stefania; Juza, Markus; Collina, Simona

    2016-01-25

    A rapid and straightforward screening protocol of chiral stationary phases (CSPs) in HPLC and SFC resulted in three different methods "fit-for-purpose", i.e. analysis and scale-up to semi-preparative enantioselective chromatography. The efficient use of these three methods allowed expedited preparation of an important drug discovery target, (R/S)-1, a potent new sigma 1 (σ1) receptor agonist. The approach taken resulted in significant savings of both time and labor for the isolation of enantiomers compared to the development of a stereo-selective synthesis. The enantiomers of 1 have been isolated allowing studies of their chirooptical properties and an in-deep comparative examination of the pharmacological profile for the individual enantiomers.

  6. Pseudopterosin synthesis from a chiral cross-conjugated hydrocarbon through a series of cycloadditions.

    Science.gov (United States)

    Newton, Christopher G; Drew, Samuel L; Lawrence, Andrew L; Willis, Anthony C; Paddon-Row, Michael N; Sherburn, Michael S

    2015-01-01

    The pseudopterosins are a family of diterpene marine natural products, which, by virtue of their interesting anti-inflammatory and analgesic properties, have attracted the attentions of many synthetic chemists. The most efficient syntheses reported to date are 14 and 20 steps in the longest linear sequence for chiral pool and enantioselective approaches, respectively, and all start with precursors that are easily mapped onto the natural product structure. Here, we describe an unconventional approach in which a chiral cross-conjugated hydrocarbon is used as the starting material for a series of three cycloadditions. Our approach has led to a significant reduction in the step count required to access these interesting natural products (10 steps chiral pool and 11 steps enantioselective). Furthermore it demonstrates that cross-conjugated hydrocarbons, erroneously considered by many to be too unstable and difficult to handle, are viable precursors for natural product synthesis.

  7. Pseudopterosin synthesis from a chiral cross-conjugated hydrocarbon through a series of cycloadditions

    Science.gov (United States)

    Newton, Christopher G.; Drew, Samuel L.; Lawrence, Andrew L.; Willis, Anthony C.; Paddon-Row, Michael N.; Sherburn, Michael S.

    2015-01-01

    The pseudopterosins are a family of diterpene marine natural products, which, by virtue of their interesting anti-inflammatory and analgesic properties, have attracted the attentions of many synthetic chemists. The most efficient syntheses reported to date are 14 and 20 steps in the longest linear sequence for chiral pool and enantioselective approaches, respectively, and all start with precursors that are easily mapped onto the natural product structure. Here, we describe an unconventional approach in which a chiral cross-conjugated hydrocarbon is used as the starting material for a series of three cycloadditions. Our approach has led to a significant reduction in the step count required to access these interesting natural products (10 steps chiral pool and 11 steps enantioselective). Furthermore it demonstrates that cross-conjugated hydrocarbons, erroneously considered by many to be too unstable and difficult to handle, are viable precursors for natural product synthesis.

  8. Enantioselective construction of quaternary N-heterocycles by palladium-catalysed decarboxylative allylic alkylation of lactams

    KAUST Repository

    Behenna, Douglas C.

    2011-12-18

    The enantioselective synthesis of nitrogen-containing heterocycles (N-heterocycles) represents a substantial chemical research effort and resonates across numerous disciplines, including the total synthesis of natural products and medicinal chemistry. In this Article, we describe the highly enantioselective palladium-catalysed decarboxylative allylic alkylation of readily available lactams to form 3,3-disubstituted pyrrolidinones, piperidinones, caprolactams and structurally related lactams. Given the prevalence of quaternary N-heterocycles in biologically active alkaloids and pharmaceutical agents, we envisage that our method will provide a synthetic entry into the de novo asymmetric synthesis of such structures. As an entry for these investigations we demonstrate how the described catalysis affords enantiopure quaternary lactams that intercept synthetic intermediates previously used in the synthesis of the Aspidosperma alkaloids quebrachamine and rhazinilam, but that were previously only available by chiral auxiliary approaches or as racemic mixtures. © 2012 Macmillan Publishers Limited. All rights reserved.

  9. Enantioselective degradation of the chiral fungicides metalaxyl and furalaxyl by Brevibacillus brevis.

    Science.gov (United States)

    Sulimma, Lutz; Bullach, Anke; Kusari, Souvik; Lamshöft, Marc; Zühlke, Sebastian; Spiteller, Michael

    2013-06-01

    For almost four decades, the chiral fungicides metalaxyl and furalaxyl have been in use in plant protection on a global scale. Both substances are distributed as racemic mixtures, yet the desirable interference in nucleic acid synthesis of harmful fungi only occurs by the (-)-R-enantiomer. As enantioselective degradation in Scheyern (Germany) and Yaoundé (Cameroon) soils has been documented, the influence of 50 isolated microorganisms on the R/S ratio was investigated. A high-pressure liquid chromatography method with a chiral column to separate enantiomers of metalaxyl and furalaxyl, and subsequent detection by tandem mass spectrometry, was employed. Only one of these microorganisms, a strain of Brevibacillus brevis, showed an enantioselective degradation pattern in liquid culture; the respective (-)-R-enantiomers were preferably degraded. Moreover, (-)-R-furalaxyl was degraded faster in cultures supplemented simultaneously with both fungicides of the same concentration. © 2013 Wiley Periodicals, Inc.

  10. Enantioselective Degradation of Rac-Metolachlor and S-Metolachlor in Soil

    Institute of Scientific and Technical Information of China (English)

    MA Yun; LIU Wei-Ping; WEN Yue-Zhong

    2006-01-01

    Separation of chiral enantiomers and the dissipation of rac-metolachlor and S-metolachlor in soil were evaluated using achiral high-performance liquid chromatography (HPLC) and chiral gas chromatography (GC) methods. Under the experimental conditions the possible metabolite was considered to be N-(2-ethyl-6-methyl-phenyl)-2-hydroxy-acetamide.Because of the presence of two chiral elements (asymmetrically substituted carbon and chiral axis), the baseline separation of metolachlor enantiomers was not achieved. S-metolachlor degraded faster in soil than rac-metolachlor. After a 42-day incubation, 73.4% of rac-metolachlor and 90.0% of S-metolachlor were degraded. However, due to the absence of biological processes the degradation process in sterilized soil showed no enantioselectivity. The results indicated that enantioselective degradations could greatly affect the environmental fate of metolachlor and should be considered when the environmental behavior of these compounds was assessed.

  11. Enantioselective Decarboxylative Alkylation Reactions: Catalyst Development, Substrate Scope, and Mechanistic Studies

    KAUST Repository

    Behenna, Douglas C.

    2011-11-14

    α-Quaternary ketones are accessed through novel enantioselective alkylations of allyl and propargyl electrophiles by unstabilized prochiral enolate nucleophiles in the presence of palladium complexes with various phosphinooxazoline (PHOX) ligands. Excellent yields and high enantiomeric excesses are obtained from three classes of enolate precursor: enol carbonates, enol silanes, and racemic β-ketoesters. Each of these substrate classes functions with nearly identical efficiency in terms of yield and enantioselectivity. Catalyst discovery and development, the optimization of reaction conditions, the exploration of reaction scope, and applications in target-directed synthesis are reported. Experimental observations suggest that these alkylation reactions occur through an unusual inner-sphere mechanism involving binding of the prochiral enolate nucleophile directly to the palladium center.

  12. Development, fabrication, and modeling of highly sensitive conjugated polymer based piezoresistive sensors in electronic skin applications

    Science.gov (United States)

    Khalili, Nazanin; Naguib, Hani E.; Kwon, Roy H.

    2016-04-01

    Human intervention can be replaced through development of tools resulted from utilizing sensing devices possessing a wide range of applications including humanoid robots or remote and minimally invasive surgeries. Similar to the five human senses, sensors interface with their surroundings to stimulate a suitable response or action. The sense of touch which arises in human skin is among the most challenging senses to emulate due to its ultra high sensitivity. This has brought forth novel challenging issues to consider in the field of biomimetic robotics. In this work, using a multiphase reaction, a polypyrrole (PPy) based hydrogel is developed as a resistive type pressure sensor with an intrinsically elastic microstructure stemming from three dimensional hollow spheres. Furthermore, a semi-analytical constriction resistance model accounting for the real contact area between the PPy hydrogel sensors and the electrode along with the dependency of the contact resistance change on the applied load is developed. The model is then solved using a Monte Carlo technique and the sensitivity of the sensor is obtained. The experimental results showed the good tracking ability of the proposed model.

  13. Conjugated-Polymer Blends for Organic Photovoltaics: Rational Control of Vertical Stratification for High Performance.

    Science.gov (United States)

    Yan, Yu; Liu, Xuan; Wang, Tao

    2017-05-01

    The photoactive layer of bulk-heterojunction organic solar cells, in a thickness range of tens to hundreds of nanometers, comprises phase-separated electron donors and acceptors after solution casting. The component distribution in the cross-section of these thin films is found to be heterogeneous, with electron donors or acceptors accumulated or depleted near the electrode interfaces. This vertical stratification of the photovoltaic blend influences device metrics through its impact on charge transport and recombination, and consequently plays an important role in determining the power conversion efficiency of photovoltaic devices. Here, different techniques, e.g., surface analysis and sputter-assisted depth-profiling, reflectivity modeling, and 3D imaging, that have been employed to characterize vertical stratification in bulk-heterojunction photovoltaic blends are reviewed. The origins of vertical stratification are summarized, including thermodynamics, kinetics, surface free energy, and selective dissolubility. The impact of correct and wrong vertical stratification to device metrics of solar cells are highlighted. Examples are then given to demonstrate how desired vertical stratification can be controlled with properly aligned device architecture to enable solar cells with high efficiency. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  14. Quinine-derived thiourea and squaramide catalyzed conjugate addition of α-nitrophosphonates to enones: asymmetric synthesis of quaternary α-aminophosphonates.

    Science.gov (United States)

    Bera, Kalisankar; Namboothiri, Irishi N N

    2015-02-01

    Conjugate addition of α-nitrophosphonates to enones was carried out in the presence of two sets of organocatalysts, viz. a quinine-thiourea and a quinine-squaramide. The quinine-thiourea provided the products possessing an α-quaternary chiral center in high enantioselectivities only in the case of electron rich enones. On the other hand, the quinine-squaramide was more efficient in that a wide variety of electron rich and electron poor enones underwent Michael addition of nitrophosphonates to afford the quaternary α-nitrophosphonates in excellent yields and enantioselectivities. The hydrogen bonding donor ability of the bifunctional catalyst, as shown in the proposed transition states, appears primarily responsible for the observed selectivity. However, a favorable π-stacking between the aryl groups of thiourea/squaramide and aryl vinyl ketone also appeared favorable. The reaction was amenable to scale up, and the enantioenriched quaternary α-nitrophosphonates could be easily transformed to synthetically and biologically useful quaternary α-aminophosphonates and other multifunctional molecules.

  15. Bacteriophytochromes control conjugation in Agrobacterium fabrum.

    Science.gov (United States)

    Bai, Yingnan; Rottwinkel, Gregor; Feng, Juan; Liu, Yiyao; Lamparter, Tilman

    2016-08-01

    Bacterial conjugation, the transfer of single stranded plasmid DNA from donor to recipient cell, is mediated through the type IV secretion system. We performed conjugation assays using a transmissible artificial plasmid as reporter. With this assay, conjugation in Agrobacterium fabrum was modulated by the phytochromes Agp1 and Agp2, photoreceptors that are most sensitive in the red region of visible light. In conjugation studies with wild-type donor cells carrying a pBIN-GUSINT plasmid as reporter that lacked the Ti (tumor inducing) plasmid, no conjugation was observed. When either agp1(-) or agp2(-) knockout donor strains were used, plasmid DNA was delivered to the recipient, indicating that both phytochromes suppress conjugation in the wild type donor. In the recipient strains, the loss of Agp1 or Agp2 led to diminished conjugation. When wild type cells with Ti plasmid and pBIN-GUS reporter plasmid were used as donor, a high rate of conjugation was observed. The DNA transfer was down regulated by red or far-red light by a factor of 3.5. With agp1(-) or agp2(-) knockout donor cells, conjugation in the dark was about 10 times lower than with the wild type donor, and with the double knockout donor no conjugation was observed. These results imply that the phytochrome system has evolved to inhibit conjugation in the light. The decrease of conjugation under different temperature correlated with the decrease of phytochrome autophosphorylation.

  16. Electrical characterization of fluorinated benzothiadiazole based conjugated copolymer – a promising material for high-performance solar cells

    Directory of Open Access Journals (Sweden)

    J. Toušek

    2015-12-01

    Full Text Available Measurements of electrical conductivity, electron work function, carrier mobility of holes and the diffusion length of excitons were performed on samples of conjugated polymers relevant to polymer solar cells. A state of the art fluorinated benzothiadiazole based conjugated copolymer (PBDTTHD − DTBTff was studied and benchmarked against the reference polymer poly-3-hexylthiophene (P3HT. We employed, respectively, four electrode conductivity measurements, Kelvin probe work function measurements, carrier mobility using charge extraction by linearly increasing voltage (CELIV measurements and diffusion length determinaton using surface photovoltage measurements.

  17. Electrical characterization of fluorinated benzothiadiazole based conjugated copolymer – a promising material for high-performance solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Toušek, J., E-mail: jiri.tousek@mff.cuni.cz; Toušková, J.; Chomutová, R. [Charles University in Prague, Faculty of Mathematics and Physics, V Holešovičkách 2, 182 00 Prague 8 (Czech Republic); Remeš, Z.; Čermák, J. [Institute of Physics of the Academy of Sciences, Cukrovarnická 10, 162 53 Prague 6 (Czech Republic); Helgesen, M.; Carlé, J. E.; Krebs, F. C. [Department of Energy Conversion and Storage, Technical University of Denmark, Frederiksborgvej 399, DK-4000 Roskilde (Denmark)

    2015-12-15

    Measurements of electrical conductivity, electron work function, carrier mobility of holes and the diffusion length of excitons were performed on samples of conjugated polymers relevant to polymer solar cells. A state of the art fluorinated benzothiadiazole based conjugated copolymer (PBDT{sub THD} − DTBTff) was studied and benchmarked against the reference polymer poly-3-hexylthiophene (P3HT). We employed, respectively, four electrode conductivity measurements, Kelvin probe work function measurements, carrier mobility using charge extraction by linearly increasing voltage (CELIV) measurements and diffusion length determinaton using surface photovoltage measurements.

  18. Enantioselective catalysis with tropos ligands in chiral ionic liquids.

    Science.gov (United States)

    Schmitkamp, Mike; Chen, Dianjun; Leitner, Walter; Klankermayer, Jürgen; Franciò, Giancarlo

    2007-10-21

    Enantioselective homogeneous rhodium-catalysed hydrogenation using tropoisomeric biphenylphosphine ligands was accomplished in readily available chiral ionic liquids and the catalytic system could be reused after extraction with scCO(2).

  19. Enantioselective alcohol synthesis using ketoreductases, lipases or an aldolase

    NARCIS (Netherlands)

    Sorgedrager, M.J.

    2006-01-01

    The demand for optically pure secondary alcohols, which has grown rapidly in recent years, has spurred the development of adequate enantioselective synthetic procedures. Although there are various chemical methods available, biocatalysts are increasingly applied due to their natural characteristic t

  20. Enantiomer separation by ultrafiltration of enantioselective micelles in multistage systems

    NARCIS (Netherlands)

    Overdevest, P.E.M.

    2000-01-01

    The Food and Bioprocess Engineering Group of Wageningen University, The Netherlands, is developing a new enantiomer separation system that is based on ultrafiltration (UF) of enantioselective micelles containing chiral selector molecules. Enantiomer molecules are optical isomers (mirror images), and

  1. Enantioselective imine reduction catalyzed by imine reductases and artificial metalloenzymes.

    Science.gov (United States)

    Gamenara, Daniela; Domínguez de María, Pablo

    2014-05-21

    Adding value to organic synthesis. Novel imine reductases enable the enantioselective reduction of imines to afford optically active amines. Likewise, novel bioinspired artificial metalloenzymes can perform the same reaction as well. Emerging proof-of-concepts are herein discussed.

  2. n-Type Water/Alcohol-Soluble Naphthalene Diimide-Based Conjugated Polymers for High-Performance Polymer Solar Cells.

    Science.gov (United States)

    Wu, Zhihong; Sun, Chen; Dong, Sheng; Jiang, Xiao-Fang; Wu, Siping; Wu, Hongbin; Yip, Hin-Lap; Huang, Fei; Cao, Yong

    2016-02-17

    With the demonstration of small-area, single-junction polymer solar cells (PSCs) with power conversion efficiencies (PCEs) over the 10% performance milestone, the manufacturing of high-performance large-area PSC modules is becoming the most critical issue for commercial applications. However, materials and processes that are optimized for fabricating small-area devices may not be applicable for the production of high-performance large-area PSC modules. One of the challenges is to develop new conductive interfacial materials that can be easily processed with a wide range of thicknesses without significantly affecting the performance of the PSCs. Toward this goal, we report two novel naphthalene diimide-based, self-doped, n-type water/alcohol-soluble conjugated polymers (WSCPs) that can be processed with a broad thickness range of 5 to 100 nm as efficient electron transporting layers (ETLs) for high-performance PSCs. Space charge limited current and electron spin resonance spectroscopy studies confirm that the presence of amine or ammonium bromide groups on the side chains of the WSCP can n-dope PC71BM at the bulk heterojunction (BHJ)/ETL interface, which improves the electron extraction properties at the cathode. In addition, both amino functional groups can induce self-doping to the WSCPs, although by different doping mechanisms, which leads to highly conductive ETLs with reduced ohmic loss for electron transport and extraction. Ultimately, PSCs based on the self-doped WSCP ETLs exhibit significantly improved device performance, yielding PCEs as high as 9.7% and 10.11% for PTB7-Th/PC71BM and PffBT4T-2OD/PC71BM systems, respectively. More importantly, with PffBT4T-2OD/PC71BM BHJ as an active layer, a prominent PCE of over 8% was achieved even when a thick ETL of 100 nm was used. To the best of our knowledge, this is the highest efficiency demonstrated for PSCs with a thick interlayer and light-harvesting layer, which are important criteria for eventually making

  3. Emerging functional chiral microporous materials: synthetic strategies and enantioselective separations

    Directory of Open Access Journals (Sweden)

    Ming Xue

    2016-11-01

    Full Text Available In recent years, chiral microporous materials with open pores have attracted much attention because of their potential applications in enantioselective separation and catalysis. This review summarizes the recent advances on chiral microporous materials, such as metal-organic frameworks (MOFs, hydrogen-bonded organic frameworks (HOFs and covalent organic frameworks (COFs. We will introduce the synthetic strategies in detail and highlight the current status of chiral microporous materials on solid enantioselective adsorption, chiral chromatography resolution and membrane separation.

  4. High Mobility Conjugated Polymers

    Science.gov (United States)

    2007-10-20

    Photoluminescence spectra taken MEH-PPV/PHT blend a more inhomogeneous nanofibers (a) and spin-cast thin films (b). environment . The red shift in the...incorporating phenoxazine as the donor and quinoline as the0 acceptor were synthesized, characterized, and explored in R= CH3 ,R, 0(BPQ-MPO) organic

  5. Synthesis of AS1411-aptamer-conjugated CdTe quantum dots with high fluorescence strength for probe labeling tumor cells.

    Science.gov (United States)

    Alibolandi, Mona; Abnous, Khalil; Ramezani, Mohammad; Hosseinkhani, Hossein; Hadizadeh, Farzin

    2014-09-01

    In this paper, we report microwave-assisted, one-stage synthesis of high-quality functionalized water-soluble cadmium telluride (CdTe) quantum dots (QDs). By selecting sodium tellurite as the Te source, cadmium chloride as the Cd source, mercaptosuccinic acid (MSA) as the capping agent, and a borate-acetic acid buffer solution with a pH range of 5-8, CdTe nanocrystals with four colors (blue to orange) were conveniently prepared at 100 °C under microwave irradiation in less than one hour (reaction time: 10-60 min). The influence of parameters such as the pH, Cd:Te molar ratio, and reaction time on the emission range and quantum yield percentage (QY%) was investigated. The structures and compositions of the prepared CdTe QDs were characterized by transmission electron microscopy, energy-dispersive X-ray spectroscopy, selective area electron diffraction, and X-ray powder diffraction experiments. The formation mechanism of the QDs is discussed in this paper. Furthermore, AS1141-aptamer-conjugated CdTe QDs in the U87MG glioblastoma cell line were assessed with a fluorescence microscope. The obtained results showed that the best conditions for obtaining a high QY of approximately 87% are a pH of 6, a Cd:Te molar ratio of 5:1, and a 30-min reaction time at 100 °C under microwave irradiation. The results showed that AS1141-aptamer-conjugated CdTe QDs could enter tumor cells efficiently. It could be concluded that a facile high-fluorescence-strength QD conjugated with a DNA aptamer, AS1411, which can recognize the extracellular matrix protein nucleolin, can specifically target U87MG human glioblastoma cells. The qualified AS1411-aptamer-conjugated QDs prepared in this study showed excellent capabilities as nanoprobes for cancer targeting and molecular imaging.

  6. Stunting correlates with high salivary and serum antibody levels after 13-valent pneumococcal conjugate vaccination of Venezuelan Amerindian children

    NARCIS (Netherlands)

    Verhagen, Lilly M; Hermsen, Meyke; Rivera-Olivero, Ismar; Sisco, María Carolina; Pinelli, Elena; Hermans, Peter W M; Berbers, Guy A M; de Waard, Jacobus H; de Jonge, Marien I

    2016-01-01

    OBJECTIVE: To determine the impact of pre-vaccination nutritional status on vaccine responses in Venezuelan Warao Amerindian children vaccinated with the 13-valent pneumococcal conjugate vaccine (PCV13) and to investigate whether saliva can be used as read-out for these vaccine responses. METHODS: A

  7. A brief perspective on the evolution of plastic electronics--from highly conducting polymers to conjugated organic semiconductors.

    Science.gov (United States)

    Skabara, Peter J

    2013-10-18

    This Viewpoint reflects on the work published in J. Chem. Soc., Chem. Commun. in 1977 by the Nobel Prize winners Shirakawa, MacDiarmid and Heeger. This paper, which is one of the most cited ChemComm articles of all time, motivated the rapid development of conducting (conjugated) polymers and the birth of plastic electronics.

  8. Folic acid conjugated self-assembled layered double hydroxide nanoparticles for high-efficacy-targeted drug delivery.

    Science.gov (United States)

    Yan, Li; Chen, Wei; Zhu, Xiaoyue; Huang, Longbiao; Wang, Zhigang; Zhu, Guangyu; Roy, V A L; Yu, K N; Chen, Xianfeng

    2013-12-04

    Enhanced selectivity and efficacy is important for advanced drug delivery. Herein, a novel type of folic acid conjugated self-assembled layered double hydroxide nanoparticles is reported. These nanoparticles have a drug loading capacity of 27 wt% and are able to enter cell nuclei and dramatically improve the efficacy of MTX.

  9. Molecular-weight dependence of interchain polaron delocalization and exciton bandwidth in high-mobility conjugated polymers

    DEFF Research Database (Denmark)

    Chang, J.F.; Clark, J.; Zhao, N.

    2006-01-01

    Interchain interactions have a profound effect on the optical as well as charge transport properties of conjugated polymer thin films. In contrast to oligomeric model systems in solution-deposited polymer thin films the study of such effects is complicated by the complex microstructure. We presen...

  10. Origins of enantioselectivity during allylic substitution reactions catalyzed by metallacyclic iridium complexes.

    Science.gov (United States)

    Madrahimov, Sherzod T; Hartwig, John F

    2012-05-16

    In depth mechanistic studies of iridium catalyzed regioselective and enantioselective allylic substitution reactions are presented. A series of cyclometalated allyliridium complexes that are kinetically and chemically competent to be intermediates in the allylic substitution reactions was prepared and characterized by 1D and 2D NMR spectroscopies and single-crystal X-ray difraction. The rates of epimerization of the less thermodynamically stable diastereomeric allyliridium complexes to the thermodynamically more stable allyliridium stereoisomers were measured. The rates of nucleophilic attack by aniline and by N-methylaniline on the isolated allyliridium complexes were also measured. Attack on the thermodynamically less stable allyliridium complex was found to be orders of magnitude faster than attack on the thermodynamically more stable complex, yet the major enantiomer of the catalytic reaction is formed from the more stable diastereomer. Comparison of the rates of nucleophilic attack to the rates of epimerization of the diastereomeric allyliridium complexes containing a weakly coordinating counterion showed that nucleophilic attack on the less stable allyliridium species is much faster than conversion of the less stable isomer to the more stable isomer. These observations imply that Curtin-Hammett conditions are not met during iridium catalyzed allylic substitution reactions by η(3)-η(1)-η(3) interconversion. Rather, these data imply that when these conditions exist for this reaction, they are created by reversible oxidative addition, and the high selectivity of this oxidative addition step to form the more stable diastereomeric allyl complex leads to the high enantioselectivity. The stereochemical outcome of the individual steps of allylic substitution was assessed by reactions of deuterium-labeled substrates. The allylic substitution was shown to occur by oxidative addition with inversion of configuration, followed by an outer sphere nucleophilic attack

  11. Enantioselective recognition at mesoporous chiral metal surfaces

    Science.gov (United States)

    Wattanakit, Chularat; Côme, Yémima Bon Saint; Lapeyre, Veronique; Bopp, Philippe A.; Heim, Matthias; Yadnum, Sudarat; Nokbin, Somkiat; Warakulwit, Chompunuch; Limtrakul, Jumras; Kuhn, Alexander

    2014-02-01

    Chirality is widespread in natural systems, and artificial reproduction of chiral recognition is a major scientific challenge, especially owing to various potential applications ranging from catalysis to sensing and separation science. In this context, molecular imprinting is a well-known approach for generating materials with enantioselective properties, and it has been successfully employed using polymers. However, it is particularly difficult to synthesize chiral metal matrices by this method. Here we report the fabrication of a chirally imprinted mesoporous metal, obtained by the electrochemical reduction of platinum salts in the presence of a liquid crystal phase and chiral template molecules. The porous platinum retains a chiral character after removal of the template molecules. A matrix obtained in this way exhibits a large active surface area due to its mesoporosity, and also shows a significant discrimination between two enantiomers, when they are probed using such materials as electrodes.

  12. Driving High-Performance n- and p-type Organic Transistors with Carbon Nanotube/Conjugated Polymer Composite Electrodes Patterned Directly from Solution

    KAUST Repository

    Hellstrom, Sondra L.

    2010-07-12

    We report patterned deposition of carbon nanotube/conjugated polymer composites from solution with high nanotube densities and excellent feature resolution. Such composites are suited for use as electrodes in high-performance transistors of pentacene and C60, with bottom-contact mobilities of ?0.5 and ?1 cm2 V-1 s-1, respectively. This represents a clear step towards development of inexpensive, high-performance all-organic circuits. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  13. Natural estrogens in dairy products: Determination of free and conjugated forms by ultra high performance liquid chromatography with tandem mass spectrometry.

