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Sample records for catalyzes enantioselective citrate

  1. Rhodium(II)-catalyzed enantioselective synthesis of troponoids.

    Science.gov (United States)

    Murarka, Sandip; Jia, Zhi-Jun; Merten, Christian; Daniliuc, Constantin-G; Antonchick, Andrey P; Waldmann, Herbert

    2015-06-22

    We report a rhodium(II)-catalyzed highly enantioselective 1,3-dipolar cycloaddition reaction between the carbonyl moiety of tropone and carbonyl ylides to afford troponoids in good to high yields with excellent enantioselectivity. We demonstrate that α-diazoketone-derived carbonyl ylides, in contrast to carbonyl ylides derived from diazodiketoesters, undergo [6+3] cycloaddition reactions with tropone to yield the corresponding bridged heterocycles with excellent stereoselectivity. PMID:25959033

  2. Cobalt-Catalyzed Enantioselective Vinylation of Activated Ketones and Imines.

    Science.gov (United States)

    Huang, Yuan; Huang, Rui-Zhi; Zhao, Yu

    2016-05-25

    We present here an unprecedented cobalt-catalyzed enantioselective vinylation of α-ketoesters, isatins, and imines to deliver a range of synthetically useful allylic alcohols and amines in high enantiopurity. This method employs commercially available and easy to handle catalysts and reagents and exhibits a high degree of practicality. The efficiency, selectivity, and operational simplicity of this catalytic system coupled with the substrate generality render this method a valuable tool in organic synthesis. PMID:27139596

  3. Enantioselective, Stereodivergent Hydroazidation and Hydroamination of Allenes Catalyzed by Acyclic Diaminocarbene (ADC) Gold(I) Complexes

    OpenAIRE

    Khrakovsky, Dimitri A.; Tao, Chuanzhou; Johnson, Miles W.; Thornbury, Richard T.; Shevick, Sophia L.; Toste, F. Dean

    2016-01-01

    The gold-catalyzed enantioselective hydroazidation and hydroamination reactions of allenes are presented herein. ADC gold(I) catalysts derived from BINAM were critical for achieving high levels of enantioselectivity in both transformations. The sense of enantioinduction is reversed for the two different nucleophiles, allowing access to both enantiomers of the corresponding allylic amines using the same catalyst enantiomer.

  4. Formal total syntheses of classic natural product target molecules via palladium-catalyzed enantioselective alkylation

    Directory of Open Access Journals (Sweden)

    Yiyang Liu

    2014-10-01

    Full Text Available Pd-catalyzed enantioselective alkylation in conjunction with further synthetic elaboration enables the formal total syntheses of a number of “classic” natural product target molecules. This publication highlights recent methods for setting quaternary and tetrasubstituted tertiary carbon stereocenters to address the synthetic hurdles encountered over many decades across multiple compound classes spanning carbohydrate derivatives, terpenes, and alkaloids. These enantioselective methods will impact both academic and industrial settings, where the synthesis of stereogenic quaternary carbons is a continuing challenge.

  5. Enantioselective Nazarov Cyclization Catalyzed by a Cinchona Alkaloid Derivative

    Science.gov (United States)

    Huang, Yu-Wen; Frontier, Alison J.

    2015-01-01

    Nucleophilic catalysts for a 1,6 addition/Nazarov cyclization/elimination sequence were evaluated for their ability to induce enantioselectivity in the electrocyclization step. Of the tertiary amines examined, it was found that a cinchona alkaloid derivative was able to generate substituted 5-hydroxy γ-methylene cyclopentenones with excellent enantioselectivity. The study results suggest that successful cyclization depends upon the ability of the dienyl diketone substrate to readily adopt an s-cis conformation. PMID:26085696

  6. Highly Diastereo- and Enantioselective CuH-Catalyzed Synthesis of 2,3-Disubstituted Indolines

    OpenAIRE

    Ascic, Erhad; Buchwald, Stephen L.

    2015-01-01

    A diastereo- and enantioselective CuH-catalyzed method for the preparation of highly functionalized indolines is reported. The mild reaction conditions and high degree of functional group compatibility as demonstrated with substrates bearing heterocycles, olefins, and substituted aromatic groups, renders this technique highly valuable for the synthesis of a variety of cis-2,3-disubstituted indolines in high yield and enantioeselectivity.

  7. 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.

  8. Enantioselective Rh-catalyzed hydrogenation of N-formyl dehydroamino esters with monodentate phosphoramidite ligands

    NARCIS (Netherlands)

    Panella, L; Aleixandre, AM; Kruidhof, GJ; Robertus, J; Feringa, BL; de Vries, JG; Minnaard, AJ; Aleixandre, Alicia Marco; Kruidhof, Gerlof J.; Feringa, Bernard

    2006-01-01

    Enantioselectivities up to > 99% ee were achieved in the rhodium-catalyzed asymmetric hydrogenation of N-formyl dehydroamino esters using morrodentate phosphoramidites as chiral ligands. The substrates were synthesized by condensation of methyl isocyanoacetate with a range of aldehydes and with cycl

  9. Enantioselective copper catalyzed allylic alkylation using Grignard reagents; Applications in synthesis

    NARCIS (Netherlands)

    Zijl, Anthoni Wouter van

    2009-01-01

    Enantioselective copper catalyzed allylic alkylation is a powerful carbon-carbon bond forming reaction. In this thesis the development of a new catalyst for the use of Grignard reagents in this reaction is described. This catalyst is based on copper and the ligand Taniaphos. The high regio- and enan

  10. Copper-Catalyzed Enantioselective Intramolecular Alkene Amination/Intermolecular Heck-Type Coupling Cascade

    OpenAIRE

    Liwosz, Timothy W.; Chemler, Sherry R.

    2012-01-01

    Enantioselective copper-catalyzed cycliza-tion of γ-alkenylsulfonamides and a δ-alkenylsulfonamide in the presence of a range of vinyl arenes results in variously functionalized 2-substituted chiral nitrogen heterocycles via a formal alkene C–H functionalization process. Application of this reaction to the concise synthesis of a 5-HT7 receptor antagonist is demonstrated.

  11. Copper-catalyzed enantioselective intramolecular alkene amination/intermolecular Heck-type coupling cascade.

    Science.gov (United States)

    Liwosz, Timothy W; Chemler, Sherry R

    2012-02-01

    Enantioselective copper-catalyzed cyclization of γ-alkenylsulfonamides and a δ-alkenylsulfonamide in the presence of a range of vinyl arenes results in variously functionalized 2-substituted chiral nitrogen heterocycles via a formal alkene C-H functionalization process. Application of this reaction to the concise synthesis of a 5-HT(7) receptor antagonist is demonstrated. PMID:22257169

  12. 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.

  13. Enantioselective direct aldol reactions catalyzed by l-prolinamide derivatives

    OpenAIRE

    Tang, Zhuo; Jiang, Fan; Cui, Xin; Gong, Liu-Zhu; Mi, Ai-Qiao; Jiang, Yao-Zhong; Wu, Yun-Dong

    2004-01-01

    l-Prolinamides 2, prepared from l-proline and simple aliphatic and aromatic amines, have been found to be active catalysts for the direct aldol reaction of 4-nitrobenzaldehyde with neat acetone at room temperature. They give moderate enantioselectivities of up to 46% enantiomeric excess (ee). The enantioselectivity increases as the amide N—H becomes a better hydrogen bond donor. l-Prolinamides 3, derived from the reaction of l-proline with α,β-hydroxyamines such that there is a terminal hydro...

  14. 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.

  15. Enantioselective Rhodium-Catalyzed Cycloisomerization of (E)-1,6-Enynes.

    Science.gov (United States)

    Deng, Xu; Ni, Shao-Fei; Han, Zheng-Yu; Guan, Yu-Qing; Lv, Hui; Dang, Li; Zhang, Xu-Mu

    2016-05-17

    An enantioselective rhodium(I)-catalyzed cycloisomerization reaction of challenging (E)-1,6-enynes is reported. This novel process enables (E)-1,6-enynes with a wide range of functionalities, including nitrogen-, oxygen-, and carbon-tethered (E)-1,6-enynes, to undergo cycloisomerization with excellent enantioselectivity, in a high-yielding and operationally simple manner. Moreover, this Rh(I) -diphosphane catalytic system also exhibited superior reactivity and enantioselectivity for (Z)-1,6-enynes. A rationale for the striking reactivity difference between (E)- and (Z)-1,6-enynes using Rh(I) -BINAP and Rh(I) -TangPhos is outlined using DFT studies to provide the necessary insight for the design of new catalyst systems and the application to synthesis. PMID:27061132

  16. Origin of enantioselectivity in benzotetramisole-catalyzed dynamic kinetic resolution of azlactones.

    Science.gov (United States)

    Liu, Peng; Yang, Xing; Birman, Vladimir B; Houk, K N

    2012-07-01

    Density functional theory (DFT) calculations were performed to investigate the origins of enantioselectivity in benzotetramisole (BTM)-catalyzed dynamic kinetic resolution of azlactones. The transition states of the fast-reacting enantiomer are stabilized by electrostatic interactions between the amide carbonyl group and the acetate anion bound to the nucleophile. The chiral BTM catalyst confines the conformation of the α-carbon and the facial selectivity of the nucleophilic attack to promote such electrostatic attractions. PMID:22686505

  17. Lipase-catalyzed highly enantioselective kinetic resolution of boron-containing chiral alcohols.

    Science.gov (United States)

    Andrade, Leandro H; Barcellos, Thiago

    2009-07-16

    The first application of enzymes as catalysts to obtain optically pure boron compounds is described. The kinetic resolution of boron-containing chiral alcohols via enantioselective transesterification catalyzed by lipases was studied. Aromatic, allylic, and aliphatic secondary alcohols containing a boronate ester or boronic acid group were resolved by lipase from Candida antartica (CALB), and excellent E values (E > 200) and high enantiomeric excesses (up to >99%) of both remaining substrates and acetylated product were obtained. PMID:19552446

  18. 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.

  19. Rapid Estimation of Enantioselectivity in Lipase-catalyzed Resolution of Glycidyl Butyrate Using pH Indicator

    Institute of Scientific and Technical Information of China (English)

    WANG Ping; WANG Lei; WANG Li-cheng; LI Chun-yuan; WANG Ren; MIAO Qing-hua; YANG Ming; WANG Zhi

    2009-01-01

    A simple method for rapid estimation of the enantioselectivity of lipase in resolution of chiral esters is described. The enantioselectivity of lipase can be estimated rapidly through comparing the dif-ference of hydrolysis rates for the racemic ester and its slow reacting enantiomer under the same condition because the difference mainly depends on the enantioselective ratio(E values). The higher the enantiose-lectivity of enzyme, the larger the difference of hydrolysis rate. The bromothymol blue(BTB) can be used as pH indicator for microplate reader to monitor the formation of acid in lipase-catalyzed hydrolysis ofesters. This method has been successfully used to rapidly estimate the enantioselectivity of several lipases in the resolution of glycidyl butyrate.

  20. Hydroxymethylation beyond Carbonylation: Enantioselective Iridium-Catalyzed Reductive Coupling of Formaldehyde with Allylic Acetates via Enantiotopic π-Facial Discrimination.

    Science.gov (United States)

    Garza, Victoria J; Krische, Michael J

    2016-03-23

    Chiral iridium complexes modified by SEGPHOS catalyze the 2-propanol-mediated reductive coupling of branched allylic acetates 1a-1o with formaldehyde to form primary homoallylic alcohols 2a-2o with excellent control of regio- and enantioselectivity. These processes, which rely on enantiotopic π-facial discrimination of σ-allyliridium intermediates, represent the first examples of enantioselective formaldehyde C-C coupling beyond aldol addition. PMID:26958737

  1. Combination of Novozym 435-catalyzed enantioselective hydrolysis and amidation for the preparation of optically active δ-hexadecalactone

    OpenAIRE

    Shimotori, Yasutaka; Hoshi, Masayuki; Miyakoshi, Tetsuo; 霜鳥, 慈岳; 星,雅之

    2015-01-01

    A new enzymatic method for synthesis of enantiomerically enriched δ-hexadecalactone (3) based on the enzymatic kinetic resolution of N-methyl-5-acetoxyhexadecanamide (1) is described. A combination of lipase-catalyzed hydrolysis and amidation improved enantioselectivity. Lipase-catalyzed amidation was also investigated. Detailed screening of solvents and additive amines was performed. The addition of cyclohexylamine to lipase-catalyzed hydrolysis afforded the best results to give both enantio...

  2. 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

  3. Quantum chemical study on the mechanism of enantioselective reduction of prochiral ketones catalyzed by oxazaborolidines

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    The ab initio molecular orbital study on the mechanism of enantioselective reduction of 3,3-dimethyl butanone-2 with borane catalyzed by chiral oxazaborolidine is performed. As illus trated, this enantioselective reduction is exothermic and goes mainly through the formations of the catalyst-borane adduct, the catalyst-borane-3,3-dimethyl butanone-2 adduct, and the cata lyst-alkoxyborane adduct with a B-O-B-N 4-member ring and through the decomposition of the catalyst-alkoxyborane adduct with the regeneration of the catalyst. During the hydride transfer in the catalyst-borane-3,3-dimethyl butanone-2 adduct to form the catalyst-alkoxyborane adduct, the hydride transfer and the formation of the B-O-B-N 4-member ring in the catalyst-alkoxyborane ad duct happen simultaneously. The controlling step for the reduction is the transfer of hydride from the borane moiety to the carbonyl carbon of 3,3-dimethyl butanone-2. The transition state for the hydride transfer is a twisted chair structure and the reduction leads to R-chiral alcohols.

  4. Enantioselective synthesis of 1,2,4-triazolines by chiral iron(II)-complex catalyzed cyclization of α-isocyano esters and azodicarboxylates.

    Science.gov (United States)

    Wang, Min; Liu, Xiaohua; He, Peng; Lin, Lili; Feng, Xiaoming

    2013-03-28

    Enantioselective cyclization of α-isocyano esters with azodicarboxylates catalyzed by Fe(II)-N,N'-dioxide complexes has been developed. Under mild conditions, a variety of 1,2,4-triazoline derivatives was obtained in high yields and enantioselectivities. PMID:23423581

  5. Cinchona alkaloid squaramide catalyzed enantioselective hydrazination/cyclization cascade reaction of α-isocyanoacetates and azodicarboxylates: synthesis of optically active 1,2,4-triazolines.

    Science.gov (United States)

    Zhao, Mei-Xin; Bi, Hong-Lei; Zhou, Hao; Yang, Hui; Shi, Min

    2013-09-20

    An efficient enantioselective hydrazination/cyclization cascade reaction of α-substituted isocyanoacetates to azodicarboxylates catalyzed by Cinchona alkaloid derived squaramide catalysts has been investigated, affording the optically active 1,2,4-triazolines in excellent yields (up to 99%) and good to excellent enantioselectivities (up to 97% ee) under mild conditions. PMID:23984761

  6. 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.

  7. Highly Enantioselective Rhodium-Catalyzed Addition of Arylboroxines to Simple Aryl Ketones: Efficient Synthesis of Escitalopram.

    Science.gov (United States)

    Huang, Linwei; Zhu, Jinbin; Jiao, Guangjun; Wang, Zheng; Yu, Xingxin; Deng, Wei-Ping; Tang, Wenjun

    2016-03-24

    Highly enantioselective additions of arylboroxines to simple aryl ketones have been achieved for the first time with a Rh/(R,R,R,R)-WingPhos catalyst, thus providing a range of chiral diaryl alkyl carbinols with excellent ee values and yields. (R,R,R,R)-WingPhos has been proven to be crucial for the high reactivity and enantioselectivity. The method has enabled a new, concise, and enantioselective synthesis of the antidepressant drug escitalopram. PMID:26933831

  8. Palladium-Catalyzed Enantioselective Heck Alkenylation of Acyclic Alkenols Using a Redox-Relay Strategy

    OpenAIRE

    Patel, Harshkumar H.; Sigman, Matthew S.

    2015-01-01

    We report a highly enantioselective intermolecular Heck reaction of alkenyl triflates and acyclic primary or racemic secondary alkenols. The mild reaction conditions permit installation of a wide range of alkenyl groups at positions β, γ or δ to a carbonyl group in high enantioselectivity. The success of this reaction is attributed to the use of electron-withdrawing alkenyl triflates, which offer selective β-hydride elimination followed by migration of the catalyst through the alkyl chain to ...

  9. Enantioselective CuH-Catalyzed Reductive Coupling of Aryl Alkenes and Activated Carboxylic Acids.

    Science.gov (United States)

    Bandar, Jeffrey S; Ascic, Erhad; Buchwald, Stephen L

    2016-05-11

    A new method for the enantioselective reductive coupling of aryl alkenes with activated carboxylic acid derivatives via copper hydride catalysis is described. Dual catalytic cycles are proposed, with a relatively fast enantioselective hydroacylation cycle followed by a slower diastereoselective ketone reduction cycle. Symmetrical aryl carboxyclic anhydrides provide access to enantioenriched α-substituted ketones or alcohols with excellent stereoselectivity and functional group tolerance. PMID:27121395

  10. 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.

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

    OpenAIRE

    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 model substrates. For the acyclic enone enantioselectivities up to 83% were achieved. (C) 1997 Elsevier Science Ltd.

  12. Enantioselective Hydrogenation of Aromatic Ketones Catalyzed by Ru Complex Using a New Bipyridyl Diphosphine

    Institute of Scientific and Technical Information of China (English)

    CHEN Li; FU Xing-Li; MING Fang-Yong; CHEN Hua; LI Xian-Jun

    2008-01-01

    A series of RuCl2(bipyridyldiphosphine)(1,2-diamine)complexes were synthesized and applied to the asymmetric hydrogenation of aromatic ketones.Solvent effect and a wide variety of aromatic ketones were explored and up to 96% enantioselectivity was achieved in the hydrogenation of o-bromoacetophenone.

  13. Enantioselective Epoxide Ring Opening Catalyzed by Bis(tetrahydroisoquinoline) N,N’-Dioxides

    Czech Academy of Sciences Publication Activity Database

    Kadlčíková, A.; Vlašná, K.; Kotora, Martin

    2011-01-01

    Roč. 76, č. 5 (2011), s. 415-422. ISSN 0010-0765 Grant ostatní: GA MŠk(CZ) LC06070; GA ČR(CZ) GAP207/11/0587 Institutional research plan: CEZ:AV0Z40550506 Keywords : asymmetric catalysis * silanes * N ligands * enantioselectivity Subject RIV: CC - Organic Chemistry Impact factor: 1.283, year: 2011

  14. Ruthenium-BINAP Catalyzed Alcohol C-H tert-Prenylation via 1,3-Enyne Transfer Hydrogenation: Beyond Stoichiometric Carbanions in Enantioselective Carbonyl Propargylation.

    Science.gov (United States)

    Nguyen, Khoa D; Herkommer, Daniel; Krische, Michael J

    2016-04-27

    The chiral ruthenium complex formed in situ from (TFA)2Ru(CO)(PPh3)2 and (R)-BINAP is found to catalyze the enantioselective C-C coupling of diverse primary alcohols with the 1,3-enyne, TMSC≡CC(Me)═CH2, to form secondary homopropargyl alcohols bearing gem-dimethyl groups. All reagents for this byproduct-free coupling are inexpensive and commercially available, making this protocol a practical alternative to stoichiometric carbanions in enantioselective carbonyl reverse prenylation. PMID:27079149

  15. Chiral Phosphoric Acid-Catalyzed Enantioselective Formal [3+2] Cycloaddition of Azomethine Imines with Enecarbamates.

    Science.gov (United States)

    Wang, Yang; Wang, Qian; Zhu, Jieping

    2016-06-01

    The first catalytic asymmetric inverse electron demand 1,3-dipolar cycloaddition of azomethine imines with enecarbamates has been developed. Isoquinoline-fused pyrazolidines containing two or three contiguous stereogenic centers were obtained in high yields with excellent regio-, diastereo-, and enantioselectivities. The pyrazolidine ring can be opened to install an aminal, α-amino nitrile, or homoallylamine function with an excellent control of the newly generated stereogenic center. Access to aminobenzo[a]quinolizidine is also documented. PMID:27135440

  16. Asymmetric Roadmap to Diverse Polycyclic Benzopyrans via Phosphine-Catalyzed Enantioselective [4 + 2]-Annulation Reaction.

    Science.gov (United States)

    Danda, Adithi; Kesava-Reddy, Naredla; Golz, Christopher; Strohmann, Carsten; Kumar, Kamal

    2016-06-01

    The catalytic addition of the amino acid derived bifunctional N-acylaminophosphine to an α-substituted allene ester generated a zwitterionic dipole that engaged the vinylogous ester function of 3-cyano-chromones in a [4 + 2] annulation reaction to deliver tetrahydroxanthones embodying three consecutive chiral centers in high yields and with excellent enantioselectivities. The established asymmetric synthesis further paves the way to two different classes of complex, sp(3)-rich tetracyclic benzopyrans via efficient cascade reactions. PMID:27187586

  17. Enantioselective synthesis of fluorinated branched allylic compounds via Ir-catalyzed allylations of functionalized fluorinated methylene derivatives.

    Science.gov (United States)

    Zhang, Hongbo; Chen, Jiteng; Zhao, Xiao-Ming

    2016-08-14

    Enantioselective introduction of the functionalized monofluorinated methylenes into the allylic fragment under Ir catalysis has been realized, which gave the fluorinated branched allyl products in good to high yields with excellent regio- and enantioselectivities. PMID:27383920

  18. Enantioselective conjugate addition of diethylzinc to chalcone catalyzed by Co(acac)2 and chiral amino alcohols

    NARCIS (Netherlands)

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

    1997-01-01

    Co(acac)2 in the presence of chiral ligands has been employed as catalyst for the enantioselective conjugate addition of diethylzinc to chalcone. With chiral amino alcohols derived from (+)-camphor, enantioselectivities up to 83% were achieved.

  19. Enantioselective synthesis of 1,2,4-triazolines catalyzed by a cinchona alkaloid-derived organocatalyst.

    Science.gov (United States)

    Shao, Qian; Chen, Jiean; Tu, Meihua; Piotrowski, David W; Huang, Yong

    2013-12-01

    An enantioselective organocatalytic process for the one-step synthesis of poly-substituted 1,2,4-triazolines is reported. The heterocycle formation is believed to go through a step-wise mechanism of nucleophilic addition of an azlactone to an azodicarboxylate in the presence of an organic base catalyst, followed by a TMSCHN2 mediated heterocyclization. Both theoretical calculations and experimental evidence suggest the pre-organization of the transition state for the chirality determining step via a unique 7-membered intramolecular hydrogen bonding. PMID:24145477

  20. Optimization of lipase-catalyzed enantioselective production of 1-phenyl 1-propanol using response surface methodology.

    Science.gov (United States)

    Soyer, Asli; Bayraktar, Emine; Mehmetoglu, Ulku

    2010-01-01

    Optically active 1-phenyl 1-propanol is used as a chiral building block and synthetic intermediate in the pharmaceutical industries. In this study, the enantioselective production of 1-phenyl 1-propanol was investigated systematically using response surface methodology (RSM). Before RSM was applied, the effects of the enzyme source, the type of acyl donor, and the type of solvent on the kinetic resolution of 1-phenyl 1-propanol were studied. The best results were obtained with Candida antartica lipase (commercially available as Novozym 435), vinyl laurate as the acyl donor, and isooctane as the solvent. In the RSM, substrate concentration, molar ratio of acyl donor to the substrate, amount of enzyme, temperature, and stirring rate were chosen as independent variables. The predicted optimum conditions for a higher enantiomeric excess (ee) were as follows: substrate concentration, 233 mM; molar ratio of acyl donor to substrate, 1.5; enzyme amount, 116 mg; temperature, 47 °C; and stirring rate, 161 rpm. A verification experiment conducted at these optimized conditions for maximum ee yielded 91% for 3 hr, which is higher than the predicted value of 83%. The effect of microwave on the ee was also investigated and ee reached 87% at only 5 min. PMID:21108142

  1. Enantioselective Sulfide Oxidation Catalyzed by 2,10-Camphanediol Derived Titanium Complex and Its Mechanism

    Institute of Scientific and Technical Information of China (English)

    ZENG Qing-Le; TANG Hong-Yan; ZHANG Song; LIU Jian-Chuan

    2008-01-01

    Cumyl hydroperoxide (CHP) and tea-butyl hydroperoxide (TBHP) produced (R)- and (S)-sulfoxide in 2,10-camphanediol-titanium catalyzed sulfoxidation, respectively. During kinetic resolution, the salfoxide configu- ration was reversed with CHP, but kept with TBHP. Based on these results and the ESI-MS data, the mechanism of sulfoxidation was proposed to be intramolecular nucleophilic oxygen transfer to a coordinated sulfide.

  2. Theoretical Mechanism Studies on the Enantioselectivity of aza-MBH-type Reaction of Nitroalkene to N-tosylimine Catalyzed by Thiourea-tertiary Amine

    International Nuclear Information System (INIS)

    The enantioselective aza-Morita Baylis Hillman reaction of nitroalkene and N-tosylimine catalyzed by thiourea-tertiary amine has been investigated using density functional theory. Enantioselectivity is dominated by the cooperative effect of non-covalent and weak covalent interactions imposed by different units of catalyst. As Lewis base, the tertiary amine unit activates nitroalkene via weak covalent bond. The weak covalent interaction orients the reaction in a major path with smaller variations of this bond. The aromatic ring unit activates N-tosylimine via π-π stacking. The non-covalent interaction selects the major path with smaller changes of the efficient packing areas. Thiourea unit donates more compact H-bonded network for species of the major path. The calculated ee value in xylene solution phase (97.6%) is much higher than that in N,N-Dimethylformamide (27.2%). Our conclusion is also supported by NBO analysis

  3. Enantioselective conjugate addition of diethylzinc to chalcone catalyzed by Co(acac)(2) and chiral amino alcohols

    NARCIS (Netherlands)

    de Vries, A.H.M.; Feringa, B.L.

    1997-01-01

    Co(acac)(2) in the presence of chiral ligands has been employed as catalyst for the enantioselective conjugate addition of diethylzinc to chalcone. With chiral amino alcohols derived from (+)-camphor, enantioselectivities up to 83% were achieved. (C) 1997 Elsevier Science Ltd.