    Science.gov (United States)

    Cavaliere, Chiara; Capriotti, Anna Laura; Foglia, Patrizia; Piovesana, Susy; Samperi, Roberto; Ventura, Salvatore; Laganà, Aldo

    2015-10-01

    Natural estrogens are synthesized by mammals in different amounts depending on the developmental stage and pregnancy/lactation period, and they may pass into milk, where they are mostly present as glucuronated and sulfated forms. In modern dairy practices, about 75% of milk is produced from pregnant cows; therefore, the amount of hormones that may pass into milk could be of concern. While estrogen determination in milk has been investigated in depth, the individual determination of estrogens and their conjugated forms in dairy products has not been fully addressed. The aim of this work was to develop and assess a sensitive method, using the peculiar retention properties of graphitized carbon black, to extract natural free estrogens and their major conjugated metabolites, without any enzymatic cleavage, from yogurt, cheese, and butter. The free and conjugated estrogens were eluted in two distinct fractions from the solid-phase extraction cartridge and analyzed separately by ultra high performance liquid chromatography coupled to tandem mass spectrometry. Recoveries were higher than 80% for all the three sample typologies. The highest matrix effects were observed for butter, which was richest in lipid content, but was below 30%. A survey on some commercial dairy products suggests that production processes decreased estrogen content.

  14. Increasing the open-circuit voltage in high-performance organic photovoltaic devices through conformational twisting of an indacenodithiophene-based conjugated polymer.

    Science.gov (United States)

    Chen, Chih-Ping; Hsu, Hsiang-Lin

    2013-10-01

    A fused ladder indacenodithiophene (IDT)-based donor-acceptor (D-A)-type alternating conjugated polymer, PIDTHT-BT, presenting n-hexylthiophene conjugated side chains is prepared. By extending the degree of intramolecular repulsion through the conjugated side chain moieties, an energy level for the highest occupied molecular orbital (HOMO) of -5.46 eV--a value approximately 0.27 eV lower than that of its counterpart PIDTDT-BT--is obtained, subsequently providing a fabricated solar cell with a high open-circuit voltage of approximately 0.947 V. The hole mobility (determined using the space charge-limited current model) in a blend film containing 20 wt% PIDTHT-BT) and 80 wt% [6,6]-phenyl-C71 butyric acid methyl ester (PC71 BM) is 2.2 × 10(-9) m(2) V(-1) s(-1), which is within the range of reasonable values for applications in organic photovoltaics. The power conversion efficiency is 4.5% under simulated solar illumination (AM 1.5G, 100 mW cm(-2)).

  15. In-situ functionalized monolithic polysiloxane-polymethacrylate composite materials from polythiol-ene double click reaction in capillary column format for enantioselective nano-high-performance liquid chromatography.

    Science.gov (United States)

    Wolter, Marc; Lämmerhofer, Michael

    2017-05-12

    This work reports on the proof-of-principle of preparation of novel one step in-situ functionalized monolithic polysiloxane-polymethacrylate composite materials in capillary columns for enantioselective nano-HPLC using a thiol-ene click reaction. Quinine carbamate as functional monomer and ethylene dimethacrylate as crosslinker were both used as ene components in a thermally initiated double click-type polymerization reaction with poly(3-mercaptopropyl)methylsiloxane as thiol component in presence of 1-propanol as porogenic solvent. Elemental analysis and on-capillary fluorescence measurement proved the successful incorporation of the functional chiral monomer into the polymer. Scanning electron microscopy images revealed a macroporous polymer morphology which is typical for a nucleation and growth mechanism of pore formation. The individual microglobules appear relatively spherical and smooth indicating a non-porous nature. Nano-HPLC experiments of the chiral monolithic capillary column provided successful enantiomer separation of N-3,5-dinitrobenzoylleucine as test compound in polar organic elution mode clearly documenting the successful implementation of the proposed concept towards new functionalized monolithic composite materials. Copyright © 2017 Elsevier B.V. All rights reserved.

  16. High nasopharyngeal carriage of non-vaccine serotypes in Western Australian aboriginal people following 10 years of pneumococcal conjugate vaccination.

    Directory of Open Access Journals (Sweden)

    Deirdre A Collins

    Full Text Available BACKGROUND: Invasive pneumococcal disease (IPD continues to occur at high rates among Australian Aboriginal people. The seven-valent pneumococcal conjugate vaccine (7vPCV was given in a 2-4-6-month schedule from 2001, with a 23-valent pneumococcal polysaccharide vaccine (23vPPV booster at 18 months, and replaced with 13vPCV in July 2011. Since carriage surveillance can supplement IPD surveillance, we have monitored pneumococcal carriage in western Australia (WA since 2008 to assess the impact of the 10-year 7vPCV program. METHODS: We collected 1,500 nasopharyngeal specimens from Aboriginal people living in varied regions of WA from August 2008 until June 2011. Specimens were cultured on selective media. Pneumococcal isolates were serotyped by the quellung reaction. RESULTS: Streptococcus pneumoniae, Haemophilus influenzae and Moraxella catarrhalis were carried by 71.9%, 63.2% and 63.3% respectively of children <5 years of age, and 34.6%, 22.4% and 27.2% of people ≥5 years. Of 43 pneumococcal serotypes identified, the most common were 19A, 16F and 6C in children <5 years, and 15B, 34 and 22F in older people. 7vPCV serotypes accounted for 14.5% of all serotypeable isolates, 13vPCV for 32.4% and 23vPPV for 49.9%, with little variation across all age groups. Serotypes 1 and 12F were rarely identified, despite causing recent IPD outbreaks in WA. Complete penicillin resistance (MIC ≥2µg/ml was found in 1.6% of serotype 19A (5.2%, 19F (4.9% and 16F (3.2% isolates and reduced penicillin susceptibility (MIC ≥0.125µg/ml in 24.9% of isolates, particularly 19F (92.7%, 19A (41.3%, 16F (29.0%. Multi-resistance to cotrimoxazole, tetracycline and erythromycin was found in 83.0% of 23F isolates. Among non-serotypeable isolates 76.0% had reduced susceptibility and 4.0% showed complete resistance to penicillin. CONCLUSIONS: Ten years after introduction of 7vPCV for Aboriginal Australian children, 7vPCV serotypes account for a small proportion of carried

  17. Dye conjugation to linseed oil by highly-effective thiol-ene coupling and subsequent esterification reactions

    OpenAIRE

    Hayashi, T; Kazlauciunas, A; Thornton, PD

    2015-01-01

    Linseed oil, a renewable material obtained from the ripened seeds of the flax plant, was conjugated with C. I. Disperse Red 1 to yield a coloured macromolecule in two experimentally-simplistic coupling steps. Firstly, the abundant presence of carbon-carbon double bonds in linseed oil was exploited to introduce carboxylic acid functionality to linseed oil via a thiol-ene reaction between linseed oil and 3-mercaptopropionic acid. C. I. Disperse Red 1 was then grafted to the carboxylic acid unit...

  18. Bidirectional enantioselective effects of the GABAB receptor agonist baclofen in two mouse models of excessive ethanol consumption.

    Science.gov (United States)

    Kasten, Chelsea R; Blasingame, Shelby N; Boehm, Stephen L

    2015-02-01

    The GABAB receptor agonist baclofen has been studied extensively in preclinical models of alcohol-use disorders, yet results on its efficacy have been uncertain. Racemic baclofen, which is used clinically, can be broken down into separate enantiomers of the drug. Baclofen has been shown to produce enantioselective effects in behavioral assays, including those modeling reflexive and sexual behavior. The current studies sought to characterize the enantioselective effects of baclofen in two separate models of ethanol consumption. The first was a Drinking-in-the-Dark procedure that provides "binge-like" ethanol access to mice by restricting access to a 2-h period, 3 h into the dark cycle. The second was a two-bottle choice procedure that utilized selectively bred High Alcohol Preferring 1 (HAP1) mice to model chronic ethanol access. HAP1 mice are selectively bred to consume pharmacologically relevant amounts of ethanol in a 24-h two-bottle choice paradigm. The results showed that baclofen yields enantioselective effects on ethanol intake in both models, and that these effects are bidirectional. Total ethanol intake was decreased by R(+)-baclofen, while total intake was increased by S(-)-baclofen in the binge-like and chronic drinking models. Whereas overall binge-like saccharin intake was significantly reduced by R(+)-baclofen, chronic intake was not significantly altered. S(-)-baclofen did not significantly alter saccharin intake. Neither enantiomer significantly affected locomotion during binge-like reinforcer consumption. Collectively, these results demonstrate that baclofen produces enantioselective effects on ethanol consumption. More importantly, the modulation of consumption is bidirectional. The opposing enantioselective effects may explain some of the variance seen in published baclofen literature.

  19. Chiral quizalofop-ethyl and its metabolite quizalofop-acid in soils: Enantioselective degradation, enzymes interaction and toxicity to Eisenia foetida.

    Science.gov (United States)

    Ma, Lin; Liu, Hui; Qu, Han; Xu, Yangguang; Wang, Peng; Sun, Mingjing; Zhou, Zhiqiang; Liu, Donghui

    2016-06-01

    An enantioselective chromatographic method to analyze enantiomers of quizalofop-ethyl and its metabolite quizalofop-acid was established using a high-performance liquid chromatography (HPLC) on (R, R) Whelk-O 1 column. The enantioselective degradation kinetics of quizalofop-ethyl and quizalofop-acid in three soils were investigated. Moreover, the interaction with urease and catalase in the soils and the acute toxicity to Eisenia foetida of quizalofop-ethyl were also determined in order to assess their metabolism mechanism and environmental risk. From the results, quizalofop-ethyl was configurationally stable and was hydrolyzed rapidly to quizalofop-acid, which also degraded enantioselectively but slowly, and the inversion of the S-(-)-quizalofop-acid into the R-(+)-quizalofop-acid was observed in Xinxiang soil. In addition, quizalofop-ethyl and quizalofop-acid enantioselectively affected urease activity but not catalase. The acute toxicity assays to earthworm indicated that the racemic quizalofop-ethyl and quizalofop-acid were more toxic than quizalofop-p-ethyl and quizalofop-p-acid respectively, dramatically, the toxicity of the metabolite was much higher than the parent compound. These results revealed the enantioselective degradation of quizalofop-ethyl and quizalofop-acid, and the differences of toxicity among the enantiomers of the parent compound and the metabolite, which should be considered in future environmental risk evaluation. Copyright © 2016 Elsevier Ltd. All rights reserved.

  20. Enantioselective reduction of ketones and imines catalyzed by (CN-box)Re(V)-oxo complexes.

    Science.gov (United States)

    Nolin, Kristine A; Ahn, Richard W; Kobayashi, Yusuke; Kennedy-Smith, Joshua J; Toste, F Dean

    2010-08-16

    The development and application of chiral, non-racemic Re(V)-oxo complexes to the enantioselective reduction of prochiral ketones is described. In addition to the enantioselective reduction of prochiral ketones, we report the application of these complexes to 1) a tandem Meyer-Schuster rearrangement/reduction to access enantioenriched allylic alcohols and 2) the enantioselective reduction of imines.

  1. Quantum chemical study on the mechanism of enantioselective reduction of prochiral ketones catalyzed by oxazaborolidines

    Institute of Scientific and Technical Information of China (English)

    LI; Ming

    2001-01-01

    [1]Corey, E. J., Bakshi, R. K., Shibata, S., Highly enantioselective borane reduction ketones catalyzed by chiral oxazaborolidines, J. Am. Chem. Soc., 1987, 109:5551-5553.[2]Wallbaum, S., Martens, J., Asymmetric syntheses with chiral oxazaborolidines, Tetrahedron Asymmetry, 1992, 3: 1475-1504.[3]Deloux, L., Srebnik, M., Asymmetric borane-catalyzed reactions, Chem. Rev., 1993, 93: 763-784.[4]Togni, A., Venanzi, L. M., Nitrogen donors in organometallic chemistry and in homogeneous catalysis, Angew Chem. Int. Ed. Engl., 1994, 33: 497-562.[5]Ager, D. J., Prakash, I., Schaad, D. R., 1,2-amino alcohols and their heterocyclic derivatives as chiral auxiliaries in asymmetric synthesis, Chem. Rev., 1996, 96: 835-875.[6]Nevalainen, V., Quantum chemical modeling of chiral catalysis, Part 4. On the hydride transfer in ketone complexes of borane adducts of oxazaborolidines and regeneration of catalyst, Tetrahedron Asymmetry, 1991, 2:1133-1155.[7]Nevalainen, V., Quantum chemical modeling of chiral catalysis, Part 8. On the conformational freedom of the ketone of ketone-borane complexes of oxazaborolidines used as catalysts in the enantioselective reduction of ketones, Tetrahedron Asymmetry. 1992, 3: 1563-1572.[8]Nevalainen, V., Quantum chemical modeling of chiral catalysis, Part 7. On the effects controlling the coordination of borane to chiral oxazaborolidines used as catalysts in the enantioselective reduction of ketones, Tetrahedron Asymmetry,1992, 3: 1441-1453.[9]Nevalainen, V., Quantum chemical modeling of chiral catalysis, Part 12. On the influence of the nature of the ring system on binding in ketone-borane complexes of chiral oxazaborolidines used as catalysts in the enantioselective reduction of ketones. Tetrahedron Asymmetry, 1993, 4: 1597-1602.[10]Nevalainen, V., Quantum chemical modeling of chiral catalysis, Part 19. Strain and stability-oxazadiboretanes potentially involved in the enantioselective reduction of ketones promoted

  2. Synthesis of an Enantipure Tetrazole-Based Homochiral Cu(I,II)-MOF for Enantioselective Separation.

    Science.gov (United States)

    Liu, Juan; Wang, Fei; Ding, Qing-Rong; Zhang, Jian

    2016-12-19

    An enantipure (1S)-1-(5-tetrazolyl)ethylamine (5-eatz) ligand was first employed to construct a homochiral porous metal-organic framework, {[Cu(I)2Cu(II)(5-eatz)2(CN(-))(H2O)](+)[NO3(-)]}·[DMF] (1), with unusual ligand-unsupported Cu···Cu interactions. Such a compound shows high stability in water and common organic solvents. Remarkably, it has high enantioselectivity toward (R,S)-1-phenylethanol and (R,S)-1-phenylpropanol with enantiomeric excess values of up to 42% and 48%, respectively.

  3. Sodium salts of anionic chiral cobalt(III) complexes as catalysts of the enantioselective Povarov reaction.

    Science.gov (United States)

    Yu, Jie; Jiang, Hua-Jie; Zhou, Ya; Luo, Shi-Wei; Gong, Liu-Zhu

    2015-09-14

    The sodium salts of anionic chiral cobalt(III) complexes (CCC(-) Na(+) ) have been found to be efficient catalysts of the asymmetric Povarov reaction of easily accessible dienophiles, such as 2,3-dihydrofuran, ethyl vinyl ether, and an N-protected 2,3-dihydropyrrole, with 2-azadienes. Ring-fused tetrahydroquinolines with up to three contiguous stereogenic centers were thus obtained in high yields, excellent diastereoselectivities (endo/exo up to >20:1), and high enantioselectivities (up to 95:5 e.r.).

  4. Catalytic enantioselective synthesis of vicinal dialkyl arrays

    NARCIS (Netherlands)

    van Zijl, Anthoni W.; Szymanski, Wiktor; Lopez, Ferrnando; Minnaard, Adriaan J.; Feringa, Ben L.

    2008-01-01

    With a consecutive "asymmetric allylic alkylation (AAA)/cross-metathesis (CM)/conjugate addition (CA)" protocol it is possible to synthesize either stereoisomer of compounds containing a vicinal dialkyl array with excellent stereoselectivity. The versatility of this protocol in natural product synth

  5. Enhanced Reciprocal Interactions between Molecular Stresses and Optoelectronic Energy Transfers for High Efficiency Long Life Devices Based on Conjugated Polymers

    Science.gov (United States)

    2014-10-15

    The sample of a thin polymer film of PS containing an amount of the conjugated polymer (MEH-PPV or P3HT) was prepared by spin-coating on glass slide...due to the absence or insufficiency of the mobile PS molecules in the soaked film where the molecular flows were enacted mainly by the movement of the...with PS) were prepared by spin coating from the solutions on glass slide. The film on the substrate was then clamped between electrodes with

  6. Copper-catalysed enantioselective stereodivergent synthesis of amino alcohols

    Science.gov (United States)

    Shi, Shi-Liang; Wong, Zackary L.; Buchwald, Stephen L.

    2016-04-01

    The chirality, or ‘handedness’, of a biologically active molecule can alter its physiological properties. Thus it is routine procedure in the drug discovery and development process to prepare and fully characterize all possible stereoisomers of a drug candidate for biological evaluation. Despite many advances in asymmetric synthesis, developing general and practical strategies for obtaining all possible stereoisomers of an organic compound that has multiple contiguous stereocentres remains a challenge. Here, we report a stereodivergent copper-based approach for the expeditious construction of amino alcohols with high levels of chemo-, regio-, diastereo- and enantioselectivity. Specifically, we synthesized these amino-alcohol products using sequential, copper-hydride-catalysed hydrosilylation and hydroamination of readily available enals and enones. This strategy provides a route to all possible stereoisomers of the amino-alcohol products, which contain up to three contiguous stereocentres. We leveraged catalyst control and stereospecificity simultaneously to attain exceptional control of the product stereochemistry. Beyond the immediate utility of this protocol, our strategy could inspire the development of methods that provide complete sets of stereoisomers for other valuable synthetic targets.

  7. Nickel-catalyzed enantioselective hydrovinylation of silyl-protected allylic alcohols:An efficient access to homoallylic alcohols with a chiral quaternary center

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    Asymmetric hydrovinylation of silyl-protected allylic alcohols catalyzed by nickel complexes of chiral spiro phosphoramidite ligands was developed.A series of homoallylic alcohols with a chiral quaternary center were produced in high yields(up to 97%) and high enantioselectivities(up to 95% ee).The reaction provides an efficient method for preparing bifunctional compounds with a chiral quaternary carbon center.

  8. Research study of conjugate materials; Conjugate material no chosa kenkyu

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    1998-03-01

    The paper reported an introductory research on possibilities of new glass `conjugate materials.` The report took up the structure and synthetic process of conjugate materials to be researched/developed, classified them according to structural elements on molecular, nanometer and cluster levels, and introduced the structures and functions. Further, as glasses with new functions to be proposed, the paper introduced transparent and high-strength glass used for houses and vehicles, light modulation glass which realizes energy saving and optical data processing, and environmentally functional glass which realizes environmental cleaning or high performance biosensor. An initial survey was also conducted on rights of intellectual property to be taken notice of in Japan and abroad in the present situation. Reports were summed up and introduced of Osaka National Research Institute, Electrotechnical Laboratory, and National Industrial Research Institute of Nagoya which are all carrying out leading studies of conjugate materials. 235 refs., 135 figs., 6 tabs.

  9. Methylenedioxy designer drugs: mass spectrometric characterization of their glutathione conjugates by means of liquid chromatography-high-resolution mass spectrometry/mass spectrometry and studies on their glutathionyl transferase inhibition potency.

    Science.gov (United States)

    Meyer, Markus R; Richter, Lilian H J; Maurer, Hans H

    2014-04-25

    Methylenedioxy designer drugs of abuse such as 3,4-methylenedioxymethamphetamine (MDMA) can be selectively toxic to serotonergic neurons and glutathione (GSH) adducts have been implicated in its neurotoxicity. The catecholic demethylenyl metabolites of MDMA, 3,4-dihydroxymethamphetamine and 3,4-dihydroxyamphetamine, are metabolically oxidized to the corresponding ortho-quinones, which are highly reactive intermediates. These intermediates can then be conjugated with GSH preventing cellular damage. Furthermore, glutathionyl transferase (GST) activity was described to be irreversibly inhibited by the catechols dopamine, α-methyldopa and their GSH conjugates. Therefore, the aims of the present work were the detection and characterization of GSH conjugates of ten methylenedioxy drugs of abuse and their phase I metabolites as well as to assess their inhibition potency on GST activity. The substrates were incubated using human placental GST with or without preincubation by cytochrome P450 enzymes preparations. GST inhibition was tested using chlorodinitrobenzene GSH conjugation as marker reaction. GSH conjugates were analyzed and characterized using LC-high-resolution-MS/MS. For confirmation of postulated fragmentation patterns, formation of GSH conjugates of selected deuterated analogs (deuterated analogue approach, DAA) of the investigated drugs was explored. For the methylenedioxy amphetamines the following steps could be identified: conjugation of the parent compounds at position 2, 5, 6, of the demethylenyl metabolites at position 2 and 5, and of the further deaminated demethylenyl metabolites at position 2. For the β-keto-phenylalkylamine and pyrrolidinophenone, conjugation of the demethylenyl metabolites and of the deaminated demethylenyl metabolites at position 2 could be identified. The DAA allowed the differentiation of the 2 and 5/6 isomers by confirmation of the postulated mass spectral fragments. Finally, the tested drugs and phase I metabolites showed no

  10. Synthesis of novel chiral tetraaza ligands and their application in enantioselective transfer hydrogenation of ketones

    Institute of Scientific and Technical Information of China (English)

    Shen Luan Yu; Yan Yun Li; Zhen Rong Dong; Jing Xing Gao

    2012-01-01

    Novel chiral tetraaza ligands (R)-N,N'-bis[2-(piperidin-l-yl)benzylidene]propane-1,2-diamine 6 and (S)-N-[2-(piperidin-1-yl)benzylidene]-3-{ [2-(piperidin-1-yl)benzylidene]amino}-alanine sodium salt 7 have been synthesized and fully characterized by NMR,IR,MS and CD spectra.The catalytic property of the ligands was investigated in Ir-catalyzed enantioselective transfer hydrogenation of ketones.The corresponding optical active alcohols were obtained with high yields and moderate ees under mild reaction conditions.

  11. Application of 7-azaisatins in enantioselective Morita–Baylis–Hillman reaction

    Directory of Open Access Journals (Sweden)

    Qing He

    2016-02-01

    Full Text Available 7-Azaisatin and 7-azaoxindole skeletons are valuable building blocks in diverse biologically active substances. Here 7-azaisatins turned out to be more efficient electrophiles than the analogous isatins in the enantioselective Morita–Baylis–Hillman (MBH reactions with maleimides using a bifunctional tertiary amine, β-isocupreidine (β-ICD, as the catalyst. This route allows a convenient approach to access multifunctional 3-hydroxy-7-aza-2-oxindoles with high enantiopurity (up to 94% ee. Other types of activated alkenes, such as acrylates and acrolein, could also be efficiently utilized.

  12. Noncovalent Substrate-Directed Enantioselective Heck Reactions: Synthesis of S- and P-Stereogenic Heterocycles.

    Science.gov (United States)

    de Azambuja, Francisco; Carmona, Rafaela C; Chorro, Tomaz H D; Heerdt, Gabriel; Correia, Carlos Roque D

    2016-08-01

    S- and P-Stereogenic heterocycles were synthesized by a remarkably simple enantioselective Heck desymmetrization reaction based on the unprecedented noncovalent directing effect of S=O and P=O functionalities. Selected prochiral symmetric substrates were efficiently arylated using the recently disclosed chiral PyraBOx ligand under mild and open-flask reaction conditions. Several five-membered aryl- sulfones, sulfoxides, and phosphine oxides were synthesized in good to excellent yields, in good to high diastereoselectivity, and enantiomeric ratios up to 98:2. Theoretical calculations also support the noncovalent directing effect of the S=O and P=O functionalities during the arylation process.

  13. Enantioselective and Regiodivergent Addition of Purines to Terminal Allenes: Synthesis of Abacavir.

    Science.gov (United States)

    Thieme, Niels; Breit, Bernhard

    2017-02-01

    The rhodium-catalyzed atom-economic asymmetric N-selective intermolecular addition of purine derivatives to terminal allenes is reported. Branched allylic purines were obtained in high yields, regioselectivity and outstanding enantioselectivity utilizing a Rh/Josiphos catalyst. Conversely, linear selective allylation of purines could be realized in good to excellent regio- and E/Z-selectivity with a Pd/dppf catalyst system. Furthermore, the new methodology was applied to a straightforward asymmetric synthesis of carbocyclic nucleoside abacavir. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  14. High Performance Small-Molecule Cathode Interlayer Materials with D-A-D Conjugated Central Skeletons and Side Flexible Alcohol/Water-Soluble Groups for Polymer Solar Cells.

    Science.gov (United States)

    Han, Jianxiong; Chen, Youchun; Chen, Weiping; Yu, Chengzhuo; Song, Xiaoxian; Li, Fenghong; Wang, Yue

    2016-12-07

    A new class of organic cathode interfacial layer (CIL) materials based on isoindigo derivatives (IID) substituted with pyridinium or sulfonate zwitterion groups were designed, synthesized, and applied in polymer solar cells (PSCs) with PTB7:PC71BM (PTB7: polythieno[3,4-b]-thiophene-co-benzodithiophene and PC71BM: [6,6]-phenyl C71-butyric acidmethyl ester) as an active layer. Compared with the control device, PSCs with an IID-based CIL show simultaneous enhancement of open-circuit voltage (Voc), short-circuit current (Jsc), and fill factor (FF). Systematic optimizations of the central conjugated core and side flexible alcohol-soluble groups demonstrated that isoindigo-based CIL material with thiophene and sulfonate zwitterion substituent groups can efficiently enhance the PSC performance. The highest power conversion efficiency (PCE) of 9.12%, which is 1.75 times that of the control device without CIL, was achieved for the PSC having an isoindigo-based CIL. For the PSCs with an isoindigo-based CIL, the molecule-dependent performance property studies revealed that the central conjugated core with D-A-D characteristics and the side chains with sulfonate zwitterions groups represents an efficient strategy for constructing high performance CILs. Our study results may open a new avenue toward high performance PSCs.

  15. Preparation of highly conjugated water-dispersible graphene-butyric acid for the enhancement of electron transfer within polyamic acid-benzoxazole: potential applications in electrochemical sensing.

    Science.gov (United States)

    Chen, Hsiao-Chien; Chen, Yen-Hsuan; Chen, Shi-Liang; Chern, Yaw-Terng; Tsai, Rung-Ywan; Hua, Mu-Yi

    2013-08-15

    To break through the long time and complex procedures for the preparation of highly conjugated reduced graphene oxide (r-GO) in developing electrochemical sensor, a time-saving and simple method is investigated in this study. One novel step of the exfoliated accompanying carboxylated graphene sheet from pristine is achieved via Friedel-Crafts acylation. By electrophilic aromatic substitution, the succinic anhydride ring is opened and attaches covalently to the graphene sheet (Gs) to form exfoliated graphene with grafted 1-one-butyric acid (Gs-BA). The grafting chain converts anions in aqueous solution to maintain Gs-BA in a stable dispersion and noticeably decreases the π-π stacking of the exfoliated Gs during the drying process. The analytical results of the absorption spectroscopy demonstrate that the conjugation of Gs-BA is not significantly destroyed by this chemical modification; Gs-BA retains the Gs electrical properties favorable for developing electrochemical sensors. When polyamic acid-benzoxazole (PAA-BO), a hydrogen peroxide (H₂O₂)-sensitive probe, hybridizes with Gs-BA to form Gs-BA-PAA-BO, the electron transfer rate relating to the response time improves markedly from 1.09 s(-1) to 38.8 s(-1). Additionally, it offers a high performance for H₂O₂ sensing in terms of sensitivity and response time, making this method applicable for developing glucose and choline biosensors.

  16. Diketopyrrolopyrrole-based Conjugated Polymer Entailing Triethylene Glycols as Side Chains with High Thin Film Charge Mobility without Post-Treatments.

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Si-Fen; Liu, Zitong; Cai, Zheng-Xu; Dyson, Matthew J.; Stingelin, Natalie; Chen, Wei; Ju, Hua-Jun; Zhang, Guan-Xin; Zhang, De-Qing

    2017-08-01

    Side chain engineering of conjugated donor-acceptor polymers is a new way to manipulate their optoelectronic properties. Two new diketopyrrolopyrrole (DPP)-terthiophene-based conjugated polymers PDPP3T-1 and PDPP3T-2, with both hydrophilic triethylene glycol (TEG) and hydrophobic alkyl chains, are reported. It is demonstrated that the incorporation of TEG chains has a significant effect on the interchain packing and thin-film morphology with noticeable effect on charge transport. Polymer chains of PDPP3T-1 in which TEG chains are uniformly distributed can self-assemble spontaneously into a more ordered thin film. As a result, the thin film of PDPP3T-1 exhibits high saturated hole mobility up to 2.6 cm(2) V-1 s(-1) without any post-treatment. This is superior to those of PDPP3T with just alkyl chains and PDPP3T-2. Moreover, the respective field effect transistors made of PDPP3T-1 can be utilized for sensing ethanol vapor with high sensitivity (down to 100 ppb) and good selectivity.

  17. Iridium-catalyzed enantioselective hydrogenation of imines in supercritical carbon dioxide

    Energy Technology Data Exchange (ETDEWEB)

    Kainz, S.; Brinkmann, A.; Leitner, W.; Pfaltz, A.

    1999-07-14

    Supercritical carbon dioxide (scCO{sub 2}) was shown to be a reaction medium with unique properties for highly efficient iridium-catalyzed enantioselective hydrogenation of prochiral imines. Cationic iridium(I) complexes with chiral phosphinodihydrooxazoles, modified with perfluoroalkyl groups in the ligand or in the anion, were synthesized and tested in the hydrogenation of N-(1-phenylethylidene)aniline. Both the side chains and the lipophilic anions increased the solubility, but the choice of the anion also had a dramatic effect on the enantioselectivity with tetrakis-3,5-bis(trifluoromethyl)phenylborate (BARF) leading to the highest asymmetric induction. (R)-N-phenyl-1-phenylethylamine was formed quantitatively within 1 h in scCO{sub 2}[d(CO{sub 2}) = 0.75 g mL{sup {minus}1}] at 40 C and a H{sub 2} pressure of 30 bar with enantiomeric excesses of up to 81% using 0.078 mol % catalyst. The use of scCO{sub 2} instead of conventional solvents such as CH{sub 2}Cl{sub 2} allowed the catalyst loading to be lowered significantly owing to a change in the rate profile of the reaction. the homogeneous nature of the catalytically active species under the reaction conditions was demonstrated and was found to depend strongly on the composition of the reaction mixture and especially on the presence of the substrate. Utilizing the selective extractive properties of scCO{sub 2}, the product could be readily separated from the catalyst, which could be recycled several times without significant loss of activity and enantioselectivity. High-pressure FT-IR and NMR investigations revealed that the reactivity of the products to form the corresponding carbamic acids plays an important role for the application of this new methodology.

  18. Enantioselective Direct Mannich-Type Reactions Catalyzed by Frustrated Lewis Acid/Brønsted Base Complexes.

    Science.gov (United States)

    Shang, Ming; Cao, Min; Wang, Qifan; Wasa, Masayuki

    2017-09-05

    An enantioselective direct Mannich-type reaction catalyzed by a sterically frustrated Lewis acid/Brønsted base complex is disclosed. Cooperative functioning of the chiral Lewis acid and achiral Brønsted base components gives rise to in situ enolate generation from monocarbonyl compounds. Subsequent reaction with hydrogen-bond-activated aldimines delivers β-aminocarbonyl compounds with high enantiomeric purity. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  19. Enantioselective Diels-Alder reactions of carboxylic ester dienophiles catalysed by titanium-based chiral Lewis acid

    Directory of Open Access Journals (Sweden)

    Yogesh K. Choughule

    2016-05-01

    Full Text Available A new titanium-based chiral Lewis acid 1 has been developed using (1R,2R-1,2-bis-(2-methoxyphenyl-ethane-1,2-diol as a chiral vicinal diol ligand. This chiral catalyst was found to exhibit uniformly high enantioselectivity towards carboxylic ester dienophiles in Diels-Alder reactions. The chiral vicinal ligand (1R,2R-1,2-bis-(2-methoxyphenyl-ethane-1,2-diol is inexpensive and is easily accessible.

  20. Enantioselective Cu-Catalyzed Arylation of Secondary Phosphine Oxides with Diaryliodonium Salts toward the Synthesis of P-Chiral Phosphines

    Science.gov (United States)

    2016-01-01

    Catalytic synthesis of nonracemic P-chiral phosphine derivatives remains a significant challenge. Here we report Cu-catalyzed enantioselective arylation of secondary phosphine oxides with diaryliodonium salts for the synthesis of tertiary phosphine oxides with high enantiomeric excess. The new process is demonstrated on a wide range of substrates and leads to products that are well-established P-chiral catalysts and ligands. PMID:27689432

  1. Enantioselective formal [3+3] cycloadditions of ketones and cyclic 1-azadienes by cascade enamine-enamine catalysis.

    Science.gov (United States)

    He, Xiao-Long; Xiao, You-Cai; Du, Wei; Chen, Ying-Chun

    2015-02-16

    An asymmetric formal [3+3] cycloaddition process with diversely structured aliphatic ketones and electron-deficient cyclic 1-azadienes was developed by cascade enamine-enamine catalysis of a cinchona-based primary amine. This sequence involved a domino Michael addition-Mannich reaction to afford spirocyclic architectures in excellent diastereo- and enantioselectivity. Importantly, high regioselectivity was realized for a number of unsymmetrical aliphatic ketone substrates.

  2. High-effciency improved symmetric successive over-relaxation preconditioned conjugate gradient method for solving large-scale finite element linear equations

    Institute of Scientific and Technical Information of China (English)

    李根; 唐春安; 李连崇

    2013-01-01

    Fast solving large-scale linear equations in the finite element analysis is a classical subject in computational mechanics. It is a key technique in computer aided engineering (CAE) and computer aided manufacturing (CAM). This paper presents a high-effciency improved symmetric successive over-relaxation (ISSOR) preconditioned conjugate gradient (PCG) method, which maintains the convergence and inherent paral-lelism consistent with the original form. Ideally, the computation can be reduced nearly by 50% as compared with the original algorithm. It is suitable for high-performance computing with its inherent basic high-effciency operations. By comparing with the nu-merical results, it is shown that the proposed method has the best performance.

  3. Thermostable alcohol dehydrogenase from Thermococcus kodakarensis KOD1 for enantioselective bioconversion of aromatic secondary alcohols.

    Science.gov (United States)

    Wu, Xi; Zhang, Chong; Orita, Izumi; Imanaka, Tadayuki; Fukui, Toshiaki; Xing, Xin-Hui

    2013-04-01

    A novel thermostable alcohol dehydrogenase (ADH) showing activity toward aromatic secondary alcohols was identified from the hyperthermophilic archaeon Thermococcus kodakarensis KOD1 (TkADH). The gene, tk0845, which encodes an aldo-keto reductase, was heterologously expressed in Escherichia coli. The enzyme was found to be a monomer with a molecular mass of 31 kDa. It was highly thermostable with an optimal temperature of 90°C and a half-life of 4.5 h at 95°C. The apparent K(m) values for the cofactors NAD(P)(+) and NADPH were similar within a range of 66 to 127 μM. TkADH preferred secondary alcohols and accepted various ketones and aldehydes as substrates. Interestingly, the enzyme could oxidize 1-phenylethanol and its derivatives having substituents at the meta and para positions with high enantioselectivity, yielding the corresponding (R)-alcohols with optical purities of greater than 99.8% enantiomeric excess (ee). TkADH could also reduce 2,2,2-trifluoroacetophenone to (R)-2,2,2-trifluoro-1-phenylethanol with high enantioselectivity (>99.6% ee). Furthermore, the enzyme showed high resistance to organic solvents and was particularly highly active in the presence of H2O-20% 2-propanol and H2O-50% n-hexane or n-octane. This ADH is expected to be a useful tool for the production of aromatic chiral alcohols.

  4. Online size-exclusion high-performance liquid chromatography light scattering and differential refractometry methods to determine degree of polymer conjugation to proteins and protein-protein or protein-ligand association states.

    Science.gov (United States)

    Kendrick, B S; Kerwin, B A; Chang, B S; Philo, J S

    2001-12-15

    Characterizing the solution structure of protein-polymer conjugates and protein-ligand interactions is important in fields such as biotechnology and biochemistry. Size-exclusion high-performance liquid chromatography with online classical light scattering (LS), refractive index (RI), and UV detection offers a powerful tool in such characterization. Novel methods are presented utilizing LS, RI, and UV signals to rapidly determine the degree of conjugation and the molecular mass of the protein conjugate. Baseline resolution of the chromatographic peaks is not required; peaks need only be sufficiently separated to represent relatively pure fractions. An improved technique for determining the polypeptide-only mass of protein conjugates is also described. These techniques are applied to determining the degree of erythropoietin glycosylation, the degree of polyethylene glycol conjugation to RNase A and brain-derived neurotrophic factor, and the solution association states of these molecules. Calibration methods for the RI, UV, and LS detectors will also be addressed, as well as online methods to determine protein extinction coefficients and dn/dc values both unconjugated and conjugated protein molecules. (c)2001 Elsevier Science.

  5. The Tcp conjugation system of Clostridium perfringens.

    Science.gov (United States)

    Wisniewski, Jessica A; Rood, Julian I

    2017-03-07

    The Gram-positive pathogen Clostridium perfringens possesses a family of large conjugative plasmids that is typified by the tetracycline resistance plasmid pCW3. Since these plasmids may carry antibiotic resistance genes or genes encoding extracellular or sporulation-associated toxins, the conjugative transfer of these plasmids appears to be important for the epidemiology of C. perfringens-mediated diseases. Sequence analysis of members of this plasmid family identified a highly conserved 35kb region that encodes proteins with various functions, including plasmid replication and partitioning. The tcp conjugation locus also was identified in this region, initially based on low-level amino acid sequence identity to conjugation proteins from the integrative conjugative element Tn916. Genetic studies confirmed that the tcp locus is required for conjugative transfer and combined with biochemical and structural analyses have led to the development of a functional model of the Tcp conjugation apparatus. This review summarises our current understanding of the Tcp conjugation system, which is now one of the best-characterized conjugation systems in Gram-positive bacteria.

  6. Pseudofaults and associated seamounts in the conjugate Arabian and Eastern Somali basins, NW Indian Ocean - New constraints from high-resolution satellite-derived gravity data

    Science.gov (United States)

    Sreejith, K. M.; Chaubey, A. K.; Mishra, Akhil; Kumar, Shravan; Rajawat, A. S.

    2016-12-01

    Marine gravity data derived from satellite altimeters are effective tools in mapping fine-scale tectonic features of the ocean basins such as pseudofaults, fracture zones and seamounts, particularly when the ocean basins are carpeted with thick sediments. We use high-resolution satellite-generated gravity and seismic reflection data to map boundaries of pseudofaults and transferred crust related to the Paleocene spreading ridge propagation in the Arabian and its conjugate Eastern Somali basins. The study has provided refinement in the position of previously reported pseudofaults and their spatial extensions in the conjugate basins. It is observed that the transferred crustal block bounded by inner pseudofault and failed spreading ridge is characterized by a gravity low and rugged basement. The refined satellite gravity image of the Arabian Basin also revealed three seamounts in close proximity to the pseudofaults, which were not reported earlier. In the Eastern Somali Basin, seamounts are aligned along NE-SW direction forming ∼300 km long seamount chain. Admittance analysis and Flexural model studies indicated that the seamount chain is isostatically compensated locally with Effective Elastic Thickness (Te) of 3-4 km. Based on the present results and published plate tectonic models, we interpret that the seamounts in the Arabian Basin are formed by spreading ridge propagation and are associated with pseudofaults, whereas the seamount chain in the Eastern Somali Basin might have probably originated due to melting and upwelling of upper mantle heterogeneities in advance of migrating/propagating paleo Carlsberg Ridge.

  7. A Quinine-Squaramide Catalyzed Enantioselective Aza-Friedel-Crafts Reaction of Cyclic Trifluoromethyl Ketimines with Naphthols and Electron-Rich Phenols.

    Science.gov (United States)

    Zhou, Ding; Huang, Zheng; Yu, Xueting; Wang, Youxin; Li, Jian; Wang, Wei; Xie, Hexin

    2015-11-20

    A highly enantioselective aza-Friedel-Crafts (aza-F-C) reaction of cyclic trifluoromethyl ketimines and naphthols/phenols was developed with fluorenyl-substituted quinine-squaramide as the catalyst. This protocol enables direct access to biologically important chiral trifluoromethyl dihydroquinazolinones with up to 99% yields and up to 99% ee's.

  8. Enantioselective reductive transformation of climbazole: A concept towards quantitative biodegradation assessment in anaerobic biological treatment processes.

    Science.gov (United States)

    Brienza, Monica; Chiron, Serge

    2017-06-01

    An efficient chiral method-based using liquid chromatography-high resolution-mass spectrometry analytical method has been validated for the determination of climbazole (CBZ) enantiomers in wastewater and sludge with quantification limits below the 1 ng/L and 2 ng/g range, respectively. On the basis of this newly developed analytical method, the stereochemistry of CBZ was investigated over time in sludge biotic and sterile batch experiments under anoxic dark and light conditions and during wastewater biological treatment by subsurface flow constructed wetlands. CBZ stereoselective degradation was exclusively observed under biotic conditions, confirming the specificity of enantiomeric fraction variations to biodegradation processes. Abiotic CBZ enantiomerization was insignificant at circumneutral pH and CBZ was always biotransformed into CBZ-alcohol due to the specific and enantioselective reduction of the ketone function of CBZ into a secondary alcohol function. This transformation was almost quantitative and biodegradation gave good first order kinetic fit for both enantiomers. The possibility to apply the Rayleigh equation to enantioselective CBZ biodegradation processes was investigated. The results of enantiomeric enrichment allowed for a quantitative assessment of in situ biodegradation processes due to a good fit (R(2) > 0.96) of the anoxic/anaerobic CBZ biodegradation to the Rayleigh dependency in all the biotic microcosms and was also applied in subsurface flow constructed wetlands. This work extended the concept of applying the Rayleigh equation towards quantitative biodegradation assessment of organic contaminants to enantioselective processes operating under anoxic/anaerobic conditions. Copyright © 2017 Elsevier Ltd. All rights reserved.

  9. Revisiting conjugate schedules.

    Science.gov (United States)

    MacAleese, Kenneth R; Ghezzi, Patrick M; Rapp, John T

    2015-07-01

    The effects of conjugate reinforcement on the responding of 13 college students were examined in three experiments. Conjugate reinforcement was provided via key presses that changed the clarity of pictures displayed on a computer monitor in a manner proportional to the rate of responding. Experiment 1, which included seven parameters of clarity change per response, revealed that responding decreased as the percentage clarity per response increased for all five participants. These results indicate that each participant's responding was sensitive to intensity change, which is a parameter of conjugate reinforcement schedules. Experiment 2 showed that responding increased during conjugate reinforcement phases and decreased during extinction phases for all four participants. Experiment 3 also showed that responding increased during conjugate reinforcement and further showed that responding decreased during a conjugate negative punishment condition for another four participants. Directions for future research with conjugate schedules are briefly discussed.

  10. Enantioselective Additions of Boronates to Chromene Acetals Catalyzed by a Chiral Brønsted acid-Lewis acid System

    Science.gov (United States)

    Moquist, Philip N.; Kodama, Tomohiro; Schaus, Scott E.

    2011-01-01

    Chiral α,β-dihydroxy carboxylic acids catalyze the enantioselective addition of alkenyl- and aryl boronates to chromene acetals. The optimal carboxylic acid is a tartaric acid amide, easily synthesized via a 3-step procedure. The reaction is enhanced by the addition of Lanthanide triflate salts such as cerium(IV)-and ytterbium(III) triflate. The chiral Brønsted acid and metal Lewis acid may be used in as low as 5 mol % relative to acetal substrate. Optimization of the reaction conditions can lead to yields >70% and enantiomeric ratios as high as 99:1. Spectroscopic and kinetic mechanistic studies demonstrate an exchange process leading to a reactive dioxoborolane intermediate leading to enantioselective addition to the pyrylium generated from the chromene acetal. PMID:20721997

  11. The Significance of Degenerate Processes to Enantioselective Olefin Metathesis Reactions Promoted by Stereogenic-at-Mo Complexes

    Science.gov (United States)

    Meek, Simon J.; Malcolmson, Steven J.; Li, Bo; Schrock, Richard R.; Hoveyda, Amir H.

    2009-01-01

    The present study provides spectroscopic and experimental evidence demonstrating that degenerate metathesis is critical to the effectiveness of this emerging class of chiral catalysts. Isolation and characterization (X-ray) of both diastereomeric complexes, as well as examination of the reactivity and enantioselectivity patterns exhibited by such initiating neophylidenes in promoting RCM processes, are disclosed. Only when sufficient amounts of ethylene are generated and inversion at Mo through degenerate processes occurs at a sufficiently rapid rate, is high enantioselectivity achieved, irrespective of the stereochemical identity of the initiating alkylidene (Curtin-Hammett kinetics). With diastereomeric metal complexes that undergo rapid interconversion, stereomutation at the metal center becomes inconsequential and stereoselective synthesis of a chiral catalyst is not required. PMID:19842640

  12. Enantioselective Construction of Pyrrolidines by Palladium-Catalyzed Asymmetric [3+2] Cycloaddition of Trimethylenemethane with Imines

    Science.gov (United States)

    Trost, Barry M.; Silverman, Steven M.

    2012-01-01

    A protocol for the enantioselective [3+2] cycloaddition of trimethylenemethane (TMM) with imines has been developed. Central to this effort were the novel phosphoramidite ligands developed in our laboratories. The conditions developed to effect an asymmetric TMM reaction using 2-trimethylsilylmethyl allyl acetate were shown to be tolerant of a wide variety of imine acceptors to provide the corresponding pyrrolidine cycloadducts with excellent yields and selectivities. Use of a bis-2-naphthyl phosphoramidite allowed the successful cycloaddition of the parent TMM with N-Boc imines, and has further permitted the reaction of substituted donors with N-tosyl aldimines and ketimines in high regio-, diastereo-, and enantioselectivity. Use of a diphenylazetidine ligand allows the complimentary synthesis of the exocyclic nitrile product shown, and we demonstrate control of the regioselectivity of the product based on manipulation of the reaction parameters. PMID:22309214

  13. Molecularly imprinted nanotubes for enantioselective drug delivery and controlled release.

    Science.gov (United States)

    Yin, Junfa; Cui, Yue; Yang, Gengliang; Wang, Hailin

    2010-11-07

    Molecularly imprinted nanotubes for enantioselective drug delivery and controlled release are fabricated by the combination of template synthesis and ATRP grafting. The release of R-propranolol from the imprinted nanotubes in rats is restricted while the release of pharmacologically active S-enantiomer is greatly promoted.

  14. Enantioselective Symmetry Breaking Directed by the Order of Process Steps

    NARCIS (Netherlands)

    Noorduin, Wim L.; Meekes, Hugo; Enckevort, Willem J.P. van; Kaptein, Bernard; Kellogg, Richard M.; Vlieg, Elias

    2010-01-01

    Going forward in reverse: The configuration of the product of grinding-induced symmetry breaking can be controlled simply by the order in which the different reaction-mixture components are combined. The underlying mechanism is based on a subtle balance between enantioselective crystal growth and di

  15. Recent advances in the enantioselective synthesis of chiral drugs

    Energy Technology Data Exchange (ETDEWEB)

    Juaristi, E. [Departamento de Quimica. Centro de Investigacion y de Estudios Avanzados del Instituto Politecnico Nacional, Mexico (Mexico)

    1997-09-01

    Because of the importance of drug chirality on biological activity, there has been increasing effort both in academic and industrial research to develop more efficient ways for the enantioselective synthesis of chiral therapeutic agents. This review presents some of the most relevant methods that have recently contributed to the advancement of this area. (Author) 45 refs.

  16. Dynamic control of chirality in phosphine ligands for enantioselective catalysis

    NARCIS (Netherlands)

    Zhao, Depeng; Neubauer, Thomas M; Feringa, Ben L

    2015-01-01

    Chirality plays a fundamental role in biology and chemistry and the precise control of chirality in a catalytic conversion is a key to modern synthesis most prominently seen in the production of pharmaceuticals. In enantioselective metal-based catalysis, access to each product enantiomer is commonly

  17. DNA and RNA induced enantioselectivity in chemical synthesis

    NARCIS (Netherlands)

    Roelfes, Gerard

    One of the hallmarks of DNA and RNA structures is their elegant chirality. Using these chiral structures to induce enantioselectivity in chemical synthesis is as enticing as it is challenging. In recent years, three general approaches have been developed to achieve this, including chirality transfer

  18. The enantioselective b-keto ester reductions by Saccharomyces cerevisiae

    OpenAIRE

    HASSAN TAJIK; KHALIL TABATABAEIAN; MAHMOOD SHAHBAZI

    2006-01-01

    The enantioselective yeast reduction of aromatic b-keto esters, by use of potassium dihydrogen phosphate, calcium phosphate (monobasic), magnesium sulfate and ammonium tartrate (diammonium salt) (10:1:1:50) in water at pH 7 as a buffer for 72–120 h with 45–90 % conversion to the corresponding aromatic -hydroxy esters was achieved by means of Saccharomyces cerevisiae.

  19. Whole cells in enantioselective reduction of benzyl acetoacetate

    Directory of Open Access Journals (Sweden)

    Joyce Benzaquem Ribeiro

    2014-09-01

    Full Text Available The β-ketoester benzyl acetoacetate was enantioselectively reduced to benzyl (S-3-hydroxybutanoate by seven microorganism species. The best result using free cells was obtained with the yeast Hansenula sp., which furnished 97% ee and 85% of conversion within 24 h. After immobilization in calcium alginate spheres, K.marxianus showed to be more stable after 2 cycles of reaction.

  20. DOTA-functionalized polylysine: a high number of DOTA chelates positively influences the biodistribution of enzymatic conjugated anti-tumor antibody chCE7agl.

    Directory of Open Access Journals (Sweden)

    Jürgen Grünberg

    Full Text Available Site-specific enzymatic reactions with microbial transglutaminase (mTGase lead to a homogenous species of immunoconjugates with a defined ligand/antibody ratio. In the present study, we have investigated the influence of different numbers of 1,4,7,10-tetraazacyclododecane-N-N'-N''-N'''-tetraacetic acid (DOTA chelats coupled to a decalysine backbone on the in vivo behavior of the chimeric monoclonal anti-L1CAM antibody chCE7agl. The enzymatic conjugation of (DOTA1-decalysine, (DOTA3-decalysine or (DOTA5-decalysine to the antibody heavy chain (via Gln295/297 gave rise to immunoconjugates containing two, six or ten DOTA moieties respectively. Radiolabeling of the immunoconjugates with (177Lu yielded specific activities of approximately 70 MBq/mg, 400 MBq/mg and 700 MBq/mg with increasing numbers of DOTA chelates. Biodistribution experiments in SKOV3ip human ovarian cancer cell xenografts demonstrated a high and specific accumulation of radioactivity at the tumor site for all antibody derivatives with a maximal tumor accumulation of 43.6±4.3% ID/g at 24 h for chCE7agl-[(DOTA-decalysine]2, 30.6±12.0% ID/g at 24 h for chCE7agl-[(DOTA3-decalysine]2 and 49.9±3.1% ID/g at 48 h for chCE7agl-[(DOTA5-decalysine]2. The rapid elimination from the blood of chCE7agl-[(DOTA-decalysine]2 (1.0±0.1% ID/g at 24 h is associated with a high liver accumulation (23.2±4.6% ID/g at 24 h. This behavior changed depending on the numbers of DOTA moieties coupled to the decalysine peptide with a slower blood clearance (5.1±1.0 (DOTA3 versus 11.7±1.4% ID/g (DOTA5, p<0.005 at 24 h and lower radioactivity levels in the liver (21.4±3.4 (DOTA3 versus 5.8±0.7 (DOTA5, p<0.005 at 24 h. We conclude that the site-specific and stoichiometric uniform conjugation of the highly DOTA-substituted decalysine ((DOTA5-decalysine to an anti-tumor antibody leads to the formation of immunoconjugates with high specific activity and excellent in vivo behavior and is a valuable option for

  1. Energetic Tuning in Spirocyclic Conjugated Polymers

    Directory of Open Access Journals (Sweden)

    Hugo Bronstein

    2016-01-01

    Full Text Available Precise control of the energy levels in a conjugated polymer is the key to allowing their exploitation in optoelectronic devices. The introduction of spirocycles into conjugated polymers has traditionally been used to enhance their solid state microstructure. Here we present a highly novel method of energetic tuning through the use of electronically active spirocyclic systems. By modifying the size and oxidation state of a heteroatom in an orthogonal spirocycle we demonstrate energetic fine tuning in both the absorption and emission of a conjugated polymer. Furthermore, the synthesis of highly novel triplet-decker spirocyclic conjugated polymers is presented. This new method of energetic manipulation in a conjugated polymer paves the way for future application targeted synthesis of polymers with electronically active spirocycles.

  2. A Conjugated Aptamer-Gold Nanoparticle Fluorescent Probe for Highly Sensitive Detection of rHuEPO-α

    Directory of Open Access Journals (Sweden)

    Zhaoyang Zhang

    2011-11-01

    Full Text Available We present here a novel conjugated aptamer-gold nanoparticle (Apt-AuNPs fluorescent probe and its application for specific detection of recombinant human erythropoietin-α (rHuEPO-α. In this nanobiosensor, 12 nm AuNPs function as both a nano-scaffold and a nano-quencher (fluorescent energy acceptor, on the surface of which the complementary sequences are linked (as cODN-AuNPs and pre-hybridized with carboxymethylfluorescein (FAM-labeled anti-rHuEPO-α aptamers. Upon target protein binding, the aptamers can be released from the AuNP surface and the fluorescence signal is restored. Key variables such as the length of linker, the hybridization site and length have been designed and optimized. Full performance evaluation including sensitivity, linear range and interference substances are also described. This nanobiosensor provides a promising approach for a simple and direct quantification of rHuEPO-α concentrations as low as 0.92 nM within a few hours.

  3. Highly selective synthesis of conjugated dienoic and trienoic esters via alkyne elementometalation-Pd-catalyzed cross-coupling.

    Science.gov (United States)

    Wang, Guangwei; Mohan, Swathi; Negishi, Ei-ichi

    2011-07-12

    All four stereoisomers (7-10) of ethyl undeca-2,4-dienoate were prepared in ≥ 98% isomeric purity by Pd-catalyzed alkenylation (Negishi coupling) using ethyl (E)- and (Z)-β-bromoacrylates. Although the stereoisomeric purity of the 2Z,4E-isomer (8) prepared by Suzuki coupling using conventional alkoxide and carbonate bases was ≤ 95%, as reported earlier, the use of CsF or (n)Bu(4)NF as a promoter base has now been found to give all of 7-10 in ≥ 98% selectivity. Other widely known methods reveal considerable limitations. Heck alkenylation was satisfactory for the syntheses of the 2E,4E and 2E,4Z isomers of ≥ 98% purity, but the purity of the 2Z,4E isomer was ≤ 95%. Mutually complementary Horner-Wadsworth-Emmons and Still-Gennari (SG) olefinations are also of considerably limited scopes. Neither 2E,4Z nor 2Z,4Z isomer is readily prepared in ≥ 90% selectivity. In addition to (2Z,4E)-dienoic esters, some (2Z,4E,6E)- and (2Z,4E,6Z)-trienoic esters have been prepared in ≥ 98% selectivity by a newly devised Pd-catalyzed alkenylation-SG olefination tandem process. As models for conjugated higher oligoenoic esters, all eight stereoisomers for ethyl trideca-2,4,6-trienoate (23-30) have been prepared in ≥ 98% overall selectivity.