  4. Enantioselective Oxidation of Alkenes with Potassium Permanganate Catalyzed by Chiral Dicationic Bisguanidinium.

    Science.gov (United States)

    Wang, Chao; Zong, Lili; Tan, Choon-Hong

    2015-08-26

    Chiral anion-controlled ion-pairing catalysis was demonstrated to be a wide-ranging strategy that can utilize a variety of cationic metal species. In a similar manner, we envision a complementary strategy using chiral cation in partnership with inorganic anionic metal salts. Herein, we report a chiral dicationic bisguanidinium-catalyzed asymmetric oxidation reaction of alkenes with potassium permanganate. Chiral induction is attributed to ion-pairing interaction between chiral cation and enolate anion. The success of the current permanganate oxidation reaction together with mechanistic insights should provide inspiration for expansion to other anionic metal salts and would open up new paradigms for asymmetric transition metal catalysis, phase-transfer catalysis, and ion-pairing catalysis. PMID:26237178

  5. An exceptional P-H phosphonite: Biphenyl-2,2'-bisfenchylchlorophosphite and derived ligands (BIFOPs in enantioselective copper-catalyzed 1,4-additions

    Directory of Open Access Journals (Sweden)

    Neudörfl J-M

    2005-08-01

    Full Text Available Abstract Biphenyl-2,2'-bisfenchol (BIFOL based chlorophosphite, BIFOP-Cl, exhibits surprisingly high stabilities against hydrolysis as well as hydridic and organometallic nucleophiles. Chloride substitution in BIFOP-Cl proceeds only under drastic conditions. New enantiopure, sterically demanding phosphorus ligands such as a phosphoramidite, a phosphite and a P-H phosphonite (BIFOP-H are hereby accessible. In enantioselective Cu-catalyzed 1,4-additions of ZnEt2 to 2-cyclohexen-1-one, this P-H phosphonite (yielding 65% ee exceeds even the corresponding phosphite and phosphoramidite.

  6. Enantioselective resolution of (R,S)-1-phenylethanol catalyzed by lipases immobilized in starch films

    International Nuclear Information System (INIS)

    Lipases from different sources and two mycelium-bound lipases, in a free or immobilized form, in ginger starch film were screened as biocatalysts in the reaction of (R,S)-1-phenylethanol (1) with vinyl acetate and other acylating agents. The effect of various reaction parameters in the resolution of (1) catalyzed by lipase from Burkholderia cepacia (BCL) immobilized in ginger starch film was evaluated (acyl donor type, alcohol:acyl donor molar ratio, temperature and organic solvent). The catalytic efficiency of BCL immobilized in polymeric blends of ginger starch and polyethylene oxide (PEO), in different compositions, was also studied. Vinyl acetate and iso-propenyl acetate furnished the highest conversion (9%) and enantiomeric excess (> 99%) of the (R)-ester. The alcohol:acyl donor molar ratio and temperature optimum were 1:1 and 28 deg respectively. The mixture of n-hexane/glycerol (9:1 v:v) was the most adequate for this reaction (conversion 23%, E > 200). The ginger starch/PEO (7:3 m/m) blend was successfully reused six times consecutively. (author)

  7. Enantioselective resolution of (R,S)-1-phenylethanol catalyzed by lipases immobilized in starch films

    Energy Technology Data Exchange (ETDEWEB)

    Hoffmann, Isabel; Silva, Vanessa D.; Nascimento, Maria da G., E-mail: graca@qmc.ufsc.b [Universidade Federal de Santa Catarina (UFSC), Florianopolis, SC (Brazil). Dept. de Quimica

    2011-07-01

    Lipases from different sources and two mycelium-bound lipases, in a free or immobilized form, in ginger starch film were screened as biocatalysts in the reaction of (R,S)-1-phenylethanol (1) with vinyl acetate and other acylating agents. The effect of various reaction parameters in the resolution of (1) catalyzed by lipase from Burkholderia cepacia (BCL) immobilized in ginger starch film was evaluated (acyl donor type, alcohol:acyl donor molar ratio, temperature and organic solvent). The catalytic efficiency of BCL immobilized in polymeric blends of ginger starch and polyethylene oxide (PEO), in different compositions, was also studied. Vinyl acetate and iso-propenyl acetate furnished the highest conversion (9%) and enantiomeric excess (> 99%) of the (R)-ester. The alcohol:acyl donor molar ratio and temperature optimum were 1:1 and 28 deg respectively. The mixture of n-hexane/glycerol (9:1 v:v) was the most adequate for this reaction (conversion 23%, E > 200). The ginger starch/PEO (7:3 m/m) blend was successfully reused six times consecutively. (author)

  8. Ruthenium Catalyzed Diastereo- and Enantioselective Coupling of Propargyl Ethers with Alcohols: Siloxy-Crotylation via Hydride Shift Enabled Conversion of Alkynes to π-Allyls.

    Science.gov (United States)

    Liang, Tao; Zhang, Wandi; Chen, Te-Yu; Nguyen, Khoa D; Krische, Michael J

    2015-10-14

    The first enantioselective carbonyl crotylations through direct use of alkynes as chiral allylmetal equivalents are described. Chiral ruthenium(II) complexes modified by Josiphos (SL-J009-1) catalyze the C-C coupling of TIPS-protected propargyl ether 1a with primary alcohols 2a-2o to form products of carbonyl siloxy-crotylation 3a-3o, which upon silyl deprotection-reduction deliver 1,4-diols 5a-5o with excellent control of regio-, anti-diastereo-, and enantioselectivity. Structurally related propargyl ethers 1b and 1c bearing ethyl- and phenyl-substituents engage in diastereo- and enantioselective coupling, as illustrated in the formation of adducts 5p and 5q, respectively. Selective mono-tosylation of diols 5a, 5c, 5e, 5f, 5k, and 5m is accompanied by spontaneous cyclization to deliver the trans-2,3-disubstituted furans 6a, 6c, 6e, 6f, 6k, and 6m, respectively. Primary alcohols 2a, 2l, and 2p were converted to the siloxy-crotylation products 3a, 3l, and 3p, which upon silyl deprotection-lactol oxidation were transformed to the trans-4,5-disubstituted γ-butyrolactones 7a, 7l, and 7p. The formation of 7p represents a total synthesis of (+)-trans-whisky lactone. Unlike closely related ruthenium catalyzed alkyne-alcohol C-C couplings, deuterium labeling studies provide clear evidence of a novel 1,2-hydride shift mechanism that converts metal-bound alkynes to π-allyls in the absence of intervening allenes. PMID:26418572

  9. Amine-Catalyzed Asymmetric (3 + 3) Annulations of β'-Acetoxy Allenoates: Enantioselective Synthesis of 4H-Pyrans.

    Science.gov (United States)

    Ni, Chunjie; Tong, Xiaofeng

    2016-06-29

    The asymmetric (3 + 3) annulations of β'-acetoxy allenoates with either 3-oxo-nitriles or pyrazolones have been realized by using 6'-deoxy-6'-[(l)-N,N-(2,2'-oxidiethyl)-valine amido]quinine (6h) as the catalyst. The three functions of catalyst 6h, including Lewis base (quinuclidine N), H-bond donor (amide NH), and Brønsted base (morpholine N), cooperatively take crucial roles on the chemo- and enantioselectivity, allowing for the construction of 4H-pyran and 4H-pyrano[2,3-c]pyrazole in high yields and enantioselectivity. PMID:27310820

  10. Diastereo- and Enantioselective Iridium Catalyzed Coupling of Vinyl Aziridines with Alcohols: Site-Selective Modification of Unprotected Diols and Synthesis of Substituted Piperidines.

    Science.gov (United States)

    Wang, Gang; Franke, Jana; Ngo, Chinh Q; Krische, Michael J

    2015-06-24

    The chiral cyclometalated π-allyliridium ortho-C,O-benzoate complex (R)-Ir-VIb derived from [Ir(cod)Cl]2, allyl acetate, 4-cyano-3-nitro-benzoic acid, and (R)-MeO-BIPHEP catalyzes the coupling of N-(p-nitrophenylsulfonyl) protected vinyl aziridine 3a with primary alcohols 1a-1l to furnish branched products of C-C bond formation 4a-4l with good levels of anti-diastereo- and enantioselectivity. In the presence of 2-propanol, but under otherwise identical conditions, vinyl aziridine 3a and aldehydes 2a-2l engage in reductive coupling to furnish an equivalent set of adducts 4a-4l with roughly equivalent levels of anti-diastereo- and enantioselectivity. Using enantiomeric iridium catalysts, vinyl aziridine 3a reacts with unprotected chiral 1,3-diols 1m-1o in a site-selective manner to deliver the diastereomeric products of C-allylation syn-4m, -4n, -4o and anti-4m, -4n, -4o, respectively, with good isolated yields and excellent levels of catalyst-directed diastereoselectivity. These adducts were directly converted to the diastereomeric 2,4,5-trisubstituted piperidines syn-5m, -5n, -5o and anti-5m, -5n, -5o. PMID:26074091

  11. High Enantioselective Novozym 435-Catalyzed Esterification of (R,S)-Flurbiprofen Monitored with a Chiral Stationary Phase

    OpenAIRE

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

    2015-01-01

    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 o...

  12. Enantioselective Synthesis of Spiroindenes by Enol-Directed Rhodium(III)-Catalyzed C–H Functionalization and Spiroannulation

    Science.gov (United States)

    Reddy Chidipudi, Suresh; Burns, David J; Khan, Imtiaz; Lam, Hon Wai

    2015-01-01

    Chiral cyclopentadienyl rhodium complexes promote highly enantioselective enol-directed C(sp2)-H functionalization and oxidative annulation with alkynes to give spiroindenes containing all-carbon quaternary stereocenters. High selectivity between two possible directing groups, as well as control of the direction of rotation in the isomerization of an O-bound rhodium enolate into the C-bound isomer, appear to be critical for high enantiomeric excesses. PMID:26404643

  13. Enantioselective construction of quaternary stereogenic carbons by the Lewis base catalyzed additions of silyl ketene imines to aldehydes.

    Science.gov (United States)

    Denmark, Scott E; Wilson, Tyler W; Burk, Matthew T; Heemstra, John R

    2007-12-01

    Silyl ketene imines derived from a variety of alpha-branched nitriles have been developed as highly useful reagents for the construction of quaternary stereogenic centers via the aldol addition reaction. In the presence of SiCl4 and the catalytic action of chiral phosphoramide (R,R)-5, silyl ketene imines undergo extremely rapid and high yielding addition to a wide variety of aromatic aldehydes with excellent diastereo- and enantioselectivity. Of particular note is the high yields and selectivities obtained from electron-rich, electron-poor, and hindered aldehydes. The nitrile function serves as a useful precursor for further synthetic manipulation. PMID:17988135

  14. Diastereo- and Enantioselective Ruthenium Catalyzed Hydrohydroxyalkylation of 2-Silyl-Butadienes: Carbonyl syn-Crotylation from the Alcohol Oxidation Level

    OpenAIRE

    Zbieg, Jason R.; Moran, Joseph; Krische, Michael J.

    2011-01-01

    Exposure of alcohols 2a-2j to 2-silyl-butadienes in the presence of ruthenium complexes modified by (R)-SEGPHOS or (R)-DM-SEGPHOS results in redox-triggered generation of allylruthenium-aldehyde pairs, which combine to form products of carbonyl crotylation 4a-4j in the absence of stoichiometric byproducts and with high levels of syn-diastereo- and enantioselectivity. In the presence of isopropanol under otherwise identical conditions, aldehydes 3a-3j are converted to an equivalent set of addu...

  15. Construction of quaternary stereogenic carbon centers through copper-catalyzed enantioselective allylic cross-coupling with alkylboranes.

    Science.gov (United States)

    Hojoh, Kentaro; Shido, Yoshinori; Ohmiya, Hirohisa; Sawamura, Masaya

    2014-05-01

    A combination of an in situ generated chiral Cu(I) /DTBM-MeO-BIPHEP catalyst system and EtOK enabled the enantioselective SN 2'-type allylic cross-coupling between alkylborane reagents and γ,γ-disubstituted primary allyl chlorides with enantiocontrol at a useful level. The reaction generates a stereogenic quaternary carbon center having three sp(3) -alkyl groups and a vinyl group. This protocol allowed the use of terminal alkenes as nucleophile precursors, thus representing a formal reductive allylic cross-coupling of terminal alkenes. A reaction pathway involving addition/elimination of a neutral alkylcopper(I) species with the allyl chloride substrate is proposed. PMID:24668885

  16. Directed evolution of an enantioselective lipase

    OpenAIRE

    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 create by molecular biological methods novel enzymes which display high enantioselectivity. Results: A bacterial lipase from Pseudomonas aeruginosa (PAL) was evolved to catalyze with high enantioselect...

  17. 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.

  18. 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.

  19. Enantioselective [3 + 2] annulation of α-substituted allenoates with β,γ-unsaturated N-sulfonylimines catalyzed by a bifunctional dipeptide phosphine

    Science.gov (United States)

    Ni, Huanzhen; Yao, Weijun

    2016-01-01

    Summary The first enantioselective [3 + 2] annulation of α-substituted allenoates with β,γ-unsaturated N-sulfonylimines is described. In the presence of a dipeptide phosphine catalyst, a wide range of highly functionalized cyclopentenes bearing an all-carbon quaternary center were obtained in moderate to good yields and with good to excellent enantioselectivities. PMID:26977194

  20. Highly enantioselective and efficient synthesis of flavanones including pinostrobin through the rhodium-catalyzed asymmetric 1,4-addition.

    Science.gov (United States)

    Korenaga, Toshinobu; Hayashi, Keigo; Akaki, Yusuke; Maenishi, Ryota; Sakai, Takashi

    2011-04-15

    An efficient synthesis of bioactive chiral flavanones (1) was achieved through the Rh-catalyzed asymmetric 1,4-addition of arylboronic acid to chromone. The reaction in toluene proceeded smoothly at room temperature in the presence of 0.5% Rh catalyst with electron-poor chiral diphosphine MeO-F(12)-BIPHEP. In this reaction, the 1,2-addition to (S)-1 frequently occurred to yield (2S,4R)-2,4-diaryl-4-chromanol as a byproduct, which could be reduced by changing the reaction solvent to CH(2)Cl(2) to deactivate the Rh catalyst (3% required). PMID:21413690

  1. 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.

  2. 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.

  3. Chemo- and Enantioselective Addition and β-Hydrogen Transfer Reduction of Carbonyl Compounds with Diethylzinc Reagent in One Pot Catalyzed by a Single Chiral Organometallic Catalyst.

    Science.gov (United States)

    Huang, Huayin; Zong, Hua; Bian, Guangling; Song, Ling

    2015-12-18

    Using a single chiral phosphoramide-Zn(II) complex as the catalyst, the asymmetric β-H transfer reduction of aromatic α-trifluoromethyl ketones and enantioselective addition of aromatic aldehydes with Et2Zn in one pot were successfully realized, affording the corresponding additive products of secondary alcohols in high yields (up to 99%) with excellent enantioselectivities (up to 98% ee) and the reduction products of α-trifluoromethyl alcohols in good to excellent yields with up to 77% ee. PMID:26579727

  4. 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

    2014-02-01

    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. PMID:24467274

  5. Enantioselective Synthesis of Polysubstituted Spiro-nitroprolinates Mediated by a (R,R)-Me-DuPhos·AgF-Catalyzed 1,3-Dipolar Cycloaddition

    OpenAIRE

    Cayuelas Rubio, Alberto; Ortiz, Ricardo; Nájera Domingo, Carmen; Sansano, Jose M.; Larrañaga Agirre, Olatz; Cózar Ruano, Abel de; Cossío Mora, Fernando Pedro

    2016-01-01

    The synthesis of constrained spirocycles is achieved effectively by means of 1,3-dipolar cyclodditions employing α-imino γ-lactones as azomethine ylide precursors and nitroalkenes as dipolarophiles. The complex formed by (R,R)-Me-DuPhos 18 and AgF is the most efficient bifunctional catalyst. Final spiro-nitroprolinates cycloadducts are obtained in good to moderate yields and both high diastereo- and enantioselectivities. Density functional theory (DFT) calculations supported the expected abso...

  6. Enantioselective synthesis of dihydrocoumarin derivatives by chiral scandium(III)-complex catalyzed inverse-electron-demand hetero-Diels-Alder reaction.

    Science.gov (United States)

    Hu, Haipeng; Liu, Yangbin; Guo, Jing; Lin, Lili; Xu, Yali; Liu, Xiaohua; Feng, Xiaoming

    2015-03-01

    An asymmetric inverse-electron-demand hetero-Diels-Alder reaction between o-quinone methides and azlactones to generate potentially pharmacological active dihydrocoumarins has been achieved efficiently by using a chiral N,N'-dioxide-Sc(III) complex as the catalyst. The desired products were obtained in high yields with excellent enantioselectivities and diastereoselectivities (up to 94% yield, 96% ee and >19 : 1 dr) under mild reaction conditions. A concerted reaction pathway was confirmed by Operando IR and control experiments. PMID:25649623

  7. Enantioselective Total Synthesis of (+)-Salvileucalin B

    OpenAIRE

    Levin, Sergiy; Nani, Roger R.; Reisman, Sarah E.

    2011-01-01

    An enantioselective total synthesis of the diterpenoid natural product (+)-salvileucalin B is reported. Key findings include a copper-catalyzed arene cyclopropanation reaction to provide the unusual norcaradiene core and a reversible retro-Claisen rearrangement of a highly functionalized norcaradiene intermediate.

  8. Highly Diastereo- and Enantioselective Michael Addition of Nitroalkanes to 2-Enoyl-Pyridine N-Oxides Catalyzed by Scandium(III)/Copper(II) Complexes.

    Science.gov (United States)

    Li, Lijun; Zhang, Sheng; Hu, Yanbin; Li, Yanan; Li, Chong; Zha, Zhenggen; Wang, Zhiyong

    2015-09-01

    A C2 -symmetric Schiff-base ligand, derived from tridentate-Schiff-base, was developed and successfully applied to the asymmetric Michael addition of nitroalkanes to 2-enoyl-pyridine N-oxides. With this newly catalytic system, an unprecedented diastereoselectivity was obtained in the asymmetric Michael addition of nitroalkanes to 2-enoyl-pyridine N-oxides. In addition, a switch in enantioselectivity was achieved by using this newly catalytic system and our previous catalyst. After a facile reduction, the optically active adduct was converted to a biologically active dihydro-2H-pyrrol 4 a. Furthermore, a connection of two tridentate-Schiff-base subunits proved to be an effective strategy in ligand design. PMID:26202331

  9. (+)-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

  10. Epoxide hydrolase-catalyzed enantioselective conversion of trans-stilbene oxide: Insights into the reaction mechanism from steady-state and pre-steady-state enzyme kinetics.

    Science.gov (United States)

    Archelas, Alain; Zhao, Wei; Faure, Bruno; Iacazio, Gilles; Kotik, Michael

    2016-02-01

    A detailed kinetic study based on steady-state and pre-steady-state measurements is described for the highly enantioselective epoxide hydrolase Kau2. The enzyme, which is a member of the α/β-hydrolase fold family, preferentially reacts with the (S,S)-enantiomer of trans-stilbene oxide (TSO) with an E value of ∼200. The enzyme follows a classical two-step catalytic mechanism with formation of an alkyl-enzyme intermediate in the first step and hydrolysis of this intermediate in a rate-limiting second step. Tryptophan fluorescence quenching during TSO conversion appears to correlate with alkylation of the enzyme. The steady-state data are consistent with (S,S) and (R,R)-TSO being two competing substrates with marked differences in kcat and KM values. The high enantiopreference of the epoxide hydrolase is best explained by pronounced differences in the second-order alkylation rate constant (k2/KS) and the alkyl-enzyme hydrolysis rate k3 between the (S,S) and (R,R)-enantiomers of TSO. Our data suggest that during conversion of (S,S)-TSO the two active site tyrosines, Tyr(157) and Tyr(259), serve mainly as electrophilic catalysts in the alkylation half-reaction, polarizing the oxirane oxygen of the bound epoxide through hydrogen bond formation, however, without fully donating their hydrogens to the forming alkyl-enzyme intermediate. PMID:26714303

  11. γ‐ and δ-Lactams through Palladium-Catalyzed Intramolecular Allylic Alkylation: Enantioselective Synthesis, NMR Investigation, and DFT Rationalization

    DEFF Research Database (Denmark)

    Bantreil, Xavier; Prestat, Guillaume; Moreno, Aitor;

    2011-01-01

    The Pd-catalyzed intramolecular allylic alkylation of unsaturated amides to give gamma- and delta-lactams has been studied in the presence of chiral ligands. Ligand (R)-3,5-tBu-MeOBIPHEP (MeOBIPHEP=6,6'-dimethoxybiphenyl-2,2-diyl)bis(diphenylphosphine)) afforded the best results and allowed the c...... reaction pathways. The calculated energy differences were in good agreement with the experimentally observed enantiomeric ratios....

  12. Congested C-C Bonds by Pd-Catalyzed Enantioselective Allyl-Allyl Cross-Coupling, A Mechanism-Guided Solution

    OpenAIRE

    Ardolino, Michael J.; Morken, James P.

    2014-01-01

    Under the influence of a chiral bidentate diphosphine ligand, the Pd-catalyzed asymmetric cross-coupling of allylboron reagents and allylic electrophiles establishes 1,5-dienes with adjacent stereocenters in high regio- and stereoselectivity. . A mechanistic study of the coupling utilizing reaction calorimetry and density functional theory analysis suggests that the reaction operates through an inner-sphere 3,3'-reductive elimination pathway, which is both rate- and stereodefining. Coupled wi...

  13. Catalytic, Enantioselective Addition of Alkyl Radicals to Alkenes via Visible-Light-Activated Photoredox Catalysis with a Chiral Rhodium Complex.

    Science.gov (United States)

    Huo, Haohua; Harms, Klaus; Meggers, Eric

    2016-06-01

    An efficient enantioselective addition of alkyl radicals, oxidatively generated from organotrifluoroborates, to acceptor-substituted alkenes is catalyzed by a bis-cyclometalated rhodium catalyst (4 mol %) under photoredox conditions. The practical method provides yields up to 97% with excellent enantioselectivities up to 99% ee and can be classified as a redox neutral, electron-transfer-catalyzed reaction. PMID:27218134

  14. 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...

  15. Catalytic Enantioselective Conversion of Epoxides to Thiiranes.

    Science.gov (United States)

    Liao, Saihu; Leutzsch, Markus; Monaco, Mattia Riccardo; List, Benjamin

    2016-04-27

    A highly efficient and enantioselective Brønsted acid catalyzed conversion of epoxides to thiiranes has been developed. The reaction proceeds in a kinetic resolution, furnishing both epoxide and thiirane in high yields and enantiomeric purity. Heterodimer formation between the catalyst and sulfur donor affords an effective way to prevent catalyst decomposition and enables catalyst loadings as low as 0.01 mol %. PMID:27070207

  16. Organocatalytic enantioselective Michael addition reactions of fluoromalonates with α,β-unsaturated aldehydes

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    A new organocatalytic enantioselective Michael addition of α-fluoromalonate to enals has been developed.The process is efficiently catalyzed by readily available chiral diphenylpyrolinol TES ether under mild reaction conditions to afford versatile highly enantioenriched fluorinated aldehydes.

  17. Synthesis of Tributyl Citrate Catalyzed by MgBr2·6H2O%六水合溴化镁催化合成柠檬酸三丁酯

    Institute of Scientific and Technical Information of China (English)

    骈继鑫; 邓功达; 王湘波; 王卫; 何林

    2014-01-01

    Green plasticizer is a hot topic in currently academic research and tributyl citrate (abbreviated as TBC) as a new“green”plastic plasticizer, gets the favour of people of all ages.The esterification reaction of citric acid and n-butyl alcohol catalyzed by MgBr2·6H2O was studied in this article.Different factors such as catalyst loading,temperature,the ratio of citric acid and n-butyl alcohol,reaction time were investigated through controlled experiments and the optimal reaction conditions were obtained.When the reaction was conducted for 4 h at 140 ℃ in the presence of 10 mol% MgBr2·6H2O and a 5.5-fold excess of n-butyl alcohol, the desired tributyl citrate could be obtained above 98% yield.The method has the advantages of short reaction time,fewer side effects,high efficiency of esterification,cheapness,etc.%绿色增塑剂是当前学术界研究的一个热点,而柠檬酸三丁酯作为一种新型绿色的塑料增塑剂受到了人们的青睐,为此,本文研究了六水合溴化镁催化一水合柠檬酸与正丁醇酯化合成绿色增塑剂柠檬酸三丁酯的反应条件,通过实验考察了催化剂用量、反应温度、酸醇物质的量比、反应时间等因素对反应的影响,确定出最佳反应条件为:催化剂用量10 mol%,酸醇物质的量比1∶5.5,反应温度140℃,反应时间为4 h,酯化率可达到98%以上。上述方法具有反应时间短,副反应少,酯化率高,价廉易得等优点。

  18. A Green Enantioselective Aldol Condensation for the Undergraduate Organic Laboratory

    Science.gov (United States)

    Bennett, George D.

    2006-01-01

    A number of laboratory exercises for the organic chemistry curriculum that emphasize enantioselective synthesis of the aldol condensation which involves the proline-catalyzed condensation between acetone and isobutyraldehyde are explored. The experiment illustrates some of the trade-offs involved in green chemistry like the use of acetone in large…

  19. Enantioselective synthesis of 4H-pyranonaphthoquinones via sequential squaramide and silver catalysis.

    Science.gov (United States)

    Kaya, Uğur; Chauhan, Pankaj; Hack, Daniel; Deckers, Kristina; Puttreddy, Rakesh; Rissanen, Kari; Enders, Dieter

    2016-01-28

    An enantioselective one-pot Michael addition/hydroalkoxylation reaction between 2-hydroxy-1,4-naphthoquinones and alkyne-tethered nitroalkenes catalyzed by a cinchona-derived squaramide and a silver(I) salt has been developed. The sequential protocol provides a direct access to 4H-pyranonaphthoquinones in moderate to very good yields and good to excellent enantioselectivities at a very low catalyst loading (0.5 mol%) of the squaramide. PMID:26660230

  20. Bio-renewable enantioselective aldol reaction in natural deep eutectic solvents

    OpenAIRE

    Martínez Flores, Regina; Berbegal, Lucía; Guillena Townley, Gabriela; Ramón Dangla, Diego José

    2016-01-01

    Among the deep eutectic solvents (DES), natural deep eutectic solvents (NADES) formed by D-glucose and racemic malic acid are suitable media to perform the enantioselective L-proline catalyzed intermolecular aldol reaction, creating simultaneously and selectively a C–C bond and a new stereocenter. The scope of the reaction was found to be broad, with products being obtained with good levels of diastereo- and enantioselectivities. Furthermore, when the reaction was performed at a large scale, ...

  1. 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

    OpenAIRE

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

    2014-01-01

    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 o...