  4. Highly selective synthesis of conjugated dienoic and trienoic esters via alkyne elementometalation–Pd-catalyzed cross-coupling

    Science.gov (United States)

    Wang, Guangwei; Mohan, Swathi; Negishi, Ei-ichi

    2011-01-01

    All four stereoisomers (7–10) of ethyl undeca-2,4-dienoate were prepared in ≥98% isomeric purity by Pd-catalyzed alkenylation (Negishi coupling) using ethyl (E)- and (Z)-β-bromoacrylates. Although the stereoisomeric purity of the 2Z,4E-isomer (8) prepared by Suzuki coupling using conventional alkoxide and carbonate bases was ≤ 95%, as reported earlier, the use of CsF or nBu4NF as a promoter base has now been found to give all of 7–10 in ≥98% selectivity. Other widely known methods reveal considerable limitations. Heck alkenylation was satisfactory for the syntheses of the 2E,4E and 2E,4Z isomers of ≥98% purity, but the purity of the 2Z,4E isomer was ≤ 95%. Mutually complementary Horner–Wadsworth–Emmons and Still–Gennari (SG) olefinations are also of considerably limited scopes. Neither 2E,4Z nor 2Z,4Z isomer is readily prepared in ≥90% selectivity. In addition to (2Z,4E)-dienoic esters, some (2Z,4E,6E)- and (2Z,4E,6Z)-trienoic esters have been prepared in ≥98% selectivity by a newly devised Pd-catalyzed alkenylation–SG olefination tandem process. As models for conjugated higher oligoenoic esters, all eight stereoisomers for ethyl trideca-2,4,6-trienoate (23–30) have been prepared in ≥98% overall selectivity. PMID:21709262

  5. Cross-Conjugated n-Dopable Aromatic Polyketone

    NARCIS (Netherlands)

    Voortman, Thomas P.; Bartesaghi, Davide; Koster, L. Jan Anton; Chiechi, Ryan C.

    2015-01-01

    This paper describes the synthesis and characterization of a high molecular weight cross-conjugated polyketone synthesized via scalable Friedel Crafts chemistry. Cross-conjugated polyketones are precursors to conjugated polyions; they become orders of magnitude more conductive after a two-electron r

  6. Cross-Conjugated n-Dopable Aromatic Polyketone

    NARCIS (Netherlands)

    Voortman, Thomas P.; Bartesaghi, Davide; Koster, L. Jan Anton; Chiechi, Ryan C.

    2015-01-01

    This paper describes the synthesis and characterization of a high molecular weight cross-conjugated polyketone synthesized via scalable Friedel Crafts chemistry. Cross-conjugated polyketones are precursors to conjugated polyions; they become orders of magnitude more conductive after a two-electron

  7. Temperature-controlled bidirectional enantioselectivity in a dynamic catalyst for asymmetric hydrogenation.

    Science.gov (United States)

    Storch, Golo; Trapp, Oliver

    2015-03-16

    Asymmetric catalysis using enantiomerically pure catalysts is one of the most widely used methods for the preparation of enantiomerically pure compounds. The separate synthesis of both enantiomerically pure compounds requires tedious and time-consuming preparation of both enantiomerically pure catalysts or chiral separation of the racemic products. Here, we report a stereochemically flexible diastereomeric rhodium(I) catalyst for asymmetric hydrogenations of prochiral (Z)-α-acetamidocinnamates and α-substituted acrylates, which changes its enantioselectivity depending on the temperature to produce each enantiomerically pure compound in high yield with constant high enantioselectivity over time. The same axially chiral rhodium(I) catalyst produces (R)-phenylalanine derivatives in enantiomeric ratios of up to 87:13 (R/S) at low temperature and up to 3:97 (R/S) of the corresponding S enantiomers after re-equilibration of the same catalyst at elevated temperature. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  8. Green self-assembly of zein-conjugated ZnO/Cd(OH)Cl hierarchical nanocomposites with high cytotoxicity and immune organs targeting

    Science.gov (United States)

    Wang, Hua-Jie; Cao, Ying; Wang, Cai-Feng; Cui, Shi-Zhong; Mi, Li-Wei; Miyazawa, Teruo

    2016-04-01

    Inorganic nanomedicines in the fight against cancer have progressed rapidly during recent years, with the synergistic advantages of multifunctional nanosystems compared to single component. Herein, a drug-combination opinion was introduced into “nanomedicine” based on the understanding of Trojan horse-anti-tumor mechanism of inorganic nano-medicines. Moreover, we reported the green and facile synthesis route of mono-dispersed and rod-like zein-conjugated ZnO/Cd(OH)Cl hierarchical nanocomposites. We found that the nanocomposites exhibited high-efficiency killing ability to tumor cells through lipid peroxidation mediated-membrane disintegration route. The safety studies in BALB/c mice didn’t detect injection anaphylaxis, hemolysis and cytotoxicity. More interestingly, the nano-composites could specially accumulate in liver and kidney, which will be helpful for targeting cure to these regional cancers.

  9. A hybrid enrichment process combining conjugated polymer extraction and silica gel adsorption for high purity semiconducting single-walled carbon nanotubes (SWCNT)

    Science.gov (United States)

    Ding, Jianfu; Li, Zhao; Lefebvre, Jacques; Cheng, Fuyong; Dunford, Jeffrey L.; Malenfant, Patrick R. L.; Humes, Jefford; Kroeger, Jens

    2015-09-01

    A novel purification process for the enrichment of sc-SWCNTs that combines selective conjugated polymer extraction (CPE) with selective adsorption using silica gel, termed hybrid-CPE (h-CPE), has been developed, providing a high purity sc-SWCNT material with a significant improvement in process efficiency and yield. Using the h-CPE protocol, a greater than 5 fold improvement in yield can be obtained compared to traditional CPE while obtaining sc-SWCNT with a purity >99.9% as assessed by absorption spectroscopy and Raman mapping. Thin film transistor devices using the h-CPE derived sc-SWCNTs as the semiconductor possess mobility values ranging from 10-30 cm2 V-1 s-1 and current ON/OFF ratio of 104-105 for channel lengths between 2.5 and 20 μm.A novel purification process for the enrichment of sc-SWCNTs that combines selective conjugated polymer extraction (CPE) with selective adsorption using silica gel, termed hybrid-CPE (h-CPE), has been developed, providing a high purity sc-SWCNT material with a significant improvement in process efficiency and yield. Using the h-CPE protocol, a greater than 5 fold improvement in yield can be obtained compared to traditional CPE while obtaining sc-SWCNT with a purity >99.9% as assessed by absorption spectroscopy and Raman mapping. Thin film transistor devices using the h-CPE derived sc-SWCNTs as the semiconductor possess mobility values ranging from 10-30 cm2 V-1 s-1 and current ON/OFF ratio of 104-105 for channel lengths between 2.5 and 20 μm. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr04851f

  10. Enantioselective stable isotope analysis (ESIA) of polar Herbicides

    Science.gov (United States)

    Maier, Michael; Qiu, Shiran; Elsner, Martin

    2013-04-01

    The complexity of aquatic systems makes it challenging to assess the environmental fate of chiral micropolutants. As an example, chiral herbicides are frequently detected in the environment (Buser and Muller, 1998); however, hydrological data is needed to determine their degradability from concentration measurements. Otherwise declining concentrations cannot unequivocally be attributed to degradation, but could also be caused by dilution effects. In contrast, isotope ratios or enantiomeric ratios are elegant alternatives that are independent of dilution and can even deliver insights into reaction mechanisms. To combine the advantages of both approaches we developed an enatioselective stable isotope analysis (ESIA) method to investigate the fate of the chiral herbicides 4-CPP ((RS)-2-(4-chlorophenoxy)-propionic acid), mecoprop (2-(4-Chloro-2-methylphenoxy)-propionic acid) and dichlorprop (2-(2,4-Dichlorophenoxy)-propionic acid). After testing the applicable concentration range of the method, enantioselective isotope fractionation was investigated by microbial degradation using dichlorprop as a model compound. The method uses enantioselective gas-chromatography (GC) to separate enantiomers. Subsequently samples are combusted online to CO2 and carbon isotope ratios are determined for each enantiomer by isotope-ratio-mass-spectrometry (IRMS). Because the analytes contain a polar carboxyl-group, samples were derivatised prior to GC-IRMS analysis with methanolic BF3 solution. Precise carbon isotope analysis (2σ ≤0.5‰) was achieved with a high sensitivity of ≥ 7 ng C that is needed on column for one analysis. Microbial degradation of the model compound dichlorprop was conducted with Delftia acidovorans MC1 and pronounced enantiomer fractionation, but no isotope fractionation was detected. The absence of isotope fractionation can be explained by two scenarios: either the degrading enzyme has no isotopic preference, or another step in the reaction without an isotopic

  11. Flexible Enantioselectivity of Tryptophanase Attributable to Benzene Ring in Heterocyclic Moiety of D-Tryptophan

    OpenAIRE

    Akihiko Shimada; Haruka Ozaki

    2012-01-01

    The invariance principle of enzyme enantioselectivity must be absolute because it is absolutely essential to the homochiral biological world. Most enzymes are strictly enantioselective, and tryptophanase is one of the enzymes with extreme absolute enantioselectivity for L-tryptophan. Contrary to conventional knowledge about the principle, tryptophanase becomes flexible to catalyze D-tryptophan in the presence of diammonium hydrogenphosphate. Since D-amino acids are ordinarily inert or functio...

  12. Enantioselective reduction of acetophenone analogues using carrot and celeriac enzymes system

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    The enantioselective reduction of acetophenone analogues catalyzed by carrot and celeriac was performed in moderate conversions and excellent enantiomeric excesses.The steric factors and electronic effects of the substituents at the aromatic ring were found to significantly affect the efficiency of the enantioselective reduction of acetophenone analogues,while they had a little effect on the enantioselectivity of acetophenone analogues reduction.It was also found that the conversions of acetophenone anal...

  13. Improved enantioselectivity of thermostable esterase from Archaeoglobus fulgidus toward (S)-ketoprofen ethyl ester by directed evolution and characterization of mutant esterases.

    Science.gov (United States)

    Kim, Jinyeong; Kim, Seungbum; Yoon, Sangyoung; Hong, Eunsoo; Ryu, Yeonwoo

    2015-08-01

    Thermostable esterases have potential applications in various biotechnology industries because of their resistance to high temperature and organic solvents. In a previous study, we isolated an esterase from Archaeoglobus fulgidus DSM 4304 (Est-AF), which showed high thermostability but low enantioselectivity toward (S)-ketoprofen ethyl ester. (R)-ketoprofenor (S)-ketoprofenis produced by esterase hydrolysis of the ester bond of (R,S)-ketoprofen ethyl ester and (S)-ketoprofen has better pharmaceutical activity and lower side effects than (R)-ketoprofen. Therefore, we have generated mutants of Est-AF that retained high thermostability whilst improving enantioselectivity. A library of Est-AF mutants was created by error-prone polymerase chain reaction, and mutants with improved enantioselectivity were isolated by site-saturation mutagenesis. The regions of Est-AF containing amino acid mutations were analyzed by homology modeling of its three-dimensional structure, and structure-based explanations for the changes in enantioselectivity are proposed. Finally, we isolated two mutants showing improved enantioselectivity over Est-AF (ee% = -16.2 ± 0.2 and E = 0.7 ± 0.0): V138G (ee% = 35.9 ± 1.0 and E = 3.0 ± 0.1) and V138G/L200R (ee% = 89.2 ± 0.2 and E = 19.5 ± 0.5). We also investigated various characteristics of these mutants and found that the mutants showed similar thermostability and resistance to additives or organic solvents to Est-AF, without a significant trade-off between activity and stability.

  14. Enantioselective analysis of citalopram and escitalopram in postmortem blood together with genotyping for CYP2D6 and CYP2C19.

    Science.gov (United States)

    Carlsson, Björn; Holmgren, Anita; Ahlner, Johan; Bengtsson, Finn

    2009-03-01

    Citalopram is marketed as a racemate (50:50) mixture of the S(+)-enantiomer and R(-)-enantiomer and the active S(+)-enantiomer (escitalopram) that possess inhibitory effects. Citalopram was introduced in Sweden in 1992 and is the most frequently used antidepressant to date in Sweden. In 2002, escitalopram was introduced onto the Swedish market for treatment of depression and anxiety disorders. The main objective of this study was to investigate S(+)-citalopram [i.e., the racemic drug (citalopram) or the enantiomer (escitalopram)] present in forensic autopsy cases positive for the presence of citalopram in routine screening using a non-enantioselective bioanalytical method. Fifty out of the 270 samples found positive by gas chromatography-nitrogen-phosphorus detection were further analyzed using enantioselective high-performance liquid chromatography. The 50 cases were genotyped for CYP2D6 and CYP2C19, as these isoenzymes are implicated in the metabolism of citalopram and escitalopram. In samples positive for racemic citalopram using the screening method for forensic autopsy cases, up to 20% would have been misinterpreted in the absence of an enantioselective method. An enantioselective method is thus necessary for correct interpretation of autopsy cases, after the enantiomer has been introduced onto the market. The percentage of poor metabolizers was 6% for CYP2D6 and 8% for CYP2C19.

  15. Poly(propylene carbonate): Insight into the Microstructure and Enantioselective Ring-Opening Mechanism

    KAUST Repository

    Salmeia, Khalifah A.

    2012-11-13

    Different poly(propylene carbonate) (PPC) microstructures have been synthesized from the alternating copolymerization of CO 2 with both racemic propylene oxide (PO) and various mixtures of PO enantiomers using chiral salen catalysts. The microstructures of the obtained copolymers as a function of polymerization time have been analyzed by a combination of chiral GC and high-resolution NMR spectroscopy. The 13C NMR spectra of selected poly(propylene carbonate) samples were recorded using a 900 MHz ( 1H) spectrometer, showing a previously unreported fine splitting of the carbonate resonances. This allowed a detailed assignment of signals for various copolymer microstructures taking into account the specifics in their stereo- and regioirregularities. For example, the enantioselectivity preference of the (R,R-salen)Co catalyst for (S)-PO at the beginning of the copolymerization leads predominantly to (S)-PO insertion, with any (R)-PO misinsertion being followed by incorporation of (S)-PO, so that the microstructure features isolated stereoerrors. K rel calculations for the copolymerization showed around 5-fold enantioselectivity for (S)-PO over (R)-PO at short reaction time. Analysis of the copolymer microstructures obtained under various reaction conditions appears to be an additional approach to differentiate the occurrence of bimetallic and bifunctional copolymerization mechanisms that are widely discussed in the literature. © 2012 American Chemical Society.

  16. Enantioselective bioaccumulation and toxic effects of metalaxyl in earthworm Eisenia foetida.

    Science.gov (United States)

    Xu, Peng; Diao, Jinling; Liu, Donghui; Zhou, Zhiqiang

    2011-05-01

    Knowledge about the enantioselective bioavailability of chiral pesticides in soil invertebrates facilitates more accurate interpretation of their environmental behaviors. In this study, the acute toxicities of R-metalaxyl and rac-metalaxyl to earthworm (Eisenia foetida) were assayed by filter paper contact test. After 48 h of exposure, the calculated LC(50) values for R- and rac-metalaxyl were 0.052 and 0.022 mg cm(-2), respectively, resulting in a two fold difference in toxicity. For uptake experiment, earthworms were exposed in soil at two dose levels (10 and 50 mg kg(dwt)(-1)). The concentrations of two enantiomers in soil and earthworm were determined by high-performance liquid chromatography based on cellulose tri-(3,5-dimethylphenyl-carbamate) chiral stationary phase. The results showed that metalaxyl was taken up by earthworm rapidly, and the bioaccumulation of metalaxyl in earthworm was enantioselective with preferential accumulation of S-enantiomer. In addition, biota to soil accumulation factor (BSAF) used to express the bioaccumulation of metalaxyl enantiomers was investigated, and significant difference was observed between rac-metalaxyl and R-metalaxyl. Copyright © 2011 Elsevier Ltd. All rights reserved.

  17. Effect of formulation and repeated applications on the enantioselectivity of metalaxyl dissipation and leaching in soil.

    Science.gov (United States)

    Celis, Rafael; Gámiz, Beatriz; Adelino, María A; Cornejo, Juan; Hermosín, María C

    2015-11-01

    Soil incubation and column leaching experiments were conducted to address the question of whether the type of formulation (unsupported versus clay supported) and repeated applications of the chiral fungicide (RS)-metalaxyl affected the enantioselectivity of its dissipation and leaching in a slightly alkaline, loamy sand agricultural soil. Regardless of the type of formulation and the number of fungicide applications, the R-enantiomer of metalaxyl was degraded faster than the S-enantiomer, but the individual degradation rates of R- and S-metalaxyl were highly affected by the different application regimes assayed (t1/2 = 2-104 days). Repeated applications accelerated the degradation of the biologically active R-metalaxyl enantiomer, whereas they led to slower degradation of the non-active S-metalaxyl enantiomer. The type of formulation had less influence on the dissipation rates of the enantiomers. For all formulations tested, soil column leachates became increasingly enriched in S-enantiomer as the number of fungicide applications was increased, and application of metalaxyl to soil columns as clay-based formulations reduced the leaching of both enantiomers. Pesticide application conditions can greatly influence the enantioselective dissipation of chiral pesticides in soil, and hence are expected to exert a great impact on both the biological efficacy and the environmental chiral signatures of pesticides applied as mixtures of enantiomers or racemates to agricultural soils. © 2014 Society of Chemical Industry.

  18. Comparison of liquid and supercritical fluid chromatography mobile phases for enantioselective separations on polysaccharide stationary phases.

    Science.gov (United States)

    Khater, Syame; Lozac'h, Marie-Anne; Adam, Isabelle; Francotte, Eric; West, Caroline

    2016-10-07

    Analysis and production of enantiomerically pure compounds is a major topic of interest when active pharmaceutical ingredients are concerned. Enantioselective chromatography has become a favourite both at the analytical and preparative scales. High-performance liquid chromatography (HPLC) and supercritical fluid chromatography (SFC) are dominating the scene and are often seen as complementary techniques. Nowadays, for economic and ecologic reasons, SFC may be preferred over normal-phase HPLC (NPLC) as it allows significant reductions in solvent consumption. However, the transfer of NPLC methods to SFC is not always straightforward. In this study, we compare the retention of achiral molecules and separation of enantiomers under supercritical fluid (carbon dioxide with ethanol or isopropanol) and liquid normal-phase (heptane with ethanol or isopropanol) elution modes with polysaccharide stationary phases in order to explore the differences between the retention and enantioseparation properties between the two modes. Chemometric methods (namely quantitative structure-retention relationships and discriminant analysis) are employed to compare the results obtained on a large set of analytes (171 achiral probes and 97 racemates) and gain some understanding on the retention and separation mechanisms. The results indicate that, contrary to popular belief, carbon dioxide - solvent SFC mobile phases are often weaker eluents than liquid mobile phases. It appears that SFC and NPLC elution modes provide different retention mechanisms. While some enantioseparations are unaffected, facilitating the transfer between the two elution modes, other enantioseparations may be drastically different due to different types and strength of interactions contributing to enantioselectivity.

  19. In silico description of differential enantioselectivity in methoxychlor O-demethylation by CYP2C enzymes.

    Science.gov (United States)

    Bikádi, Zsolt; Hazai, Eszter

    2008-09-01

    Methoxychlor undergoes metabolism by cytochrome P450 (CYP) enzymes forming a chiral mono-phenolic derivative (Mono-OH-M) as main metabolite. In the current study, members of the CYP2C family were examined for their chiral preference in Mono-OH-M formation. CYP2C9 and CYP2C19 possessed high enantioselectivity favoring the formation of S-Mono-OH-M; CYP2C3 showed no enantioselectivity, whereas CYP2C5 slightly favored the formation of R-Mono-OH-M. Molecular modeling calculations were utilized in order to explain the observed differences in chiral preference of CYP2C enzymes. Molecular docking calculations could describe neither the existence of chiral preference in metabolism, nor the enantiomer which is preferentially formed. Molecular dynamic calculations were also carried out and were found to be useful for accurate description of chiral preference in biotransformation of methoxychlor by CYP2C enzymes. An in silico model capable of predicting chiral preference in cytochrome P450 enzymes in general can be developed based on the analysis of the stability and rigidity parameters of interacting partners during molecular dynamic simulation.

  20. Enantioselective Dissipation of Acephate and Its Metabolite, Methamidophos, during Tea Cultivation, Manufacturing, and Infusion.

    Science.gov (United States)

    Pan, Rong; Chen, Hongping; Wang, Chen; Wang, Qinghua; Jiang, Ying; Liu, Xin

    2015-01-26

    The enantioselective dissipation of acephate and its metabolite, methamidophos, was investigated during tea cultivation, manufacturing, and infusion, using QuEChERS sample preparation technique and gas chromatography coupled with a BGB-176 chiral column. Results showed that (+)-acephate and (-)-acephate dissipated following first-order kinetics in fresh tea leaves with half-lives of 1.8 and 1.9 days, respectively. Acephate was degraded into a more toxic metabolite, methamidophos. Preferential dissipation and translocation of (+)-acephate may exist in tea shoots, and (-)-methamidophos was degraded more rapidly than (+)-methamidophos. During tea manufacturing, drying and spreading (or withering) played important roles in the dissipation of acephate enantiomers. The enantiometic fractions of acephate changed from 0.495-0.496 to 0.479-0.486 (P ≤ 0.0081), whereas those of methamidophos changed from 0.576-0.630 to 0.568-0.645 (P ≤ 0.0366 except for green tea manufacturing on day 1), from fresh tea leaves to made tea. In addition, high transfer rates (>80%) and significant enantioselectivity (P ≤ 0.0042) of both acephate and its metabolite occurred during tea brewing.

  1. Application of exogenous mixture of glutathione and stable isotope labeled glutathione for trapping reactive metabolites in cryopreserved human hepatocytes. Detection of the glutathione conjugates using high resolution accurate mass spectrometry.

    Science.gov (United States)

    Mezine, Igor; Bode, Chris; Raughley, Bethany; Bhoopathy, Sid; Roberts, Kenneth J; Owen, Albert J; Hidalgo, Ismael J

    2013-08-25

    Metabolites (including reactive metabolites) of troglitazone were generated by incubation with cryopreserved human hepatocytes and trapped in the presence of an exogenous mixture of unlabeled and stable isotope labeled (SIL: [1,2-(13)C, (15)N]-glycine) glutathione (GSH/SIL-GSH). The incubation samples were analyzed using liquid chromatography-high resolution accurate mass spectrometry (LC-HRAMS) implemented on a LTQ Orbitrap mass spectrometer. The GSH conjugates of the reactive metabolites were detected via a characteristic mono-isotopic pattern (peaks separated by 3.0037u). Analysis of the incubation samples led to detection of a number of previously described GSH conjugates, as well as two novel methylated GSH conjugates, which were partially characterized based on accurate mass measurements and MS/MS data. The addition of exogenous GSH led to an increase in the apparent level of detected GSH conjugates. Kinetic isotopic measurements showed that the rates of incorporation of exogenous GSH are conjugate-specific. In conclusion, this approach, based on the use of a mixture of GSH/SIL-GSH, allows facile capture and detection of reactive metabolites in human hepatocytes. Moreover, the data suggest that routine addition of glutathione to the assay medium may be advisable for experiments with cryopreserved hepatocytes. Copyright © 2013 Elsevier Ireland Ltd. All rights reserved.

  2. Bright conjugated polymer nanoparticles containing a biodegradable shell produced at high yields and with tuneable optical properties by a scalable microfluidic device.

    Science.gov (United States)

    Abelha, T F; Phillips, T W; Bannock, J H; Nightingale, A M; Dreiss, C A; Kemal, E; Urbano, L; deMello, J C; Green, M; Dailey, L A

    2017-02-02

    This study compares the performance of a microfluidic technique and a conventional bulk method to manufacture conjugated polymer nanoparticles (CPNs) embedded within a biodegradable poly(ethylene glycol) methyl ether-block-poly(lactide-co-glycolide) (PEG5K-PLGA55K) matrix. The influence of PEG5K-PLGA55K and conjugated polymers cyano-substituted poly(p-phenylene vinylene) (CN-PPV) and poly(9,9-dioctylfluorene-2,1,3-benzothiadiazole) (F8BT) on the physicochemical properties of the CPNs was also evaluated. Both techniques enabled CPN production with high end product yields (∼70-95%). However, while the bulk technique (solvent displacement) under optimal conditions generated small nanoparticles (∼70-100 nm) with similar optical properties (quantum yields ∼35%), the microfluidic approach produced larger CPNs (140-260 nm) with significantly superior quantum yields (49-55%) and tailored emission spectra. CPNs containing CN-PPV showed smaller size distributions and tuneable emission spectra compared to F8BT systems prepared under the same conditions. The presence of PEG5K-PLGA55K did not affect the size or optical properties of the CPNs and provided a neutral net electric charge as is often required for biomedical applications. The microfluidics flow-based device was successfully used for the continuous preparation of CPNs over a 24 hour period. On the basis of the results presented here, it can be concluded that the microfluidic device used in this study can be used to optimize the production of bright CPNs with tailored properties with good reproducibility.

  3. Evaluation of iodovinyl antibody conjugates: Comparison with a p-iodobenzoyl conjugate and direct radioiodination

    Energy Technology Data Exchange (ETDEWEB)

    Hadley, S.W.; Wilbur, D.S. (NeoRx Corporation, Seattle, WA (USA))

    1990-03-01

    The preparations and conjugations of 2,3,5,6-tetrafluorophenyl 5-(125I/131I)iodo-4-pentenoate (7a) and 2,3,5,6-tetrafluorophenyl 3,3-dimethyl-5-(125I/131I)iodo-4-pentenoate (7b) to monoclonal antibodies are reported. Reagents 7a and 7b were prepared in high radiochemical yield by iododestannylation of their corresponding 5-tri-n-butylstannyl precursors. Radioiodinated antibody conjugates were prepared by reaction of 7a or 7b with the protein at basic pH. Evaluation of these conjugates by several in vitro procedures demonstrated that the radiolabel was attached to the antibody in a stable manner and that the conjugates maintained immunoreactivity. Comparative dual-isotope biodistribution studies of a monoclonal antibody Fab fragment conjugate of 7a and 7b with the same Fab fragment labeled with N-succinimidyl p-(131I)iodobenzoate (PIB, p-iodobenzoate, 2) or directly radioiodinated have been carried out in tumor-bearing nude mice. Coinjection of the Fab conjugate of 7a with the Fab conjugate of 2 demonstrated that the biodistributions were similar in most organs, except the neck tissue (thyroid-containing) and the stomach, which contained substantially increased levels of the 7a label. Coinjection of the Fab conjugate of 7a with the Fab fragment radioiodinated by using the chloramine-T method demonstrated that the biodistributions were remarkably similar, suggesting roughly equivalent in vivo deiodination of these labeled antibody fragments. Coinjection of the Fab conjugate of 7a with the Fab conjugate of 7b indicated that there was {approximately} a 2-fold reduction in the amount of in vivo deiodination of the 7b conjugate as compared to the 7a conjugate.

  4. Copper-catalyzed asymmetric conjugate addition of organometallic reagents to extended Michael acceptors

    Directory of Open Access Journals (Sweden)

    Thibault E. Schmid

    2015-12-01

    Full Text Available The copper-catalyzed asymmetric conjugate addition (ACA of nucleophiles onto polyenic Michael acceptors represents an attractive and powerful methodology for the synthesis of relevant chiral molecules, as it enables in a straightforward manner the sequential generation of two or more stereogenic centers. In the last decade, various chiral copper-based catalysts were evaluated in combination with different nucleophiles and Michael acceptors, and have unambiguously demonstrated their usefulness in the control of the regio- and enantioselectivity of the addition. The aim of this review is to report recent breakthroughs achieved in this challenging field.

  5. In vitro and in vivo evaluation of Alexa Fluor 680-bombesin[7-14]NH2 peptide conjugate, a high-affinity fluorescent probe with high selectivity for the gastrin-releasing peptide receptor.

    Science.gov (United States)

    Ma, Lixin; Yu, Ping; Veerendra, Bhadrasetty; Rold, Tammy L; Retzloff, Lauren; Prasanphanich, Adam; Sieckman, Gary; Hoffman, Timothy J; Volkert, Wynn A; Smith, Charles J

    2007-01-01

    Gastrin-releasing peptide (GRP) receptors are overexpressed on several types of human cancer cells, including breast, prostate, small cell lung, and pancreatic cancers. Bombesin (BBN), a 14-amino acid peptide that is an analogue of human GRP, binds to GRP receptors with very high affinity and specificity. The aim of this study was to develop a new fluorescent probe based on BBN having high tumor uptake and optimal pharmacokinetics for specific targeting and optical imaging of human breast cancer tissue. In this study, solid-phase peptide synthesis was used to produce H(2)N-glycylglycylglycine-BBN[7-14]NH(2) peptide with the following general sequence: H(2)N-G-G-G-Q-W-A-V-G-H-L-M-(NH(2)). This conjugate was purified by reversed-phase high-performance liquid chromatography and characterized by electrospray-ionization mass spectra. The fluorescent probe Alexa Fluor 680-G-G-G-BBN[7-14]NH(2) conjugate was prepared by reaction of Alexa Fluor 680 succinimidyl ester to H(2)N-G-G-G-BBN[7-14]NH(2) in dimethylformamide (DMF). In vitro competitive binding assays, using (125)I-Tyr(4)-BBN as the radiolabeling gold standard, demonstrated an inhibitory concentration 50% value of 7.7 +/- 1.4 nM in human T-47D breast cancer cells. Confocal fluorescence microscopy images of Alexa Fluor 680-G-G-G-BBN[7-14]NH(2) in human T-47D breast cancer cells indicated specific uptake, internalization, and receptor blocking of the fluorescent bioprobe in vitro. In vivo investigations in SCID mice bearing xenografted T-47D breast cancer lesions demonstrated the ability of this new conjugate to specifically target tumor tissue with high selectivity and affinity.

  6. In Vitro and In Vivo Evaluation of Alexa Fluor 680-Bombesin[7–14]NH2 Peptide Conjugate, a High-Affinity Fluorescent Probe with High Selectivity for the Gastrin-Releasing Peptide Receptor

    Directory of Open Access Journals (Sweden)

    Lixin Ma

    2007-05-01

    Full Text Available Gastrin-releasing peptide (GRP receptors are overexpressed on several types of human cancer cells, including breast, prostate, small cell lung, and pancreatic cancers. Bombesin (BBN, a 14–amino acid peptide that is an analogue of human GRP, binds to GRP receptors with very high affinity and specificity. The aim of this study was to develop a new fluorescent probe based on BBN having high tumor uptake and optimal pharmacokinetics for specific targeting and optical imaging of human breast cancer tissue. In this study, solid-phase peptide synthesis was used to produce H2N-glycylglycylglycine-BBN[7–14]NH2 peptide with the following general sequence: H2N-G-G-G-Q-W-A-V-G-H-L-M-(NH2. This conjugate was purified by reversed-phase high-performance liquid chromatography and characterized by electrospray-ionization mass spectra. The fluorescent probe Alexa Fluor 680-G-G-G-BBN[7–14]NH2 conjugate was prepared by reaction of Alexa Fluor 680 succinimidyl ester to H2N-G-G-G-BBN[7–14]NH2 in dimethylformamide (DMF. In vitro competitive binding assays, using 125I-Tyr4-BBN as the radiolabeling gold standard, demonstrated an inhibitory concentration 50% value of 7.7 ± 1.4 nM in human T-47D breast cancer cells. Confocal fluorescence microscopy images of Alexa Fluor 680-G-G-G-BBN[7–14]NH2 in human T-47D breast cancer cells indicated specific uptake, internalization, and receptor blocking of the fluorescent bioprobe in vitro. In vivo investigations in SCID mice bearing xenografted T-47D breast cancer lesions demonstrated the ability of this new conjugate to specifically target tumor tissue with high selectivity and affinity.

  7. Enantioselective extraction of terbutaline enantiomers by lipophilic tartaric acid

    Institute of Scientific and Technical Information of China (English)

    唐课文; 周春山

    2003-01-01

    Distribution behavior of terbutaline enantiomers was examined in the aqueous and organic solvent of a two-phase system containing L-dibenzoyltartaric acid and lipophilic phase transfer reagent of Na-tetraphenylborate. The influences of pH, organic solvents, concentrations of Na-tetraphenylborate and L-dibenzoyltartaric acid on the partition coefficients and enantioselectivity of terbutaline enantiomers, were investigated. The results show that tetraphenylborate lipophilic anion and terbutaline enantiomers form two lipophilic salt complexes , which facilitates the solubility of the enantiomers in the organic phase. L-dibenzoyltartaric acid forms more stable complexes with enantiomer Ⅱ than with enantiomer I . Enantioselectivity and partition coefficient increase with the addition of the length of alkyl chain of alcohols. pH and concentrations of lipophilic anion and L-dibenzoyltartaric acid influence them obviously and differently.

  8. The enantioselective b-keto ester reductions by Saccharomyces cerevisiae

    Directory of Open Access Journals (Sweden)

    HASSAN TAJIK

    2006-09-01

    Full Text Available The enantioselective yeast reduction of aromatic b-keto esters, by use of potassium dihydrogen phosphate, calcium phosphate (monobasic, magnesium sulfate and ammonium tartrate (diammonium salt (10:1:1:50 in water at pH 7 as a buffer for 72–120 h with 45–90 % conversion to the corresponding aromatic -hydroxy esters was achieved by means of Saccharomyces cerevisiae.

  9. Cyclodextrin Derivatives as Chiral Supramolecular Receptors for Enantioselective Sensing

    Directory of Open Access Journals (Sweden)

    Uwe Pieles

    2006-06-01

    Full Text Available In view of the chiral nature of many bio-molecules (and all bio-macromolecules,most of therapeutically active compounds which target these molecules need to be chiraland “good handed” to be effective. In addition to asymmetric synthetic and separationmethodologies, enantioselective chemical sensors, able to distinguish between twoenantiomers of the same molecule, are of relevance. In order to design these sensing tools,two major classes of enantioselective layers have been developed. The first is based onmolecularly imprinted polymers which are produced (polymerized in the presence of theirtarget, thus the polymeric material keep in “memory” the size and the shape of this moleculeand the system could be used for sensing (not reviewed here. The second approach makesuse of sensitive layers containing chiral macrocyclic receptors able of stereoselectivemolecular recognition; these receptors are mainly based on cyclodextrins. In thiscontribution, are reviewed achievements in the use of native or chemically modifiedcyclodextrins for chiral sensing purposes (at interfaces. Potentialities of other chiralmacrocycles based on calixarenes, calix-resorcinarenes or crown-ethers as supramolecularreceptors for enantioselective sensing are discussed.

  10. Visualization of phase conjugate ultrasound waves passed through inhomogeneous layer.

    Science.gov (United States)

    Yamamoto, K; Pernod, P; Preobrazhensky, V

    2004-04-01

    Compensation of phase distortions of ultrasound beams by means of parametric phase conjugation is visualized. Quasi-plane and focused primary beams were distorted by a polymer aberration layer introduced between the primary wave source and the wave phase conjugator. It is demonstrated acousto-optically that, while the acoustic field is strongly irregular in the area between aberration layer and conjugator, the phase conjugate wave visibly reproduces the primary beams in the area between the layer and the primary wave source. The phenomenon is observed in supercritical mode of parametric amplification when intensity of phase conjugate wave is high enough for manifestations of acoustic nonlinearities in water.

  11. Highly Efficient Electrocatalysts for Oxygen Reduction Reaction Based on 1D Ternary Doped Porous Carbons Derived from Carbon Nanotube Directed Conjugated Microporous Polymers

    KAUST Repository

    He, Yafei

    2016-10-11

    © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.One-dimensional (1D) porous materials have shown great potential for gas storage and separation, sensing, energy storage, and conversion. However, the controlled approach for preparation of 1D porous materials, especially porous organic materials, still remains a great challenge due to the poor dispersibility and solution processability of the porous materials. Here, carbon nanotube (CNT) templated 1D conjugated microporous polymers (CMPs) are prepared using a layer-by-layer method. As-prepared CMPs possess high specific surface areas of up to 623 m2 g-1 and exhibit strong electronic interactions between p-type CMPs and n-type CNTs. The CMPs are used as precursors to produce heteroatom-doped 1D porous carbons through direct pyrolysis. As-produced ternary heteroatom-doped (B/N/S) 1D porous carbons possess high specific surface areas of up to 750 m2 g-1, hierarchical porous structures, and excellent electrochemical-catalytic performance for oxygen reduction reaction. Both of the diffusion-limited current density (4.4 mA cm-2) and electron transfer number (n = 3.8) for three-layered 1D porous carbons are superior to those for random 1D porous carbon. These results demonstrate that layered and core-shell type 1D CMPs and related heteroatom-doped 1D porous carbons can be rationally designed and controlled prepared for high performance energy-related applications.

  12. Enantioselective silver nanoclusters: Preparation, characterization and photoluminescence spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Farrag, Mostafa, E-mail: mostafafarrag@aun.edu.eg

    2016-09-01

    prepared silver nanoclusters were investigated using nitrogen adsorption-desorption at −196 °C. Specific surface area S{sub BET}, pore volume and average pore diameter were calculated. - Highlights: • New wet chemistry method to prepare mirror image small silver clusters protected by penicillamine. • Preparation enantioselective catalysts by easy wet chemistry method. • The synthesized silver clusters have photoluminescence properties. • The synthesized silver clusters show high Anisotropy factors up to 3 × 10{sup −4}. • The adsorption isotherms of all synthesized clusters are mainly of type II of Brunaue’s classification.

  13. Segmented conjugated polymers

    Indian Academy of Sciences (India)

    G Padmanaban; S Ramakrishnan

    2003-08-01

    Segmented conjugated polymers, wherein the conjugation is randomly truncated by varying lengths of non-conjugated segments, form an interesting class of polymers as they not only represent systems of varying stiffness, but also ones where the backbone can be construed as being made up of chromophores of varying excitation energies. The latter feature, especially when the chromophores are fluorescent, like in MEHPPV, makes these systems particularly interesting from the photophysics point of view. Segmented MEHPPV- samples, where x represents the mole fraction of conjugated segments, were prepared by a novel approach that utilizes a suitable precursor wherein selective elimination of one of the two eliminatable groups is affected; the uneliminated units serve as conjugation truncations. Control of the composition x of the precursor therefore permits one to prepare segmented MEHPPV- samples with varying levels of conjugation (elimination). Using fluorescence spectroscopy, we have seen that even in single isolated polymer chains, energy migration from the shorter (higher energy) chromophores to longer (lower energy) ones occurs – the extent of which depends on the level of conjugation. Further, by varying the solvent composition, it is seen that the extent of energy transfer and the formation of poorly emissive inter-chromophore excitons are greatly enhanced with increasing amounts of non-solvent. A typical S-shaped curve represents the variation of emission yields as a function of composition suggestive of a cooperative collapse of the polymer coil, reminiscent of conformational transitions seen in biological macromolecules.

  14. High-level fluoroquinolone resistant Salmonella enterica serovar Kentucky ST198 epidemic clone with IncA/C conjugative plasmid carrying bla(CTX-M-25) gene.

    Science.gov (United States)

    Wasyl, Dariusz; Kern-Zdanowicz, Izabela; Domańska-Blicharz, Katarzyna; Zając, Magdalena; Hoszowski, Andrzej

    2015-01-30

    Multidrug resistant Salmonella Kentucky strains have been isolated from turkeys in Poland since 2009. Multiple mutations within chromosomal genes gyrA and parC were responsible for high-level ciprofloxacin resistance. One of the isolates was extended spectrum β-lactamase- (ESBL) positive: the strain 1643/2010 carried a conjugative 167,779 bps plasmid of IncA/C family. The sequence analysis revealed that it carried a blaCTX-M-25 gene and an integron with another β-lactamase encoding gene-blaOXA-21. This is the first known report of a CTX-M-25 encoding gene both in Poland and in Salmonella Kentucky world-wide, as well as in the IncA/C plasmid. Analysis of the integron showed a novel arrangement of gene cassettes-aacA4, aacC-A1 and blaOXA-21 where the latter might result from an intergeneric gene transfer. The study confirmed Salmonella Kentucky population isolated in Poland belongs to global epidemics of high level fluoroquinolone resistant clone ST198 that can carry rare β-lactamase genes. Copyright © 2014 Elsevier B.V. All rights reserved.

  15. Highly Efficient p-i-n Perovskite Solar Cells Utilizing Novel Low-Temperature Solution-Processed Hole Transport Materials with Linear π-Conjugated Structure.

    Science.gov (United States)

    Li, Yang; Xu, Zheng; Zhao, Suling; Qiao, Bo; Huang, Di; Zhao, Ling; Zhao, Jiao; Wang, Peng; Zhu, Youqin; Li, Xianggao; Liu, Xicheng; Xu, Xurong

    2016-09-01

    Alternative low-temperature solution-processed hole-transporting materials (HTMs) without dopant are critical for highly efficient perovskite solar cells (PSCs). Here, two novel small molecule HTMs with linear π-conjugated structure, 4,4'-bis(4-(di-p-toyl)aminostyryl)biphenyl (TPASBP) and 1,4'-bis(4-(di-p-toyl)aminostyryl)benzene (TPASB), are applied as hole-transporting layer (HTL) by low-temperature (sub-100 °C) solution-processed method in p-i-n PSCs. Compared with standard poly(3,4-ethylenedioxythiophene): poly(styrenesulfonic acid) (PEDOT:PSS) HTL, both TPASBP and TPASB HTLs can promote the growth of perovskite (CH3 NH3 PbI3 ) film consisting of large grains and less grain boundaries. Furthermore, the hole extraction at HTL/CH3 NH3 PbI3 interface and the hole transport in HTL are also more efficient under the conditions of using TPASBP or TPASB as HTL. Hence, the photovoltaic performance of the PSCs is dramatically enhanced, leading to the high efficiencies of 17.4% and 17.6% for the PSCs using TPASBP and TPASB as HTL, respectively, which are ≈40% higher than that of the standard PSC using PEDOT:PSS HTL.

  16. Catalytic Enantioselective Alkylation of Benzaldehyde with Diethylzinc Using Chiral Nonracemic (Thio)-phosphoramidates

    NARCIS (Netherlands)

    Hulst, Ron; Heres, Hero; Fitzpatrick, Kevin; Peper, Nathalie C.M.W.; Kellogg, Richard M.

    1996-01-01

    Two chiral nonracemic γ-amino alcohols, ephedrine thiol and the corresponding (thio)-phosphoramidates have been examined as catalysts for the enantioselective alkylation of benzaldehyde by diethylzinc. Addition of titanium tetraisopropoxide increases the yield as well as the enantioselectivity; 1-ph

  17. Enantioselective Addition of Organolithium Reagents to Imines Mediated by C2-Symmetric Bis(aziridine) Ligands

    DEFF Research Database (Denmark)

    Johansson, F.; Tanner, David Ackland

    1998-01-01

    The C-2-symmetric bis(aziridine) ligands 1 - 5 have been screened in the enantioselective addition of organolithium reagents to imines. Ligand 1 (used in stoichiometric amounts) was found to be superior in terms of chemical yield and enantioselectivity, the best result being 90% yield and 89% e.e...

  18. Catalytic Enantioselective Alkylation of Benzaldehyde with Diethylzinc Using Chiral Nonracemic (Thio)-phosphoramidates

    NARCIS (Netherlands)

    Hulst, Ron; Heres, Hero; Fitzpatrick, Kevin; Peper, Nathalie C.M.W.; Kellogg, Richard M.

    1996-01-01

    Two chiral nonracemic γ-amino alcohols, ephedrine thiol and the corresponding (thio)-phosphoramidates have been examined as catalysts for the enantioselective alkylation of benzaldehyde by diethylzinc. Addition of titanium tetraisopropoxide increases the yield as well as the enantioselectivity; 1-ph

  19. A solid-supported organocatalyst for continuous-flow enantioselective aldol reactions.

    Science.gov (United States)

    Ayats, Carles; Henseler, Andrea H; Pericàs, Miquel A

    2012-02-13

    Asymmetric aldol reactions catalyzed by a novel polystyrene-immobilized proline derivative occur in short reaction times with excellent diastereo- and enantioselectivity. The catalyst can be recovered by simple filtration and shows very high reusability. The high activity depicted by the supported catalyst and its chemical and mechanical stability have allowed its application in packed-bed reactors for continuous flow processing. This system can produce enantio- and diastereomerically pure aldol adducts under continuous flow conditions with a residence time of 26 min. Furthermore, the reactor allowed processing of four different aldol products in sequence without any decrease in both catalytic activity and optical purity. The effective catalyst loading could be reduced to 1.6% (six-fold reduction of catalyst loading compared to the corresponding batch process).

  20. Effect of conjugated linoleic acid (CLA) on lipid profile and liver histology in laboratory rats fed high-fructose diet.

    Science.gov (United States)

    Kostogrys, Renata B; Pisulewski, Paweł M

    2010-11-01

    The objective of the study was to assess the effect of CLA on serum lipid profile, plasma malondialdehyde and liver histology in Wistar rats fed high-fructose diet. Eighteen rats were randomly assigned to three experimental groups and fed for the next 21 days. The experimental diets were: I, Control; II, Fructose (63.2% of fructose); and III, CLA+Fructose (1% CLA and 63.2% of fructose). The experimental treatments had no effect on body weight of the rats. The LDL+VLDL cholesterol, TG and liver weight were significantly increased in animals fed Fructose. MDA concentrations were significantly increased in rats fed Fructose diet but CLA+Fructose diet had no effect on this marker. In the same line, the histological examination of the livers showed a series of morphological alterations, notably hepatic steatosis in animals fed high-fructose diet. No signs of the steatosis in rats fed CLA+Fructose diet were observed. In conclusion, CLA in high-fructose diet, decreases serum LDL+VLDL and TG and plasma MDA concentrations as well as liver weight and liver cholesterol, thus opposing the effects of high-fructose diet and showing a potential antiatherogenic effect. Similarly, dietary CLA fed at 1% level (w/w) in high-fructose diet, prevented steatosis observed histologically in livers of rats fed high-fructose diets.

  1. Energetic tuning in spirocyclic conjugated polymers

    OpenAIRE

    Hugo Bronstein; Frank D. King

    2016-01-01

    Precise control of the energy levels in a conjugated polymer is the key to allowing their exploitation in optoelectronic devices. The introduction of spirocycles into conjugated polymers has traditionally been used to enhance their solid state microstructure. Here we present a highly novel method of energetic tuning through the use of electronically active spirocyclic systems. By modifying the size and oxidation state of a heteroatom in an orthogonal spirocycle we demonstrate energetic fine t...

  2. Enantioselective esterification of (R,S)-2-methylalkanoic acid with Carica papaya lipase in organic solvents.

    Science.gov (United States)

    Chang, Chun-Sheng; Ho, Ssu-Ching

    2011-11-01

    Isooctane was the best reaction medium for the enantioselective esterification of (R,S)-2-methylalkanoic acid with n-butanol using Carica papaya lipase as catalyst. Increasing linear alkyl-chain length of racemic 2-methylalkanoic acids from ethyl to hexyl increased the enantioselectivity (E) from 2.1 to 98.2 for the esterification of racemic 2-methylalkanoic acids with n-butanol at 35°C. Decreasing reaction temperature from 40 to 20°C increased the enantioselectivity (E) from 14 to 33 for the esterification of racemic 2-methylhexanoic acids with n-butanol. We obtained a maximum enantioselectivity, of E = 24.3, for the enantioselective esterification of racemic 2-methylhexanoic acids with n-butanol in isooctane at water activity 0.33, and at 35°C.

  3. Origins of enantioselectivity in asymmetric ketone hydrogenation catalyzed by a RuH2(binap)(cydn) complex: insights from a computational study.

    Science.gov (United States)

    Feng, Ran; Xiao, Ang; Zhang, Xin; Tang, Yanhui; Lei, Ming

    2013-02-14

    In this paper, the origins of enantioselectivity in asymmetric ketone hydrogenation catalyzed by RuH(2)(binap)(cydn) (cydn = trans-1,2-diaminocyclohexane) were discussed. Fifteen substrates involving aromatic, heteroaromatic, olefinic and dialkyl prochiral ketones were used to probe the catalytic mechanism and find an effective way to predict the chirality of the products. The calculated results demonstrate that the hydrogen transfer (HT) step from the Ru complex to the ketone substrate is the chirality-determining step in the H(2)-hydrogenation of ketones. The hydrogenation of aromatic-alkyl ketones can give higher enantiomeric excess (ee) values than that of dialkyl ketones. An interesting intermediate (denoted as ) could be formed if there is an α-hydrogen for R/R' groups of the ketone due to the H(2)-H(α) interaction. Two substituent groups of the ketone could rotate around the C=O axis in two directions, clockwise or counter-clockwise. This rotation, with the big or conjugative substituent group away from/toward the closer binap ligand of the Ru catalyst, will form favorable/unfavorable chiral products with an Re-/Si- intermediate structure. On the contrary, if there is no such α-hydrogen in any substituent group of the ketone, ABS and another intermediate (denoted as INT) would not exist. This study indicates that the conjugative effect of the substituent groups of the ketone play an important role in differentiating the R/R' groups of the ketone, while steric and electrostatic effects contribute to a minor extent. Furthermore, the disparity of the R and R' groups of the ketone is of importance in the enantioselectivity and the favorable chiral alcohol is formed when the structure of the conjugative/big substituent group is away from the closer binap ligand of the RuH(2)(binap)(cydn) catalyst. According to the three factors of the substituent group and the fourth quadrant theory, the enantioselectivity of 91 prochiral ketones catalyzed by a series of Ru

  4. Qualidade conjugal: mapeando conceitos

    Directory of Open Access Journals (Sweden)

    Clarisse Mosmann

    2006-12-01

    Full Text Available Apesar da ampla utilização do conceito de qualidade conjugal, identifica-se falta de clareza conceitual acerca das variáveis que o compõem. Esse artigo apresenta revisão da literatura na área com o objetivo de mapear o conceito de qualidade conjugal. Foram analisadas sete principais teorias sobre o tema: Troca Social, Comportamental, Apego, Teoria da Crise, Interacionismo Simbólico. Pelos postulados propostos nas diferentes teorias, podem-se identificar três grupos de variáveis fundamentais na definição da qualidade conjugal: recursos pessoais dos cônjuges, contexto de inserção do casal e processos adaptativos. Neste sentido, a qualidade conjugal é resultado do processo dinâmico e interativo do casal, razão deste caráter multidimensional.

  5. Polymers for Protein Conjugation

    Directory of Open Access Journals (Sweden)

    Gianfranco Pasut

    2014-01-01

    Full Text Available Polyethylene glycol (PEG at the moment is considered the leading polymer for protein conjugation in view of its unique properties, as well as to its low toxicity in humans, qualities which have been confirmed by its extensive use in clinical practice. Other polymers that are safe, biodegradable and custom-designed have, nevertheless, also been investigated as potential candidates for protein conjugation. This review will focus on natural polymers and synthetic linear polymers that have been used for protein delivery and the results associated with their use. Genetic fusion approaches for the preparation of protein-polypeptide conjugates will be also reviewed and compared with the best known chemical conjugation ones.

  6. High-resolution spectroscopy of jet-cooled 1,1'-diphenylethylene: electronically excited and ionic states of a prototypical cross-conjugated system.

    Science.gov (United States)

    Smolarek, Szymon; Vdovin, Alexander; Rijs, Anouk; van Walree, Cornelis A; Zgierski, Marek Z; Buma, Wybren J

    2011-09-01

    The photophysics of a prototypical cross-conjugated π-system, 1,1'-diphenylethylene, have been studied using high-resolution resonance enhanced multiphoton ionization excitation spectroscopy and zero kinetic energy photoelectron spectroscopy, in combination with advanced ab initio calculations. We find that the excitation spectrum of S(1) displays extensive vibrational progressions that we identify to arise from large changes in the torsional angles of the phenyl rings upon electronic excitation. The extensive activity of the antisymmetric inter-ring torsional vibration provides conclusive evidence for a loss of symmetry upon excitation, leading to an inequivalence of the two phenyl rings. Nonresonant zero kinetic energy photoelectron spectroscopy from the ground state of the neutral molecule to the ground state of the radical cation, on the other hand, demonstrates that upon ionization symmetry is retained, and that the geometry changes are considerably smaller. Apart from elucidating how removal of an electron affects the structure of the molecule, these measurements provide an accurate value for the adiabatic ionization energy (65274 ± 1 cm(-1) (8.093 eV)). Zero kinetic energy photoelectron spectra obtained after excitation of vibronic levels in S(1) confirm these conclusions and provide us with an extensive atlas of ionic vibronic energy levels. For higher excitation energies the excitation spectrum of S(1) becomes quite congested and shows unexpected large intensities. Ab initio calculations strongly suggest that this is caused by a conical intersection between S(1) and S(2). © 2011 American Chemical Society

  7. D-π-A-π-A Strategy to Design Benzothiadiazole-carbazole-based Conjugated Polymer with High Solar Cell Voltage and Enhanced Photocurrent.

    Science.gov (United States)

    Zhou, Manxi; Wang, Min; Zhu, Lei; Yang, Zhenqing; Jiang, Chao; Cao, Dapeng; Li, Qifang

    2015-12-01

    The theoretical calculations are used to find that D-π-A-π-A style conjugated polymer PC-TBTBT is more efficient for solar cells application than the D-π-A analog PC-TBT because the D-π-A-π-A structure has a narrower band gap and higher molar absorption coefficient and redshift spectrum. Motivated by the theoretical prediction, 5,6-bis(octyloxy)-2,1,3-benzothiadiazole and 2,7-carbazole are adopted to synthesize the D-π-A-π-A style PC-TBTBT (M(w) = 31.1 kDa) and D-π-A analog PC-TBT (M(w) = 87.5 kDa) by Suzuki coupling reaction. Experimental results confirm that D-π-A-π-A PC-TBTBT-based solar cell shows a power conversion efficiency (PCE) of 4.74% with high V(OC) of 0.99 V and enhanced J(SC) of 9.70 mA cm(-2). The PCE and J(SC) achieve improvements of 17% and 26%, respectively, compared to the D-π-A PC-TBT-based solar cell.

  8. Graphene Oxide-terpyridine Conjugate: A Highly Selective Colorimetric and Sensitive Fluorescence Nano-chemosensor for Fe2+ in Aqueous Media

    Directory of Open Access Journals (Sweden)

    Bagher Eftekhari-Sis

    2016-07-01

    Full Text Available A graphene oxide-terpyridine conjugate (GOTC based colorimetric and fluorescent nano-chemosensor was synthesized. It showed high selectivity and sensitivity for Fe2+ and Fe3+ ions in neutral aqueous solution over other metal ions such as Li+, Na+, Ba2+, Ca2+, Al3+, Cd2+, Co2+, Cu2+, Hg2+, Mn2+, Ni2+, Pb2+, Zn2+, Cr3+ and Ag+. In absorption spectra, upon addition of Fe2+ or Fe3+, the sensor displayed a peak at 568 nm, by changing the color of the solution from light pink for GOTC to light magenta and deep magenta for Fe3+ and Fe2+, respectively. Also, the fluorescence studies revealed that, Fe2+, Fe3+ and Co2+ quench the emission of GOTC at 473 nm, while other metal ions do not quench the fluorescence of GOTC in solution. Colorimetric and fluorescence techniques could be used for detection of Fe2+ ion concentration at least about 6-10 μM in water solution. The sensing on test paper was also investigated for the naked-eye detection of Fe2+.