  2. Citrat og nyresten

    DEFF Research Database (Denmark)

    Osther, P J

    1993-01-01

    Citrate is an important naturally occurring inhibitor of calcium stone formation in urine. Urinary citrate excretion was examined in 43 consecutive patients with recurrent idiopathic calcium nephrolithiasis and in 50 normal controls by a specific enzymatic technique. Hypocitraturia (<1.6 mmol/24h...

  3. Enantioselective polyene cyclizations.

    Science.gov (United States)

    Ungarean, Chad N; Southgate, Emma H; Sarlah, David

    2016-06-28

    The cyclization of polyolefins represents a powerful tool for the rapid generation of molecular complexity. Within the last decade, significant discoveries have been made in the development of methods for converting prochiral polyene substrates into the corresponding polycyclic products with high levels of enantiocontrol. This review highlights advances in the area of enantioselective polyene cyclizations and their use in the synthesis of complex secondary metabolites. PMID:27143099

  4. Gastrointestinal citrate absorption in nephrolithiasis

    Science.gov (United States)

    Fegan, J.; Khan, R.; Poindexter, J.; Pak, C. Y.

    1992-01-01

    Gastrointestinal absorption of citrate was measured in stone patients with idiopathic hypocitraturia to determine if citrate malabsorption could account for low urinary citrate. Citrate absorption was measured directly from recovery of orally administered potassium citrate (40 mEq.) in the intestinal lavage fluid, using an intestinal washout technique. In 7 stone patients citrate absorption, serum citrate levels, peak citrate concentration in serum and area under the curve were not significantly different from those of 7 normal subjects. Citrate absorption was rapid and efficient in both groups, with 96 to 98% absorbed within 3 hours. The absorption of citrate was less efficient from a tablet preparation of potassium citrate than from a liquid preparation, probably due to a delayed release of citrate from wax matrix. However, citrate absorption from solid potassium citrate was still high at 91%, compared to 98% for a liquid preparation. Thus, hypocitraturia is unlikely to be due to an impaired gastrointestinal absorption of citrate in stone patients without overt bowel disease.

  5. Synthetic Study of Pactamycin: Enantioselective Construction of the Pactamycin Core with Five Contiguous Stereocenters.

    Science.gov (United States)

    Yamaguchi, Mami; Hayashi, Minami; Hamada, Yasumasa; Nemoto, Tetsuhiro

    2016-05-20

    A synthetic study of pactamycin is described. Enantioselective construction of the aminocyclopentitol core of pactamycin bearing five contiguous stereocenters was achieved based on an organocatalytic asymmetric aziridination of 2-cyclopentene-1-one, a regio- and diastereoselective 1,3-dipolar cycloaddition, and a rhodium-catalyzed C-H amination reaction. PMID:27171747

  6. 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).

  7. Enantioselective additions of copper acetylides to cyclic iminium and oxocarbenium ions

    Science.gov (United States)

    Liu, Jixin; Dasgupta, Srimoyee

    2015-01-01

    Summary The development of enantioselective, copper-catalyzed alkynylations of cyclic iminium and oxocarbenium ions is reviewed. The use of chiral copper-based catalysts has enabled high yields and enantioselectivites in the formation of nitrogen- and oxygen-containing heterocycles with α-stereogenic centers. This review highlights both the accomplishments and the future work needed in this important area. PMID:26877791

  8. Enantioselective Synthesis of SNAP-7941: Chiral Dihydropyrimidone Inhibitor of MCH1-R

    OpenAIRE

    Goss, Jennifer M.; Schaus, Scott E.

    2008-01-01

    An enantioselective synthesis of SNAP-7941, a potent melanin concentrating hormone receptor antagonist, was achieved using two organocatalytic methods. The first method utilized to synthesize the enantioenriched dihydropyrimidone core was the Cinchona alkaloid-catalyzed Mannich reaction of β-keto esters to acyl imines and the second was chiral phosphoric acid-catalyzed Biginelli reaction. Completion of the synthesis was accomplished via selective urea formation at the N3 position of the dihyd...

  9. Microreactors for Studying Enantioselective Reactions

    Czech Academy of Sciences Publication Activity Database

    Pavlorková, Jana

    Prague: Faculty of Chemical Technology, ICT, 2014. [Conference of Post-graduate Students. Prague (CZ), 26.06.2014] Institutional support: RVO:67985858 Keywords : enantioselective reactions * microreactors * molecular chirality Subject RIV: CI - Industrial Chemistry, Chemical Engineering

  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. Enantioselective Synthesis of Chiral Piperidines via the Stepwise Dearomatization/Borylation of Pyridines.

    Science.gov (United States)

    Kubota, Koji; Watanabe, Yuta; Hayama, Keiichi; Ito, Hajime

    2016-04-01

    We have developed a novel approach for the synthesis of enantioenriched 3-boryl-tetrahydropyridines via the Cu(I)-catalyzed regio-, diastereo-, and enantioselective protoborylation of 1,2-dihydropyridines, which were obtained by the partial reduction of the pyridine derivatives. This dearomatization/enantioselective borylation stepwise strategy provides facile access to chiral piperidines together with the stereospecific transformation of a stereogenic C-B bond from readily available starting materials. Furthermore, the utility of this method is demonstrated for the concise synthesis of the antidepressant drug (-)-paroxetine. A theoretical study of the reaction mechanism is also described. PMID:26967578

  12. The concise synthesis of chiral tfb ligands and their application to the rhodium-catalyzed asymmetric arylation of aldehydes

    OpenAIRE

    Nishimura, Takahiro; Kumamoto, Hana; Nagaosa, Makoto; Hayashi, Tamio

    2009-01-01

    New C2-symmetric tetrafluorobenzobarrelene ligands were prepared and applied successfully to the rhodium-catalyzed asymmetric addition of arylboronic acids to aromatic aldehydes giving chiral diarylmethanols in high yield with high enantioselectivity.

  13. 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. PMID:24302540

  14. 油包水微乳液中抗体酶催化布洛芬酯选择性水解的酶学特性%Enzymological Characteristics of Catalytic Antibody-catalyzed enantioselective Hydrolysis of Ibuprofen Ester in Water-in-oil microemulsion

    Institute of Scientific and Technical Information of China (English)

    杨根生; 戚映丹; 欧志敏; 姚善泾

    2009-01-01

    The asymmetric hydrolyzation of racemic ibuprofen ester is one of the most important methods for chiral separation of ibuprofen. A catalytic antibody that accelerates the rate of enantioselective hydrolysis of ibuprofen methyl ester was successfully elicited against an immunogen consisting of tetrahedral sulfate hapten attached to bovine serum albumin (BSA). The rate constant enhancement factor Kcat/Kuncat was about 1.6x104. The catalytic activity of the catalytic antibody in a reverse micelle reaction system based on sodium b/s (2-ethylhexyl) sodium sulfosuccinate (AOT) in isooctane was studied. Kinetic analysis of the catalytic antibody-catalyzed reaction was found to be possible in this system. Kinetic studies showed that hydrolysis in the microemulsion system follow Michaelis-Menten kinetics. The catalytic antibody can also accelerate catalysis of S-ibuprofen methyl ester in the microemulsion system. Temperature effects, the pH profile, Km,app and Kcat were determined. The dependence of the catalytic antibody hydrolytic activity on the Wo (molar ratio of water to surfactant) showed a bell-shaped curve, presenting a maximum at about wo = 21.%根据过渡态理论设计和合成了能诱导产生催化选择性水解布洛芬甲酯的催化抗体的四面体硫酸盐半抗原,并与牛血清白蛋白(BSA)偶联制备成免疫源,通过免疫手段成功筛选出具有加速选择性水解生成S-布洛芬的特异性催化抗体.其Kcat,app/Kuncat,app达1.6x104.进一步地将催化抗体运用到W/O微乳体系(反胶束)中进行布洛芬酯的选择性水解研究,其动力学研究证明其催化过程同样遵循Michaelis.Menten方程.考察了pH值和温度对催化初速度影响,Wo(体系中水和琥珀酸二辛酯磺酸钠(AOT)的摩尔比)对催化初速度影响呈现为钟罩型,最适的Wo.为21.

  15. Cyclopalladated complexes in enantioselective catalysis

    Energy Technology Data Exchange (ETDEWEB)

    Dunina, Valeria V; Gorunova, Olga N; Zykov, P A; Kochetkov, Konstantin A

    2011-01-31

    The results of the use of optically active palladacycles in enantioselective catalysis of [3,3]-sigmatropic rearrangements, aldol condensation, the Michael reaction and cross-coupling are analyzed. Reactions with allylic substrates or reagents and some other transformations are considered.

  16. Cyclopalladated complexes in enantioselective catalysis

    Science.gov (United States)

    Dunina, Valeria V.; Gorunova, Olga N.; Zykov, P. A.; Kochetkov, Konstantin A.

    2011-01-01

    The results of the use of optically active palladacycles in enantioselective catalysis of [3,3]-sigmatropic rearrangements, aldol condensation, the Michael reaction and cross-coupling are analyzed. Reactions with allylic substrates or reagents and some other transformations are considered.

  17. Understanding water effect on Candida antarctica lipase B activity and enantioselectivity towards secondary alcohols.

    OpenAIRE

    Léonard, Valérie; Marton, Z; Lamare, Sylvain; Hult, Karl; Graber, Marianne

    2009-01-01

    6 pages International audience The effect of water activity (aW) on Candida antarctica lipase B (CALB) activity and enantioselectivity towards secondary alcohols was assessed. Experimental results for the resolution of racemic pentan-2-ol, hexan-3-ol, butan-2-ol and octan-4-ol by immobilized CALB-catalyzed acylation with methyl propanoate, were obtained by using a solid/gas reactor. Water and substrate adsorption mechanism on immobilized CALB, were then studied using moisture sorption a...

  18. Enantioselective modular synthesis of cyclohexenones: total syntheses of (+)-crypto- and (+)-infectocaryone.

    Science.gov (United States)

    Franck, Géraldine; Brödner, Kerstin; Helmchen, Günter

    2010-09-01

    A modular synthesis of cyclohexenones is described and applied to the first enantioselective total syntheses of (+)-crypto- and (+)-infectocaryone. Key steps in the synthesis of cyclohexenones are an iridium-catalyzed allylic alkylation, nucleophilic allylation, and ring-closing metathesis. On the way to (+)-cryptocaryone, a catch and release strategy involving an iodolactonization/elimination and a regioselective C-acylation were used. PMID:20677804

  19. Enantioselective Cross-Coupling of meso-Epoxides with Aryl Halides

    OpenAIRE

    Zhao, Yang; Weix, Daniel J.

    2015-01-01

    The first enantioselective cross-electrophile coupling of aryl bromides with meso-epoxides to form trans-β-arylcycloalkanols is presented. The reaction is catalyzed by a combination of (bpy)NiCl2 and a chiral titanocene under reducing conditions. Yields range from 57 to 99% with 78–95% enantiomeric excess. The 30 examples include a variety of functional groups (ether, ester, ketone, nitrile, ketal, trifluoromethyl, sulfonamide, sulfonate ester), both aryl and vinyl halides, and five- to seven...

  20. Gold(I)-Catalyzed enantioselective synthesis of functionalized indenes

    OpenAIRE

    Martínez Cuezva, Alberto; García García, Patricia; Fernández Rodríguez, Manuel A.; Rodríguez, Félix; Sanz Díez, Roberto

    2010-01-01

    MEC/FEDER (CTQ2007-61436/BQU, FPU grant to A.M., Ramon y Cajal and Juan de la Cierva contracts to M.A.F.-R. and P.G.-G.) and Junta de Castilla y Leon (BU021A09) for financial support. We also thank Dr. A. Mendoza (Universidad de Oviedo) for his assistance with the X-ray crystallographic analysis

  1. Citrate-Stabilized Gold Nanorods

    OpenAIRE

    Mehtala, Jonathan G; Zemlyanov, Dmitry Y.; Max, Joann P.; Kadasala, Naveen; Zhao, Shou; Wei, Alexander

    2014-01-01

    Stable aqueous dispersions of citrate-stabilized gold nanorods (cit-GNRs) have been prepared in scalable fashion by surfactant exchange from cetyltrimethylammonium bromide (CTAB)-stabilized GNRs, using polystyrenesulfonate (PSS) as a detergent. The surfactant exchange process was monitored by infrared spectroscopy, surface-enhanced Raman scattering (SERS), and X-ray photoelectron spectroscopy (XPS). The latter established the quantitative displacement of CTAB (by PSS) and of PSS (by citrate)....

  2. Enhancement of Aminoacylase Activity by Sodium Citrate

    Institute of Scientific and Technical Information of China (English)

    于范利; 曹志方; 李森; 周海梦

    2001-01-01

    Kidney and other tissues of animals and humans have a high concentration of citrate which is an important intermediate substance in the citrate cycle. Citrate may play an important physiological role in metabolism. In this paper, we studied the interaction of the sodium salt of citrate with aminoacylase which is an important enzyme in metabolism and found sodium citrate can enhance the activity of aminoacylase. The maximum enzyme activity induced by sodium citrate increased approximately 3 folds over the enzyme activity without sodium citrate. The initial reaction rates (Ⅴ) for different concentrations of sodium citrate were obtained, showing that sodium citrate is a non-competitive activator. The result of the ANS binding fluorescence measurements for aminoacylase indicated that increasing sodium citrate concentrations markedly increased the ANS binding fluorescence with a blue shift of the emission spectra peak. This suggests the formation of more hydrophobic regions. Aggregates formed quickly when aminoacylase was incubated with sodium citrate (0.3 mol/L) and guanidinium chloride (0- 3. 5 mol/L). Aminoacylase lost enzyme activity in the guanidinium chloride more quickly in the presence of sodium citrate than in the absence of sodium citrate. The intrinsic fluorescence emission intensity decreased more quickly and the red shift of the emission spectra peak was larger than that without sodium citrate.

  3. 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.

  4. Studies on Atropo-Enantioselective Synthesis of the Natural Chiral Axial Biaryls

    Institute of Scientific and Technical Information of China (English)

    LIN Guo-Qiang

    2004-01-01

    Ary-aryl bond formation plays an important role in modem organic synthesis. These bonds are very of ten occurred in natural products such as alkaloids as well as in numerous biologically active parts of pharmaceutical and agrochemical specialties. In addition, they are also the scaffolds of some of the most efficient and selective ligands for asymmetric catalysts, especially when atropisomery is possible.In this report, we report the structure and the enantioselective synthesis of some natural occurring bioactive products. The focus will be Mainly in our recently discovered Ni(0) catalyzed homo-coupling and cross-coupling of aryl halide with coumarinyl mesylates and the enantioselective synthesis of phthalides in the presence of bidentated ligands with up to 99% e.e.

  5. Enantioselective synthesis of tetrafluorinated ribose and fructose.

    Science.gov (United States)

    Linclau, Bruno; Boydell, A James; Timofte, Roxana S; Brown, Kylie J; Vinader, Victoria; Weymouth-Wilson, Alexander C

    2009-02-21

    A perfluoroalkylidene lithium mediated cyclisation approach for the enantioselective synthesis of a tetrafluorinated aldose (ribose) and of a tetrafluorinated ketose (fructose), both in the furanose and in the pyranose form, is described. PMID:19194597

  6. Chiral Diamine-catalyzed Asymmetric Aldol Reaction

    Institute of Scientific and Technical Information of China (English)

    LI Hui; XU Da-zhen; WU Lu-lu; WANG Yong-mei

    2012-01-01

    A highly efficient catalytic system composed of a simple and commercially available chiral primary diamine (1R,2R)-cyclohexane-1,2-diamine(6) and trifluoroacetic acid(TFA) was employed for asymmetric Aldol reaction in i-PrOH at room temperature.A loading of 10%(molar fraction) catalyst 6 with TFA as a cocatalyst could catalyze the Aldol reactions of various ketones or aldehydes with a series of aromatic aldehydes,furnishing Aldol products in moderate to high yields(up to >99%) with enantioselectivities of up to >99% and diastereoselectivities of up to 99:1.

  7. Enantioselective Allylic C-H Oxidation of Terminal Olefins to Isochromans by Palladium(II)/Chiral Sulfoxide Catalysis.

    Science.gov (United States)

    Ammann, Stephen E; Liu, Wei; White, M Christina

    2016-08-01

    The enantioselective synthesis of isochroman motifs has been accomplished by palladium(II)-catalyzed allylic C-H oxidation from terminal olefin precursors. Critical to the success of this goal was the development and utilization of a novel chiral aryl sulfoxide-oxazoline (ArSOX) ligand. The allylic C-H oxidation reaction proceeds with the broadest scope and highest levels of asymmetric induction reported to date (avg. 92 % ee, 13 examples with greater than 90 % ee). PMID:27376625

  8. Catalytic, enantioselective, vinylogous aldol reactions.

    Science.gov (United States)

    Denmark, Scott E; Heemstra, John R; Beutner, Gregory L

    2005-07-25

    In 1935, R. C. Fuson formulated the principle of vinylogy to explain how the influence of a functional group may be felt at a distant point in the molecule when this position is connected by conjugated double-bond linkages to the group. In polar reactions, this concept allows the extension of the electrophilic or nucleophilic character of a functional group through the pi system of a carbon-carbon double bond. This vinylogous extension has been applied to the aldol reaction by employing "extended" dienol ethers derived from gamma-enolizable alpha,beta-unsaturated carbonyl compounds. Since 1994, several methods for the catalytic, enantioselective, vinylogous aldol reaction have appeared, with which varying degrees of regio- (site), enantio-, and diastereoselectivity can be attained. In this Review, the current scope and limitations of this transformation, as well as its application in natural product synthesis, are discussed. PMID:15940727

  9. Novel Pincer Complex-Catalyzed Transformations : Including Asymmetric Catalysis

    OpenAIRE

    Aydin, Juhanes

    2009-01-01

    This thesis is focused on the development of new pincer complex-catalyzed transformations. Optimization of the catalytic properties (fine-tuning) was directed to increase the catalytic activity as well as the chemo-, stereo- and enantioselectivity of the complexes. This was achieved by varying the heteroatoms in the terdentate pincer ligand, by changing the electronic properties of the coordinated aryl moiety and by implementing chiral functionalities in the pincer complexes. In the cross-cou...

  10. Organocatalytic Asymmetric α-Chlorination of 1,3-Dicarbonyl Compounds Catalyzed by 2-Aminobenzimidazole Derivatives

    Directory of Open Access Journals (Sweden)

    Daniel Serrano Sánchez

    2016-01-01

    Full Text Available Bifunctional chiral 2-aminobenzimidazole derivatives 1 and 2 catalyze the enantioselective stereodivergent α-chlorination of β-ketoesters and 1,3-diketone derivatives with up to 50% ee using N-chlorosuccinimide (NCS or 2,3,4,4,5,6-hexachloro-2,5-cyclohexadien-1-one as electrophilic chlorine sources.

  11. Palladium(0)-Catalyzed Intermolecular Allylic Dearomatization of Indoles by a Formal [4+2] Cycloaddition Reaction.

    Science.gov (United States)

    Gao, Run-Duo; Xu, Qing-Long; Zhang, Bo; Gu, Yiting; Dai, Li-Xin; You, Shu-Li

    2016-08-01

    Bridged indoline derivatives were synthesized by an intermolecular Pd-catalyzed allylic dearomatization reaction of substituted indoles. The reaction between indoles and allyl carbonates bearing a nucleophilic alcohol side-chain proceeds in a cascade fashion, providing bridged indolines in excellent enantioselectivity. PMID:27321285

  12. Regulatory Citrate Lyase Mutants of Salmonella typhimurium

    OpenAIRE

    Kulla, Hans G.

    1983-01-01

    Citrate lyase, the key enzyme of anaerobic citrate catabolism, could not be deleted from Salmonella typhimurium. The only class of mutants found had a mode of covalent regulation that strongly resembled the Escherichia coli system: citrate lyase was only active, i.e., acetylated, when a cosubstrate was present.

  13. Regulatory citrate lyase mutants of Salmonella typhimurium.

    Science.gov (United States)

    Kulla, H G

    1983-01-01

    Citrate lyase, the key enzyme of anaerobic citrate catabolism, could not be deleted from Salmonella typhimurium. The only class of mutants found had a mode of covalent regulation that strongly resembled the Escherichia coli system: citrate lyase was only active, i.e., acetylated, when a cosubstrate was present. PMID:6336740

  14. 21 CFR 582.5449 - Manganese citrate.

    Science.gov (United States)

    2010-04-01

    ... 21 Food and Drugs 6 2010-04-01 2010-04-01 false Manganese citrate. 582.5449 Section 582.5449 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) ANIMAL... Supplements 1 § 582.5449 Manganese citrate. (a) Product. Manganese citrate. (b) Conditions of use....

  15. 21 CFR 184.1449 - Manganese citrate.

    Science.gov (United States)

    2010-04-01

    ... 21 Food and Drugs 3 2010-04-01 2009-04-01 true Manganese citrate. 184.1449 Section 184.1449 Food... Specific Substances Affirmed as GRAS § 184.1449 Manganese citrate. (a) Manganese citrate (Mn3(C6H5O7)2, CAS... manganese carbonate from manganese sulfate and sodium carbonate solutions. The filtered and...

  16. 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.

  17. Enantioselective Total Synthesis of (+)-Steenkrotin A and Determination of Its Absolute Configuration.

    Science.gov (United States)

    Pan, Saiyong; Gao, Beiling; Hu, Jialei; Xuan, Jun; Xie, Hujun; Ding, Hanfeng

    2016-01-18

    The first enantioselective total synthesis of (+)-steenkrotin A has been achieved in 18 steps and 4.2 % overall yield. The key features of the strategy entail a Rh-catalyzed O-H bond insertion followed by an intramolecular carbonyl-ene reaction, two sequential SmI2 -mediated Ueno-Stork and ketyl-olefin cyclizations, and a cascade intramolecular aldol condensation/vinylogous retro-aldol/aldol process with inversion of the relative configuration at the C7 position. The absolute configuration of (+)-steenkrotin A was determined based on the stepwise construction of the stereocenters during the total synthesis. PMID:26660855

  18. Catalytic aerobic oxidation and tandem enantioselective cycloaddition in cascade multicomponent synthesis.

    Science.gov (United States)

    Potowski, Marco; Merten, Christian; Antonchick, Andrey P; Waldmann, Herbert

    2015-03-23

    An efficient multicomponent cascade transformation for the highly diastereo- and enantioselective synthesis of complex natural product inspired polycyclic products from simple starting materials is described. The cascade is initiated by copper-catalyzed aerobic CH oxidation of cyclopentadiene to cyclopentadienone followed by double catalytic asymmetric 1,3-dipolar cycloaddition of azomethine ylides. The cascade synthesis efficiently yields structurally complex 5,5,5-tricyclic products with eight stereocenters with good yields and excellent diastereo- and enantiocontrol using one catalyst. PMID:25676025

  19. Enantioselective cross-coupling of meso-epoxides with aryl halides.

    Science.gov (United States)

    Zhao, Yang; Weix, Daniel J

    2015-03-11

    The first enantioselective cross-electrophile coupling of aryl bromides with meso-epoxides to form trans-β-arylcycloalkanols is presented. The reaction is catalyzed by a combination of (bpy)NiCl2 and a chiral titanocene under reducing conditions. Yields range from 57 to 99% with 78-95% enantiomeric excess. The 30 examples include a variety of functional groups (ether, ester, ketone, nitrile, ketal, trifluoromethyl, sulfonamide, sulfonate ester), both aryl and vinyl halides, and five- to seven-membered rings. The intermediacy of a carbon radical is strongly suggested by the conversion of cyclooctene monoxide to an aryl [3.3.0]bicyclooctanol. PMID:25716775

  20. Genome-wide identification of citrus ATP-citrate lyase genes and their transcript analysis in fruits reveals their possible role in citrate utilization.

    Science.gov (United States)

    Hu, Xiao-Mei; Shi, Cai-Yun; Liu, Xiao; Jin, Long-Fei; Liu, Yong-Zhong; Peng, Shu-Ang

    2015-02-01

    ATP-citrate lyase (ACL, EC4.1.3.8) catalyzes citrate to oxaloacetate and acetyl-CoA in the cell cytosol, and has important roles in normal plant growth and in the biosynthesis of some secondary metabolites. We identified three ACL genes, CitACLα1, CitACLα2, and CitACLβ1, in the citrus genome database. Both CitACLα1 and CitACLα2 encode putative ACL α subunits with 82.5 % amino acid identity, whereas CitACLβ1 encodes a putative ACL β subunit. Gene structure analysis showed that CitACLα1 and CitACLα2 had 12 exons and 11 introns, and CitACLβ1 had 16 exons and 15 introns. CitACLα1 and CitACLβ1 were predominantly expressed in flower, and CitACLα2 was predominantly expressed in stem and fibrous roots. As fruits ripen, the transcript levels of CitACLα1, CitACLβ1, and/or CitACLα2 in cultivars 'Niuher' and 'Owari' increased, accompanied by significant decreases in citrate content, while their transcript levels decreased significantly in 'Egan No. 1' and 'Iyokan', although citrate content also decreased. In 'HB pummelo', in which acid content increased as fruit ripened, and in acid-free pummelo, transcript levels of CitACLα2, CitACLβ1, and/or CitACLα1 increased. Moreover, mild drought stress and ABA treatment significantly increased citrate contents in fruits. Transcript levels of the three genes were significantly reduced by mild drought stress, and the transcript level of only CitACLβ1 was significantly reduced by ABA treatment. Taken together, these data indicate that the effects of ACL on citrate use during fruit ripening depends on the cultivar, and the reduction in ACL gene expression may be attributed to citrate increases under mild drought stress or ABA treatment. PMID:25120169

  1. Enantioselective disposition of albuterol in humans.

    Science.gov (United States)

    Boulton, D W; Fawcett, J P

    1996-01-01

    The study of enantioselective disposition of chiral drugs is important to provide a rationale of plasma concentration-effect relationships, which are often misleading when based on total drug concentration. It is also important when considering new dosage routes or formulations in order to optimize therapeutic plasma concentrations of the active enantiomer. Improvements in the sensitivity and selectivity of biological assays coupled with the developments in chiral analysis have made it possible to study the enantioselective disposition of drugs. Although valuable pharmacokinetic data were obtained for the beta 2-agonists by nonenantioselective methodology, more recent chiral studies have revealed the existence of extensive enantioselectivity in the disposition of these agents. The most significant features of the enantioselective disposition of albuterol are the relatively rapid plasma clearance and low bioavailability of the eutomer. Although this in itself does not necessarily justify the development of a single enantiomer formulation, the implications of the high levels of distomer after i.v. and oral dosing await clarification. Similarly, more work is required to elucidate the consequences of the major difference in disposition between albuterol and terbutaline in humans through both in vivo and in vitro studies of the mechanisms giving rise to this phenomenon. The enantioselective disposition of the other clinically used beta 2-agonists, such as fenoterol, formoterol, and salmeterol also needs to be characterized. The metabolism of the majority of beta 2-agonists is generally by conjugation to give one major metabolite. The situation is therefore uncomplicated by multiple metabolic pathways, which may differ in the extent and direction of their enantioselectivity. Many beta 2-agonists are excreted largely unchanged in the urine making studies of urinary excretion accessible without the requirement for very sensitive assays. The realization that the enantiomers

  2. Directed Evolution of an Enantioselective Epoxide Hydrolase : Uncovering the Source of Enantioselectivity at Each Evolutionary Stage

    OpenAIRE

    Reetz, Manfred T.; Bocola, Marco; Wang, Li-Wen; Sanchis, Joaquin; Cronin, Annette; Arand, Michael; Zou, Jinyu; Archelas, Alain; Bottalla, Anne-Lise; Naworyta, Agata; Mowbray, Sherry L.

    2009-01-01

    Directed evolution of enzymes as enantioselective catalysts in organic chemistry is an alternative to traditional asymmetric catalysis using chiral transition-metal complexes or organocatalysts, the different approaches often being complementary. Moreover, directed evolution studies allow us to learn more about how enzymes perform mechanistically. The present study concerns a previously evolved highly enantioselective mutant of the epoxide hydrolase from Aspergillus niger in the hydrolytic ki...

  3. Citrate pharmacokinetics and calcium levels during high-flux dialysis with regional citrate anticoagulation

    OpenAIRE

    Kozik-Jaromin, Justyna; Nier, Volker; Heemann, Uwe; Kreymann, Bernhard; Böhler, Joachim

    2009-01-01

    Background. Regional citrate anticoagulation is a very effective anticoagulation method for haemodialysis. However, it is not widely used, primarily due to the risk of hypocalcaemia. We studied citrate and calcium kinetics to better understand safety aspects of this anticoagulation method. Methods. During 15 haemodialysis treatments with a calcium-free dialysis solution, citrate was infused pre-dialyser and calcium was substituted post-dialyser. Systemic and extracorporeal citrate and calcium...

  4. 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.

  5. 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.

  6. Membrane Topology of the Sodium Ion-dependent Citrate Carrier of Klebsiella pneumoniae. Evidence for a New Structural Class of Secondary Transporters

    OpenAIRE

    Geest, Marleen van; Lolkema, Juke S.

    1996-01-01

    The predicted secondary structure model of the sodium ion-dependent citrate carrier of Klebsiella pneumoniae (CitS) presents the 12-transmembrane helix motif observed for many secondary transporters. Biochemical evidence presented in this paper is not consistent with this model. N-terminal and C-terminal fusions of CitS with the biotin acceptor domain of the oxaloacetate decarboxylase of K. pneumoniae catalyze citrate transport, showing the correct folding of the CitS part of the fusion prote...

  7. PipPhos and MorfPhos : Privileged monodentate phosphoramidite ligands for rhodium-catalyzed asymmetric hydrogenation

    NARCIS (Netherlands)

    Bernsmann, Heiko; van den Berg, M; Hoen, Robert; Minnaard, AJ; Mehler, G; Reetz, MT; De Vries, JG; Feringa, BL

    2005-01-01

    A library of 20 monodentate phosphoramidite ligands has been prepared and applied in rhodium-catalyzed asymmetric hydrogenation. This resulted in the identification of two ligands, PipPhos and MorfPhos, that afford excellent and in several cases unprecedented enantioselectivities in the hydrogenatio

  8. Synthesis of novel chiral phosphine-triazine ligand derived from α-phenylethylamine for Pd-catalyzed asymmetric allylic alkylation

    Institute of Scientific and Technical Information of China (English)

    Jia Di Huang; Xiang Ping Hu; Zhuo Zheng

    2008-01-01

    A novel chiral phosphine-triazine ligand was synthesized from chiral model reaction of Pd-catalyzed allylic alkylation of rac-l,3-diphenylprop-2-en-l-yl pivalate with dimethyl malonate, good enantioselectivity (90% e.e.) was obtained by using this ligand.

  9. (Salen)Ti(Ⅳ)-Catalyzed Asymmetric Ring-opening of meso Epoxides Using Dithiophosphorus Acid as the Nucleophile

    Institute of Scientific and Technical Information of China (English)

    Zheng Hong ZHOU; Zhao Ming LI; Bing LIU; Kang Ying LI; Li Xin WANG; Guo Feng ZHAO; Qi Lin ZHOU; Chu Chi TANG

    2006-01-01

    The asymmetric ring-opening of epoxides with dithiophosphorus acids catalyzed by a (salen)Ti(Ⅳ) complex formed in situ from the reaction of Ti(OPr-i)4 and the chiral Schiff base derived from (1R,2R)-(+)-diaminocyclohexane was realized. The resulting products were obtained with low to good enantioselectivity (up to 73% ee).

  10. Ru/Me-BIPAM-Catalyzed Asymmetric Addition of Arylboronic Acids to Aliphatic Aldehydes and α-Ketoesters

    Directory of Open Access Journals (Sweden)

    Momoko Watanabe

    2011-06-01

    Full Text Available A ruthenium-catalyzed asymmetric arylation of aliphatic aldehydes and α-ketoesters with arylboronic acids has been developed, giving chiral alkyl(arylmethanols and α-hydroxy esters in good yields. The use of a chiral bidentate phosphoramidite ligand (Me-BIPAM achieved excellent enantioselectivities.

  11. Highly enantioselective synthesis of beta-heteroaryl-substituted dihydrochalcones through Friedel-Crafts alkylation of indoles and pyrrole.

    Science.gov (United States)

    Wang, Wentao; Liu, Xiaohua; Cao, Weidi; Wang, Jun; Lin, Lili; Feng, Xiaoming

    2010-02-01

    A highly enantioselective Friedel-Crafts (F-C) alkylation of indoles and pyrrole with chalcone derivatives catalyzed by a chiral N,N'-dioxide-Sc(OTf)(3) complex has been developed that tolerates a wide range of substrates. The reaction proceeds in moderate to excellent yields and high enantioselectivities (85-92 % enantiomeric excess) using 2 mol % (for indole) or 0.5 mol % (for pyrrole) catalyst loading, which showed the potential value of the catalyst system. Meanwhile, a strong positive nonlinear effect was observed. On the basis of the experimental results and previous reports, a possible working model is proposed to explain the origin of the activation and asymmetric induction. PMID:20013964

  12. Enantioselectivity in environmental risk assessment of modern chiral pesticides

    Energy Technology Data Exchange (ETDEWEB)

    Ye Jing [MOE Key Lab of Environmental Remediation and Ecosystem Health, College of Environmental and Resource Science, Zhejiang University, Hangzhou 310027 (China); Zhao Meirong [Research Center of Environmental Science, Zhejiang University of Technology, Hangzhou 310032 (China); Liu Jing [MOE Key Lab of Environmental Remediation and Ecosystem Health, College of Environmental and Resource Science, Zhejiang University, Hangzhou 310027 (China); Liu Weiping, E-mail: wliu@zju.edu.c [MOE Key Lab of Environmental Remediation and Ecosystem Health, College of Environmental and Resource Science, Zhejiang University, Hangzhou 310027 (China); Research Center of Environmental Science, Zhejiang University of Technology, Hangzhou 310032 (China)

    2010-07-15

    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. - Chiral pesticides could pose unpredictable enantioselective toxicity on non-target organisms.

  13. Enantioselectivity in environmental risk assessment of modern chiral pesticides

    International Nuclear Information System (INIS)

    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. - Chiral pesticides could pose unpredictable enantioselective toxicity on non-target organisms.

  14. Redox-Triggered C–C Coupling of Alcohols and Vinyl Epoxides: Diastereo- and Enantioselective Formation of All-Carbon Quaternary Centers via tert-(Hydroxy)-Prenylation

    OpenAIRE

    Feng, Jiajie; Garza, Victoria J.; Krische, Michael J.

    2014-01-01

    Iridium catalyzed primary alcohol oxidation triggers reductive C–O bond cleavage of isoprene oxide to form aldehyde-allyliridium pairs that combine to form products of tert-(hydroxy)-prenylation, a motif found in >2000 terpenoid natural products. Curtin–Hammett effects are exploited to enforce high levels of anti-diastereo- and enantioselectivity in the formation of an all-carbon quaternary center. The present redox-triggered carbonyl additions occur in the absence of stoichiometric byproduct...

  15. 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.

  16. Enantioselective aldol reactions with masked fluoroacetates

    Science.gov (United States)

    Saadi, Jakub; Wennemers, Helma

    2016-03-01

    Despite the growing importance of organofluorines as pharmaceuticals and agrochemicals, the stereoselective introduction of fluorine into many prominent classes of natural products and chemotherapeutic agents is difficult. One long-standing unsolved challenge is the enantioselective aldol reaction of fluoroacetate to enable access to fluorinated analogues of medicinally relevant acetate-derived compounds, such as polyketides and statins. Herein we present fluoromalonic acid halfthioesters as biomimetic surrogates of fluoroacetate and demonstrate their use in highly stereoselective aldol reactions that proceed under mild organocatalytic conditions. We also show that the methodology can be extended to formal aldol reactions with fluoroacetaldehyde and consecutive aldol reactions. The synthetic utility of the fluorinated aldol products is illustrated by the synthesis of a fluorinated derivative of the top-selling drug atorvastatin. The results show the prospects of the method for the enantioselective introduction of fluoroacetate to access a wide variety of highly functionalized fluorinated compounds.

  17. Robust, chiral, and porous BINAP-based metal-organic frameworks for highly enantioselective cyclization reactions.

    Science.gov (United States)

    Sawano, Takahiro; Thacker, Nathan C; Lin, Zekai; McIsaac, Alexandra R; Lin, Wenbin

    2015-09-30

    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. PMID:26335305

  18. 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.

  19. From a Sequential to a Concurrent Reaction in Aqueous Medium: Ruthenium-Catalyzed Allylic Alcohol Isomerization and Asymmetric Bioreduction.

    Science.gov (United States)

    Ríos-Lombardía, Nicolás; Vidal, Cristian; Liardo, Elisa; Morís, Francisco; García-Álvarez, Joaquín; González-Sabín, Javier

    2016-07-18

    The ruthenium-catalyzed redox isomerization of allylic alcohols was successfully coupled with the enantioselective enzymatic ketone reduction (mediated by KREDs) in a concurrent process in aqueous medium. The overall transformation, formally the asymmetric reduction of allylic alcohols, took place with excellent conversions and enantioselectivities, under mild reaction conditions, employing commercially and readily available catalytic systems, and without external coenzymes or cofactors. Optimization resulted in a multistep approach and a genuine cascade reaction where the metal catalyst and biocatalyst coexist from the beginning. PMID:27258838

  20. Chiral amides via copper-catalysed enantioselective conjugate addition

    NARCIS (Netherlands)

    Schoonen, Anne K.; Fernández-Ibáñez, M. Ángeles; Fañanás-Mastral, Martín; Teichert, Johannes F.; Feringa, Bernard

    2014-01-01

    A highly enantioselective one pot procedure for the synthesis of β-substituted amides was developed starting from the corresponding α,β-unsaturated esters. This new methodology is based on the copper-catalysed enantioselective conjugate addition of Grignard reagents to α,β-unsaturated esters and sub

  1. Anaphylaxis related to fentanyl citrate

    Directory of Open Access Journals (Sweden)

    Gaurav Singh Tomar

    2012-01-01

    Full Text Available Anaphylaxis is a fulminant, unexpected, immunoglobulin E-mediated allergic reaction that can be triggered by multiple agents. Common causative agents include neuromuscular blocking drugs, latex, antibiotics, colloids, hypnotics, and opioids. Fentanyl citrate, however, is an extremely unusual cause of anaphylaxis. Pulmonary edema, although uncommon in anaphylaxis, can be a prominent feature, as was in one of the patient. An adverse drug reaction is a noxious or unintended reaction to a drug that is administered in standard doses by the proper route for the purpose of prophylaxis, diagnosis, or treatment. Reactions are classified into two major subtypes: type A, which are dose dependent and predictable; and type B, which are not dose dependent and unpredictable. Unpredictable reactions include immune (allergic or no immune drug hypersensitivity reactions and are related to genetic susceptibilities or undefined mechanisms (formally called idiosyncratic and intolerance reactions. A drug allergy is always associated with an immune mechanism for which evidence of drug-specific antibodies or activated T lymphocytes can be shown. In the last few years, many novel drugs have entered clinical practice (i.e., biologic agents generating novel patterns of drug hypersensitivity reactions. As old drugs continue to be used, new clinical and biologic techniques enable improvement in the diagnosis of these reactions.

  2. Improvement of enantioselectivity of the B-type halohydrin hydrogen-halide-lyase from Corynebacterium sp. N-1074.

    Science.gov (United States)

    Watanabe, Fumiaki; Yu, Fujio; Ohtaki, Akashi; Yamanaka, Yasuaki; Noguchi, Keiichi; Odaka, Masafumi; Yohda, Masafumi

    2016-09-01

    Halohydrin hydrogen-halide-lyase (H-Lyase) is a bacterial enzyme involved in the degradation of halohydrins. This enzyme catalyzes the intramolecular nucleophilic displacement of a halogen by a vicinal hydroxyl group in halohydrins, producing the corresponding epoxides. The H-Lyases have been classified into A, B and C subtypes based on amino acid sequence similarities. These enzymes have attracted much attention as industrial catalysts in the synthesis of chiral chemicals from prochiral halohydrins. In the present study, we constructed mutants of B-type H-Lyase from Corynebacterium sp. N-1074 (HheB) displaying higher enantioselectivity by structure-based site-directed mutagenesis and random mutagenesis. A triple mutant of HheB exhibited 98.5% enantioselectivity, the highest ever reported, toward (R)-4-chloro-3-hydroxy-butyronitrile production, with the yield reaching approximately two-fold that of the wild-type enzyme. We discuss the structural basis of the high enantioselectivity and productivity of the mutant by comparing the crystal structures of the mutant HheB and the wild-type enzyme in complex with or without the substrate analogue. PMID:27215832

  3. Asymmetric Michael Addition of Activated Alkenes to Nitro Alkenes Catalyzed by Organic Catalyst

    Institute of Scientific and Technical Information of China (English)

    XUE Dong; CHEN Yong-Chun; CUI Xin; WANG Qi-Wei; ZHU Jin; DENG Jin-Gen

    2003-01-01

    @@ Enantioselective Michael addition is one of the most powerfulbond-forming reaction in organic synthesis. [1] A mong the Michael acceptors, nitro alkenes are very attractive, because the nitro group is the most electron-withdrawing group known and it can serve as masked functionality to be further transformed after the addition has taken place. [2] Recently, asymmetric Michael reactions catalyzed by organic catalyst have draw much attention.[3

  4. Mean platelet volume measurement, EDTA or citrate?

    Science.gov (United States)

    Dastjerdi, Mansour Siavash; Emami, Tajolmolouk; Najafian, Alireza; Amini, Masoud

    2006-10-01

    Most laboratories use EDTA for anticoagulation of whole blood prior to automated cell counting but due to platelet swelling, mean platelet volume (MPV) values may increase with its use. MPV changes may be less with acid citrate based anticoagulation. As MPV is a marker of platelet function and its precise measurement is important in a number of clinical situations, this study was performed to assess if EDTA and citrate based anticoagulated blood samples can be used interchangeably for MPV measurement. In this cross sectional descriptive study, EDTA and citrate based anticoagulated blood samples of the same patients were assessed by auto-analyzer within 1 h of sampling. In the 61 evaluated patients, there was a close correlation between MPV as measured by EDTA and citrate, but mean MPV measured from EDTA samples was 0.66 fL (9%) more than citrate. There was also a significant negative correlation between platelets count and MPV by both methods. The results of our study reveal that MPV can be measured accurately by both methods of anticoagulation; EDTA and citrate if analysis be performed within 1 h of sampling. PMID:17607580

  5. Phenylalanine Aminomutase-Catalyzed Addition of Ammonia to Substituted Cinnamic Acids : a Route to Enantiopure alpha- and beta-Amino Acids

    NARCIS (Netherlands)

    Szymanski, Wiktor; Wu, Bian; Weiner, Barbara; Wildeman, Stefaan de; Feringa, Ben L.; Janssen, Dick B.

    2009-01-01

    An approach is described for the synthesis of aromatic alpha- and beta-amino acids that Uses phenylalanine aminomutase to catalyze a highly enantioselective addition of ammonia to substituted cinnamic acids. The reaction has a broad scope and yields Substituted alpha- and beta-phenylalanines with ex

  6. Chiral N-1-adamantyl-N-trans-cinnamylaniline type ligands: synthesis and application to palladium-catalyzed asymmetric allylic alkylation of indoles.

    Science.gov (United States)

    Mino, Takashi; Nishikawa, Kenji; Asano, Moeko; Shima, Yamato; Ebisawa, Toshibumi; Yoshida, Yasushi; Sakamoto, Masami

    2016-08-21

    Such chiral phosphine-internal olefin hybrid type ligands as N-1-adamantyl-N-cinnamylaniline derivatives 1 with C(aryl)-N(amine) bond axial chirality were synthesized and utilized for the palladium-catalyzed asymmetric allylic alkylation of indoles to afford the desired products in high enantioselectivities (up to 98% ee). PMID:27425209

  7. Asymmetric Construction of Benzindoloquinolizidine: Application of An Organocatalytic Enantioselective Conjugate Addition-Cyclization Cascade Reaction

    International Nuclear Information System (INIS)

    We have developed the synthetic methodology of enantioenriched benzindoloquinolizidines based on the organocatalytic enantioselective conjugate addition-cyclization cascade reaction of o-N-(3-indoleacetyl)amino-cinnamaldehydes with malonates followed by an acid-catalyzed intramolecular Pictet-Spengler type cyclization. The asymmetric reaction using diphenylprolinol TMS ether as an organocatalyst produces the desired products with good to excellent yields and high enantioselectivities (up to 98% ee). The evaluation of the applications of this synthetic methodology for generating enantioenriched benzindolo-quinolizidines and studies on the biological activity of these compounds against human prostate cancer in particular are now in progress. Results of these studies will be presented in due course. Many new types of chemical reactions have been developed to facilitate easier synthesis of complex compounds. Among the strategies, domino reactions, which have been utilized for the efficient and stereoselective construction of complex molecules from simple precursors in a single process, are widely used due to their high synthetic efficiency by reducing both the number of synthetic operation required and the quantities of chemicals and solvents used

  8. 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. PMID:17583959

  9. Asymmetric Construction of Benzindoloquinolizidine: Application of An Organocatalytic Enantioselective Conjugate Addition-Cyclization Cascade Reaction

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Cheolwoong; Seo, Seung Woo; Lee, Yona; Kim, Sunggon [Kyonggi Univ., Suwon (Korea, Republic of)

    2014-02-15

    We have developed the synthetic methodology of enantioenriched benzindoloquinolizidines based on the organocatalytic enantioselective conjugate addition-cyclization cascade reaction of o-N-(3-indoleacetyl)amino-cinnamaldehydes with malonates followed by an acid-catalyzed intramolecular Pictet-Spengler type cyclization. The asymmetric reaction using diphenylprolinol TMS ether as an organocatalyst produces the desired products with good to excellent yields and high enantioselectivities (up to 98% ee). The evaluation of the applications of this synthetic methodology for generating enantioenriched benzindolo-quinolizidines and studies on the biological activity of these compounds against human prostate cancer in particular are now in progress. Results of these studies will be presented in due course. Many new types of chemical reactions have been developed to facilitate easier synthesis of complex compounds. Among the strategies, domino reactions, which have been utilized for the efficient and stereoselective construction of complex molecules from simple precursors in a single process, are widely used due to their high synthetic efficiency by reducing both the number of synthetic operation required and the quantities of chemicals and solvents used.

  10. Catalytic Enantioselective Functionalization of Unactivated Terminal Alkenes.

    Science.gov (United States)

    Coombs, John R; Morken, James P

    2016-02-01

    Terminal alkenes are readily available functional groups which appear in α-olefins produced by the chemical industry, and they appear in the products of many contemporary synthetic reactions. While the organic transformations that apply to alkenes are amongst the most studied reactions in all of chemical synthesis, the number of reactions that apply to nonactivated terminal alkenes in a catalytic enantioselective fashion is small in number. This Minireview highlights the cases where stereocontrol in catalytic reactions of 1-alkenes is high enough to be useful for asymmetric synthesis. PMID:26764019

  11. Aziridino Alcohols as Catalysts for the Enantioselective Addition of Diethylzinc to Aldehydes

    DEFF Research Database (Denmark)

    Tanner, David Ackland; Kornø, Hanne Tøfting; Guijarro, David;

    1998-01-01

    -symmetric aziridino diols 4a - 4h have been prepared from tartaric acid, and also catalyze the organozinc addition reaction with high chemicals yields and up to 94% e.e. C-2-symmetric ligands 5a - 5c, with ether sidechains, were less efficient (46% e.e. at best). The most efficient ligand (4c) was also......The chiral aziridino alcohols 1 -3 have been prepared either from amino acids (1a from serine; 1b - 1i and 3 from threonine; 2a - 2e from allo-threonine) or via asymmetric synthesis (1j, 1k, 1l and 2f from methyl cinnamate). These easily available ligands act as catalysts for the enantioselective...

  12. 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.

  13. Sodium bicarbonate and sodium citrate: ergogenic aids?

    Science.gov (United States)

    Requena, Bernardo; Zabala, Mikel; Padial, Paulino; Feriche, Belén

    2005-02-01

    Numerous studies have used exogenous administration of sodium bicarbonate (NaHCO(3)) and sodium citrate (Na-citrate) in an attempt to enhance human performance. After ingestion of NaHCO(3) and Na-citrate, two observations have been made: (a) There was great individual variability in the ergogenic benefit reached, which can be attributed to the level of physical conditioning of the subjects and to their tolerance of the buffer substance; and (b) the subjects who had ingested NaHCO(3) and Na-citrate show higher levels of pH, bicarbonate, and lactate ions concentrations in their exercising blood than do the subjects who had ingested the placebo. A majority of the studies have suggested that the ingestion of both substances provides an ergogenic effect due to the establishment and maintenance of an elevated pH level during exercise. However, the exact mechanism by which the ergogenic effects occur has not been demonstrated conclusively. Sodium bicarbonate and Na-citrate seem to be effective in activities with a sufficient duration to generate a difference in the hydrogen ion gradient, characterized by a very high intensity and involving large muscular groups. However, in activities of equally high intensity, but with longer duration, the results obtained have been conflicting and inconclusive. PMID:15705037

  14. Vibrational study of tamoxifen citrate polymorphism

    Science.gov (United States)

    Gamberini, M. C.; Baraldi, C.; Tinti, A.; Palazzoli, F.; Ferioli, V.

    2007-09-01

    The trans isomer of ( Z)-2-[ p-(1,2-diphenyl-butenyl)phenoxy]- N, N-dimethyletylamine (tamoxifen) is well known for its endocrine activity as an antiestrogenic agent. Its citrate salt, a widely used pharmaceutical agent, appears in three main polymorphic forms, two of which are well known (I and II) and another form not yet well evidenced. A vibrational study has been conducted for identifying the two known polymorphic forms of tamoxifen citrate (I and II) and for characterising the other form (form III) examined in this study. Other techniques for the characterization of the different polymorphs, such as XRDP, have been used.

  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. Enantioselective Degradation of Triadimefon in Green-house Soil

    OpenAIRE

    Liu Hong Cheng; Feng Lei; Shao Jingliang; Niu Zhi Rui; Li Qiwan

    2015-01-01

    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 ...

  17. Enantioselective Determination of Fluoxetine and Norfluoxetine in Wastewater

    OpenAIRE

    Ribeiro, Ana R.; Maia, Alexandra S.; Moreira, Irina S.; Afonso, Carlos; Castro, Paula M. L.; Tiritan, Maria E.

    2013-01-01

    Microbial degradation of chiral compounds during wastewater treatment processes can be enantioselective and needs chiral analytical methodology to discriminate the biodegradation of both enantiomers. An enantioselective HPLC-FD method was developed and validated to monitor the degradation of fluoxetine (FLX) enantiomers by wastewater and the possible formation of its metabolite norfluoxetine (NFLX). The Solid Phase Extraction (SPE) of 50 mL of wastewater samples on 500 mg ...

  18. Energy-dependent inactivation of citrate lyase in Enterobacter aerogenes.

    Science.gov (United States)

    Kulla, H; Gottschalk, G

    1977-12-01

    Enterobacter aerogenes was grown in continous culture with ammonia as the growth-limiting substrate, and changes in citrate lyase and citrate synthase activities were monitored after growth shifts from anaerobic growth on citrate to aerobic growth on citrate, aerobic growth on glucose, anaerobic growth on glucose, and anaerobic growth on glucose plus nitrate. Citrate lyase was inactivated during aerobic growth on glucose and during anaerobic growth with glucose plus nitrate. Inactivation did not occur during anaerobic growth on glucose, and as a result of the simultaneous presence of citrate lyase and citrate synthase, growth difficulties were observed. Citrate lyase inactivation consisted of deacetylation of the enzyme. The corresponding deacetylase could not be demonstrated in cell extracts, and it is concluded that, as in a number of other inactivations, electron transport to oxygen or nitrate was required for inactivation. PMID:924971

  19. Palladium-Catalyzed Decarbonylative Dehydration for the Synthesis of α-Vinyl Carbonyl Compounds and Total Synthesis of (-)-Aspewentins A, B, and C.

    Science.gov (United States)

    Liu, Yiyang; Virgil, Scott C; Grubbs, Robert H; Stoltz, Brian M

    2015-09-28

    The direct α-vinylation of carbonyl compounds to form a quaternary stereocenter is a challenging transformation. It was discovered that δ-oxocarboxylic acids can serve as masked vinyl compounds and be unveiled by palladium-catalyzed decarbonylative dehydration. The carboxylic acids are readily available through enantioselective acrylate addition or asymmetric allylic alkylation. A variety of α-vinyl quaternary carbonyl compounds are obtained in good yields, and an application in the first enantioselective total synthesis of (-)-aspewentins A, B, and C is demonstrated. PMID:26230413

  20. Physicochemical action of potassium-magnesium citrate in nephrolithiasis

    Science.gov (United States)

    Pak, C. Y.; Koenig, K.; Khan, R.; Haynes, S.; Padalino, P.