  9. Ir-Catalyzed Enantioselective Hydrogenation of 2H-1,4-Benzoxazines with a Chiral 1,2,3,4- Tetrahydro-l-naphthylamine Derived Phosphine-aminophosphine Ligand

    Institute of Scientific and Technical Information of China (English)

    胡娟; 王道永; 郑卓; 胡向平

    2012-01-01

    Unsymmetrical hybrid chiral phosphine-aminophosphine ligand derived from 1,2,3,4-tetrahydro-l-naphthyl- amine has been found to be highly efficient in the Ir-catalyzed asymmetric hydrogenation of various 3-aryl-2H-1,4-benzoxazines, providing good enantioselectivities (up to 95% ee) and high catalytic activity (S/C up to 5000).

  10. Highly red-shifted NIR emission from a novel anthracene conjugated polymer backbone containing Pt( ii ) porphyrins

    KAUST Repository

    Freeman, D. M. E.

    2015-11-30

    © The Royal Society of Chemistry 2016. We present the synthesis of a novel diphenylanthracene (DPA) based semiconducting polymer. The polymer is solubilised by alkoxy groups attached directly to a DPA monomer, meaning the choice of co-monomer is not limited to exclusively highly solubilising moieties. Interestingly, the polymer shows a red-shifted elecroluminescence maximum (510 nm) when compared to its photoluminescence maximum (450 nm) which we attribute to excimer formation. The novel polymer was utilised as a host for a covalently-linked platinum(ii) complexed porphyrin dopant. Emission from these polymers was observed in the NIR and again showed almost a 100 nm red shift from photoluminescence to electroluminescence. This work demonstrates that utilising highly aggregating host materials is an effective tool for inducing red-shifted emission in OLEDs.

  11. Dynamic-template-directed multiscale assembly for large-area coating of highly-aligned conjugated polymer thin films

    Science.gov (United States)

    Mohammadi, Erfan; Zhao, Chuankai; Meng, Yifei; Qu, Ge; Zhang, Fengjiao; Zhao, Xikang; Mei, Jianguo; Zuo, Jian-Min; Shukla, Diwakar; Diao, Ying

    2017-07-01

    Solution processable semiconducting polymers have been under intense investigations due to their diverse applications from printed electronics to biomedical devices. However, controlling the macromolecular assembly across length scales during solution coating remains a key challenge, largely due to the disparity in timescales of polymer assembly and high-throughput printing/coating. Herein we propose the concept of dynamic templating to expedite polymer nucleation and the ensuing assembly process, inspired by biomineralization templates capable of surface reconfiguration. Molecular dynamic simulations reveal that surface reconfigurability is key to promoting template-polymer interactions, thereby lowering polymer nucleation barrier. Employing ionic-liquid-based dynamic template during meniscus-guided coating results in highly aligned, highly crystalline donor-acceptor polymer thin films over large area (>1 cm2) and promoted charge transport along both the polymer backbone and the π-π stacking direction in field-effect transistors. We further demonstrate that the charge transport anisotropy can be reversed by tuning the degree of polymer backbone alignment.

  12. CFD modeling and experimental validation of heat and mass transfer in wood poles subjected to high temperatures: a conjugate approach

    Science.gov (United States)

    Younsi, R.; Kocaefe, D.; Poncsak, S.; Kocaefe, Y.; Gastonguay, L.

    2008-03-01

    In this article, a coupling method is presented in the case of high thermal treatment of a wood pole and a three-dimensional numerical simulation is proposed. The conservation equations for the wood sample are obtained using diffusion equation with variables diffusion coefficients and the incompressible Reynolds averaged Navier Stokes equations have been solved for the flow field. The connection between the two problems is achieved by expressing the continuity of the state variables and their respective fluxes through the interface. Turbulence closure is obtained by the use of the standard k ɛ model with the usual wall function treatment. The model equations are solved numerically by the commercial package ANSYS-CFX10. The wood pole was subjected to high temperature treatment under different operating conditions. The model validation is carried out via a comparison between the predicted values with those obtained experimentally. The comparison of the numerical and experimental results shows good agreement, implying that the proposed numerical algorithm can be used as a useful tool in designing high-temperature wood treatment processes. A parametric study was also carried out to determine the effects of several parameters such as initial moisture content, wood aspect ratio and final gas temperature on temperature and moisture content distributions within the samples during heat treatment.

  13. Applications of Tris(4-(thiophen-2-ylphenylamine- and Dithienylpyrrole-based Conjugated Copolymers in High-Contrast Electrochromic Devices

    Directory of Open Access Journals (Sweden)

    Tzi-Yi Wu

    2016-05-01

    Full Text Available Tris(4-(thiophen-2-ylphenylamine- and dithienylpyrrole-based copolymers (P(TTPA-co-DIT and P(TTPA-co-BDTA were electropolymerized on ITO electrode by applying constant potentials of 1.0, 1.1, and 1.2 V. Spectroelectrochemical investigations revealed that P(TTPA-co-DIT film displayed more color changes than P(TTPA-co-BDTA film. The P(TTPA-co-DIT film is yellow in the neutral state, yellowish-green and green in the intermediate state, and blue (1.2 V in highly oxidized state. The ∆Tmax of the P(TTPA-co-DIT and P(TTPA-co-BDTA films were measured as 60.3% at 1042 nm and 47.1% at 1096 nm, respectively, and the maximum coloration efficiency (η of P(TTPA-co-DIT and P(TTPA-co-BDTA films were calculated to be 181.9 cm2·C−1 at 1042 nm and 217.8 cm2·C−1 at 1096 nm, respectively, in an ionic liquid solution. Dual type electrochromic devices (ECDs consisting of P(TTPA-co-DIT (or P(TTPA-co-BDTA anodic copolymer, ionic liquid-based electrolyte, and poly(3,4-(2,2-diethylpropylenedioxythiophene (PProDOT-Et2 cathodic polymer were constructed. P(TTPA-co-BDTA/PProDOT-Et2 ECD showed high ΔTmax (48.1% and high coloration efficiency (649.4 cm2·C−1 at 588 nm. Moreover, P(TTPA-co-DIT/PProDOT-Et2 and P(TTPA-co-BDTA/PProDOT-Et2 ECDs displayed satisfactory optical memory and long term switching stability.

  14. High-frequency conjugal plasmid transfer from gram-negative Escherichia coli to various gram-positive coryneform bacteria.

    Science.gov (United States)

    Schäfer, A; Kalinowski, J; Simon, R; Seep-Feldhaus, A H; Pühler, A

    1990-03-01

    We report on the mobilization of shuttle plasmids from gram-negative Escherichia coli to gram-positive corynebacteria mediated by P-type transfer functions. Introduction of plasmids into corynebacteria was markedly enhanced after heat treatment of the recipient cells. High-frequency plasmid transfer was also observed when the restriction system of the recipient was mutated. On the basis of our data, we conclude that efficient DNA transfer from gram-negative to gram-positive bacteria, at least to coryneform bacteria, is conceivable in certain natural ecosystems.

  15. Engineering chiral porous metal-organic frameworks for enantioselective adsorption and separation

    Science.gov (United States)

    Peng, Yongwu; Gong, Tengfei; Zhang, Kang; Lin, Xiaochao; Liu, Yan; Jiang, Jianwen; Cui, Yong

    2014-07-01

    The separation of racemic molecules is of substantial significance not only for basic science but also for technical applications, such as fine chemicals and drug development. Here we report two isostructural chiral metal-organic frameworks decorated with chiral dihydroxy or -methoxy auxiliares from enantiopure tetracarboxylate-bridging ligands of 1,1‧-biphenol and a manganese carboxylate chain. The framework bearing dihydroxy groups functions as a solid-state host capable of adsorbing and separating mixtures of a range of chiral aromatic and aliphatic amines, with high enantioselectivity. The host material can be readily recycled and reused without any apparent loss of performance. The utility of the present adsorption separation is demonstrated in the large-scale resolution of racemic 1-phenylethylamine. Control experiments and molecular simulations suggest that the chiral recognition and separation are attributed to the different orientations and specific binding energies of the enantiomers in the microenvironment of the framework.

  16. Enantioselective effects of methamidophos on the coelomocytes lysosomal membrane stability of Eisenia fetida.

    Science.gov (United States)

    Chen, Linhua; Lu, Xianting; Ma, Yun

    2012-12-01

    Many of organophosphorous insecticides are chiral compounds. In this study, the enantioselective effects of organophosphate insecticide methamidophos on the coelomocytes lysosomal membrane stability of earthworm Eisenia fetida were studied: (1) The enantiomers of methamidophos were absolutely separated by high-performance liquid chromatography with a commercial chiral column; (2) The neutral red retention assay was used to judge the lysosomal membrane stability. The results showed that with the concentration increasing, lysosomal membranes have been significantly destroyed by individual stereoisomers and racemate of methamidophos. The neutral red retention times were significantly descended from 76.88 to 29.78 min. Both (+)- and (-)-methamidophos showed more prone to destroy the integrity of the lysosomal membrane than the racemate. However, the different effect between stereoisomers is slight.

  17. Silicon Effect on the Enantioselective Transcyanation of Acetyltrimethylsilane Examined by Different Oxynitrilases

    Institute of Scientific and Technical Information of China (English)

    2005-01-01

    The synthesis of optically active (R)- and (S)-2-trimethylsilyl-2-hydroxyl propionitrile by enantioselective transcyanation of acetyltrimethylsilane with acetone cyanohydrin was successfully carried out using defatted plum, loquat , peach, almond or apple seed meals as (R)-oxynitrilase source and using Manihot esculenta leaves as (S)-oxynitrilase source in a biphasic system with good conversion and high enantiomeric excess. Comparative study demonstrated that silicon atom in substrate showed great effect on the reaction and due to the unique characteristics of silicon atom, both the substrate conversion and the product e.e. of the transcyanation of acetyltrimethylsilane were much higher than those of its carbon counterpart 3,3-dimethyl-2-butanone for all examined oxynitrilases.

  18. Kinetics of Lipase Catalyzed Enantioselective Esterification of Racemic Ibuprofen in Isooctane

    Institute of Scientific and Technical Information of China (English)

    谢渝春; 刘会洲; 陈家镛

    2000-01-01

    The kinetics of Candida rugosa lipase catalyzed esteritlcation of racemic ibuprofen with n-butanol in isooctane was studied. The kinetic study was carried out with the addition of 0.1% and 2% (by volume) of water for enzyme activation respectively when celite was added into isooctane for enzyme dispersion. The specific initial rate for S-ibuprofen can be fitted with the Ping Pong Bi Bi mechanism with dead-end competitive inhibition by the alcohol. The time courses of the enantioselective esteriflcation of the two ibuprofen enantiomers with different initial substrate concentrations and water contents were simulated with a model in which both effects of enzyme inactivation by long term reaction and reversed hydrolytic reaction under high water content were taken into consideration.

  19. Enantioselective Hydrolysis of Phenyl Glycidyl Ether Catalyzed by Newly Isolated Bacillus Megaterium ECU1001

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    @@Microbial epoxide hydrolases from bacterial and fungal sources?1? are hi ghly versatile catalysts for the asymmetric hydrolysis of chiral epoxides which are extensively employed as useful building blocks for the synthesis of various biologically active products in the pharmaceutical and agrochemical industries. Microorganism means allows an unlimited supply of these enzymes for preparative -scale applications. Phenyl glycidyl ether (PGE), an aryl epoxide, is a potenti ally useful compound in the synthesis of chiral amino alcohols and bioactive com pounds such as ?blockers. No suitable biocatalyst with sufficiently high enan tioselectivity (E?20) for the kinetic resolution of this compound was previ ously found among bacteria and fungi. This prompted us to screen epoxide hydrola se-producing microorganisms with higher enantioselectivity toward phenyl glycid yl ether from soil samples.

  20. Multivalent polyglycerol supported imidazolidin-4-one organocatalysts for enantioselective Friedel–Crafts alkylations

    Directory of Open Access Journals (Sweden)

    Tommaso Pecchioli

    2015-05-01

    Full Text Available The first immobilization of a MacMillan’s first generation organocatalyst onto dendritic support is described. A modified tyrosine-based imidazolidin-4-one was grafted to a soluble high-loading hyperbranched polyglycerol via a copper-catalyzed alkyne–azide cycloaddition (CuAAC reaction and readily purified by dialysis. The efficiency of differently functionalized multivalent organocatalysts 4a–c was tested in the asymmetric Friedel–Crafts alkylation of N-methylpyrrole with α,β-unsaturated aldehydes. A variety of substituted enals was investigated to explore the activity of the catalytic system which was also compared with monovalent analogues. The catalyst 4b showed excellent turnover rates and no loss of activity due to immobilization, albeit moderate enantioselectivities were observed. Moreover, easy recovery by selective precipitation allowed the reuse of the catalyst for three cycles.

  1. The Chemistry and Biology of Oligonucleotide Conjugates

    Science.gov (United States)

    Juliano, R.L.; Ming, Xin; Nakagawa, Osamu

    2012-01-01

    CONSPECTUS Short DNA or RNA oligonucleotides have tremendous potential as therapeutic agents. Because of their ability to engage in Watson-Crick base pairing they can interact with messenger mRNA or pre-mRNA targets with high selectivity and thus offer the possibility of precise manipulation of gene expression. This possibility has engendered extensive efforts to develop oligonucleotides as drugs, with many candidates already in clinical trials. However, a major impediment to the maturation of oligonucleotide-based therapeutics is the fact that these relatively large and usually highly charged molecules have great difficulty crossing cellular membranes and thus in penetrating to their sites of action in the cytosol or nucleus. In this Account we first summarize some basic aspects of the biology of antisense and siRNA oligonucleotides and then discuss chemical conjugation as an approach to improving the intracellular delivery and therapeutic potential of these agents. Our emphasis will be on the pharmacological ramifications of oligonucleotide conjugates rather than the details of conjugation chemistry. One important approach has been conjugation with ligands designed to bind to particular receptors and thus provide specificity to the interaction of cells with oligonucleotides. Another approach has been to couple antisense or siRNA with agents such as cell penetrating peptides that are designed to provoke escape of the conjugate from intracellular vesicular compartments. Both of these approaches have enjoyed some success. However, there remains much to be learned before oligonucleotide conjugates can find an important place in human therapeutics. PMID:22353142

  2. Characterization of local electrochemical doping of high performance conjugated polymer for photovoltaics using scanning droplet cell microscopy.

    Science.gov (United States)

    Gasiorowski, Jacek; Mardare, Andrei Ionut; Sariciftci, Niyazi Serdar; Hassel, Achim Walter

    2013-12-15

    The electrochemical oxidation of a next generation low bandgap high performance photovoltaic material namely poly[4,8-bis-substituted-benzo[1,2-b:4,5-b0]dithiophene-2,6-diyl-alt-4-substituted-thieno[3,4-b] thiophene-2,6-diyl] (PBDTTT-c) thin film was investigated using a scanning droplet cell microscope. Cyclic voltammetry was used for the basic characterization of the oxidation/doping of PBDTTT-c. Application of the different final potentials during the electrochemical study provides a close look to the oxidation kinetics. The electrical properties of both doped and undoped PBDTTT-c were analyzed in situ by electrochemical impedance spectroscopy giving the possibility to correlate the changes in the doping level with the subsequent changes in the resistance and capacitance. As a result one oxidation peak was found during the cyclic voltammetry and in potentiostatic measurements. From Mott-Schottky analysis a donor concentration of 2.3 × 10(20) cm(-3) and a flat band potential of 1.00 V vs. SHE were found. The oxidation process resulted in an increase of the conductivity by two orders of magnitude reaching a maximum for the oxidized form of 1.4 S cm(-1).

  3. Crocins with high levels of sugar conjugation contribute to the yellow colours of early-spring flowering crocus tepals.

    Science.gov (United States)

    Rubio Moraga, Angela; Ahrazem, Oussama; Rambla, José Luis; Granell, Antonio; Gómez Gómez, Lourdes

    2013-01-01

    Crocus sativus is the source of saffron spice, the processed stigma which accumulates glucosylated apocarotenoids known as crocins. Crocins are found in the stigmas of other Crocuses, determining the colourations observed from pale yellow to dark red. By contrast, tepals in Crocus species display a wider diversity of colours which range from purple, blue, yellow to white. In this study, we investigated whether the contribution of crocins to colour extends from stigmas to the tepals of yellow Crocus species. Tepals from seven species were analysed by UPLC-PDA and ESI-Q-TOF-MS/MS revealing for the first time the presence of highly glucosylated crocins in this tissue. β-carotene was found to be the precursor of these crocins and some of them were found to contain rhamnose, never before reported. When crocin profiles from tepals were compared with those from stigmas, clear differences were found, including the presence of new apocarotenoids in stigmas. Furthermore, each species showed a characteristic profile which was not correlated with the phylogenetic relationship among species. While gene expression analysis in tepals of genes involved in carotenoid metabolism showed that phytoene synthase was a key enzyme in apocarotenoid biosynthesis in tepals. Expression of a crocetin glucosyltransferase, previously identified in saffron, was detected in all the samples. The presence of crocins in tepals is compatible with the role of chromophores to attract pollinators. The identification of tepals as new sources of crocins is of special interest given their wide range of applications in medicine, cosmetics and colouring industries.

  4. Characterization of local electrochemical doping of high performance conjugated polymer for photovoltaics using scanning droplet cell microscopy☆

    Science.gov (United States)

    Gasiorowski, Jacek; Mardare, Andrei Ionut; Sariciftci, Niyazi Serdar; Hassel, Achim Walter

    2013-01-01

    The electrochemical oxidation of a next generation low bandgap high performance photovoltaic material namely poly[4,8-bis-substituted-benzo[1,2-b:4,5-b0]dithiophene-2,6-diyl-alt-4-substituted-thieno[3,4-b] thiophene-2,6-diyl] (PBDTTT-c) thin film was investigated using a scanning droplet cell microscope. Cyclic voltammetry was used for the basic characterization of the oxidation/doping of PBDTTT-c. Application of the different final potentials during the electrochemical study provides a close look to the oxidation kinetics. The electrical properties of both doped and undoped PBDTTT-c were analyzed in situ by electrochemical impedance spectroscopy giving the possibility to correlate the changes in the doping level with the subsequent changes in the resistance and capacitance. As a result one oxidation peak was found during the cyclic voltammetry and in potentiostatic measurements. From Mott–Schottky analysis a donor concentration of 2.3 × 1020 cm−3 and a flat band potential of 1.00 V vs. SHE were found. The oxidation process resulted in an increase of the conductivity by two orders of magnitude reaching a maximum for the oxidized form of 1.4 S cm−1. PMID:25843970

  5. Enhanced luminescence properties of highly threaded conjugated polyelectrolytes with potassium counter-ions upon blending with poly(ethylene oxide)

    Science.gov (United States)

    Latini, Gianluca; Winroth, Gustaf; Brovelli, Sergio; McDonnell, Shane O.; Anderson, Harry L.; Mativetsky, Jeffrey M.; Samorı, Paolo; Cacialli, Franco

    2010-06-01

    The photophysics and electroluminescence (EL) of thin films of unthreaded and cyclodextrin-encapsulated poly(4,4'-diphenylenevinylene) (PDV) with potassium countercations, blended with poly(ethylene oxide) (PEO) are investigated as a function of the PEO concentration. We show that three main factors contribute to increasing the photoluminescence (PL) quantum efficiency as a result of suppressed intermolecular interactions, namely: the high degree of encapsulation of the polyrotaxanes, the relatively large countercation (e.g., compared to lithium), and the complexation of the rotaxanes with PEO. By facilitating cationic transport to the negative electrodes, PEO also leads to devices with enhanced electron injection and improved charge balance, whose operation therefore resembles that of "virtually unipolar" light-emitting electrochemical cells. This effect, together with the enhanced PL efficiency, leads to higher EL efficiency for both polyrotaxanes and unthreaded polymers, upon addition of the PEO. We show that the concurrent exploitation of the various strategies above lead to an overall EL efficiency that is approximately twice the value previously reported for Li-based PDV. A blueshift of the EL spectrum during the devices turn-on is also reported and analyzed in terms of interference and doping effects.

  6. Crocins with high levels of sugar conjugation contribute to the yellow colours of early-spring flowering crocus tepals.

    Directory of Open Access Journals (Sweden)

    Angela Rubio Moraga

    Full Text Available Crocus sativus is the source of saffron spice, the processed stigma which accumulates glucosylated apocarotenoids known as crocins. Crocins are found in the stigmas of other Crocuses, determining the colourations observed from pale yellow to dark red. By contrast, tepals in Crocus species display a wider diversity of colours which range from purple, blue, yellow to white. In this study, we investigated whether the contribution of crocins to colour extends from stigmas to the tepals of yellow Crocus species. Tepals from seven species were analysed by UPLC-PDA and ESI-Q-TOF-MS/MS revealing for the first time the presence of highly glucosylated crocins in this tissue. β-carotene was found to be the precursor of these crocins and some of them were found to contain rhamnose, never before reported. When crocin profiles from tepals were compared with those from stigmas, clear differences were found, including the presence of new apocarotenoids in stigmas. Furthermore, each species showed a characteristic profile which was not correlated with the phylogenetic relationship among species. While gene expression analysis in tepals of genes involved in carotenoid metabolism showed that phytoene synthase was a key enzyme in apocarotenoid biosynthesis in tepals. Expression of a crocetin glucosyltransferase, previously identified in saffron, was detected in all the samples. The presence of crocins in tepals is compatible with the role of chromophores to attract pollinators. The identification of tepals as new sources of crocins is of special interest given their wide range of applications in medicine, cosmetics and colouring industries.

  7. Bisguanidinium dinuclear oxodiperoxomolybdosulfate ion pair-catalyzed enantioselective sulfoxidation

    OpenAIRE

    Zong, Lili; Wang, Chao; Moeljadi, Adhitya Mangala Putra; Ye, Xinyi; Ganguly, Rakesh; Li, Yongxin; Hirao, Hajime; Tan, Choon-Hong

    2016-01-01

    Catalytic use of peroxomolybdate for asymmetric transformations has attracted increasing attention due to its catalytic properties and application in catalysis. Herein, we report chiral bisguanidinium dinuclear oxodiperoxomolybdosulfate [BG]2+[(μ-SO4)Mo2O2(μ-O2)2(O2)2]2− ion pair, as a catalyst for enantioselective sulfoxidation using aqueous H2O2 as the terminal oxidant. The ion pair catalyst is isolatable, stable and useful for the oxidation of a range of dialkyl sulfides. The practical uti...

  8. Enantioselective Stereodivergent Nucleophile-Dependent Isothiourea-Catalysed Domino Reactions.

    Science.gov (United States)

    Matviitsuk, Anastassia; Taylor, James E; Cordes, David B; Slawin, Alexandra M Z; Smith, Andrew D

    2016-12-05

    α,β-Unsaturated acyl ammoniums generated from the reaction of α,β-unsaturated 2,4,6-trichlorophenol (TCP) esters bearing a pendent enone with an isothiourea organocatalyst are versatile intermediates in a range of enantioselective nucleophile-dependent domino processes to form complex products of diverse topology with excellent stereoselectivity. Use of either 1,3-dicarbonyls, acyl benzothiazoles, or acyl benzimidazoles as nucleophiles allows three distinct, diastereodivergent domino reaction pathways to be accessed to form various fused polycyclic cores containing multiple contiguous stereocentres. © 2016 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.

  9. Development of Environment-Friendly Insecticides Based on Enantioselectivity: Bifenthrin as a Case.

    Science.gov (United States)

    Qian, Yi; Zhou, Peixue; Zhang, Quan

    2017-01-01

    Chiral insecticides significantly contribute to the environmental pollutions recently. As the development of industry and agriculture, increasing number of chiral insecticides are to be introduced into the market. However, their enantioselective toxicology to ecosystem still remains uncertain. In this review, we embarked on a structured search of bibliographic databases for peer-reviewed articles regarding the enantioselective effects of bifenthrin, a typical chiral insecticide, on both target and non-target species. With this enantioselective property of chiral insecticides, they often exhibit adverse effects on non-target species enantioselectively. Specifically, the enantioselective effects of bifenthrin on target and non-target organisms were discussed. In target species, R-bifenthrin exerts more significant activities in deinsectization, compared with S-bifenthrin. On the other hand, Sbifenthrin is more toxic to non-target species than R-bifenthrin, which suggests that the application of sole enantiomer is more efficient and environment-friendly than that of racemate. This review confirms the choice of environment-friendly insecticides from the perspective of the enantioselectivity of chiral insecticides. To make insecticides more efficient to target species and less toxic to non-target species, further research should be done to investigated the potential effects of targetactive enantiomers on non-target organisms as well as the enantioselective fate of enantiomers in multiple environmental matrix.

  10. Substitution of Val72 residue alters the enantioselectivity and activity of Penicillium expansum lipase.

    Science.gov (United States)

    Tang, Lianghua; Su, Min; Zhu, Ling; Chi, Liying; Zhang, Junling; Zhou, Qiong

    2013-01-01

    Error-prone PCR was used to create more active or enantioselective variants of Penicillium expansum lipase (PEL). A variant with a valine to glycine substitution at residue 72 in the lid structure exhibited higher activity and enantioselectivity than those of wild-type PEL. Site-directed saturation mutagenesis was used to explore the sequence-function relationship and the substitution of Val72 of P. expansum lipase changed both catalytic activity and enantioselectivity greatly. The variant V72A, displayed a highest enantioselectivity enhanced to about twofold for the resolution of (R, S)-naproxen (E value increased from 104 to 200.7 for wild-type PEL and V72A variant, respectively). In comparison to PEL, the variant V72A showed a remarkable increase in specific activity towards p-nitrophenyl palmitate (11- and 4-fold increase at 25 and 35 °C, respectively) whereas it had a decreased thermostability. The results suggest that the enantioselective variant V72A could be used for the production of pharmaceutical drugs such as enantiomerically pure (S)-naproxen and the residue Val 72 of P. expansum lipase plays a significant role in the enantioselectivity and activity of this enantioselective lipase.

  11. Conjugated microporous polymers: design, synthesis and application.

    Science.gov (United States)

    Xu, Yanhong; Jin, Shangbin; Xu, Hong; Nagai, Atsushi; Jiang, Donglin

    2013-10-21

    Conjugated microporous polymers (CMPs) are a class of organic porous polymers that combine π-conjugated skeletons with permanent nanopores, in sharp contrast to other porous materials that are not π-conjugated and with conventional conjugated polymers that are nonporous. As an emerging material platform, CMPs offer a high flexibility for the molecular design of conjugated skeletons and nanopores. Various chemical reactions, building blocks and synthetic methods have been developed and a broad variety of CMPs with different structures and specific properties have been synthesized, driving the rapid growth of the field. CMPs are unique in that they allow the complementary utilization of π-conjugated skeletons and nanopores for functional exploration; they have shown great potential for challenging energy and environmental issues, as exemplified by their excellent performance in gas adsorption, heterogeneous catalysis, light emitting, light harvesting and electrical energy storage. This review describes the molecular design principles of CMPs, advancements in synthetic and structural studies and the frontiers of functional exploration and potential applications.