    1992-01-01

    Effect of potassium-magnesium citrate on urinary biochemistry and crystallization of stone-forming salts was compared with that of potassium citrate at same dose of potassium in five normal subjects and five patients with calcium nephrolithiasis. Compared to the placebo phase, urinary pH rose significantly from 6.06 +/- 0.27 to 6.48 +/- 0.36 (mean +/- SD, p less than 0.0167) during treatment with potassium citrate (50 mEq/day for 7 days) and to 6.68 +/- 0.31 during therapy with potassium-magnesium citrate (containing 49 mEq K, 24.5 mEq Mg, and 73.5 mEq citrate per day). Urinary pH was significantly higher during potassium-magnesium citrate than during potassium citrate therapy. Thus, the amount of undissociated uric acid declined from 118 +/- 61 mg/day during the placebo phase to 68 +/- 54 mg/day during potassium citrate treatment and, more prominently, to 41 +/- 46 mg/day during potassium-magnesium citrate therapy. Urinary magnesium rose significantly from 102 +/- 25 to 146 +/- 37 mg/day during potassium-magnesium citrate therapy but not during potassium citrate therapy. Urinary citrate rose more prominently during potassium-magnesium citrate therapy (to 1027 +/- 478 mg/day from 638 +/- 252 mg/day) than during potassium citrate treatment (to 932 +/- 297 mg/day). Consequently, urinary saturation (activity product) of calcium oxalate declined significantly (from 1.49 x 10(-8) to 1.03 x 10(-8) M2) during potassium-magnesium citrate therapy and marginally (to 1.14 x 10(-8) M2) during potassium citrate therapy.(ABSTRACT TRUNCATED AT 250 WORDS).

  1. 21 CFR 184.1195 - Calcium citrate.

    Science.gov (United States)

    2010-04-01

    ... Food Chemicals Codex, 3d ed. (1981), pp. 49 and 50, which is incorporated by reference in accordance with 5 U.S.C. 552(a) and 1 CFR part 51. Copies are available from the National Academy Press, 2101... 21 Food and Drugs 3 2010-04-01 2009-04-01 true Calcium citrate. 184.1195 Section 184.1195 Food...

  2. 21 CFR 184.1625 - Potassium citrate.

    Science.gov (United States)

    2010-04-01

    .... (b) The ingredient meets the specifications of the Food Chemicals Codex, 3d ed. (1981), p. 242, which is incorporated by reference in accordance with 5 U.S.C. 552(a) and 1 CFR part 51. Copies are... 21 Food and Drugs 3 2010-04-01 2009-04-01 true Potassium citrate. 184.1625 Section 184.1625...

  3. 21 CFR 184.1751 - Sodium citrate.

    Science.gov (United States)

    2010-04-01

    ...) The ingredient meets the specifications of the Food Chemicals Codex, 3d ed. (1981), pp. 283-284, which is incorporated by reference in accordance with 5 U.S.C. 552(a) and 1 CFR part 51. Copies are... 21 Food and Drugs 3 2010-04-01 2009-04-01 true Sodium citrate. 184.1751 Section 184.1751 Food...

  4. 14 N NQR spectrum of sildenafil citrate

    Science.gov (United States)

    Stephenson, David; Singh, Nadia

    2015-04-01

    The 14N nuclear quadrupole resonance (NQR) spectrum of sildenafil citrate tablets has been recorded allowing the quadrupole coupling constants and asymmetry parameters of all six unique nitrogen atoms in its structure to be determined. A density function calculation gives results that are largely in agreement with the experimental values.

  5. 14N NQR spectrum of sildenafil citrate

    International Nuclear Information System (INIS)

    The 14N nuclear quadrupole resonance (NQR) spectrum of sildenafil citrate tablets has been recorded allowing the quadrupole coupling constants and asymmetry parameters of all six unique nitrogen atoms in its structure to be determined. A density function calculation gives results that are largely in agreement with the experimental values

  6. 21 CFR 522.800 - Droperidol and fentanyl citrate injection.

    Science.gov (United States)

    2010-04-01

    ... 21 Food and Drugs 6 2010-04-01 2010-04-01 false Droperidol and fentanyl citrate injection. 522.800... § 522.800 Droperidol and fentanyl citrate injection. (a) Specifications. Droperidol and fentanyl citrate injection is a sterile solution containing 20 milligrams of droperidol and 0.4 milligram of fentanyl...

  7. 21 CFR 172.370 - Iron-choline citrate complex.

    Science.gov (United States)

    2010-04-01

    ... 21 Food and Drugs 3 2010-04-01 2009-04-01 true Iron-choline citrate complex. 172.370 Section 172... CONSUMPTION Special Dietary and Nutritional Additives § 172.370 Iron-choline citrate complex. Iron-choline citrate complex made by reacting approximately equimolecular quantities of ferric hydroxide, choline,...

  8. 21 CFR 573.580 - Iron-choline citrate complex.

    Science.gov (United States)

    2010-04-01

    ... 21 Food and Drugs 6 2010-04-01 2010-04-01 false Iron-choline citrate complex. 573.580 Section 573.580 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED... Food Additive Listing § 573.580 Iron-choline citrate complex. Iron-choline citrate complex made...

  9. Ventricular tachycardia after administration of sildenafil citrate: a case report

    Directory of Open Access Journals (Sweden)

    Rasmussen Jeppe G

    2007-08-01

    Full Text Available Abstract Background It has not previously been reported that sildenafil citrate causes malignant arrhythmias in humans. Case presentation A 41-year-old man developed sustained ventricular tachycardia following sildenafil citrate administration. Conclusion It cannot be dismissed that this patient experienced ventricular tachycardia as an adverse effect of sildenafil citrate administration.

  10. Ventricular tachycardia after administration of sildenafil citrate: a case report

    OpenAIRE

    Rasmussen Jeppe G; Toft Egon; Frøbert Ole

    2007-01-01

    Abstract Background It has not previously been reported that sildenafil citrate causes malignant arrhythmias in humans. Case presentation A 41-year-old man developed sustained ventricular tachycardia following sildenafil citrate administration. Conclusion It cannot be dismissed that this patient experienced ventricular tachycardia as an adverse effect of sildenafil citrate administration.

  11. Probing the "additive effect" in the proline and proline hydroxamic acid catalyzed asymmetric addition of nitroalkanes to cyclic enones.

    Science.gov (United States)

    Hanessian, Stephen; Govindan, Subramaniyan; Warrier, Jayakumar S

    2005-11-01

    The effect of chirality and steric bulk of 2,5-disubstituted piperazines as additives in the conjugate addition of 2-nitropropane to cyclohexenone, catalyzed by l-proline, was investigated. Neither chirality nor steric bulk affects the enantioselectivity of addition, which gives 86-93% ee in the presence of achiral and chiral nonracemic 2,5-disubstituted piperazines. Proline hydroxamic acid is shown for the first time to be an effective organocatalyst in the same Michael reaction. PMID:16189834

  12. Citrate Anticoagulation for CRRT in Children: Comparison with Heparin

    Directory of Open Access Journals (Sweden)

    Sara Nicole Fernández

    2014-01-01

    Full Text Available Regional anticoagulation with citrate is an alternative to heparin in continuous renal replacement therapies, which may prolong circuit lifetime and decrease hemorrhagic complications. A retrospective comparative cohort study based on a prospective observational registry was conducted including critically ill children undergoing CRRT. Efficacy, measured as circuit survival, and secondary effects of heparin and citrate were compared. 12 patients on CRRT with citrate anticoagulation and 24 patients with heparin anticoagulation were analyzed. Median citrate dose was 2.6 mmol/L. Median calcium dose was 0.16 mEq/kg/h. Median heparin dose was 15 UI/kg/h. Median circuit survival was 48 hours with citrate and 31 hours with heparin (P=0.028. 66.6% of patients treated with citrate developed mild metabolic alkalosis, which was directly related to citrate dose. There were no cases of citrate intoxication: median total calcium/ionic calcium index (CaT/I of 2.16 and a maximum CaT/I of 2.33, without metabolic acidosis. In the citrate group, 45.5% of patients developed hypochloremia and 27.3% hypomagnesemia. In the heparin group, 27.8% developed hypophosphatemia. Three patients were moved from heparin to citrate to control postoperatory bleeding. In conclusion citrate is a safe and effective anticoagulation method for CRRT in children and it achieves longer circuit survival than heparin.

  13. Citrate Anticoagulation for CRRT in Children: Comparison with Heparin

    Science.gov (United States)

    Fernández, Sara Nicole; Santiago, Maria José; López-Herce, Jesús; García, Miriam; Del Castillo, Jimena; Alcaraz, Andrés José; Bellón, Jose María

    2014-01-01

    Regional anticoagulation with citrate is an alternative to heparin in continuous renal replacement therapies, which may prolong circuit lifetime and decrease hemorrhagic complications. A retrospective comparative cohort study based on a prospective observational registry was conducted including critically ill children undergoing CRRT. Efficacy, measured as circuit survival, and secondary effects of heparin and citrate were compared. 12 patients on CRRT with citrate anticoagulation and 24 patients with heparin anticoagulation were analyzed. Median citrate dose was 2.6 mmol/L. Median calcium dose was 0.16 mEq/kg/h. Median heparin dose was 15 UI/kg/h. Median circuit survival was 48 hours with citrate and 31 hours with heparin (P = 0.028). 66.6% of patients treated with citrate developed mild metabolic alkalosis, which was directly related to citrate dose. There were no cases of citrate intoxication: median total calcium/ionic calcium index (CaT/I) of 2.16 and a maximum CaT/I of 2.33, without metabolic acidosis. In the citrate group, 45.5% of patients developed hypochloremia and 27.3% hypomagnesemia. In the heparin group, 27.8% developed hypophosphatemia. Three patients were moved from heparin to citrate to control postoperatory bleeding. In conclusion citrate is a safe and effective anticoagulation method for CRRT in children and it achieves longer circuit survival than heparin. PMID:25157369

  14. Lipase-catalyzed Kinetic Resolution of Racemic 1-Trimethylsilylethanol in Organic Solvent

    Institute of Scientific and Technical Information of China (English)

    吴虹; 宗敏华; 王菊芳; 罗涤衡; 娄文勇

    2004-01-01

    The enantioselective esterification of racemic 1-trimethylsilylethanol with acids catalyzed by lipase in organic solvent was successfully performed. The influence of some factors on the reaction was investigated. Among the four lipases explored, Candlda rugosa lipase (CRL) showed the highest activity and enantioselectivity. Octanoic acid was the best acyl donor among the eleven acids studied and n-hexane was the most suitable medium for the reaction. The optimum shaking rate and temperature were found to be 150 r-rain-i and 20~(3 to 30~C, respectively.The enantiomeric excess of the remaining (S)-(-)-1-trimethylsilylethanol was 93% when substrate conversion was 53% upon incubation of the reaction mixture at 30~C, 150 r-rain-i for 12 h.

  15. Enantioselective Recognition of Chiral Carboxylic Acids by a β-Amino Acid and 1,10-Phenanthroline Based Chiral Fluorescent Sensor

    OpenAIRE

    Yonghong Zhang; Fangzhi Hu; Bin Wang; Xiaomei Zhang; Chenjiang Liu

    2015-01-01

    A novel chiral 1,10-phenanthroline-based fluorescent sensor was designed and synthesized from optical active β-amino acids. It used 1,10-phenanthroline moiety as a fluorescent signaling site and binding site, with optically active β-amino acids as a chiral barrier site. Notably, the optically active β-amino acids were obtained by a Lewis base catalyzed hydrosilylation of β-enamino esters according to our former work. The chiral sensor has been used to conduct the enantioselective recognition ...

  16. Redox-triggered C-C coupling of alcohols and vinyl epoxides: diastereo- and enantioselective formation of all-carbon quaternary centers via tert-(hydroxy)-prenylation.

    Science.gov (United States)

    Feng, Jiajie; Garza, Victoria J; Krische, Michael J

    2014-06-25

    Iridium catalyzed primary alcohol oxidation triggers reductive C-O bond cleavage of isoprene oxide to form aldehyde-allyliridium pairs that combine to form products of tert-(hydroxy)-prenylation, a motif found in >2000 terpenoid natural products. Curtin-Hammett effects are exploited to enforce high levels of anti-diastereo- and enantioselectivity in the formation of an all-carbon quaternary center. The present redox-triggered carbonyl additions occur in the absence of stoichiometric byproducts, premetalated reagents, and discrete alcohol-to-aldehyde redox manipulations. PMID:24915473

  17. Pyrolytic citrate synthesis and ozone annealing

    International Nuclear Information System (INIS)

    A pyrolytic procedure is described that via a citrate synthesis allowed us to obtain very fine grained YBCO powders that, after a first furnace thermal treatment in ozone, results already to contain a large amount of superconducting microcrystals. A second identical thermal treatment gives a final product strongly textured, as shown by magnetic torque measurements. Complementary structural and diamagnetic measurement show the high quality of these sintered pellets. The role covered by both the pyrolytic preparation and the ozone annealing are discussed

  18. Pyrolitic citrate synthesis and ozone annealing

    International Nuclear Information System (INIS)

    A pyrolytic procedure that via a citrate synthesis allowed to obtain very fine grained YBCO powders that, after a first furnace thermal treatment in ozone, result already to contain a large amount of superconducting microcystals is described. A second identical thermal treatment gives a final product strongly textured, as shown by magnetic torque measurements. Complementary structural and diamagnetic measurements show the high quality of these sintered pellets. The role covered by both the pyrolytic preparation and the ozone annealing are discussed

  19. Photodynamical Properties of Various Phthalocyanine Citrates

    Czech Academy of Sciences Publication Activity Database

    Drobek, M.; Klusoň, Petr; Hejda, S.; Krýsa, J.; Rakušan, J.

    Prague: ICT Prague Press, 2010 - (Krýsa, J.), s. 68 ISBN 978-80-7080-750-7. [European Meeting on Solar Chemistry and Photocatalysis: Environmental Applications /6./. Prague (CZ), 13.06.2010-16.06.2010] R&D Projects: GA AV ČR KAN400720701; GA MŠk 1M0577 Institutional research plan: CEZ:AV0Z40720504 Keywords : phthalocyanine citrates * photodynamical properties Subject RIV: CA - Inorganic Chemistry

  20. Sildenafil Citrate in Fetal Growth Restriction

    OpenAIRE

    Panda, Subrat; Das, Ananya; Md Nowroz, Hossain

    2014-01-01

    Background Pregnancies with early onset fetal growth restriction have poor perinatal outcome. Sildenafil citrate (PDE -5 inhibitor) as a vasodilator increases utero-placental blood flow and potentiates fetal growth. Case Presentation In this study, a case was examined and Sildenafil was administered for her. It was found that Sildenafil improved the uterine blood flow with a favorable fetal outcome at delivery. Conclusion Sildenafil, as a vasodilator has emerged as a potential management opti...

  1. An enantioselective formal synthesis of montelukast sodium.

    Science.gov (United States)

    Bollikonda, Satyanarayana; Mohanarangam, Saravanan; Jinna, Rajender Reddy; Kandirelli, Venkata Kiran Kumar; Makthala, Laxman; Sen, Saikat; Chaplin, David A; Lloyd, Richard C; Mahoney, Thomas; Dahanukar, Vilas Hareshwar; Oruganti, Srinivas; Fox, Martin E

    2015-04-17

    A formal synthesis of the antiasthma drug montelukast sodium is described, wherein the key chiral diol intermediate was accessed with greater convergence of the C-C bond-forming steps as compared to previous routes. Improved synthetic efficiency was achieved by deploying homogeneous metal-based catalysis in two pivotal steps. In the first, a tandem Mizoroki-Heck reaction and double-bond isomerization between a previously known allyl alcohol intermediate and a hindered 2-(2-halophenyl)propan-2-ol secured direct access to the 3-(2-(2-hydroxypropan-2-yl)phenyl)-1-phenylpropan-1-one moiety in the product. In the second step, asymmetric hydrogenation of the ketone functionality in the Mizoroki-Heck reaction product provided a convenient method to introduce the benzylic alcohol chiral center and obtain the desired chiral diol precursor of montelukast sodium. A detailed catalyst screening led to the identification of ((R)-Xyl-BINAP)((R,R)-DPEN)RuCl2 as a catalyst that afforded an enantioselectivity of 99% ee in the hydrogenation step on a multigram lab scale at a molar substrate:catalyst loading of 5000:1. PMID:25807000

  2. Scalable enantioselective total synthesis of taxanes

    Science.gov (United States)

    Mendoza, Abraham; Ishihara, Yoshihiro; Baran, Phil S.

    2012-01-01

    Taxanes form a large family of terpenes comprising over 350 members, the most famous of which is Taxol (paclitaxel), a billion-dollar anticancer drug. Here, we describe the first practical and scalable synthetic entry to these natural products via a concise preparation of (+)-taxa-4(5),11(12)-dien-2-one, which has a suitable functional handle with which to access more oxidized members of its family. This route enables a gram-scale preparation of the ‘parent’ taxane—taxadiene—which is the largest quantity of this naturally occurring terpene ever isolated or prepared in pure form. The characteristic 6-8-6 tricyclic system of the taxane family, containing a bridgehead alkene, is forged via a vicinal difunctionalization/Diels-Alder strategy. Asymmetry is introduced by means of an enantioselective conjugate addition that forms an all-carbon quaternary centre, from which all other stereocentres are fixed through substrate control. This study lays a critical foundation for a planned access to minimally oxidized taxane analogues and a scalable laboratory preparation of Taxol itself.

  3. In vitro enantioselective human liver microsomal metabolism and prediction of in vivo pharmacokinetic parameters of tetrabenazine by DLLME-CE.

    Science.gov (United States)

    Bocato, Mariana Zuccherato; de Lima Moreira, Fernanda; de Albuquerque, Nayara Cristina Perez; de Gaitani, Cristiane Masetto; de Oliveira, Anderson Rodrigo Moraes

    2016-09-01

    A new capillary electrophoresis method for the enantioselective analysis of cis- and trans- dihydrotetrabenazine (diHTBZ) after in vitro metabolism by human liver microsomes (HLMs) was developed. The chiral electrophoretic separations were performed by using tris-phosphate buffer (pH 2.5) containing 1% (w/v) carboxymethyl-β-CD as background electrolyte with an applied voltage of +15kV and capillary temperature kept at 15°C. Dispersive liquid-liquid microextraction was employed to extract the analytes from HLMs. Dichloromethane was used as extraction solvent (75μL) and acetone as disperser solvent (150μL). The method was validated according to official guidelines and showed to be linear over the concentration range of 0.29-19.57μmolL(-1) (r=0.9955) for each metabolite enantiomer. Within- and between-day precision and accuracy evaluated by relative standard deviation and relative error were lower than 15% for all enantiomers. The stability assay showed that the analytes kept stable under handling, storage and in metabolism conditions. After method validation, an enantioselective in vitro metabolism and in vivo pharmacokinetic prediction was carried out. This study showed a stereoselective metabolism and the observed kinetic profile indicated a substrate inhibition behavior. DiHTBZ enantiomers were catalyzed mainly by CYP2C19 and the predicted clearance suggests that liver metabolism is the main route for TBZ elimination which supports the literature data. PMID:27381871

  4. Optimization and multigram scalability of a catalytic enantioselective borylative migration for the synthesis of functionalized chiral piperidines.

    Science.gov (United States)

    Kim, You-Ri; Hall, Dennis G

    2016-05-18

    The development of new, efficient and economical methods for the preparation of functionalized, optically enriched piperidines is important in the field of drug discovery where this class of heterocycles is often deemed a privileged structure. We have optimized a Pd-catalyzed enantioselective borylative migration of an alkenyl nonaflate derivative of the simple precursor, N-Boc-4-piperidone. This anomalous borylation reaction lends access to a chiral optically enriched piperidinyl allylic boronate that can be employed in carbonyl allylboration and stereoselective cross-coupling to produce substituted dehydropiperidines related to numerous pharmaceutical agents. A systematic fine-tuning of reaction conditions revealed that diethyl ether and the green solvent cyclopentyl methyl ether are suitable reaction solvents providing the highest enantioselectivity (up to 92% ee) under a low catalyst loading of 3 mol%. Optimization of the aldehyde allylboration step led to higher yields with further solvent economy. The multigram-scalability of the entire process was demonstrated under the reaction conditions that provide optimal atom-economy and efficiency. PMID:27143333

  5. 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.

  6. 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...... establish the trans homodecalin system found in the natural product...... catalysis, and an intramolecular aryne capture cyclization reaction. Pivotal to the successful completion of the synthesis was a sequence involving ring expansion from a [6-5-4] tricycle to a [6-7] bicyclic core followed by stereoselective hydrogenation of a sterically occluded tri-substituted olefin to...

  7. Reinvestigation of a Catalytic, Enantioselective Alkene Dibromination and Chlorohydroxylation.

    Science.gov (United States)

    Denmark, Scott E; Carson, Nessa

    2015-12-01

    Attempts to reproduce eight, putative, enantioselective dibromination and chlorohydroxylation reactions from oft-cited literature studies are described. The reactions were performed with full fidelity to the original report wherever possible. Analysis of the enantiomeric composition was performed by chiral stationary phase HPLC or SFC (CSP-HPLC or CSP-SFC), as opposed to the original report, which used chiral shift reagent NMR spectroscopy. After careful study, the reported levels of enantioselectivity were found to be incorrect. Possible explanations for the false positive results are discussed. PMID:26566099

  8. Regio- and Enantioselective Synthesis of Azole Hemiaminal Esters by Lewis Base Catalyzed Dynamic Kinetic Resolution.

    Science.gov (United States)

    Piotrowski, David W; Kamlet, Adam S; Dechert-Schmitt, Anne-Marie R; Yan, Jiangli; Brandt, Thomas A; Xiao, Jun; Wei, Liuqing; Barrila, Mark T

    2016-04-13

    We report a modular three-component dynamic kinetic resolution (DKR) that affords enantiomerically enriched hemiaminal esters derived from azoles and aldehydes. The novel and scalable reaction can be used to synthesize valuable substituted azoles in a regioselective manner by capping (e.g., acylation) of the equilibrating azole-aldehyde adduct. With the use of a prolinol-derived DMAP catalyst as the chiral Lewis base, the products can be obtained in high chemical yield and with high enantiomeric excess. The DKR was performed on a multikilogram scale to produce a tetrazole prodrug fragment for a leading clinical candidate that posed formidable synthesis challenges. PMID:27003237

  9. Highly enantioselective phenylacetylene addition to aromatic ketones catalyzed by cinchona alkaloid-aluminum complexes.

    Science.gov (United States)

    Liu, Lei; Wang, Rui; Kang, Yong-Feng; Chen, Chao; Xu, Zhao-Qing; Zhou, Yi-Feng; Ni, Ming; Cai, Hua-Qing; Gong, Mao-Zhen

    2005-02-01

    The catalytic asymmetric addition of phenylacetylene to aromatic ketones is reported. The catalyst, generated from commercially available Cinchona alkaloids and industrially available triethylaluminum, gives the expected tertiary alcohols with good enantiomeric excess (70-89%) and yields (60-83%). No previous case has been reported successfully using triethylaluminum as a Lewis acid in the asymmetric alkynylation of carbonylic derivatives, and thus we provide a new method to obtain optically active tertiary propargyl alcohols. PMID:15675878

  10. A Dual Lewis Base Activation Strategy for Enantioselective Carbene-Catalyzed Annulations

    OpenAIRE

    Izquierdo, Javier; Orue, Ane; Scheidt, Karl A.

    2013-01-01

    A dual activation strategy integrating NHC catalysis and a second Lewis base has been developed. NHC-bound homoenolate equivalents derived from α,β-unsaturated aldehydes combine with transient reactive o-quinione methides in an enatioselective formal [4+3] fashion to access 2-benzoxopinones. The overall approach provides a general blueprint for the integration of carbene catalysis with additional Lewis base activations modes.

  11. Enantioselective Ring Opening of meso-Cyclohexene Epoxide with Phenyllithium Catalyzed by Chiral Schiff Base Ligands

    OpenAIRE

    Norma Aidé Cortez; Lucía Z. Flores López; Miguel Parra Hake; Gerardo Aguirre; Lars H. Hellberg; Ratnasamy Somanathan

    2004-01-01

    Se ha sintetizado una biblioteca de ligandos quirales tipo; base de Schiff a partir de aldehídos aromáticos y aminoalcoholes; quirales. Se midió la capacidad catalítica de estos ligandos en la apertura; asimétrica del anillo de meso-epóxido de ciclohexeno con fenillitio; para dar (1S,2R)-fenilciclohexanol con 9-67% ee.

  12. Asymmetric Total Synthesis of Propindilactone G, Part 2: Enantioselective Construction of the Fully Functionalized BCDE Ring System.