  12. Enantioselective piezoelectric quartz crystal sensor for d-methamphetamine based on a molecularly imprinted polymer.

    Science.gov (United States)

    Arenas, Leveriza F; Ebarvia, Benilda S; Sevilla, Fortunato B

    2010-08-01

    A piezoelectric quartz crystal (PQC) sensor based on a molecularly imprinted polymer (MIP) has been developed for enantioselective and quantitative analysis of d-(+)-methamphetamine (d(+)-MA). The sensor was produced by bulk polymerization and the resulting MIP was then coated on the gold electrode of an AT-cut quartz crystal. Conditions such as volume of polymer coating, curing time, type of PQC, baseline solvent, pH, and buffer type were found to affect the sensor response and were therefore optimized. The PQC-MIP gave a stable response to different concentrations of d(+)-MA standard solutions (response time = 10 to 100 s) with good repeatability (RSD = 0.03 to 3.09%; n = 3), good reproducibility (RSD = 3.55%; n = 5), and good reversibility (RSD = 0.36%; n = 3). The linear range of the sensor covered five orders of magnitude of analyte concentration, ranging from 10(-5) to 10(-1) microg mL(-1), and the limit of detection was calculated as 11.9 pg d(+)-MA mL(-1) . The sensor had a highly enantioselective response to d(+)-MA compared with its response to l(-)-MA, racemic MA, and phentermine. The developed sensor was validated by applying it to human urine samples from drug-free individuals spiked with standard d(+)-MA and from a confirmed MA user. Use of the standard addition method (SAM) and samples spiked with d(+)-MA at levels ranging from 1 x 10(-3) to 1 x 10(-2) microg mL(-1) showed recovery was good (95.3 to 110.9%).

  13. Enantioselective Degradation and Chiral Stability of Metalaxyl-M in Tomato Fruits.

    Science.gov (United States)

    Jing, Xu; Yao, Guojun; Wang, Peng; Liu, Donghui; Qi, Yanli; Zhou, Zhiqiang

    2016-05-01

    Metalaxyl is an important chiral acetanilide fungicide, and the activity almost entirely originates from the R-enantiomer. Racemic metalaxyl has been gradually replaced by the enantiopure R-enantiomer (metalaxyl-M). In this study a chiral residue analysis method for metalaxyl and the metabolite metalaxyl acid was set up based on high-performance liquid chromatography tandem mass spectroscopy (HPLC-MS/MS). The enantioselective degradation and chiral stability of metalaxyl-M in tomato fruits in two geographically distinct regions of China (Heilongjiang and Hunan Province) were evaluated and the enantioselectivity of metalaxyl acid was also investigated. Tomato plants grew under field conditions with a one-time spray application of metalaxyl-M wettable powder. It was found that R-metalaxyl was not chirally stable and the inactive S-metalaxyl was detected in tomato fruits. At day 40, S-metalaxyl derived from R-metalaxyl accounted for 32% and 26% of the total amount of metalaxyl, respectively. The metabolites R-metalaxyl acid and S-metalaxyl acid were both observed in tomato, and the ratio of S-metalaxyl acid to the sum of S- and R-metalaxyl acid was 36% and 28% at day 40, respectively. For both metalaxyl and metalaxyl acid, the half-life of the S-enantiomer was longer than the R-enantiomer. The results indicated that the enantiomeric conversion should be considered in the bioactivity evaluation and environmental pollution assessment. Chirality 28:382-386, 2016. © 2016 Wiley Periodicals, Inc. © 2016 Wiley Periodicals, Inc.

  14. Enantioselective toxicities of chiral ionic liquids 1-alkyl-3-methyl imidazolium tartrate on Scenedesmus obliquus.

    Science.gov (United States)

    Liu, Huijun; Zhang, Xiaoqiang; Dong, Ying; Chen, Caidong; Zhu, Shimin; Ma, Xiangjuan

    2015-12-01

    Ionic liquids (ILs) are being used in various industries during the last few decades, while the good solubility and high stability of ILs may pose a potential threat to the aquatic environment. Effect of chiral ionic liquids (CILs) 1-alkyl-3-methyl imidazolium tartrate (RMIM T) on Scenedesmus obliquus (S.obliquus) was studied. The growth rate inhibition and cell membrane permeability increased with increasing RMIM T concentration and increasing alkyl chain lengths. The IC50 values of D-(-)-tartrate 1-hexyl-3-methyl imidazolium (D-(-)-HMIM T) were 28.30, 12.23,10.15 and 14.41 mg/L, respectively, at 24, 48, 72 and 96h. While that of L-(+)-tartrate 1-hexyl-3-methyl imidazolium (L-(+)-HMIM T) were 15.97, 7.91, 9.43 and 12.04 mg/L respectively. The concentration of chl a, chl b and chl (a+b) decreased with increasing RMIM T concentration. The chlorophyll fluorescence parameters (F0, Fv/Fm, Fv/F0, Y(II), ETR and NPQ) were affected by RMIM T, indicating that the RMIM T will damage the PSII, inhibit the transmission of excitation energy, decrease the efficiency of photosynthesis. The results showed that there were enantioselective toxicity of RMIM T to algae, and the toxicity of L-(+)-RMIM T was greater than that of D-(-)-RMIM T, but the enantioselective difference becomes smaller with increasing exposure time, and with the increasing carbon chain length of cation, indicating that cation properties may have a larger effect on toxicity than anion properties.

  15. β-D-glucosyl conjugates of highly potent inhibitors of blood coagulation factor Xa bearing 2-chorothiophene as a P1 motif.

    Science.gov (United States)

    Lopopolo, Gianfranco; de Candia, Modesto; Panza, Luigi; Romano, Maria Rosaria; Lograno, Marcello Diego; Campagna, Francesco; Altomare, Cosimo

    2012-09-01

    We synthesized a novel O-glucoside of the recently reported potent factor Xa (fXa) inhibitor 1, which bears a 5-chlorothien-2-yl moiety and 1-isopropylpiperidine as fragments that bind the S1 and S4 enzyme pockets, respectively. A β-D-glucosyl unit was conjugated through an ether-linked C3-alkyl spacer to the central phenyl ring of 1. The synthesized β-D-glucose-based compound 16 achieved picomolar inhibitory potency against human fXa (K(i)=60 pM) and high selectivity over thrombin and other serine proteases. In addition to the chlorothienyl S1 binder, a large gain in ΔG resulted from the addition of protonated 1-isopropylpiperidine (ΔΔG=29.7-30.5 kJ mol(-1)), which should bind to the aromatic S4 pocket through efficient cation-π and C-H···π interactions. Instead, the C3-alkyl-linked glucose fragment, which is likely directed toward the solvent outside the enzyme binding site, improves ΔG by an average of 2.9-3.8 kJ mol(-1) . Compound 16 showed sub-micromolar in vitro anticoagulant activity, as assessed by prothrombin time (PT) and activated thromboplastin time (aPTT) clotting assays in pooled human plasma (PT(2) and aPTT(2) equal to 0.135 and 0.389 μM, respectively). Although compound 16 was 1.4-fold less active than parent compound 1 in the ex vivo anticoagulant assay in mice, it showed a significant (1.6-fold) prolongation of PT relative to controls (P<0.05) 60 min after oral dosing (75 mg kg(-1)). Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  16. Catalytic enantioselective amination of alcohols by the use of borrowing hydrogen methodology: cooperative catalysis by iridium and a chiral phosphoric acid.

    Science.gov (United States)

    Zhang, Yao; Lim, Ching-Si; Sim, Derek Sui Boon; Pan, Hui-Jie; Zhao, Yu

    2014-01-27

    The catalytic asymmetric reduction of ketimines has been explored extensively for the synthesis of chiral amines, with reductants ranging from Hantzsch esters, silanes, and formic acid to H2 gas. Alternatively, the amination of alcohols by the use of borrowing hydrogen methodology has proven a highly atom economical and green method for the production of amines without an external reductant, as the alcohol substrate serves as the H2 donor. A catalytic enantioselective variant of this process for the synthesis of chiral amines, however, was not known. We have examined various transition-metal complexes supported by chiral ligands known for asymmetric hydrogenation reactions, in combination with chiral Brønsted acids, which proved essential for the formation of the imine intermediate and the transfer-hydrogenation step. Our studies led to an asymmetric amination of alcohols to provide access to a wide range of chiral amines with good to excellent enantioselectivity.

  17. Enantioselective Metabolism of Flufiprole in Rat and Human Liver Microsomes.

    Science.gov (United States)

    Lin, Chunmian; Miao, Yelong; Qian, Mingrong; Wang, Qiang; Zhang, Hu

    2016-03-23

    The enantioselective metabolism of flufiprole in rat and human liver microsomes in vitro was investigated in this study. The separation and determination were performed using a liquid chromatography system equipped with a triple-quadrupole mass spectrometer and a Lux Cellulose-2 chiral column. The enantioselective metabolism of rac-flufiprole was dramatically different in rat and human liver microsomes in the presence of the β-nicotinamide adenine dinucleotide phosphate regenerating system. The half-lives (t1/2) of flufiprole in rat and human liver microsomes were 7.22 and 21.00 min, respectively, for R-(+)-flufiprole, whereas the values were 11.75 and 17.75 min, respectively, for S-(-)-flufiprole. In addition, the Vmax of R-(+)-flufiprole was about 3-fold that of S-(-)-flufiprole in rat liver microsomes, whereas its value in the case of S-(-)-flufiprole was about 2-fold that of R-(+)-flufiprole in human liver microsomes. The CLint of rac-flufiprole also showed opposite enantioselectivy in rat and human liver microsomes. The different compositions and contents of metabolizing enzyme in the two liver microsomes might be the reasons for the difference in the metabolic behavior of the two enantiomers.

  18. Enantioselective effects of metalaxyl on soil enzyme activity.

    Science.gov (United States)

    Yue, Heng; Fang, Song; Zhang, Yizhi; Ning, Yang; Yu, Weisong; Kong, Fanyu; Qiu, Jun

    2016-12-01

    The enantioselective effects of the chiral pesticide metalaxyl on soil enzyme activity were investigated. Incubation experiments were conducted to investigate the effects of metalaxyl enantiomers at different concentrations on the activities of urease, invertase, and catalase as well as the type of activity change (activation vs. inhibition) at different times during incubation. The results indicated that the effects of metalaxyl on the activity of soil enzymes were not only related to the concentration of the enantiomers and soil incubation time, but also to the chiral configuration, suggesting the effects were enantioselective. A pattern of inhibition-recovery-slight stimulation was observed in urease activity of the soil samples treated with metalaxyl enantiomers, but the effects of (-) -R-metalaxyl were stronger than those of (+)-S-metalaxyl at the same concentration. Invertase activity in soil samples treated with metalaxyl enantiomers initially sharply decreased before finally returning to the normal level, and the effects of (+)-S-metalaxyl were stronger than those of (-) -R-metalaxyl at the same concentration. Metalaxyl enantiomers influenced catalase activity in a pattern of slight stimulation-inhibition-recovery, and the effects of (-) -R-metalaxyl were stronger than those of (+)-S-metalaxyl at the same concentration. © 2016 Wiley Periodicals, Inc.

  19. Discovery of enantioselectivity of urea inhibitors of soluble epoxide hydrolase.

    Science.gov (United States)

    Manickam, Manoj; Pillaiyar, Thanigaimalai; Boggu, PullaReddy; Venkateswararao, Eeda; Jalani, Hitesh B; Kim, Nam-Doo; Lee, Seul Ki; Jeon, Jang Su; Kim, Sang Kyum; Jung, Sang-Hun

    2016-07-19

    Soluble epoxide hydrolase (sEH) hydrolyzes epoxyeicosatrienoic acids (EETs) in the metabolic pathway of arachidonic acid and has been considered as an important therapeutic target for chronic diseases such as hypertension, diabetes and inflammation. Although many urea derivatives are known as sEH inhibitors, the enantioselectivity of the inhibitors is not highlighted in spite of the stereoselective hydrolysis of EETs by sEH. In an effort to explore the importance of enantioselectivity in the urea scaffold, a series of enantiomers with the stereocenter adjacent to the urea nitrogen atom were prepared. The selectivity of enantiomers of 1-(α-alkyl-α-phenylmethyl)-3-(3-phenylpropyl)ureas showed wide range differences up to 125 fold with the low IC50 value up to 13 nM. The S-configuration with planar phenyl and small alkyl groups at α-position is crucial for the activity and selectivity. However, restriction of the free rotation of two α-groups with indan-1-yl or 1,2,3,4-tetrahydronaphthalen-1-yl moiety abolishes the selectivity between the enantiomers, despite the increase in activity up to 13 nM. The hydrophilic group like sulfonamido group at para position of 3-phenylpropyl motif of 1-(α-alkyl-α-phenylmethyl-3-(3-phenylpropyl)urea improves the activity as well as enantiomeric selectivity. All these ureas are proved to be specific inhibitor of sEH without inhibition against mEH.

  20. Photophysical Diversity of Water-Soluble Fluorescent Conjugated Polymers Induced by Surfactant Stabilizers for Rapid and Highly Selective Determination of 2,4,6-Trinitrotoluene Traces.

    Science.gov (United States)

    Alizadeh, Naader; Akbarinejad, Alireza; Ghoorchian, Arash

    2016-09-21

    The increasing application of fluorescence spectroscopy in development of reliable sensing platforms has triggered a lot of research interest for the synthesis of advanced fluorescent materials. Herein, we report a simple, low-cost strategy for the synthesis of a series of water-soluble conjugated polymer nanoparticles with diverse emission range using cationic (hexadecyltrimethylammonium bromide, CTAB), anionic (sodium dodecylbenzenesulfonate, SDBS), and nonionic (TX114) surfactants as the stabilizing agents. The role of surfactant type on the photophisical and sensing properties of resultant polymers has been investigated using dynamic light scattering (DLS), FT-IR, UV-vis, fluorescence, and energy dispersive X-ray (EDS) spectroscopies. The results show that the surface polarity, size, and spectroscopic and sensing properties of conjugated polymers could be well controlled by the proper selection of the stabilizer type. The fluorescent conjugated polymers exhibited fluorescence quenching toward nitroaromatic compounds. Further studies on the fluorescence properties of conjugated polymers revealed that the emission of the SDBS stabilized polymer, N-methylpolypyrrole-SDBS (NMPPY-SDBS), is strongly quenched by 2,4,6-trinitrotoluene molecule with a large Stern -Volmer constant of 59 526 M(-1) and an excellent detection limit of 100 nM. UV-vis and cyclic voltammetry measurements unveiled that fluorescence quenching occurs through a charge transfer mechanism between electron rich NMPPY-SDBS and electron deficient 2,4,6-trinitrotoluene molecules. Finally, the as-prepared conjugated polymer and approach were successfully applied to the determination of 2,4,6-trinitrotoluene in real water samples.

  1. Methotrexate and epirubicin conjugates as potential antitumor drugs

    Directory of Open Access Journals (Sweden)

    Szymon Wojciech Kmiecik

    2017-07-01

    Full Text Available Introduction: The use of hybrid molecules has become one of the most significant approaches in new cytotoxic drug design. This study describes synthesis and characterization of conjugates consisting of two well-known and characterized chemotherapeutic agents: methotrexate (MTX and epirubicin (EPR. The synthesized conjugates combine two significant anticancer strategies: combinatory therapy and targeted therapy. These two drugs were chosen because they have different mechanisms of action, which can increase the anticancer effect of the obtained conjugates. MTX, which is a folic acid analog, has high cytotoxic properties and can serve as a targeting moiety that can reach folate receptors (FRs overexpresing tumor cells. Combination of nonselective drugs such as EPR with MTX can increase the selectivity of the obtained conjugates, while maintaining the high cytotoxic properties.Materials and methods: Conjugates were purified by RP-HPLC and the structure was investigated by MS and MS/MS methods. The effect of the conjugates on proliferation of LoVo, LoVo/Dx, MCF-7 and MV-4-11 human cancer cell lines was determined by SRB or MTT assay.Results: The conjugation reaction results in the formation of monosubstituted (α, γ and disubstituted MTX derivatives. In vitro proliferation data demonstrate that the conjugates synthesized in our study show lower cytotoxic properties than both chemotherapeutics used alone.Discussion: Epirubicin cytotoxicity was not observed in obtained conjugates. Effective drugs release after internalization needs further investigation.

  2. A different approach to enantioselective organic synthesis

    DEFF Research Database (Denmark)

    Lennartson, Anders; Olsson, Susanne; Sundberg, Jonas

    2009-01-01

    Voilà, optical activity: Both enantiomers of 1-chloroindene have been synthesized in high selectivity from solely achiral starting materials, and without using optically active catalysts (see scheme). These symmetry-breaking syntheses provide a proof-of-concept for a new approach to asymmetric sy...... synthesis. NCS=N-chlorosuccinimide....

  3. Conjugation in "Escherichia coli"

    Science.gov (United States)

    Phornphisutthimas, Somkiat; Thamchaipenet, Arinthip; Panijpan, Bhinyo

    2007-01-01

    Bacterial conjugation is a genetic transfer that involves cell-to-cell between donor and recipient cells. With the current method used to teach students in genetic courses at the undergraduate level, the transconjugants are identified using bacterial physiology and/or antibiotic resistance. Using physiology, however, is difficult for both…

  4. DNA-cell conjugates

    Science.gov (United States)

    Hsiao, Shih-Chia; Francis, Matthew B.; Bertozzi, Carolyn; Mathies, Richard; Chandra, Ravi; Douglas, Erik; Twite, Amy; Toriello, Nicholas; Onoe, Hiroaki

    2016-05-03

    The present invention provides conjugates of DNA and cells by linking the DNA to a native functional group on the cell surface. The cells can be without cell walls or can have cell walls. The modified cells can be linked to a substrate surface and used in assay or bioreactors.

  5. Peptide-Carrier Conjugation

    DEFF Research Database (Denmark)

    Hansen, Paul Robert

    2015-01-01

    To produce antibodies against synthetic peptides it is necessary to couple them to a protein carrier. This chapter provides a nonspecialist overview of peptide-carrier conjugation. Furthermore, a protocol for coupling cysteine-containing peptides to bovine serum albumin is outlined....

  6. Enantioselective Rh-Catalyzed Hydroacylation of Olefins: From Serendipitous Discovery to Rational Design

    Science.gov (United States)

    Murphy, Stephen K.

    2015-01-01

    Rh-catalysed hydroacylation allows the construction of chiral ketones from olefins and aldehydes. Since James' and Young's serendipitous discovery of the enantioselective 4-pentenal cyclisation, both intra and intermolecular variants have emerged that enable broader applications. PMID:25277153

  7. Enantioselective accumulation of (--)-pinoresinol through O-demethylation of (+/-)-eudesmin by Aspergillus niger.

    Science.gov (United States)

    Kasahara, H; Miyazawa, M; Kameoka, H

    1997-04-01

    Microbial transformation of (+/-)-eudesmin by Aspergillus niger was investigated. Enantioselective accumulation of (--)-pinoresinol was shown through O-demethylation of (+/-)-eudesmin. This fungus O- demethylated both enantiomers of eudesmin, but the conversion rates for each enantiomer were clearly different.

  8. Using Natural Cinchona Alkaloids to Promote the Enantioselective Addition of Dialkylzinc to N-Diphenylphosphinylimines

    Institute of Scientific and Technical Information of China (English)

    张海乐; 方春梅; 李昕; 龚流柱; 宓爱巧; 崔欣; 蒋耀忠

    2003-01-01

    Cinchona alkaloids are utilized as chiral ligands to promote the enantioselective addition of dialkylzinc to N-diphenyiphosphinylirnlnes affording enantiomerically enriched N-diphenyiphosphinylamines in up to 91% ee.

  9. Coupling of permeabilized microorganisms for efficient enantioselective reduction of ketone with cofactor recycling.

    Science.gov (United States)

    Zhang, Jie; Witholt, Bernard; Li, Zhi

    2006-01-28

    A novel, simple and efficient cofactor recycling method for enantioselective bioreduction has been developed by the use of permeabilized cells of a reductase-containing microorganism and a glucose dehydrogenase-containing microorganism

  10. Asymmetric Synthesis of N-(Diphenylphosphinyl)furfurylamine by the Enantioselective Alkylation of Furfurylimine

    Institute of Scientific and Technical Information of China (English)

    2005-01-01

    Optically active N-(diphenylphosphinyl)furfurylamines 2 with good ee values were obtained by the enantioselective addition of dialkylzincs to furfuryl imine 1 in the presence of chiral aminoalcohol derivatives and oxazolines.

  11. Ultrasound-promoted Lipase-catalyzed Enantioselective Transesterification of (R,S)-Glycidol

    Institute of Scientific and Technical Information of China (English)

    AN Bai-yi; XIE Xiao-na; XUN Er-na; WANG Jia-xin; WANG Ren; SUN Ruo-xi; WANG Lei; WANG Zhi

    2011-01-01

    Enantioselective transesterification of glycidol with vinyl butyrate as an acyl donor was investigated in the presence of Bacillus subtilis lipase(BSL2) as catalyst.Comparison studies demonstrate the advantage of ultrasound over the conventional shaking for the enzymatic reaction in non-aqueous media.The effects of reaction conditions(ultrasound power,temperature,water activity and pH) on the activity and enantioselectivity were also investigated.Under the optimum conditions,the synthetic activity of BSL2 was 2.95 μmol·min-1·mg-1 and the enantioselectivity(E value) was 52.2.Compared with conventional shaking,ultrasound made the synthetic activity and the enantioselectivity increase 9.5-fold and 1.4-fold,respectively.Furthermore,the repeated use of BSL2 for five cycles resulted in no obvious loss of enzyme activity,suggesting that the enzyme is stable under low power ultrasound conditions.

  12. Residue Val237 is critical for the enantioselectivity of Penicillium expansum lipase.

    Science.gov (United States)

    Tang, Lianghua; Su, Min; Chi, Liying; Zhang, Junling; Zhang, Huihui; Zhu, Ling

    2014-03-01

    The shape of the hydrophobic tunnel leading to the active site of Penicillium expansum lipase (PEL) was redesigned by single-point mutations, in order to better understand enzyme enantioselectivity towards naproxen. A variant with a valine-to-glycine substitution at residue 237 exhibited almost no enantioselectivity (E = 1.1) compared with that (E = 104) of wild-type PEL. The function of the residue, Val237, in the hydrophobic tunnel was further analyzed by site-directed mutagenesis. For each of these variants a significant decrease of enantioselectivity (E < 7) was observed compared with that of wild-type enzyme. Further docking result showed that Val237 plays the most important role in stabilizing the correct orientation of (R)-naproxen. Overall, these results indicate that the residue Val237 is the key amino acid residue maintaining the enantioselectivity of the lipase.

  13. Enantioselective micro-2D-HPLC determination of aspartic acid in the pineal glands of rodents with various melatonin contents.

    Science.gov (United States)

    Han, Hai; Miyoshi, Yurika; Oyama, Tsubasa; Konishi, Ryoko; Mita, Masashi; Hamase, Kenji

    2011-10-01

    Enantioselective determination of aspartic acid (Asp) in the pineal gland of rodents with various melatonin contents was performed using a highly sensitive and selective two-dimensional HPLC system. After derivatization of the amino group with 4-fluoro-7-nitro-2,1,3-benzoxadiazole (NBD-F), NBD-Asp was separated using a capillary monolithic ODS column in the first dimension. The fraction of NBD-Asp was automatically collected and transferred to the second dimension, and the D- and L-Asp were separated and determined using a narrowbore enantioselective column. Large amounts of D-Asp were observed in the pineal gland of the rats and specific strains of mice (C3H and CBA) possessing a high concentration of melatonin in their pineal gland. On the other hand, the amounts of D-Asp were small in the pineal gland of mice possessing a trace or no melatonin in their pineal gland (ddY, ICR, C57BL and BALB/c). In other tissues and physiological fluids, no significant strain-dependent changes of the D-Asp amounts were observed. These results indicate that large amounts of D-Asp are present only in the pineal gland containing large amounts of melatonin, and special care should be taken when selecting mouse strains for the investigation of D-Asp.

  14. Potencial de biocatálise enantiosseletiva de lipases microbianas Potential of enantioselective biocatalysis by microbial lipases

    Directory of Open Access Journals (Sweden)

    Patrícia de O. Carvalho

    2005-08-01

    Full Text Available Microbial lipases have a great potential for commercial applications due to their stability, selectivity and broad substrate specificity because many non-natural acids, alcohols or amines can be used as the substrate. Three microbial lipases isolated from Brazilian soil samples (Aspergillus niger; Geotrichum candidum; Penicillium solitum were compared in terms of their stability and as biocatalysts in the enantioselective esterification using racemic substrates in organic medium. The lipase from Aspergillus niger showed the highest activity (18.2 U/mL and was highly thermostable, retaining 90% and 60% activity at 50 ºC and 60 ºC after 1 hour, respectively. In organic medium, this lipase provided the best results in terms of enantiomeric excess of the (S-active acid (ee = 6.1% and conversion value (c = 20% in the esterification of (R,S-ibuprofen with 1-propanol in isooctane. The esterification reaction of the racemic mixture of (R,S-2-octanol with decanoic acid proceeded with high enantioselectivity when lipase from Aspergillus niger (E = 13.2 and commercial lipase from Candida antarctica (E = 20 were employed.

  15. Molecular and Merrifield supported chiral diamines for enantioselective addition of ZnR2 (R = Me, Et) to ketones.

    Science.gov (United States)

    Calvillo-Barahona, Mercedes; Cordovilla, Carlos; Genov, Miroslav N; Martínez-Ilarduya, Jesús M; Espinet, Pablo

    2013-10-28

    Chiral 1,2-ethylenediamines have been previously reported as active catalysts in the enantioselective addition reactions of ZnR2 to either methyl- or trifluoromethyl-ketones. Subtle changes in the molecular structure of different catalysts are described herein and lead to a dramatic effect in their catalytic activity. From these findings, we demonstrate the selective reactivity of the ligands used in the addition of ZnR2 (R = Me, Et) to methyl- and trifluoromethyl-ketones offering an enantioselective access either to chiral non-fluorinated alcohols or to chiral fluorinated tertiary alcohols. Considering the importance of the chiral trifluoromethyl carbinol fragment in several biologically active compounds, we have extended the scope of the addition reaction of ZnEt2 to several trifluoromethylketones catalyzed by (R,R)-1,2-diphenylethylenediamine derivatives. This work explores a homogeneous approach that provides excellent yields and very high ee and the use of a heterogenized tail-tied ligand affording moderate ee, high yields and allowing an easier handling and recycling.

  16. Biodistribution of ~(99)Tc~m Labelled Dextran Conjugates for Sentinel Lymph Node Detection

    Institute of Scientific and Technical Information of China (English)

    2011-01-01

    Mannosylated dextran conjugates showed high receptor affinity to the receptors on the surface of macrophages in the lymph node. 99Tcm labelled mannosylated dextran conjugates could be used for sentinel lymph node (SLN) detection. In this paper,

  17. Design and Enantioselective Construction of Axially Chiral Naphthyl-Indole Skeletons.

    Science.gov (United States)

    Zhang, Hong-Hao; Wang, Cong-Shuai; Li, Can; Mei, Guang-Jian; Li, Yuxue; Shi, Feng

    2017-01-02

    The first enantioselective construction of a new class of axially chiral naphthyl-indole skeletons has been established by organocatalytic asymmetric coupling reactions of 2-naphthols with 2-indolylmethanols (up to 99 % yield, 97:3 e.r.). This approach not only affords a new type of axially chiral heterobiaryl backbone, but also provides a new catalytic enantioselective strategy for constructing axially chiral biaryl scaffolds by making use of the C3-electrophilicity of 2-indolylmethanols.