    Science.gov (United States)

    Zhang, Jia-Jun; You, Lin; Wang, Yue-Fan; Li, Yuan-He; Liang, Xin-Ting; Zhang, Bo; Yang, Shou-Liang; Su, Qi; Chen, Jia-Hua; Yang, Zhen

    2016-05-01

    The enantioselective synthesis of the fully functionalized BCDE tetracyclic ring system of propindilactone G (A) is reported. Several synthetic methods were developed and applied to achieve this goal, including: 1) an asymmetric Diels-Alder reaction in the presence of Hayashi's catalyst for the synthesis of optically pure key intermediate 3; 2) an intramolecular Pauson-Khand reaction (PKR) for the stereoselective synthesis of the BCDE ring with an all-carbon chiral quaternary center at the C13 position by using the TMS-substituted acetylene as the substrate; and 3) Pd-catalyzed reductive hydrogenolysis for the stereoselective synthesis of the fully functionalized BCDE tetracyclic ring system. The chemistry developed herein provided a greater understanding of the total synthesis propindilactone G (A) and its analogues. PMID:26991420

  13. Characterization, crystallization and preliminary X-ray diffraction analysis of an (S)-specific esterase (pfEstA) from Pseudomonas fluorescens KCTC 1767: enantioselectivity for potential industrial applications

    International Nuclear Information System (INIS)

    An enantioselective esterase (pfEstA) from P. fluorescens KCTC 1767 was crystallized in space group P212121 and diffraction data were collected to a resolution of 1.9 Å. The structures and reaction mechanisms of enantioselective hydrolases, which can be used in industrial applications such as biotransformations, are largely unknown. Here, the X-ray crystallographic study of a novel (S)-specific esterase (pfEstA) from Pseudomonas fluorescens KCTC 1767, which can be used in the production of (S)-ketoprofen, is described. Multiple sequence alignments with other hydrolases revealed that pfEstA contains a conserved Ser67 within the S-X-X-K motif as well as a highly conserved Tyr156. Recombinant protein containing an N-terminal His tag was expressed in Escherichia coli, purified to homogeneity and characterized using SDS–PAGE, MALDI-TOF MS and enantioselective analysis. pfEstA was crystallized using a solution consisting of 1 M sodium citrate, 0.1 M CHES pH 9.5, and X-ray diffraction data were collected to a resolution of 1.9 Å with an Rmerge of 7.9%. The crystals of pfEstA belonged to space group P212121, with unit-cell parameters a = 65.31, b = 82.13, c = 100.41 Å, α = β = γ = 90°

  14. Urinary Citrate: A view in Chronic Renal Failure

    Directory of Open Access Journals (Sweden)

    SANTHOSH KUMAR.N

    2013-12-01

    Full Text Available Aim & Objective: To evaluate the 24 hour urinary citrate levels in chronic renal failure and healthy controls and to define the role of urinary citrates in the chronic renal failures. Materials and Methods: The 24 hours urinary citrates, Blood urea, Serum creatinine, Na+, K+were evaluated in 25 chronic renal failure patients and25 healthy subjects taken as controls. In both groups participants were on their usual diet. In addition, none of the participant was taking any drugs that could interfere with the citrate excretion. Results: The mean 24 hour urinary citrate excretion in patients and healthy controls was 296.3 ± 8.543mg and 323.9 ± 4.304mg respectively. Using previously defined values of normal urinary citrates as more than 320 mg.The difference in 24 hour urinary citrateexcretion in all patients and healthy control was statistically significant (

    citrate excretion in recurrent renal failures and healthy controls. Uniformly low citrate excretion in patients indicates that low citrate levels may be a feature seen in predisposing factor for renal failure

  15. Ti-catalyzed straightforward synthesis of exocyclic allenes.

    Science.gov (United States)

    Muñoz-Bascón, Juan; Hernández-Cervantes, Carmen; Padial, Natalia M; Alvarez-Corral, Míriam; Rosales, Antonio; Rodríguez-García, Ignacio; Oltra, J Enrique

    2014-01-13

    Exocyclic allenes constitute useful building blocks in organic synthesis and have recently been identified as key intermediates in the synthesis of natural products. Here the first general method for the most straightforward synthesis of exocyclic allenes reported to date is presented. This method is based on the Barbier-type cyclization of propargyl halides catalyzed by titanium; a safe, abundant, and ecofriendly metal. The reaction proceeds under mild conditions compatible with different functional groups and provides good yields of five-, six-, and seven-membered carbocycles and nitrogen-containing heterocycles bearing an exocyclic allene group. Experimental evidence supporting the proposed reaction mechanism is also provided. Moreover, this procedure can be carried out in an enantioselective manner by using chiral titanocene(III) catalysts. The utility of this method has been proved in the synthesis of the natural alkaloid stemoamide. PMID:24339337

  16. Docking of the Periplasmic FecB Binding Protein to the FecCD Transmembrane Proteins in the Ferric Citrate Transport System of Escherichia coli▿

    OpenAIRE

    Braun, Volkmar; Herrmann, Christina

    2007-01-01

    Citrate-mediated iron transport across the cytoplasmic membrane is catalyzed by an ABC transporter that consists of the periplasmic binding protein FecB, the transmembrane proteins FecC and FecD, and the ATPase FecE. Salt bridges between glutamate residues of the binding protein and arginine residues of the transmembrane proteins are predicted to mediate the positioning of the substrate-loaded binding protein on the transmembrane protein, based on the crystal structures of the ABC transporter...

  17. Iron-, Cobalt-, and Nickel-Catalyzed Asymmetric Transfer Hydrogenation and Asymmetric Hydrogenation of Ketones.

    Science.gov (United States)

    Li, Yan-Yun; Yu, Shen-Luan; Shen, Wei-Yi; Gao, Jing-Xing

    2015-09-15

    Chiral alcohols are important building blocks in the pharmaceutical and fine chemical industries. The enantioselective reduction of prochiral ketones catalyzed by transition metal complexes, especially asymmetric transfer hydrogenation (ATH) and asymmetric hydrogenation (AH), is one of the most efficient and practical methods for producing chiral alcohols. In both academic laboratories and industrial operations, catalysts based on noble metals such as ruthenium, rhodium, and iridium dominated the asymmetric reduction of ketones. However, the limited availability, high price, and toxicity of these critical metals demand their replacement with abundant, nonprecious, and biocommon metals. In this respect, the reactions catalyzed by first-row transition metals, which are more abundant and benign, have attracted more and more attention. As one of the most abundant metals on earth, iron is inexpensive, environmentally benign, and of low toxicity, and as such it is a fascinating alternative to the precious metals for catalysis and sustainable chemical manufacturing. However, iron catalysts have been undeveloped compared to other transition metals. Compared with the examples of iron-catalyzed asymmetric reduction, cobalt- and nickel-catalyzed ATH and AH of ketones are even seldom reported. In early 2004, we reported the first ATH of ketones with catalysts generated in situ from iron cluster complex and chiral PNNP ligand. Since then, we have devoted ourselves to the development of ATH and AH of ketones with iron, cobalt, and nickel catalysts containing novel chiral aminophosphine ligands. In our study, the iron catalyst containing chiral aminophosphine ligands, which are expected to control the stereochemistry at the metal atom, restrict the number of possible diastereoisomers, and effectively transfer chiral information, are successful catalysts for enantioselective reduction of ketones. Among these novel chiral aminophosphine ligands, 22-membered macrocycle P2N4

  18. Asymmetric epoxidation of allylic alcohols catalyzed by vanadium-binaphthylbishydroxamic Acid complex.

    Science.gov (United States)

    Noji, Masahiro; Kobayashi, Toshihiro; Uechi, Yuria; Kikuchi, Asami; Kondo, Hisako; Sugiyama, Shigeo; Ishii, Keitaro

    2015-03-20

    A vanadium-binaphthylbishydroxamic acid (BBHA) complex-catalyzed asymmetric epoxidation of allylic alcohols is described. The optically active binaphthyl-based ligands BBHA 2a and 2b were synthesized from (S)-1,1'-binaphthyl-2,2'-dicarboxylic acid and N-substituted-O-trimethylsilyl (TMS)-protected hydroxylamines via a one-pot, three-step procedure. The epoxidations of 2,3,3-trisubstituted allylic alcohols using the vanadium complex of 2a were easily performed in toluene with a TBHP water solution to afford (2R)-epoxy alcohols in good to excellent enantioselectivities. PMID:25714329

  19. Trienamine catalyzed asymmetric synthesis and biological investigation of a cytochalasin B-inspired compound collection.

    Science.gov (United States)

    Sellstedt, Magnus; Schwalfenberg, Melanie; Ziegler, Slava; Antonchick, Andrey P; Waldmann, Herbert

    2016-01-01

    Due to their enhanced metabolic needs many cancers need a sufficient supply of glucose, and novel inhibitors of glucose import are in high demand. Cytochalasin B (CB) is a potent natural glucose import inhibitor which also impairs the actin cytoskeleton leading to undesired toxicity. With a view to identifying selective glucose import inhibitors we have developed an enantioselective trienamine catalyzed synthesis of a CB-inspired compound collection. Biological analysis revealed that indeed actin impairment can be distinguished from glucose import inhibition and led to the identification of the first selective glucose import inhibitor based on the basic structural architecture of cytochalasin B. PMID:26606903

  20. Scandium-catalyzed asymmetric 1,6-addition of 3-substituted oxindoles to linear dienyl ketones.

    Science.gov (United States)

    Wang, Zhen; Kang, Tengfei; Yao, Qian; Ji, Jie; Liu, Xiaohua; Lin, Lili; Feng, Xiaoming

    2015-05-18

    The first example of a N,N'-dioxide-Sc(III) -catalyzed 1,6-addition of 3-substituted oxindoles to dienyl ketones has been developed. This procedure tolerates a relatively wide range of 3-substituted oxindoles under mild conditions, facilitating the preparation of various chiral oxindoles with quaternary stereocenters. In addition, the reliable catalyst was found to be effective in the asymmetric 1,6-addition of both δ-unsubstituted and δ-methyl-substituted dienyl ketones, achieving excellent regioselectivities and enantioselectivities (up to>99 % ee). PMID:25847816

  1. Copper-catalyzed asymmetric conjugate addition of organometallic reagents to extended Michael acceptors

    Science.gov (United States)

    Schmid, Thibault E; Drissi-Amraoui, Sammy; Crévisy, Christophe; Baslé, Olivier

    2015-01-01

    Summary 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. PMID:26734090

  2. 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.

  3. Kinetic analysis of the hydrolysis of methyl parathion using citrate-stabilized 10 nm gold nanoparticles.

    Science.gov (United States)

    Nita, Rafaela; Trammell, Scott A; Ellis, Gregory A; Moore, Martin H; Soto, Carissa M; Leary, Dagmar H; Fontana, Jake; Talebzadeh, Somayeh F; Knight, D Andrew

    2016-02-01

    "Ligand-free" citrate-stabilized 10 nm gold nanoparticles (AuNPs) promote the hydrolysis of the thiophosphate ester methyl parathion (MeP) on the surface of gold as a function of pH and two temperature values. At 50 °C, the active surface gold atoms show catalytic turnover ∼4 times after 8 h and little turnover of gold surface atoms at 25 °C with only 40% of the total atoms being active. From Michaelis-Menten analysis, k(cat) increases between pH 8 and 9 and decreases above pH 9. A global analysis of the spectral changes confirmed the stoichiometric reaction at 25 °C and the catalytic reaction at 50 °C and mass spectrometry confirmed the identity of p-nitrophenolate (PNP) product. Additional decomposition pathways involving oxidation and hydrolysis independent of the formation of PNP were also seen at 50 °C for both catalyzed and un-catalyzed reactions. This work represents the first kinetic analysis of ligand-free AuNP catalyzed hydrolysis of a thiophosphate ester. PMID:26547026

  4. Enantioselective total synthesis of (R)-(−)-complanine

    OpenAIRE

    Kamanos, Krystal A D; Jonathan M. Withey

    2012-01-01

    A route is described for the enantioselective synthesis of (R)-(−)-complanine, a marine natural product isolated from Eurythoe complanata, and known to be a causative agent in inflammation. An organocatalytic, asymmetric oxyamination of a homoconjugated all-Z-dienal intermediate provides versatile and efficient access to the natural product.

  5. Enantioselective total synthesis of (R)-(−)-complanine

    OpenAIRE

    Kamanos, Krystal A D; Jonathan M. Withey

    2012-01-01

    A route is described for the enantioselective synthesis of (R)-(−)-complanine, a marine natural product isolated from Eurythoe complanata, and known to be a causative agent in inflammation. An organocatalytic, asymmetric oxyamination of a homoconjugated all-Z-dienal intermediate provides versatile and efficient access to the natural product.

  6. DNA and RNA induced enantioselectivity in chemical synthesis

    NARCIS (Netherlands)

    Roelfes, Gerard

    2007-01-01

    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

  7. Design of flavin-cyclodextrin conjugates for enantioselective sulfoxidations

    Czech Academy of Sciences Publication Activity Database

    Zelenka, J.; Kraus, Tomáš; Cibulka, R.

    Praha : Czech Chemical Society, 2015. s. 158. [Liblice 2015. Advances in Organic, Bioorganic and Pharmaceutical Chemistry /50./. 06.11.2015-08.11.2015, Olomouc] Institutional support: RVO:61388963 Keywords : organocatalysis * enantioselective oxidations * flavin- cyclodextrin conjugates Subject RIV: CC - Organic Chemistry

  8. Loop grafting of Bacillus subtilis lipase A: inversion of enantioselectivity.

    Science.gov (United States)

    Boersma, Ykelien L; Pijning, Tjaard; Bosma, Margriet S; van der Sloot, Almer M; Godinho, Luís F; Dröge, Melloney J; Winter, Remko T; van Pouderoyen, Gertie; Dijkstra, Bauke W; Quax, Wim J

    2008-08-25

    Lipases are successfully applied in enantioselective biocatalysis. Most lipases contain a lid domain controlling access to the active site, but Bacillus subtilis Lipase A (LipA) is a notable exception: its active site is solvent exposed. To improve the enantioselectivity of LipA in the kinetic resolution of 1,2-O-isopropylidene-sn-glycerol (IPG) esters, we replaced a loop near the active-site entrance by longer loops originating from Fusarium solani cutinase and Penicillium purpurogenum acetylxylan esterase, thereby aiming to increase the interaction surface for the substrate. The resulting loop hybrids showed enantioselectivities inverted toward the desired enantiomer of IPG. The acetylxylan esterase-derived variant showed an inversion in enantiomeric excess (ee) from -12.9% to +6.0%, whereas the cutinase-derived variant was improved to an ee of +26.5%. The enantioselectivity of the cutinase-derived variant was further improved by directed evolution to an ee of +57.4%. PMID:18721749

  9. Side arm strategy for catalyst design: modifying bisoxazolines for remote control of enantioselection and related.

    Science.gov (United States)

    Liao, Saihu; Sun, Xiu-Li; Tang, Yong

    2014-08-19

    higher efficiency and diastereo- and enantioselectivity with better impurity tolerance and stability. Moreover, in several TOX-metal complex catalyzed reactions such as Friedel-Crafts reaction and [3 + 2] cycloaddition, stereoselectivity could be switched based on reaction conditions. These ligands were particularly prominent in the remote controls of enantioselection such as the conjugate additions to alkylidene malonates and ring-opening/cyclization cascades of cyclopropanes, for which high stereoselectivity is usually difficult to achieve due to the poor chiral communication. The works by us and other groups have demonstrated that the side arm strategy can be employed as a general principle for ligand and catalyst design and should not be limited to the BOX scaffolds and the reactions described in this Account. Wide application of the new strategy in organometallic homogeneous catalysis can be anticipated. PMID:24837859

  10. Muon Catalyzed Fusion

    Science.gov (United States)

    Armour, Edward A.G.

    2007-01-01

    Muon catalyzed fusion is a process in which a negatively charged muon combines with two nuclei of isotopes of hydrogen, e.g, a proton and a deuteron or a deuteron and a triton, to form a muonic molecular ion in which the binding is so tight that nuclear fusion occurs. The muon is normally released after fusion has taken place and so can catalyze further fusions. As the muon has a mean lifetime of 2.2 microseconds, this is the maximum period over which a muon can participate in this process. This article gives an outline of the history of muon catalyzed fusion from 1947, when it was first realised that such a process might occur, to the present day. It includes a description of the contribution that Drachrnan has made to the theory of muon catalyzed fusion and the influence this has had on the author's research.

  11. Diffuse abdominal gallium-67 citrate uptake in salmonella infections

    International Nuclear Information System (INIS)

    Two pediatric patients with salmonella infections (one with typhoid fever and the second with salmonella C2 gastroenteritis), had a diffuse abdominal uptake of Ga-67 citrate. The possible explanation for this finding is discussed. Salmonella infection should be included as a cause in the differential diagnosis of diffuse accumulation of Ga-67 citrate

  12. Citrate increases glass transition temperature of vitrified sucrose preparations

    NARCIS (Netherlands)

    Kets, E.P.W.; Lipelaar, P.J.; Hoekstra, F.A.; Vromans, H.

    2004-01-01

    The aim of this study was to investigate the effect of sodium citrate on the properties of dried amorphous sucrose glasses. Addition of sodium citrate to a sucrose solution followed by freeze-drying or convective drying resulted in a glass transition temperature (T-g) that was higher than the well-s

  13. Injectable citrate-modified Portland cement for use in vertebroplasty.

    Science.gov (United States)

    Wynn-Jones, Gareth; Shelton, Richard M; Hofmann, Michael P

    2014-11-01

    The injectability of Portland cement (PC) with several citrate additives was investigated for use in clinical applications such as vertebroplasty (stabilization of a fractured vertebra with bone cement) using a syringe. A 2-wt % addition of sodium or potassium citrate with PC significantly improved cement injectability, decreased cement setting times from over 2 h to below 25 min, while increasing the compressive strength to a maximum of 125 MPa. Zeta-potential measurements indicated that the citrate anion was binding to one or more of the positively charged species causing charged repulsion between cement particles which dispersed aggregates and caused the liquefying effect of the anion. Analysis of the hydrating phases of PC indicated that the early strength producing PC phase (ettringite) developed within the first 2 h of setting following addition of the citrate anion, while this did not occur in the control cement (PC only). Within 24 h ettringite developed in PC as well as calcium-silicate-hydrate (C-S-H), the major setting phase of PC, whereas cements containing citrate did not develop this phase. The evidence suggested that in the presence of citrate the cements limited water supply appeared to be utilized for ettringite formation, producing the early strength of the citrate cements. The present study has demonstrated that it is possible to modify PC with citrate to both improve the injectability and crucially reduce the setting times of PC while improving the strength of the cement. PMID:24711245

  14. 21 CFR 520.622b - Diethylcarbamazine citrate syrup.

    Science.gov (United States)

    2010-04-01

    ... 21 Food and Drugs 6 2010-04-01 2010-04-01 false Diethylcarbamazine citrate syrup. 520.622b Section... Diethylcarbamazine citrate syrup. (a)(1) Specifications. Each milliliter of syrup contains 60 milligrams of... veterinarian. (b)(1) Specifications. Each milliliter of syrup contains 60 milligrams of...

  15. 21 CFR 520.622c - Diethylcarbamazine citrate chewable tablets.

    Science.gov (United States)

    2010-04-01

    ....622c, see the List of CFR Sections Affected, which appears in the Finding Aids section of the printed... 21 Food and Drugs 6 2010-04-01 2010-04-01 false Diethylcarbamazine citrate chewable tablets. 520... Diethylcarbamazine citrate chewable tablets. (a) Specifications. Each chewable tablet contains 30, 45, 60, 120,...

  16. 21 CFR 520.622a - Diethylcarbamazine citrate tablets.

    Science.gov (United States)

    2010-04-01

    ... 21 Food and Drugs 6 2010-04-01 2010-04-01 false Diethylcarbamazine citrate tablets. 520.622a... Diethylcarbamazine citrate tablets. (a) Sponsors. (1) See 015579 in § 510.600(c) of this chapter for use of 50, 200, and 400 milligram tablets for prevention of heartworm disease in dogs and as an aid in the...

  17. 21 CFR 520.623 - Diethylcarbamazine citrate, oxibendazole chewable tablets.

    Science.gov (United States)

    2010-04-01

    ... 21 Food and Drugs 6 2010-04-01 2010-04-01 false Diethylcarbamazine citrate, oxibendazole chewable tablets. 520.623 Section 520.623 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND... § 520.623 Diethylcarbamazine citrate, oxibendazole chewable tablets. (a) Specifications. Each...

  18. Structural Basis for Norovirus Inhibition and Fucose Mimicry by Citrate

    Energy Technology Data Exchange (ETDEWEB)

    Hansman, Grant S.; Shahzad-ul-Hussan, Syed; McLellan, Jason S.; Chuang, Gwo-Yu; Georgiev, Ivelin; Shimoike, Takashi; Katayama, Kazuhiko; Bewley, Carole A.; Kwong, Peter D. (NIAID)

    2012-01-20

    Human noroviruses bind with their capsid-protruding domains to histo-blood-group antigens (HBGAs), an interaction thought to direct their entry into cells. Although human noroviruses are the major cause of gastroenteritis outbreaks, development of antivirals has been lacking, mainly because human noroviruses cannot be cultivated. Here we use X-ray crystallography and saturation transfer difference nuclear magnetic resonance (STD NMR) to analyze the interaction of citrate with genogroup II (GII) noroviruses. Crystals of citrate in complex with the protruding domain from norovirus GII.10 Vietnam026 diffracted to 1.4 {angstrom} and showed a single citrate bound at the site of HBGA interaction. The citrate interaction was coordinated with a set of capsid interactions almost identical to that involved in recognizing the terminal HBGA fucose, the saccharide which forms the primary conserved interaction between HBGAs and GII noroviruses. Citrate and a water molecule formed a ring-like structure that mimicked the pyranoside ring of fucose. STD NMR showed the protruding domain to have weak affinity for citrate (460 {mu}M). This affinity, however, was similar to the affinities of the protruding domain for fucose (460 {mu}M) and H type 2 trisaccharide (390 {mu}M), an HBGA shown previously to be specifically recognized by human noroviruses. Importantly, competition STD NMR showed that citrate could compete with HBGA for norovirus binding. Together, the results suggest that citrate and other glycomimetics have the potential to block human noroviruses from binding to HBGAs.

  19. 99mTc-Citrate versus 67Ga-citrate for the scintigraphic visualization of inflammatory lesions

    International Nuclear Information System (INIS)

    Citric acid was labeled with 99mTc with an efficiency of > 99%. The biodistribution of 99mTc-citrate was studied in mice with turpentine-induced abscesses in comparison to 67Ga-citrate. The max. abscess/muscle concentration ratios were 4.61 ± 1.92 (3 h) for 99mTc-citrate and 4.76 ± 2.04 (4 h) for 67Ga-citrate. Arthritis was induced in 10 rabbits by intra-articular injection of ovalbumin Scintigrams obtained 4 days later and at 3 h post-injection of 99mTc-citrate showed increased activity involving the synovium. The max. arthritic/contralateral knee ratio was 3.19 ± 1.29 (3 h) and 6.47 ± 3.71 (24 h) for 99mTc- and 67Ga-citrate, respectively. The blood clearance curve of 99mTc-citrate in rabbits was biexponential with a fast and a slow component, compared to mono-exponential clearance of 67Ga-citrate. In 10 patients with rheumatoid arthritis whole-body scintigrams and spot images of involved joints indicated localization of the tracer in inflamed tissues. The mean target-to-soft tissue ratios were 3.04 ± 0.81 and 4.95 ± 2.56 for 99mTc-citrate and 99mTc-MDP, respectively. Renal clearance of radioactivity was evident from the scintigrams. Our results demonstrated that 99mTc-citrate is effective as a radiopharmaceutical for the visualization of inflammatory lesions and may be preferred to 67Ga-citrate due to the ideal physical characteristics of the radionuclide, easy preparation, low cost, early accumulation and the preference for the renal route of excretion. (Author)

  20. Organocatalysts for enantioselective synthesis of fine chemicals: definitions, trends and developments

    Directory of Open Access Journals (Sweden)

    Chiara Palumbo

    2015-02-01

    Full Text Available Organocatalysis, that is the use of small organic molecules to catalyze organic transformations, has been included among the most successful concepts in asymmetric catalysis, and it has been used for the enantioselective construction of C–C, C–N, C–O, C–S, C–P and C–halide bonds. Since the seminal works in early 2000, the scientific community has been paying an ever-growing attention to the use of organocatalysts for the synthesis, with high yields and remarkable stereoselectivities, of optically active fine chemicals of interest for the pharmaceutical industry. A brief overview is here presented about the two main classes of substrate activation by the catalyst: covalent organocatalysis and non-covalent organocatalysis, with a more stringent focus on some recent outcomes in the field of the latter and of hydrogen bond-based catalysis. Finally, some successful examples of heterogenization of organocatalysts are also discussed, in the view of a potential industrial exploitation.

  1. Synthesis and characterization of biomimetic citrate-based biodegradable composites.

    Science.gov (United States)

    Tran, Richard T; Wang, Liang; Zhang, Chang; Huang, Minjun; Tang, Wanjin; Zhang, Chi; Zhang, Zhongmin; Jin, Dadi; Banik, Brittany; Brown, Justin L; Xie, Zhiwei; Bai, Xiaochun; Yang, Jian

    2014-08-01

    Natural bone apatite crystals, which mediate the development and regulate the load-bearing function of bone, have recently been associated with strongly bound citrate molecules. However, such understanding has not been translated into bone biomaterial design and osteoblast cell culture. In this work, we have developed a new class of biodegradable, mechanically strong, and biocompatible citrate-based polymer blends (CBPBs), which offer enhanced hydroxyapatite binding to produce more biomimetic composites (CBPBHAs) for orthopedic applications. CBPBHAs consist of the newly developed osteoconductive citrate-presenting biodegradable polymers, crosslinked urethane-doped polyester and poly (octanediol citrate), which can be composited with up to 65 wt % hydroxyapatite. CBPBHA networks produced materials with a compressive strength of 116.23 ± 5.37 MPa comparable to human cortical bone (100-230 MPa), and increased C2C12 osterix gene and alkaline phosphatase gene expression in vitro. The promising results above prompted an investigation on the role of citrate supplementation in culture medium for osteoblast culture, which showed that exogenous citrate supplemented into media accelerated the in vitro phenotype progression of MG-63 osteoblasts. After 6 weeks of implantation in a rabbit lateral femoral condyle defect model, CBPBHA composites elicited minimal fibrous tissue encapsulation and were well integrated with the surrounding bone tissues. The development of citrate-presenting CBPBHA biomaterials and preliminary studies revealing the effects of free exogenous citrate on osteoblast culture shows the potential of citrate biomaterials to bridge the gap in orthopedic biomaterial design and osteoblast cell culture in that the role of citrate molecules has previously been overlooked. PMID:23996976

  2. L-Proline catalyzed aldol reactions between acetone and aldehydes in supercritical fluids:An environmentally friendly reaction procedure

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    The direct asymmetric aldol reaction between various aldehydes and acetone catalyzed by L-proline catalyst was successfully carried out in supercritical CO2 (scCO2) and 1,1,1,2-tetrafluoroethane (R-134a) fluids.The enantioselectivity of 84% ee to the targeted product was achieved under 20 MPa,40 °C,and 15 mol% of the catalyst in supercritical CO2 (scCO2) fluid.The effects of reaction parameters,such as temperature,pressure,catalyst loading and different substituted aldehydes on both enantioselectivity and aldol yield were discussed.The titled reaction was also performed in 1,1,1,2-tetrafluoroethane,and the obtained results were compared with those in scCO2.This new reaction procedure provides an environmental asymmetric aldol reaction system as compared with that in organic solvents.

  3. Promiscuous enantioselective (−)-γ-lactamase activity in the Pseudomonas fluorescens esterase I

    OpenAIRE

    Torres, Leticia L.; Schließmann, Anna; Schmidt, Marlen; Silva-Martín, Noella; Hermoso, Juan A.; Berenguer, José; Bornscheuer, Uwe T.; Hidalgo, Aurelio

    2012-01-01

    A promiscuous but very enantioselective (−)-γ-lactamase activity in the kinetic resolution of the Vince lactam (2-azabicyclo[2.2.1]hept-5-en-3-one) was detected in the Pseudomonas fluorescens esterase I (PFEI). The lactamase activity was increased 200-fold by the introduction of a point mutation and resulted as enantioselective as the Microbacterium sp. enzyme used industrially in this resolution. The structural and mechanistic determinants for the catalytic promiscuity and enantioselectivity...

  4. Large-scale ruthenium- and enzyme-catalyzed dynamic kinetic resolution of (rac-1-phenylethanol

    Directory of Open Access Journals (Sweden)

    Bäckvall Jan-E

    2007-12-01

    Full Text Available Abstract The scale-up of the ruthenium- and enzyme-catalyzed dynamic kinetic resolution (DKR of (rac-1-phenylethanol (2 is addressed. The immobilized lipase Candida antarctica lipase B (CALB was employed for the resolution, which shows high enantioselectivity in the transesterification. The ruthenium catalyst used, (η 5-C5Ph5RuCl(CO2 1, was shown to possess very high reactivity in the "in situ" redox racemization of 1-phenylethanol (2 in the presence of the immobilized enzyme, and could be used in 0.05 mol% with high efficiency. Commercially available isopropenyl acetate was employed as acylating agent in the lipase-catalyzed transesterifications, which makes the purification of the product very easy. In a successful large-scale DKR of 2, with 0.05 mol% of 1, (R-1-phenylethanol acetate (3 was obtained in 159 g (97% yield in excellent enantiomeric excess (99.8% ee.

  5. 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.

  6. 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.

  7. Reinvestigation of a Catalytic, Enantioselective Alkene Dibromination and Chlorohydroxylation

    OpenAIRE

    Denmark, Scott E.; Carson, Nessa

    2015-01-01

    Attempts to reproduce eight, putative, enantioselective dibromination and chlorohydroxylation reactions from oftcited literature studies are described. The reactions were performed with full fidelity to the original report wherever possible. Analysis of the enantiomeric composition was performed by chiral stationary phase HPLC or SFC (CSP-HPLC or CSP-SFC), as opposed to the original report, which used chiral shift reagent NMR spectroscopy. After careful study, the reported levels of enantiose...

  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. Enantioselective reduction of acetyldimethylphenylsilane by Trigonopsis variabilis (DSM 70714)

    OpenAIRE

    Syldatk, C.; Andree, H.; Stoffregen, A.; F. Wagner; Stumpf, B; Ernst, L; Zilch, H.; Tacke, Reinhold

    2012-01-01

    Growing and resting cells of the yeast Trigonapsis variabilis (DSM 70714) can be used for the enantioselective reduction of the organosilicon compound acetyldimethylphenylsilane (J) to give optically active (R)-(1-hydroxyethyl)dimethylphenylsilane [(R)-2] in good yields. The enantiomeric purity of the isolated product was determined tobe 62-86% ee depending on the substrate concentration used. Both substrate and product caused an inhibition of the reaction at concentrations higher than 0.35 a...

  10. A Chiral Electrophilic Selenium Catalyst for Highly Enantioselective Oxidative Cyclization.

    Science.gov (United States)

    Kawamata, Yu; Hashimoto, Takuya; Maruoka, Keiji

    2016-04-27

    Chiral electrophilic selenium catalysts have been applied to catalytic asymmetric transformations of alkenes over the past two decades. However, highly enantioselective reactions with a broad substrate scope have not yet been developed. We report the first successful example of this reaction employing a catalyst based on a rigid indanol scaffold, which can be easily synthesized from a commercially available indanone. The reaction efficiently converts β,γ-unsaturated carboxylic acids into various enantioenriched γ-butenolides under mild conditions. PMID:27064419

  11. Role of Ga-67 citrate imaging in pancreatitis

    Energy Technology Data Exchange (ETDEWEB)

    Aburano, T.; Yokoyama, K.; Hisada, K.; Kakuma, K.; Ichiyanagi, K.

    1988-11-01

    Two patients with pancreatitis in whom an area of predominant uptake of Ga-67 citrate was demonstrated involving the entire pancreas are presented. Ultrasound and x-ray CT did not reveal any morphologic abnormalities in the pancreas, whereas Ga-67 citrate imaging indicated the presence of active inflammatory change. Ga-67 citrate imaging may be useful in confirming the diagnosis of acute pancreatitis or acute exacerbation of chronic pancreatitis based on clinical and laboratory data, especially when ultrasound and/or x-ray CT cannot reveal any morphologic abnormalities in the pancreas.

  12. Enantioselective S-oxygenation of para-methoxyphenyl-1,3-dithiolane by various tissue preparations: effect of estradiol.

    Science.gov (United States)

    Cashman, J R; Olsen, L D; Lambert, C E; Presas, M J

    1990-02-01

    Liver, kidney, and lung microsomes prepared from nonpretreated female Sprague-Dawley rats catalyze the NADPH- and oxygen-dependent S-oxygenation of para-methoxyphenyl-1,3-dithiolane. Studies on the biochemical mechanism of dithiolane S-oxygenation in liver, kidney, and lung microsomes suggest that this reaction is catalyzed in a diastereoselective and enantioselective fashion by the flavin-containing monooxygenase and, to a lesser extent, the cytochromes P-450. This conclusion is based on results examining the effects of selective cytochrome P-450 inhibitors and positive effectors, microsome heat-inactivation treatment, and alternate substrates for the flavin-containing monooxygenase. Liver and kidney microsomes prepared from ovarectomized female rats tended to have decreased S-oxygenase activity, compared with nonpretreated female rats, whereas ovarectomized rats pretreated with estradiol had markedly lower S-oxygenase activity. In contrast, lung microsomal S-oxygenase activity, which is low in pulmonary microsomes from nonpretreated female rats, increases 2-4-fold after ovariectomization and estradiol pretreatment. In female Sprague-Dawley rats, estradiol pretreatment is mainly responsible for the large decrease (or increase) in S-oxygenase activity observed in the tissues examined, although it is unlikely that estradiol alone controls flavin-containing monooxygenase S-oxygenase activity. PMID:2304455

  13. 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

  14. Injectable citrate-modified Portland cement for use in vertebroplasty

    OpenAIRE

    Wynn-Jones, Gareth; Shelton, Richard M.; Hofmann, Michael P

    2014-01-01

    The injectability of Portland cement (PC) with several citrate additives was investigated for use in clinical applications such as vertebroplasty (stabilization of a fractured vertebra with bone cement) using a syringe. A 2-wt % addition of sodium or potassium citrate with PC significantly improved cement injectability, decreased cement setting times from over 2 h to below 25 min, while increasing the compressive strength to a maximum of 125 MPa. Zeta-potential measurements indicated that the...

  15. Why sildenafil and sildenafil citrate monohydrate crystals are not stable?

    OpenAIRE

    Sawatdee, Somchai; Pakawatchai, Chaveng; Nitichai, Kwanjai; Srichana, Teerapol; PHETMUNG, Hirihattaya

    2015-01-01

    Sildenafil citrate was crystallized by various techniques aiming to determine the behavior and factors affecting the crystal growth. There are only 2 types of sildenafil obtaining from crystallization: sildenafil (1) and sildenafil citrate monohydrate (2). The used techniques were (i) crystallization from saturated solutions, (ii) addition of an antisolvent, (iii) reflux and (iv) slow solvent evaporation method. By pursuing these various methods, our work pointed that the best formation of cr...

  16. Highly Enantioselective Formation of α-Allyl-α-Arylcyclopentanones via Pd-Catalysed Decarboxylative Asymmetric Allylic Alkylation.

    Science.gov (United States)

    Akula, Ramulu; Doran, Robert; Guiry, Patrick J

    2016-07-11

    A highly enantioselective Pd-catalysed decarboxylative asymmetric allylic alkylation of cyclopentanone derived α-aryl-β-keto esters employing the (R,R)-ANDEN-phenyl Trost ligand has been developed. The product (S)-α-allyl-α-arylcyclopentanones were obtained in excellent yields and enantioselectivities (up to >99.9 % ee). This represents one of the most highly enantioselective formations of an all-carbon quaternary stereogenic center reported to date. This reaction was demonstrated on a 4.0 mmol scale without any deterioration of enantioselectivity and was exploited as the key enantioselective transformation in an asymmetric formal synthesis of the natural product (+)-tanikolide. PMID:27191198

  17. Tritium catalyzed deuterium tokamaks

    International Nuclear Information System (INIS)

    A preliminary assessment of the promise of the Tritium Catalyzed Deuterium (TCD) tokamak power reactors relative to that of deuterium-tritium (D-T) and catalyzed deuterium (Cat-D) tokamaks is undertaken. The TCD mode of operation is arrived at by converting the 3He from the D(D,n)3He reaction into tritium, by neutron capture in the blanket; the tritium thus produced is fed into the plasma. There are three main parts to the assessment: blanket study, reactor design and economic analysis and an assessment of the prospects for improvements in the performance of TCD reactors (and in the promise of the TCD mode of operation, in general)

  18. Citrate-release-mediated aluminum resistance is coupled to the inducible expression of mitochondrial citrate synthase gene in Paraserianthes falcataria.

    Science.gov (United States)

    Osawa, Hiroki; Kojima, Katsumi

    2006-05-01

    Aluminum (Al) resistance in some leguminous plants is achieved by enhanced citrate release from roots. Enhancement requires several hours for complete activation and is postulated to involve Al-responsive genes or components. We examined the mechanism of Al-induced citrate release by studying the relationship between citrate release and expression of the mitochondrial citrate synthase (mCS) gene in three leguminous trees. Root elongation in Leucaena leucocephala (Lam.) de Wit was arrested within 24 h by 30 microM Al, whereas root elongation in Paraserianthes falcataria (L.) Neilson and Acacia mangium Willd. was inhibited mangium maintained enhanced release and accumulation of citrate for at least 28 days in response to Al treatment. Aluminum increased the accumulation of mCS transcripts in P. falcataria roots, but not in L. leucocephala roots, and thus up-regulation decreased following removal of Al. Lanthanum did not alter the expression level of mCS. Aluminum increased mCS activity concomitantly with enhanced mCS gene expression in P. falcataria, whereas it did not affect mCS activity in L. leucocephala. Aluminum content in root apices of P. falcataria was increased by cycloheximide, supporting the idea that de novo synthesis of proteins is a prerequisite for Al resistance. Our findings suggest that Al-inducible expression of mCS coupled with enhanced citrate release mediates Al resistance in P. falcataria. PMID:16452070

  19. Kinase-Catalyzed Biotinylation

    OpenAIRE

    Senevirathne, Chamara; Green, Keith D.; Pflum, Mary Kay H.

    2012-01-01

    Kinase-catalyzed protein phosphorylation plays an essential role in a variety of biological processes. Methods to detect phosphoproteins and phosphopeptides in cellular mixtures will aid in cell biological and signaling research. Our laboratory recently discovered the utility of γ-modified ATP analogues as tools for studying phosphorylation. Specifically, ATP-biotin can be used for labeling and visualizing phosphoproteins from cell lysates. Because the biotin tag is suitable for protein detec...

  20. Phosphine-Catalyzed [2 + 4] Annulation of Allenoates with Thiazolone-Derived Alkenes: Synthesis of Functionalized 6,7-Dihydro-5H-pyrano[2,3-d]thiazoles.

    Science.gov (United States)

    Wang, Chang; Gao, Zhenzhen; Zhou, Leijie; Yuan, Chunhao; Sun, Zhanhu; Xiao, Yumei; Guo, Hongchao

    2016-07-15

    Phosphine-catalyzed [2 + 4] annulation of allenoates with thiazolone-derived alkenes has been achieved under mild conditions, giving biologically important 6,7-dihydro-5H-pyrano[2,3-d]thiazole derivatives in high to excellent yields. With the use of Kwon's phosphine as the chiral catalyst, optically active products were obtained in good yields with excellent enantioselectivities. PMID:27378106

  1. Preparation of lead titanate zirconate from metal citrates

    International Nuclear Information System (INIS)

    Lead titanate zirconate (PZT) preparation from its metal constituent citrates have been investigated. Metal citrates were obtained by forced precipitation using a dehydration alcohol mixture. Salt solutions of lead nitrate and octahydrated zirconyl chloride, and titanium tetrachloride were treated separately with citric acid and ammonium hydroxide. Zirconium, titanium and lead oxides resulted from thermal decomposition of corresponding citrates at 5000 C, 4500 C and 2500 C, respectively. Lead titanate (PT) and lead zirconate (P Z) were obtained by calcining at 4500 C and 5000 C, respectively, after adequate heating of citrates mechanically mixed in ethyl ether. PZT samples were obtained with different starting stoichiometry. Rhombohedral PZT-1 53/47 sample was prepared from co precipitating zirconyl ammonium and ammonium lead citrates in presence of ethanolic titanium oxide dispersion, and calcinating at 8000 C. Rhombohedral PZT-q 52/48 sample was obtained from heating at 5000 C for 2 hours a mixture of metal citrates coprecipitated by dehydration mixture of acetone-ethanol-formic acid (2:1:0,06). Tetragonal PZT-m stoichiometry 53/47 sample were obtained by calcining at after 6000 C for 2 hours after heating a mechanically mixed metal citrates. PT phase arose at 4000 C. PZT-m powders obtained in a range of 4000 C-8000 C were isostatically pressed, and sintered at 11000 C and 12000 C in saturated Pb O atmosphere. Rhombohedral sintered PZT was obtained with 7,78 g.cm-3 at 12000 C. (author). 123 refs, 53 figs, 32 tabs

  2. Alkali absorption and citrate excretion in calcium nephrolithiasis

    Science.gov (United States)

    Sakhaee, K.; Williams, R. H.; Oh, M. S.; Padalino, P.; Adams-Huet, B.; Whitson, P.; Pak, C. Y.

    1993-01-01

    The role of net gastrointestinal (GI) alkali absorption in the development of hypocitraturia was investigated. The net GI absorption of alkali was estimated from the difference between simple urinary cations (Ca, Mg, Na, and K) and anions (Cl and P). In 131 normal subjects, the 24 h urinary citrate was positively correlated with the net GI absorption of alkali (r = 0.49, p < 0.001). In 11 patients with distal renal tubular acidosis (RTA), urinary citrate excretion was subnormal relative to net GI alkali absorption, with data from most patients residing outside the 95% confidence ellipse described for normal subjects. However, the normal relationship between urinary citrate and net absorbed alkali was maintained in 11 patients with chronic diarrheal syndrome (CDS) and in 124 stone-forming patients devoid of RTA or CDS, half of whom had "idiopathic" hypocitraturia. The 18 stone-forming patients without RTA or CDS received potassium citrate (30-60 mEq/day). Both urinary citrate and net GI alkali absorption increased, yielding a significantly positive correlation (r = 0.62, p < 0.0001), with the slope indistinguishable from that of normal subjects. Thus, urinary citrate was normally dependent on the net GI absorption of alkali. This dependence was less marked in RTA, confirming the renal origin of hypocitraturia. However, the normal dependence was maintained in CDS and in idiopathic hypocitraturia, suggesting that reduced citrate excretion was largely dietary in origin as a result of low net alkali absorption (from a probable relative deficiency of vegetables and fruits or a relative excess of animal proteins).

  3. Enzyme-Catalyzed Henry Reaction in Choline Chloride-Based Deep Eutectic Solvents.

    Science.gov (United States)

    Tian, Xuemei; Zhang, Suoqin; Zheng, Liangyu

    2016-01-01

    The enzyme-catalyzed Henry reaction was realized using deep eutectic solvents (DESs) as a reaction medium. The lipase from Aspergillus niger (lipase AS) showed excellent catalytic activity toward the substrates aromatic aldehydes and nitromethane in choline chloride:glycerol at a molar ratio of 1:2. Addition of 30 vol% water to DES further improved the lipase activity and inhibited DES-catalyzed transformation. A final yield of 92.2% for the lipase AS-catalyzed Henry reaction was achieved under optimized reaction conditions in only 4 h. In addition, the lipase AS activity was improved by approximately 3-fold in a DES-water mixture compared with that in pure water, which produced a final yield of only 33.4%. Structural studies with fluorescence spectroscopy showed that the established strong hydrogen bonds between DES and water may be the main driving force that affects the spatial conformation of the enzyme, leading to a change in lipase activity. The methodology was also extended to the aza-Henry reaction, which easily occurred in contrast to that in pure water. The enantioselectivity of both Henry and aza-Henry reactions was not found. However, the results are still remarkable, as we report the first use of DES as a reaction medium in a lipase-catalyzed Henry reaction. PMID:26437947

  4. Permanent microporosity and enantioselective sorption in a chiral open framework.

    Science.gov (United States)

    Bradshaw, Darren; Prior, Timothy J; Cussen, Edmund J; Claridge, John B; Rosseinsky, Matthew J

    2004-05-19

    A homochiral microporous material is presented. The phase has 47% permanently porous void volume and is shown to have >1 nm diameter pores with three-dimensional channels using probe molecule sorption. Enantioselective guest sorption is strongly dependent on guest size. The homochiral microporous phase was identified by reactive selection from a first-generation chiral but nonporous framework. Chiral permanent porosity is established by directional noncovalent interactions between framework-forming and nonframework forming components of the stable second-generation material, which become stronger upon loss of the guests from the pore system. PMID:15137776

  5. Advances in enantioselective separations using electromigration capillary techniques.

    Science.gov (United States)

    Preinerstorfer, Beatrix; Lämmerhofer, Michael; Lindner, Wolfgang

    2009-01-01

    The most recent literature dealing with enantioselective separations and stereoselective analyses of chiral entities including especially pharmaceuticals, phytochemicals, biochemicals, agrochemicals, fine chemicals and specific test compounds by electromigration techniques such as CE, MEKC, MEEKC, CEC and microchip CE is reviewed. The review covers literature from 2007 until mid-2008, i.e. studies that were published after the appearance of the latest review article on that topic in Electrophoresis by Gübitz and Schmid (see Electrophoresis 2007, 28, 114). Particular attention is given to the description of new chiral selector systems, studies on separation mechanisms and applications in the above-specified electromigration techniques. PMID:19107703

  6. Enantioselective Recognition of Chiral Carboxylic Acids by a β-Amino Acid and 1,10-Phenanthroline Based Chiral Fluorescent Sensor

    Directory of Open Access Journals (Sweden)

    Yonghong Zhang

    2015-05-01

    Full Text Available A novel chiral 1,10-phenanthroline-based fluorescent sensor was designed and synthesized from optical active β-amino acids. It used 1,10-phenanthroline moiety as a fluorescent signaling site and binding site, with optically active β-amino acids as a chiral barrier site. Notably, the optically active β-amino acids were obtained by a Lewis base catalyzed hydrosilylation of β-enamino esters according to our former work. The chiral sensor has been used to conduct the enantioselective recognition of chiral mono and dicarboxylic acids derivatives. Using this fluorescent sensor, a moderate “turn-off” fluorescence-diminishment response towards enantiomer of tartaric acids, and proline was observed. It found that l-enantiomers quench the chiral fluorescence sensor more efficiently than d-enantiomers due to the absolute configuration of the β-amino acid.

  7. Synthesis of chiral N-phosphoryl aziridines through enantioselective aziridination of alkenes with phosphoryl azide via Co(II-based metalloradical catalysis

    Directory of Open Access Journals (Sweden)

    Jingran Tao

    2014-06-01

    Full Text Available The Co(II complex of a new D2-symmetric chiral porphyrin 3,5-DiMes-QingPhyrin, [Co(P6], can catalyze asymmetric aziridination of alkenes with bis(2,2,2-trichloroethylphosphoryl azide (TcepN3 as a nitrene source. This new Co(II-based metalloradical aziridination is suitable for different aromatic olefins, producing the corresponding N-phosphorylaziridines in good to excellent yields (up to 99% with moderate to high enantioselectivities (up to 85% ee. In addition to mild reaction conditions and generation of N2 as the only byproduct, this new metalloradical catalytic system is highlighted with a practical protocol that operates under neutral and non-oxidative conditions.

  8. 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. PMID:22972595

  9. Theoretical Study on Sulfur Dioxide Absorption with Citrate Solution

    Institute of Scientific and Technical Information of China (English)

    薛娟琴; 洪涛; 王召启; 李林波

    2006-01-01

    The citrate absorption of SO2 is currently one of the most successful and economic methods to harness sulfur dioxide pollution.In order to theoretically elucidate the mechanism of SO2 absorption by citrate solution and provide theoretical instruction for experiments and industrial process, the theory of multi-buffer solution, combined with computer numerical calculation methods, was applied to study the distribution parameters of the components of the citrate solution in the process of SO2 absorption and the following results were obtained: (1) HCi2- and H2Ci- in the citrate solution played the dominant role in the absorption and desorption processes; (2) Through the calculation for the buffer capacity of citrate solution, it was found that the pH of the absorption and desorption solution should be in the range of 2~8, while at pH=4.5 the buffer capacity reached its maximum. Some valuable parameters were obtained, which are instructive to the ensuing experiments and industrial design.

  10. Electrodeposition of Sn-Zn-Cu alloys from citrate solutions

    International Nuclear Information System (INIS)

    The first stage of this study involves the development of stable baths for electrodepositing Sn-Zn-Cu alloys; these developments are based on thermodynamic models of citrate baths and experiments exploring the stability of the baths. The effects of the sodium citrate (complexation agent) concentration and the pH of the solution on the stability of the baths were examined experimentally. The stability of the baths was determined through spectrophotometric analysis. Stable baths designed for the electrodeposition of Sn-Zn-Cu alloys were produced in the range of dominant citrate complexes with highly negative charge (the reduction process is strongly inhibited by high activation energy). Voltammetric studies and potentiostatic deposition were conducted to analyse the co-deposition of tin, zinc, and copper, and the co-evolution of hydrogen. The effect of the solution pH, the concentration of sodium citrate and the hydrodynamic conditions on the electrodeposition process and the composition of the deposits were examined. The deposits were analysed using chemical (μXRF) as also grain size and phase analysis (X-ray diffraction). The possibility of electrodepositing Sn-Zn-Cu alloys from citrate solutions was confirmed. The tin content of these coatings varied from 60 to 96 wt.%, the copper content varied from 3.5 to 20.5 wt.%, and the zinc content reached up to approximately 37.5 wt.%

  11. Catalyzed Ceramic Burner Material

    Energy Technology Data Exchange (ETDEWEB)

    Barnes, Amy S., Dr.

    2012-06-29

    Catalyzed combustion offers the advantages of increased fuel efficiency, decreased emissions (both NOx and CO), and an expanded operating range. These performance improvements are related to the ability of the catalyst to stabilize a flame at or within the burner media and to combust fuel at much lower temperatures. This technology has a diverse set of applications in industrial and commercial heating, including boilers for the paper, food and chemical industries. However, wide spread adoption of catalyzed combustion has been limited by the high cost of precious metals needed for the catalyst materials. The primary objective of this project was the development of an innovative catalyzed burner media for commercial and small industrial boiler applications that drastically reduce the unit cost of the catalyzed media without sacrificing the benefits associated with catalyzed combustion. The scope of this program was to identify both the optimum substrate material as well as the best performing catalyst construction to meet or exceed industry standards for durability, cost, energy efficiency, and emissions. It was anticipated that commercial implementation of this technology would result in significant energy savings and reduced emissions. Based on demonstrated achievements, there is a potential to reduce NOx emissions by 40,000 TPY and natural gas consumption by 8.9 TBtu in industries that heavily utilize natural gas for process heating. These industries include food manufacturing, polymer processing, and pulp and paper manufacturing. Initial evaluation of commercial solutions and upcoming EPA regulations suggests that small to midsized boilers in industrial and commercial markets could possibly see the greatest benefit from this technology. While out of scope for the current program, an extension of this technology could also be applied to catalytic oxidation for volatile organic compounds (VOCs). Considerable progress has been made over the course of the grant

  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 lipase. PMID:24338160

  13. Alkali absorption and citrate excretion in calcium nephrolithiasis

    Science.gov (United States)

    Sakhaee, K.; Williams, R. H.; Oh, M. S.; Padalino, P.; Adams-Huet, B.; Whitson, P.; Pak, C. Y.

    1993-01-01

    The role of net gastrointestinal (GI) alkali absorption in the development of hypocitraturia was investigated. The net GI absorption of alkali was estimated from the difference between simple urinary cations (Ca, Mg, Na, and K) and anions (Cl and P). In 131 normal subjects, the 24 h urinary citrate was positively correlated with the net GI absorption of alkali (r = 0.49, p mEq/day). Both urinary citrate and net GI alkali absorption increased, yielding a significantly positive correlation (r = 0.62, p reduced citrate excretion was largely dietary in origin as a result of low net alkali absorption (from a probable relative deficiency of vegetables and fruits or a relative excess of animal proteins).

  14. 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. PMID:25311959

  15. 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. PMID:24080002

  16. RNA-Cleaving DNA Enzymes with Altered Regio- or Enantioselectivity

    Science.gov (United States)

    Ordoukhanian, Phillip; Joyce, Gerald F.

    2002-01-01

    In vitro evolution methods were used to obtain DNA enzymes that cleave either a 2',5' - phosphodiester following a wibonucleotide or a 3',5' -phosphodiester following an L-ribonucleotide. Both enzymes can operate in an intermolecular reaction format with multiple turnover. The DNA enzyme that cleaves a 2',5' -phosphodiester exhibits a k(sub cat) of approx. 0.01/ min and catalytic efficiency, k(sub cat)/k(sub m) of approx. 10(exp 5)/ M min. The enzyme that cleaves an L-ribonudeotide is about 10-fold slower and has a catalytic efficiency of approx. 4 x 10(exp 5)/ M min. Both enzymes require a divalent metal cation for their activity and have optimal catalytic rate at pH 7-8 and 35-50 C. In a comparison of each enzyme s activity with either its corresponding substrate that contains an unnatural ribonudeotide or a substrate that instead contains a standard ribonucleotide, the 2',5' -phosphodiester-deaving DNA enzyme exhibited a regioselectivity of 6000- fold, while the L-ribonucleotide-cleaving DNA enzyme exhibited an enantioselectivity of 50-fold. These molecules demonstrate how in vitro evolution can be used to obtain regio- and enantioselective catalysts that exhibit specificities for nonnatural analogues of biological compounds.