  18. Asymmetric Synthesis of Optically Active Spirocyclic Indoline Scaffolds through an Enantioselective Reduction of Indoles

    KAUST Repository

    Borrmann, Ruediger

    2016-11-30

    An enantioselective synthesis of spirocyclic indoline scaffolds was achieved by applying an asymmetric iridium-catalyzed hydrogenation of 3H-indoles. Low catalyst loadings and mild reaction conditions provide a broad range of differently substituted products with excellent yields and enantioselectivities. The developed methodology allows an efficient synthesis of this important spirocyclic structural motif, which is present in numerous biologically active molecules and privileged structures in medicinal chemistry.

  19. Lipase-catalyzed enantioselective esterification of flurbiprofen with n-butanol

    OpenAIRE

    2000-01-01

    The influences of water activity and solvent hydrophobicity on the kinetics of the lipase-catalyzed enantioselective esterification of flurbiprofen with n-butanol were investigated. The solvent effect was not similar for lipases from Candida rugosa (Crl), Mucor javanicus (Mjl), and porcine pancreas (Ppl). The lipase-catalyzed reaction rates in different solvents across a wide range of water activities revealed that the Ppl-catalyzed reaction exhibited no enantioselectivity and no substantial ...

  20. Biomarkers of Oxidative Stress in the Assessment of Enantioselective Toxicity of Chiral Pesticides.

    Science.gov (United States)

    Ye, Xiaoqing; Liu, Ying; Li, Feixue

    2017-01-01

    In biological systems, the individual stereoisomers of chiral substances possess significantly different biochemical properties because the specific structure-activity relationships are required for a common site on biomolecules. In the past decade, there has been increasing concern over the enantioselective toxicity of environmental chiral pollutants, especially chiral pesticides. Different responses and activities of a pair of enantiomers of chiral pesticides were often observed. Therefore, assessment of the enantioselective toxicological properties of chiral pesticides is a prerequisite in application of single-isomer products and particularly important for environmental protection. The development of biomarkers that can predict enantioselective effects from chiral pesticides has recently been gained more and more attention. The biomarkers of oxidative stress have become a topic of significant interest for toxic assessments. In this review, we summarized current knowledge and advances in the understanding of enantiomeric oxidative processes in biological systems in response to chiral pesticides. The consistent results in two types of chiral insecticides (synthetic pyrethroids and organochlorine pesticides) showed the significant difference in cytotoxicity of enantiomers, suggesting the antioxidant enzymes are reliable biomarkers for the assessment of toxicity of chiral chemicals. Results indicate that antioxidant enzymes are sensitive and valid biomarkers to assess the oxidative damage caused by chiral herbicides. In addition, it can be inferred that the enantioselectivity of chiral herbicides on antioxidant enzymes exists in other species. Compared with insecticides and herbicides, researches about the enantioselectivity of oxidative stress caused by chiral fungicides are quite limited. Only two kinds of chiral fungicides has been used to study the enantioselectivity of oxidative stress by now. The current knowledge that enantioselective processes of oxidative

  1. Catalytic Enantioselective Allylic Amination of Olefins for the Synthesis of ent-Sitagliptin.

    Science.gov (United States)

    Bao, Hongli; Bayeh, Liela; Tambar, Uttam K

    2013-11-01

    The presence of nitrogen atoms in most chiral pharmaceutical drugs has motivated the development of numerous strategies for the synthesis of enantioenriched amines. Current methods are based on the multi-step transformation of pre-functionalized allylic electrophiles into chiral allylic amines. The enantioselective allylic amination of unactivated olefins represents a more direct and attractive strategy. We report the enantioselective synthesis of ent-sitagliptin via an allylic amination of an unactivated terminal olefin.

  2. Preliminary Exploration on Properties of the Equidistant Conjugate Points of Higher Dimensional Simplex

    Institute of Scientific and Technical Information of China (English)

    ZENG Jian-guo

    2013-01-01

    In this paper,the concept of the equidistant conjugate points of a triangle to the n-dimensional Euclidean space is extended.The concept of equidistant conjugate point in high dimensional simplex is defined,and the property of the equidistant conjugate points of a triangle is generalized to high dimensional simplex.

  3. Achieving regio- and enantioselectivity of P450-catalyzed oxidative CH activation of small functionalized molecules by structure-guided directed evolution.

    Science.gov (United States)

    Agudo, Rubén; Roiban, Gheorghe-Doru; Reetz, Manfred T

    2012-07-09

    Directed evolution of the monooxygenase P450-BM3 utilizing iterative saturation mutagenesis at and near the binding site enables a high degree of both regio- and enantioselectivity in the oxidative hydroxylation of cyclohexene-1-carboxylic acid methyl ester. Wild-type P450-BM3 is 84% regioselective for the allylic 3-position with 34% enantioselectivity in favor of the R alcohol. Mutants enabling R selectivity (>95% ee) or S selectivity (>95% ee) were evolved, while reducing other oxidation products and thus maximizing regioselectivity to >93%. Control of the substrate-to-enzyme ratio is necessary for obtaining optimal and reproducible enantioselectivities, an observation which is important in future protein engineering of these mono-oxygenases. An E. coli strain capable of NADPH regeneration was also engineered, simplifying directed evolution of P450 enzymes in general. These synthetic results set the stage for subsequent stereoselective and stereospecific chemical transformations to form more complex compounds, thereby illustrating the viability of combining genetically altered enzymes as catalysts in organic chemistry with traditional chemical methods.

  4. Enantioselective column coupled electrophoresis employing large bore capillaries hyphenated with tandem mass spectrometry for ultra-trace determination of chiral compounds in complex real samples.

    Science.gov (United States)

    Piešťanský, Juraj; Maráková, Katarína; Kovaľ, Marián; Havránek, Emil; Mikuš, Peter

    2015-12-01

    A new multidimensional analytical approach for the ultra-trace determination of target chiral compounds in unpretreated complex real samples was developed in this work. The proposed analytical system provided high orthogonality due to on-line combination of three different methods (separation mechanisms), i.e. (1) isotachophoresis (ITP), (2) chiral capillary zone electrophoresis (chiral CZE), and (3) triple quadrupole mass spectrometry (QqQ MS). The ITP step, performed in a large bore capillary (800 μm), was utilized for the effective sample pretreatment (preconcentration and matrix clean-up) in a large injection volume (1-10 μL) enabling to obtain as low as ca. 80 pg/mL limits of detection for the target enantiomers in urine matrices. In the chiral CZE step, the different chiral selectors (neutral, ionizable, and permanently charged cyclodextrins) and buffer systems were tested in terms of enantioselectivity and influence on the MS detection response. The performance parameters of the optimized ITP - chiral CZE-QqQ MS method were evaluated according to the FDA guidance for bioanalytical method validation. Successful validation and application (enantioselective monitoring of renally eliminated pheniramine and its metabolite in human urine) highlighted great potential of this chiral approach in advanced enantioselective biomedical applications.

  5. Enantioselective degradation of Bromocyclene in sewage plants

    Energy Technology Data Exchange (ETDEWEB)

    Bester, K. [Duisburg-Essen Univ. (Germany). FG Siedlungswasser- und Abfallwirtschaft/Inst. fuer Umweltanalytik

    2004-09-15

    Bromocyclene has been utilised as insecticide against ectoparasites, however the production in Germany was stopped around 1995. Until that time it was used in pet care as well as in sheep farming. Due to its high bioaccumulation it was detected not only in sewage systems and sewage treatment plants, but also in fresh water fish. Enatioselective determination at that time was used to obtain results on the biodegradation of Bromocyclene in fish. Considering the long time period since the phase out of Bromocyclene it was surprising it was easily identified in sludge samples from 2002.

  6. Short communication: Milk fat depression induced by conjugated linoleic acid and a high-oil and low-fiber diet occurs equally across the day in Holstein cows.

    Science.gov (United States)

    Ma, L; Cook, K L; Bauman, D E; Harvatine, K J

    2015-03-01

    Recently, a circadian rhythm of milk and milk component synthesis has been characterized that is partially dependent on the timing of feed intake. Our objective was to determine if inhibition of milk fat synthesis during diet-induced milk fat depression occurred to a higher degree during certain phases of the day. A retrospective analysis was conducted on 2 experiments that induced milk fat depression while milking cows 3 times per day at equal intervals. The response at each milking was analyzed using mixed model ANOVA with repeated measures. In experiment 1, nine multiparous Holstein cows were arranged in a 3×3 Latin square design, and treatments were control, 3-d intravenous infusion of 10 g/d of trans-10,cis-12 conjugated linoleic acid (CLA), and a low-forage and high-fat diet for 10 d. In experiment 2, ten multiparous ruminally cannulated cows were arranged in a replicated design and milk samples were collected during a control period or after 5 d of abomasal infusion of 10 g/d of CLA. The daily pattern of milk fat concentration and yield did not differ between treatments in either experiment. In experiment 1, an effect was found of treatment and milking time on milk fat concentration and yield. Similarly, in experiment 2, main effects were found of treatment and milking time on milk fat concentration and an effect of treatment, but no effect of milking time on milk fat yield. Milk fat percent was increased from 3.41 to 4.06% and 3.25 to 3.48% from the morning to the afternoon milking in experiments 1 and 2, respectively. Additionally, milk fatty acid profile, including trans intermediates, was changed over the day in experiment 1, but the magnitude of the changes were small and the pattern did not differ among treatments. A daily rhythm of milk fat concentration and yield was observed in cows milked 3 times a day, but milk fat depression decreases milk fat yield equally over the day.

  7. Emerging pneumococcal carriage serotypes in a high-risk population receiving universal 7-valent pneumococcal conjugate vaccine and 23-valent polysaccharide vaccine since 2001

    Directory of Open Access Journals (Sweden)

    Stubbs Liz

    2009-08-01

    Full Text Available Abstract Background In Australia in June 2001, a unique pneumococcal vaccine schedule commenced for Indigenous infants; seven-valent pneumococcal conjugate vaccine (7PCV given at 2, 4, and 6 months of age and 23-valent pneumococcal polysaccharide vaccine (23PPV at 18 months of age. This study presents carriage serotypes following this schedule. Methods We conducted cross sectional surveys of pneumococcal carriage in Aboriginal children 0 to 6 years of age living in remote Aboriginal communities (RACs in 2003 and 2005. Nasal secretions were collected and processed according to published methods. Results 902 children (mean age 25 months living in 29 communities in 2003 and 818 children (mean age 35 months in 17 communities in 2005 were enrolled. 87% children in 2003 and 96% in 2005 had received two or more doses of 7PCV. From 2003 to 2005, pneumococcal carriage was reduced from 82% to 76% and reductions were apparent in all age groups; 7PCV-type carriage was reduced from 11% to 8%, and 23PPV-non-7PCV-type carriage from 31% to 25% respectively. Thus non-23PPV-type carriage increased from 57% to 67%. All these changes were statistically significant, as were changes for some specific serotypes. Shifts could not be attributed to vaccination alone. The top 10 of 40 serotypes identified were (in descending order 16F, 19A, 11A, 6C, 23B, 19F, 6A, 35B, 6B, 10A and 35B. Carriage of penicillin non-susceptible (MIC > = 0.12 μg/mL strains (15% overall was detected in serotypes (descending order 19A, 19F, 6B, 16F, 11A, 9V, 23B, and in 4 additional serotypes. Carriage of azithromycin resistant (MIC > = 2 μg/mL strains (5% overall, was detected in serotypes (descending order 23B, 17F, 9N, 6B, 6A, 11A, 23F, and in 10 additional serotypes including 6C. Conclusion Pneumococcal carriage remains high (~80% in this vaccinated population. Uptake of both pneumococcal vaccines increased, and carriage was reduced between 2003 and 2005. Predominant serotypes in combined

  8. Controlled Conjugated Backbone Twisting for an Increased Open-Circuit Voltage while Having a High Short-Circuit Current in Poly(hexylthiophene) Derivatives

    KAUST Repository

    Ko, Sangwon

    2012-03-21

    Conjugated polymers with nearly planar backbones have been the most commonly investigated materials for organic-based electronic devices. More twisted polymer backbones have been shown to achieve larger open-circuit voltages in solar cells, though with decreased short-circuit current densities. We systematically impose twists within a family of poly(hexylthiophene)s and examine their influence on the performance of polymer:fullerene bulk heterojunction (BHJ) solar cells. A simple chemical modification concerning the number and placement of alkyl side chains along the conjugated backbone is used to control the degree of backbone twisting. Density functional theory calculations were carried out on a series of oligothiophene structures to provide insights on how the sterically induced twisting influences the geometric, electronic, and optical properties. Grazing incidence X-ray scattering measurements were performed to investigate how the thin-film packing structure was affected. The open-circuit voltage and charge-transfer state energy of the polymer:fullerene BHJ solar cells increased substantially with the degree of twist induced within the conjugated backbone-due to an increase in the polymer ionization potential-while the short-circuit current decreased as a result of a larger optical gap and lower hole mobility. A controlled, moderate degree of twist along the poly(3,4-dihexyl-2,2′:5′,2′′- terthiophene) (PDHTT) conjugated backbone led to a 19% enhancement in the open-circuit voltage (0.735 V) vs poly(3-hexylthiophene)-based devices, while similar short-circuit current densities, fill factors, and hole-carrier mobilities were maintained. These factors resulted in a power conversion efficiency of 4.2% for a PDHTT:[6,6]-phenyl-C 71-butyric acid methyl ester (PC 71BM) blend solar cell without thermal annealing. This simple approach reveals a molecular design avenue to increase open-circuit voltage while retaining the short-circuit current. © 2012 American

  9. A hierarchically nanostructured composite of MnO{sub 2}/conjugated polymer/graphene for high-performance lithium ion batteries

    Energy Technology Data Exchange (ETDEWEB)

    Guo, Chun Xian; Chen, Tao; Li, Chang Ming [Institute for Clean Energy and Advanced Materials, Southwest University, Chongqing 400715 (China); School of Chemical and Biomedical Engineering, Nanyang Technological University (Singapore); Wang, Min; Lou, Xiong Wen [School of Chemical and Biomedical Engineering, Nanyang Technological University (Singapore)

    2011-10-15

    A hierarchically nanostructured composite of MnO{sub 2}/conjugated polymer/graphene is designed and fabricated for lithium ion batteries. The composite can produce a reversible capacity more than ten times that of plain MnO{sub 2}-based devices. The described approach can be used to create desired hierarchically nanostructured composite electrodes for broad applications in energy conversion/storage systems. (Copyright copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  10. Flexible Enantioselectivity of Tryptophanase Attributable to Benzene Ring in Heterocyclic Moiety of D-Tryptophan

    Directory of Open Access Journals (Sweden)

    Akihiko Shimada

    2012-05-01

    Full Text Available The invariance principle of enzyme enantioselectivity must be absolute because it is absolutely essential to the homochiral biological world. Most enzymes are strictly enantioselective, and tryptophanase is one of the enzymes with extreme absolute enantioselectivity for L-tryptophan. Contrary to conventional knowledge about the principle, tryptophanase becomes flexible to catalyze D-tryptophan in the presence of diammonium hydrogenphosphate. Since D-amino acids are ordinarily inert or function as inhibitors even though they are bound to the active site, the inhibition behavior of D-tryptophan and several inhibitors involved in this process was examined in terms of kinetics to explain the reason for this flexible enantioselectivity in the presence of diammonium hydrogenphosphate. Diammonium hydrogenphosphate gave tryptophanase a small conformational change so that D-tryptophan could work as a substrate. As opposed to other D-amino acids, D-tryptophan is a very bulky amino acid with a benzene ring in its heterocyclic moiety, and so we suggest that this structural feature makes the catalysis of D-tryptophan degradation possible, consequently leading to the flexible enantioselectivity. The present results not only help to understand the mechanism of enzyme enantioselectivity, but also shed light on the origin of homochirality.

  11. Flexible enantioselectivity of tryptophanase attributable to benzene ring in heterocyclic moiety of d-tryptophan.

    Science.gov (United States)

    Shimada, Akihiko; Ozaki, Haruka

    2012-01-01

    The invariance principle of enzyme enantioselectivity must be absolute because it is absolutely essential to the homochiral biological world. Most enzymes are strictly enantioselective, and tryptophanase is one of the enzymes with extreme absolute enantioselectivity for L-tryptophan. Contrary to conventional knowledge about the principle, tryptophanase becomes flexible to catalyze D-tryptophan in the presence of diammonium hydrogenphosphate. Since D-amino acids are ordinarily inert or function as inhibitors even though they are bound to the active site, the inhibition behavior of D-tryptophan and several inhibitors involved in this process was examined in terms of kinetics to explain the reason for this flexible enantioselectivity in the presence of diammonium hydrogenphosphate. Diammonium hydrogenphosphate gave tryptophanase a small conformational change so that D-tryptophan could work as a substrate. As opposed to other D-amino acids, D-tryptophan is a very bulky amino acid with a benzene ring in its heterocyclic moiety, and so we suggest that this structural feature makes the catalysis of D-tryptophan degradation possible, consequently leading to the flexible enantioselectivity. The present results not only help to understand the mechanism of enzyme enantioselectivity, but also shed light on the origin of homochirality.

  12. Enantioselectivity in tebuconazole and myclobutanil non-target toxicity and degradation in soils.

    Science.gov (United States)

    Li, Yuanbo; Dong, Fengshou; Liu, Xingang; Xu, Jun; Han, Yongtao; Zheng, Yongquan

    2015-03-01

    Tebuconazole and myclobutanil are two widely used triazole fungicides, both comprising two enantiomers with different fungicidal activity. However, their non-target toxicity and environmental behavior with respect to enantioselectivity have received limited attention. In the present study, tebuconazole and myclobutanil enantiomers were isolated and used to evaluate the occurrence of enantioselectivity in their acute toxicity to three non-target organisms (Scenedesmus obliquus, Daphnia magna, and Danio rerio). Significant differences were found: R-(-)-tebuconazole was about 1.4-5.9 times more toxic than S-(+)-tebuconazole; rac-myclobutanil was about 1.3-6.1 and 1.4-7.3 more toxic than (-)-myclobutanil and (+)-myclobutanil, respectively. Enantioselectivity was further investigated in terms of fungicide degradation in seven soil samples, which were selected to cover a broad range of soil properties. In aerobic or anaerobic soils, the S-(+)-tebuconazole degraded faster than R-(-)-tebuconazole, and the enantioselectivity showed a correlation with soil organic carbon content. (+)-Myclobutanil was preferentially degraded than (-)-myclobutanil in aerobic soils, whereas both enantiomers degraded at similar rates in anaerobic soils. Apparent correlations of enantioselectivity with soil pH and soil texture were observed for myclobutanil under aerobic conditions. In addition, both fungicides were configurationally stable in soils, i.e., no enantiomerization was found. Enantioselectivity may be a common phenomenon in both aquatic toxicity and biodegradation of chiral triazole fungicides, and this should be considered when assessing ecotoxicological risks of these compounds in the environment.

  13. Integrative assessment of enantioselectivity in endocrine disruption and immunotoxicity of synthetic pyrethroids

    Energy Technology Data Exchange (ETDEWEB)

    Zhao Meirong [Research Center of Environmental Science, College of Biological and Environmental Engineering, Zhejiang University of Technology, Hangzhou 310032 (China); Chen Fang [College of Environmental Science and Engineering, Zhejiang Gongshang University, Hangzhou 310018 (China); Wang Cui; Zhang Quan [Research Center of Environmental Science, College of Biological and Environmental Engineering, Zhejiang University of Technology, Hangzhou 310032 (China); Gan Jianying [Department of Environmental Sciences, University of California, Riverside, CA 92521 (United States); Liu Weiping, E-mail: wliu@zjut.edu.c [Research Center of Environmental Science, College of Biological and Environmental Engineering, Zhejiang University of Technology, Hangzhou 310032 (China)

    2010-05-15

    The increasing release of chiral chemicals into the environment dictates attention to a better understanding of enantioselectivity in their human and ecotoxicological effects. Although enantioselectivity has been considered in many recent studies, there is little effort for discerning the connection between different processes, and as such, our current knowledge about chiral contaminants is rather scattered and incoherent. In this study, we simultaneously evaluated enantioselectivity of two chiral pesticides, lambda-cyhalothrin (LCT) and (Z)-cis-bifenthrin (cis-BF), in immunotoxicity to macrophage cells (RAW264.7), and endocrine disruption activity in human breast carcinoma cell line MCF-7. Analysis of cell proliferation, cell viability, apoptosis, and receptor gene expression showed significant differences between the enantiomers of LCT or cis-BF in estrogenic potential and immunocytotoxicity. The selectivity in these effects consistently followed the same direction, with (-)-LCT or 1S-cis-BF displaying a greater activity than its counterpart. The consistency was attributed to interplaying mechanisms in the closely interacting immune and endocrine systems. The underlying interplays suggest that other chiral xenobiotics may also show a directional enantioselectivity in immunotoxicity and endocrine toxicity. Given that many biological processes are inter-related, enantioselectivity may follow specific patterns that can be revealed via integrative assessments as demonstrated in this study. - Chiral contaminants should consider multiple effects and relate directions of enantioselectivity to their interplaying processes.

  14. Synthesis by high-efficiency liquid-phase (HELP) method of oligonucleotides conjugated with high-molecular weight polyethylene glycols (PEGs)

    National Research Council Canada - National Science Library

    Bonora, G M; Zaramella, S; Veronese, F M

    1998-01-01

    .... The large scale production of these molecules as demanded for commercial purposes is hampered by the heterogeneity of the solid-phase processes and by the low reactivity of high-molecular weight PEGs in solution...

  15. Enantioselectivity of the Musk Odor Sensation

    Institute of Scientific and Technical Information of China (English)

    G. Fráter; P. Kraft

    2005-01-01

    @@ 1Introduction Chiral recognition of substrates is one of the most characteristic phenomena of biological activity. And one of the most fundamental biological activities of chemical substances is their smell. In 1991, Linda Buck and Richard Axel[1] discovered a large multigene family that en codes odorant receptors, for which they were awarded the 2004 Nobel Prize in Medicine and Physiology. These odorant receptors are highly homologous,consist of ca. 320 amino acids, and show a heptahelical transmembrane structure as typical for G-protein-coupled receptors. In the human genome, 347 putative full-length olfactory receptor genes have been identified,which allow via characteristic activation patterns of the associated glomeruli the differentiation of more than 10 000 odorants. Since the odorant receptors are built from enantiomerically pure amino acids, they are themselves chiral. Consequently, one would expect a strong diastereomeric interaction, and enantiomeric pairs of odorants should thus differ significantly in both their odor character and their strengths or odor threshold.

  16. Palladacyclic imidazoline-naphthalene complexes: synthesis and catalytic performance in Pd(II)-catalyzed enantioselective reactions of allylic trichloroacetimidates.

    Science.gov (United States)

    Cannon, Jeffrey S; Frederich, James H; Overman, Larry E

    2012-02-17

    A new family of air- and moisture-stable enantiopure C,N-palladacycles (PIN-acac complexes) were prepared in good overall yield in three steps from 2-iodo-1-naphthoic acid and enantiopure β-amino alcohols. Three of these PIN complexes were characterized by single-crystal X-ray analysis. As anticipated, the naphthalene and imidazoline rings of PIN-acac complexes 18a and 18b were canted significantly from planarity and projected the imidazoline substituents R(1) and R(2) on opposite faces of the palladium square plane. Fifteen PIN complexes were evaluated as catalysts for the rearrangement of prochiral (E)-allylic trichloroacetimidate 19 (eq 2) and the S(N)2' allylic substitution of acetic acid with prochiral (Z)-allylic trichloroacetimidate 23. Although these complexes were kinetically poor catalysts for the Overman rearrangement, they were good catalysts for the allylic substitution reaction, providing branched allylic esters in high yield. However, enantioselectivities were low to moderate and significantly less than that realized with palladacyclic complexes of the COP family. Computational studies support an anti-acetoxypalladation/syn-deoxypalladation mechanism analogous to that observed with COP catalysts. The computational study further suggests that optimizing steric influence in the vicinity of the carbon ligand of a chiral C,N-palladacycle, rather than near the nitrogen heterocycle, is the direction to pursue in future development of improved enantioselective catalysts of this motif.

  17. Proline Based Chiral Ionic Liquids for Enantioselective Michael Reaction

    Directory of Open Access Journals (Sweden)

    Kaoru Nobuoka

    2014-01-01

    Full Text Available Chiral ionic liquids, starting from (S-proline, have been prepared and evaluated the ability of a chiral catalyst. In Michael reaction of trans-β-nitrostyrene and cyclohexanone, all the reactions were carried out under homogeneous conditions without any solvent except for excess cyclohexanone. The chiral ionic liquid catalyst with the positive charge delocalized bulky pyrrolidinium cation shows excellent yields (up to 92%, diastereoselectivities (syn/anti = 96/4, and enantioselectivities (up to 95% ee and could be reused at least three times without any loss of its catalytic activity. Such results demonstrated a promising new approach for green and economic chiral synthesis by using the chiral ionic liquids as a chiral catalyst and a chiral medium.

  18. Enantioselective degradation of metalaxyl in anaerobic activated sewage sludge.

    Science.gov (United States)

    Chen, Shengwen; Liu, Weiping

    2009-03-01

    Enantioselective degradation occurs frequently for chiral pesticides in field matrices and under laboratory conditions. Metalaxyl is a chiral compound and important fungicide. In this study, the degradation of Rac- and R-metalaxyl under anaerobic conditions was studied. The degradation processes were found to follow first-order kinetics. The degradation of the S-enantiomer (T (1/2) = 2.10 days) was much faster than the R-enantiomer (T (1/2) = 8.44 days). The half-life of the Rac-metalaxyl mixture was 4.05 days, which was higher than the S-enantiomer, but lower than the R-enantiomer. These results confirm the need for emphasizing the importance of examining the fate of the stereoisomers in an environmental system.

  19. Bisguanidinium dinuclear oxodiperoxomolybdosulfate ion pair-catalyzed enantioselective sulfoxidation

    Science.gov (United States)

    Zong, Lili; Wang, Chao; Moeljadi, Adhitya Mangala Putra; Ye, Xinyi; Ganguly, Rakesh; Li, Yongxin; Hirao, Hajime; Tan, Choon-Hong

    2016-11-01

    Catalytic use of peroxomolybdate for asymmetric transformations has attracted increasing attention due to its catalytic properties and application in catalysis. Herein, we report chiral bisguanidinium dinuclear oxodiperoxomolybdosulfate [BG]2+[(μ-SO4)Mo2O2(μ-O2)2(O2)2]2- ion pair, as a catalyst for enantioselective sulfoxidation using aqueous H2O2 as the terminal oxidant. The ion pair catalyst is isolatable, stable and useful for the oxidation of a range of dialkyl sulfides. The practical utility was illustrated using a gram-scale synthesis of armodafinil, a commercial drug, with the catalyst generated in situ from 0.25 mol% of bisguanidinium and 2.5 mol% of Na2MoO4.2H2O. Structural characterization of this ion pair catalyst has been successfully achieved using single-crystal X-ray crystallography.

  20. Photomechanical actuation of ligand geometry in enantioselective catalysis.

    Science.gov (United States)

    Kean, Zachary S; Akbulatov, Sergey; Tian, Yancong; Widenhoefer, Ross A; Boulatov, Roman; Craig, Stephen L

    2014-12-22

    A catalyst that couples a photoswitch to the biaryl backbone of a chiral bis(phosphine) ligand, thus allowing photochemical manipulation of ligand geometry without perturbing the electronic structure is reported. The changes in catalyst activity and selectivity upon switching can be attributed to intramolecular mechanical forces, thus laying the foundation for a new class of catalysts whose selectivity can be varied smoothly and in situ over a useful range by controlling molecular stress experienced by the catalyst during turnover. Forces on the order of 100 pN are generated, thus leading to measurable changes in the enantioselectivities of asymmetric Heck arylations and Trost allylic alkylations. The differential coupling between applied force and competing stereochemical pathways is quantified and found to be more efficient for the Heck arylations.