  17. 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. PMID:27092411

  18. Efficacy of preventing hemodialysis catheter infections with citrate lock.

    Science.gov (United States)

    Silva, Jorge; Antunes, Jorge; Carvalho, Telmo; Ponce, Pedro

    2012-10-01

    Prevalent use of tunneled dialysis catheters can reach 30%. Infection remains the most serious catheter-related problem. Catheter locks are increasingly used for prevention, but are not yet recommended either by the Food and Drug Association or European Medicines Agency, on the basis of increasing bacterial resistance or lock toxicity. The aim was to test safety and effectiveness of citrate. A prospective, interventional study was conducted to assess the safety and efficacy of a 30% citrate lock in preventing catheter-related bacteremia (CRB). A total of 157 prevalent tunneled catheters were locked with citrate and prospectively followed during a 1-year period. The primary endpoint was first CRB diagnosed according to two of the diagnostic criteria for Catheter Infection of Centers for Disease Control and Prevention (CDC), namely definite and probable infection. The CDC criterion of possible but not proved infection was not considered. This citrate lock cohort (n = 157) had 10 episodes of CRB. We observed 0.49 CRB episodes/1000 patient-days and the mean infection-free catheter day was 130.6 ± 100.9. No clinically relevant adverse events were observed. No proved tunnel or exit site infection was observed and no patients died because of CRB. Catheter obstruction episodes were reported on 69 occasions out of 14 catheters. These results were compared with an historical cohort from a previous study of catheter locking with low-dose gentamicin and did not show significant difference in efficacy. Citrate lock is effective in preventing CRB. No toxicity was observed. The use of citrate lock may have advantages over antibiotic locks: no reported bacterial resistance, lower industrial cost, and less manipulation. PMID:22515732

  19. Formation of colloidal silver nanoparticles: Capping action of citrate

    International Nuclear Information System (INIS)

    Colloidal silver sols of long-time stability are formed in the γ-irradiation of 1.0 x 10-4 M AgClO4 solutions, which also contain 0.3 M 2-propanol, 2.5 x 10-2 M N2O, and sodium citrate in various concentrations. The reduction of Ag+ in these solutions is brought about by the 1-hydroxyalkyl radical generated in the radiolysis of 2-propanol; citrate does not act as a reductant but solely as a stabilizer of the colloidal particles formed. Its concentration is varied in the range from 5.0 x 10-5 to 1.5 x 10-3 M, and the size and size distribution of the silver particles are studied by electron microscopy. At low citrate concentration, partly agglomerated large particles are formed that have many imperfections. In an intermediate range (a few 10-4 M), well-separated particles with a rather narrow size distribution and little imperfections are formed, the size slightly decreasing with increasing citrate concentration. At high citrate concentrations, large lumps of coalesced silver particles are present, due to destabilization by the high ionic strength of the solution. These findings are explained by two growth mechanisms: condensation of small silver clusters (type-1 growth), and reduction of Ag+ on silver particles via radical-to-particle electron transfer (type-2 growth). The particles formed in the intermediate range of citrate concentration were studied by high-resolution electron microscopy and computer simulations. They constitute icosahedra and cuboctahedra

  20. Effect of sildenafil citrate on penile erection of rhesus macaques

    Institute of Scientific and Technical Information of China (English)

    Xun-BinHuang; Cheng-LiangXiong; Cheng-GaoYu; Jie-LingZhou; Ji-YunShen

    2004-01-01

    Aim: To examine the effect of sildenafil citrate on penile erection of male rhesus macaque. Methods:Twenty Macaca mulatta were divided into the sildenafil treated and the control groups of l0 animals each. The penile size, the corpus cavernosal electromyogram (EMG) and the intra-corpus cavernosal pressure (ICP) were determined. Results: The diameter of penis and the ICP were significantly increased and the corpus cavernosal EMG significantly reduced in the sildenafil group. Conclusion: Sildenafil citrate increases the penile size and ICP and reduces the corpus cavernosal EMG in male rhesus macaque. (Asian J Androl 2004 Sep; 6: 233-235)

  1. Gastric fluid pH in patients receiving sodium citrate.

    Science.gov (United States)

    Viegas, O J; Ravindran, R S; Shumacker, C A

    1981-07-01

    Gastric fluid pH was measured following induction of anesthesia and placement of an endotracheal tube in 30 surgical patients undergoing elective operations. None of the patients received an anticholinergic drug before surgery. Fifteen patients who had been given 15 ml of sodium citrate 15 to 20 minutes before induction of anesthesia had a mean pH of 6.2 +/- 0.8. The control group, which also consisted of 15 patients, had a mean pH of 2.1 +/- 1.4. The increase in gastric pH noted following sodium citrate would result in reduced pulmonary reaction should aspiration occur. PMID:7195668

  2. Hemodiafiltration using pre-dilutional on-line citrate dialysate: A new technique for regional citrate anticoagulation: A feasibility study

    Directory of Open Access Journals (Sweden)

    Radhouane Bousselmi

    2015-01-01

    Full Text Available A prospective, observational, feasibility study was carried out on four patients with end-stage renal failure undergoing bicarbonate hemodialysis to study the feasibility of an on-line hemodiafiltration technique using a citrate dialysate with pre-dilutional infusion of citrate as a technique for regional citrate anticoagulation. All patients had contraindication to systemic heparin anticoagulation. The dialysis technique consisted of an on-line hemodiafiltration with a citrate dialysate without calcium using a Fresenius 4008S dialysis machine and Fresenius Polysulfone F60 dialyzers. The infusion solution was procured directly from the dialysate and was infused into the arterial line. To avoid the risk of hypocalcemia, calcium gluconate was infused to the venous return line. The study was carried out in two stages. During the first stage, the citrate infusion rate was 80 mL/min and the calcium infusion rate was 9 mmol/h. At the second stage, the rates were 100 mL/min and 11 mmol/h, respectively. The primary endpoint of this study was the incidence of thrombosis in the extracorporeal blood circuit and/or the dialyzer. A total of 78 sessions were conducted. All the sessions were well tolerated clinically and there were no major incidents in any of the four patients. At the first stage of the study, there were five incidences of small clots in the venous blood chamber, an incidence of extracorporeal blood circuit thrombosis of 12.5%. At the second stage of the study, no cases of extracorporeal blood circuit or dialyzer thrombosis were noted. Hemodiafiltration with on-line citrate dialysate infusion to the arterial line is safe and allows an effective regional anticoagulation of the extracorporeal blood circuit without the need for systemic anticoagulation.

  3. Enantioselective synthesis of epi-(+)-Sch 642305: observation of an interesting diastereoselection during RCM

    OpenAIRE

    Mehta, Goverdhan; Shinde, Harish M

    2005-01-01

    In an approach towards the enantioselective total synthesis of the novel bioactive natural product Sch 642305, an unusual diastereoselection during the key RCM reaction, resulted in the synthesis of the 11-epi-isorner of Sch 642305.

  4. ENANTIOSELECTIVE TRANSFORMATION OF CHIRAL PCBS AND THE INSECTICIDE FIPRONIL IN NATURAL ANOXIC SEDIMENTS

    Science.gov (United States)

    In this study, we examined the microbial transformation of two chiral PCB congeners and the insecticide fipronil in natural sediment microcosms. The specific goals of the study were to identify biotransformation pathways and determine if enantioselective microbial transformation ...

  5. Purification and characterisation of a novel enantioselective epoxide hydrolase from Aspergillus niger M200

    Czech Academy of Sciences Publication Activity Database

    Kotík, Michael; Kyslík, Pavel

    2006-01-01

    Roč. 1760, - (2006), s. 245-252. ISSN 0006-3002 Institutional research plan: CEZ:AV0Z50200510 Keywords : epoxide hydrolase * enantioselectivity * aspergillus niger Subject RIV: EE - Microbiology, Virology

  6. Catalyzing alignment processes

    DEFF Research Database (Denmark)

    Lauridsen, Erik Hagelskjær; Jørgensen, Ulrik

    2004-01-01

    time and in combination with other social processes establish more aligned and standardized environmental performance between countries. However, examples of the introduction of environmental management suggests that EMS’ only plays a minor role in developing the actual environmental objectives......This paper describes how environmental management systems (EMS) spur the circulation of processes that support the constitution of environmental issues as specific environ¬mental objects and objectives. EMS catalyzes alignmentprocesses that produce coherence among the different elements involved...... they are implemented in and how the changing context is reflected in the environmental objectives that are established and prioritised. Our argument is, that the ability of the standard to achieve an impact is dependant on the constitution of ’coherent’ environmental issues in the context, where the management system...

  7. Enantioselective Total Synthesis and Confirmation of the Absolute and Relative Stereochemistry of Streptorubin B

    OpenAIRE

    Hu, Dennis X.; Clift, Michael D.; Lazarski, Kiel E.; Thomson, Regan J.

    2010-01-01

    The enantioselective total synthesis of the pyrrolophane natural product streptorubin B is described. Key steps in the concise route include application of a one-pot enantioselective aldol cyclization/Wittig reaction and an anionic oxy-Cope rearrangement to forge the crucial 10-membered ring. Comparisons between CD-spectra of synthetic and natural samples of streptorubin B, coupled with X-ray crystallography, allowed for the determination of the absolute stereochemistry of this natural produc...

  8. Enantioselective Alternating Copolymerization of Propylene with Carbon Monoxide Using Cationic Palladium-Chiral Diphosphine Catalyst

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    Enantioselective alternating copolymerization of carbon monoxide with propylene was carried out using palladium catalyst modified by 1,4-3,6-dianhydro-2,5-dideoxy-2,5-bis (diphenylphosphino)-L-iditol (DDPPI). The chiral diphosphine was proved to be effective at enantioselective copolymerization. Optical rotation, elemental analysis, 1H, 13C-NMR and IR spectra showed that the copolymer was optically active, isotactic, alternating poly(1,4-ketone) structure.

  9. Highly Enantioselective Cascade Transformations by Merging Heterogeneous Transition Metal Catalysis with Asymmetric Aminocatalysis

    OpenAIRE

    Luca Deiana; Samson Afewerki; Carlos Palo-Nieto; Oscar Verho; Johnston, Eric V.; Armando Córdova

    2012-01-01

    The concept of combining heterogeneous transition metal and amine catalysis for enantioselective cascade reactions has not yet been realized. This is of great advantage since it would allow for the recycling of expensive and non-environmentally friendly transition metals. We disclose that the use of a heterogeneous Pd-catalyst in combination with a simple chiral amine co-catalyst allows for highly enantioselective cascade transformations. The preparative power of this process has been demonst...

  10. Acetylphosphonate as a Surrogate of Acetate or Acetamide in Organocatalyzed Enantioselective Aldol Reactions

    Science.gov (United States)

    Guang, Jie; Guo, Qunsheng

    2012-01-01

    Highly enantioselective aldol reactions of acetylphosphonates and activated carbonyl compounds was realized with cinchona alkaloid derived catalysts, in which the acetylphosphonate was directly used as an enolate precursor for the first time. The aldol product obtained was converted in situ to its corresponding ester or amide through methanolysis or aminolysis. The overall process may be viewed as formal highly enantioselective acetate or acetamide aldol reactions, which are very difficult to achieve directly with organocatalytic methods. PMID:22650245

  11. Ferric Citrate Controls Phosphorus and Delivers Iron in Patients on Dialysis

    OpenAIRE

    Lewis, Julia B.; Sika, Mohammed; Koury, Mark J.; Chuang, Peale; Schulman, Gerald; Smith, Mark T.; Whittier, Frederick C.; Linfert, Douglas R.; Galphin, Claude M.; Athreya, Balaji P.; Nossuli, A. Kaldun Kaldun; Chang, Ingrid J.; Blumenthal, Samuel S.; Manley, John; Zeig, Steven

    2014-01-01

    Patients on dialysis require phosphorus binders to prevent hyperphosphatemia and are iron deficient. We studied ferric citrate as a phosphorus binder and iron source. In this sequential, randomized trial, 441 subjects on dialysis were randomized to ferric citrate or active control in a 52-week active control period followed by a 4-week placebo control period, in which subjects on ferric citrate who completed the active control period were rerandomized to ferric citrate or placebo. The primary...

  12. Improved cyclopropanation activity of histidine-ligated cytochrome P450 enables the enantioselective formal synthesis of levomilnacipran.

    Science.gov (United States)

    Wang, Z Jane; Renata, Hans; Peck, Nicole E; Farwell, Christopher C; Coelho, Pedro S; Arnold, Frances H

    2014-06-23

    Engineering enzymes capable of modes of activation unprecedented in nature will increase the range of industrially important molecules that can be synthesized through biocatalysis. However, low activity for a new function is often a limitation in adopting enzymes for preparative-scale synthesis, reaction with demanding substrates, or when a natural substrate is also present. By mutating the proximal ligand and other key active-site residues of the cytochrome P450 enzyme from Bacillus megaterium (P450-BM3), a highly active His-ligated variant of P450-BM3 that can be employed for the enantioselective synthesis of the levomilnacipran core was engineered. This enzyme, BM3-Hstar, catalyzes the cyclopropanation of N,N-diethyl-2-phenylacrylamide with an estimated initial rate of over 1000 turnovers per minute and can be used under aerobic conditions. Cyclopropanation activity is highly dependent on the electronic properties of the P450 proximal ligand, which can be used to tune this non-natural enzyme activity. PMID:24802161

  13. Polymeric architectures of bismuth citrate based on dimeric building blocks

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    Four bismuth complexes, (H2En)[Bi2(cit)2(H2O)4/3]·(H2O)x (1), (H2En)3[Bi2(cit)2Cl4]·(H2O)x (2), (HPy)2[Bi2(cit)2(H2O)8/5]·(H2O)x (3) and (H2En)[Bi2(cit)2](H2O)x (4) [cit = citrate4-; En = ethylenediamine; Py = pyridine] have been synthesized and crystallized. The crystal structures reveal that the basic building blocks in all of these complexes are bismuth citrate dimeric units which combine to form polymeric architectures. The embedded protonated ethylenediamine and pyridine moieties in the polymeric frameworks have been identified by X-ray crystallography and solid-state cross polarization/magic angle spinning (CP/MAS) 13C NMR. Based on the framework of complex 1, a structural model of a clinically used antiulcer drug, ranitidine bismuth citrate (RBC) was generated. The behavior of the protonated amine-bismuth citrate complexes in acidic aqueous solution has been studied by electrospray ionization-mass spectrometry (ESI-MS).

  14. Tumour imaging using technetium-99m-citrate

    International Nuclear Information System (INIS)

    Sixteen patients with soft tissue malignancy or fibroadenoma of the breast (Group A) were imaged using 99mTc-citrate. Majority of the patients (n=14) has new untreated lesions. Appreciable skeletal uptake of the tracer was serendipitously noticed in all cases. One of these had widespread bone metastases seen almost identically in 99mTc-citrate and 99mTc-MDP studies. Accordingly, 10 patients (Group B) having more than 40 malignant lesions on the bone scan underwent 99mTc-citrate study. In group A, accumulation of the tracer was seen in all malignant breast nodules and axillary lymphnode mass (n=4), medullary carcinoma of the thyroid along with its metastasis and a carcinoid (n=4) and an ovarian malignancy. Uptake and outflow pattern could differentiate fibroadenoma (n=3) from carcinoma of the breast. No significant uptake was seen in liver secondaries (n>10), lymphoma lesions (n=5), papillary carcinoma of thyroid, renal cell and embryonal cell carcinoma. In group B patients, the radiotracer accumulated well in the metastatic lesions while there was distinctly lesser uptake in normal/degenerated joints compared to the bone scan. The study shows potential of the tracer in imaging soft tissue malignancies. Bone scanning with 99mTc-citrate is an interesting possibility since mechanism of its uptake appears to be different to 99mTc-MDP. (author)

  15. Enhanced citrate production through gene insertion in Aspergillus niger

    DEFF Research Database (Denmark)

    Jongh, Wian de; Nielsen, Jens

    2007-01-01

    The effect of inserting genes involved in the reductive branch of the tricarboxylic acid (TCA) cycle on citrate production by Aspergillus niger was evaluated. Several different genes were inserted individually and in combination, i.e. malate dehydrogenase (mdh2) from Saccharomyces cerevisiae, two...

  16. {sup 14}N NQR spectrum of sildenafil citrate

    Energy Technology Data Exchange (ETDEWEB)

    Stephenson, David, E-mail: david.stephenson@sta.uwi.edu; Singh, Nadia [University of the West Indies, Chemistry Department (Trinidad and Tobago)

    2015-04-15

    The {sup 14}N nuclear quadrupole resonance (NQR) spectrum of sildenafil citrate tablets has been recorded allowing the quadrupole coupling constants and asymmetry parameters of all six unique nitrogen atoms in its structure to be determined. A density function calculation gives results that are largely in agreement with the experimental values.

  17. Nutritional and Hormonal Regulation of Citrate and Carnitine/Acylcarnitine Transporters: Two Mitochondrial Carriers Involved in Fatty Acid Metabolism.

    Science.gov (United States)

    Giudetti, Anna M; Stanca, Eleonora; Siculella, Luisa; Gnoni, Gabriele V; Damiano, Fabrizio

    2016-01-01

    The transport of solutes across the inner mitochondrial membrane is catalyzed by a family of nuclear-encoded membrane-embedded proteins called mitochondrial carriers (MCs). The citrate carrier (CiC) and the carnitine/acylcarnitine transporter (CACT) are two members of the MCs family involved in fatty acid metabolism. By conveying acetyl-coenzyme A, in the form of citrate, from the mitochondria to the cytosol, CiC contributes to fatty acid and cholesterol synthesis; CACT allows fatty acid oxidation, transporting cytosolic fatty acids, in the form of acylcarnitines, into the mitochondrial matrix. Fatty acid synthesis and oxidation are inversely regulated so that when fatty acid synthesis is activated, the catabolism of fatty acids is turned-off. Malonyl-CoA, produced by acetyl-coenzyme A carboxylase, a key enzyme of cytosolic fatty acid synthesis, represents a regulator of both metabolic pathways. CiC and CACT activity and expression are regulated by different nutritional and hormonal conditions. Defects in the corresponding genes have been directly linked to various human diseases. This review will assess the current understanding of CiC and CACT regulation; underlining their roles in physio-pathological conditions. Emphasis will be placed on the molecular basis of the regulation of CiC and CACT associated with fatty acid metabolism. PMID:27231907

  18. Integrative assessment of enantioselectivity in endocrine disruption and immunotoxicity of synthetic pyrethroids

    International Nuclear Information System (INIS)

    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.

  19. 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.

  20. Enzyme Basis for pH Regulation of Citrate and Pyruvate Metabolism by Leuconostoc oenos

    NARCIS (Netherlands)

    Ramos, Ana; Lolkema, Juke S.; Konings, Wilhelmus; Santos, Helena

    1995-01-01

    Citrate and pyruvate metabolism by nongrowing cells of Leuconostoc oenos was investigated. 13C nuclear magnetic resonance (NMR) spectroscopy was used to elucidate the pathway of citrate breakdown and to probe citrate or pyruvate utilization, noninvasively, in living cell suspensions. The utilization

  1. 76 FR 19997 - Determination That FENTORA (Fentanyl Citrate) Buccal Tablet, 300 Micrograms, Was Not Withdrawn...

    Science.gov (United States)

    2011-04-11

    ... HUMAN SERVICES Food and Drug Administration Determination That FENTORA (Fentanyl Citrate) Buccal Tablet... determined that FENTORA (fentanyl citrate) buccal tablet, 300 micrograms (mcg), was not withdrawn from sale... drug applications (ANDAs) for fentanyl citrate buccal tablet, 300 mcg, if all other legal...

  2. The influence of ferric (III citrate on ATP-hydrolases of Desulfuromonas acetoxidans ІМV В-7384

    Directory of Open Access Journals (Sweden)

    O. Maslovska

    2013-02-01

    Full Text Available Desulfuromonas acetoxidans obtains energy for growth by the anaerobic oxidation of organic compounds with the carbon dioxide formation. It was found that ferrum and manganese are used as terminal electron acceptors in the processes of anaerobic respiration, such as dissimilative Fe3+- and Mn4+-reduction, carried out by these bacteria (Lovely, 1991. D. acetoxidans ІМV B-7384 can be used as anode biocatalyst in microbial fuel cell with high electron recovery through acetate oxidation to the electric current as a result of electron transfer to the anode or 3d-type transition metals, such as ferrum and manganese, in the process of their reduction. Investigation of biochemical changes of D. acetoxidans ІМV B-7384 under the influence of Fe (III compounds is important for optimization of the process of bacterial electricity generation. ATP-hydrolase is located in cytoplasmic membrane, and its subunits are exposed to both the cytoplasm and the external environment. Therefore, the changes of that enzyme activity can be used as an indicator of various stress exposure. Presence of ferric iron ions in the bacterial growth medium could catalyze generation of organic reactive oxygen species, such as peroxyl (ROO- and alkoxyl (RO- radicals. Lipid peroxidation is one of the main reasons of cell damage and it’s following death under the influence of reactive oxygen metabolites. It is known that lipid peroxidation and membrane transport processes are somehow interrelated, but mechanisms of such interaction are still unidentified. In our previous researche we have shown the influence of ferric (III citrate on the intensity of lipid peroxidation of D. аcetoxidans ІМV В-7384. Significant increase of the content of lipid peroxidation products (lipid hydroperoxides, conjugated dienes and malondialdehyde in bacterial cells has been observed under the addition of ferric (III citrate into the cultural medium. The increase of the concentration of lipid

  3. Short, Enantioselective Total Synthesis of Highly Oxidized Taxanes.

    Science.gov (United States)

    Yuan, Changxia; Jin, Yehua; Wilde, Nathan C; Baran, Phil S

    2016-07-11

    In the realm of natural product chemistry, few isolates have risen to the level of fame justifiably accorded to Taxol (1) and its chemical siblings. This report describes the most concise route to date for accessing the highly oxidized members of this family. As representative members of taxanes containing five oxygen atoms, decinnamoyltaxinine E (2) and taxabaccatin III (3), have succumbed to enantioselective total synthesis for the first time in only 18 steps from a simple olefin starting material. The strategy holistically mimics nature's approach (two-phase synthesis) and features a carefully choreographed sequence of stereoselective oxidations and a remarkable redox-isomerization to set the key trans-diol present in 2 and 3. This work lays the critical groundwork necessary to access even higher oxidized taxanes such as 1 in a more practical fashion, thus empowering a medicinal chemistry campaign that is not wedded to semi-synthesis. PMID:27240325

  4. Combinatorial evolution of site- and enantioselective catalysts for polyene epoxidation

    Science.gov (United States)

    Lichtor, Phillip A.; Miller, Scott J.

    2012-12-01

    Selectivity in the catalytic functionalization of complex molecules is a major challenge in chemical synthesis. The problem is magnified when there are several possible stereochemical outcomes and when similar functional groups occur repeatedly within the same molecule. Selective polyene oxidation provides an archetypical example of this challenge. Historically, enzymatic catalysis has provided the only precedents. Although non-enzymatic catalysts that meet some of these challenges became known, a comprehensive solution has remained elusive. Here, we describe low molecular weight peptide-based catalysts, discovered through a combinatorial synthesis and screening protocol, that exhibit site- and enantioselective oxidation of certain positions of various isoprenols. This diversity-based approach, which exhibits features reminiscent of the directed evolution of enzymes, delivers catalysts that compare favourably to the state-of-the-art for the asymmetric oxidation of these compounds. Moreover, the approach culminated in catalysts that exhibit alternative-site selectivity in comparison to oxidation catalysts previously described.

  5. The Palladium-Catalyzed Aerobic Kinetic Resolution of Secondary Alcohols: Reaction Development, Scope, and Applications

    KAUST Repository

    Ebner, Davidâ C.

    2009-12-07

    The first palladium-catalyzed enantioselective oxidation of secondary alcohols has been developed, utilizing the readily available diamine (-)-sparteine as a chiral ligand and molecular oxygen as the stoichiometric oxidant. Mechanistic insights regarding the role of the base and hydrogen-bond donors have resulted in several improvements to the original system. Namely, addition of cesium carbonate and tert-butyl alcohol greatly enhances reaction rates, promoting rapid resolutions. The use of chloroform as solvent allows the use of ambient air as the terminal oxidant at 23 degrees C, resulting in enhanced catalyst selectivity. These improved reaction conditions have permitted the successful kinetic resolution of benzylic, allylic, and cyclopropyl secondary alcohols to high enantiomeric excess with good-to-excellent selectivity factors. This catalyst system has also been applied to the desymmetrization of meso-diols, providing high yields of enantioenriched hydroxyketones.

  6. Lipase-Catalyzed Kinetic Resolution of Novel Antifungal N-Substituted Benzimidazole Derivatives.

    Science.gov (United States)

    Łukowska-Chojnacka, Edyta; Staniszewska, Monika; Bondaryk, Małgorzata; Maurin, Jan K; Bretner, Maria

    2016-04-01

    A series of new N-substituted benzimidazole derivatives was synthesized and their antifungal activity against Candida albicans was evaluated. The chemical step included synthesis of appropriate ketones containing benzimidazole ring, reduction of ketones to the racemic alcohols, and acetylation of alcohols to the esters. All benzimidazole derivatives were obtained with satisfactory yields and in relatively short times. All synthesized compounds exhibit significant antifungal activity against Candida albicans 900028 ATCC (% cell inhibition at 0.25 μg concentration > 98%). Additionally, racemic mixtures of alcohols were separated by lipase-catalyzed kinetic resolution. In the enzymatic step a transesterification reaction was applied and the influence of a lipase type and solvent on the enantioselectivity of the reaction was studied. The most selective enzymes were Novozyme SP 435 and lipase Amano AK from Pseudomonas fluorescens (E > 100). PMID:26922853

  7. Asymmetric, Three-Component, One-Pot Synthesis of Spiropyrazolones and 2,5-Chromenediones from Aldol Condensation/NHC-Catalyzed Annulation Reactions.

    Science.gov (United States)

    Wang, Lei; Li, Sun; Chauhan, Pankaj; Hack, Daniel; Philipps, Arne R; Puttreddy, Rakesh; Rissanen, Kari; Raabe, Gerhard; Enders, Dieter

    2016-04-01

    A novel one-pot, three-component diastereo- and enantioselective synthesis of spiropyrazolones has been developed involving the aldol condensation of an enal to generate α,β-unsaturated pyrazolones, which react with a second equivalent of enal through an N-heterocyclic carbene (NHC)-catalyzed [3+2] annulation. The desired spirocyclopentane pyrazolones are obtained in moderate to good yields and good to excellent stereoselectivities. Alternatively, starting from cyclic 1,3-diketones, 2,5-chromenediones are available through [2+4] annulation. PMID:26864437

  8. Metformin-clomiphene citrate vs. clomiphene citrate alone: Polycystic ovarian syndrome

    Directory of Open Access Journals (Sweden)

    Aqueela Ayaz

    2013-01-01

    Full Text Available Background: Polycystic ovary syndrome (PCOS is the commonest endocrinopathy in women that is associated with reproductive and metabolic disorders. Objectives: We compared the ovulation and conception rates after the treatment with clomiphene citrate (CC alone and in combination with metformin in infertile patients presented with polycystic ovarian syndrome (PCOS. Materials and Methods: This randomized controlled trial of independent cases and controls was conducted at the Department of Obstetrics and Gynecology, Hera General Hospital, Makkah, Saudi Arabia from February 01 to December 31, 2008. The 42 subjects diagnosed as PCOS were divided into group A and B (21 subjects in each for management with CC + metformin and CC alone, respectively. Group A received 500 mg three times a day of metformin continuously from the first cycle for 6 months or till pregnancy was confirmed. In both groups CC was started at a dose of 50 mg from day-2 till day-6 of the menstrual cycle. The dose of CC was increased to 100 mg in second and 150 mg in third cycle, and then remained 150 mg for the remaining three cycles. With ovulation the dose of CC was unaltered in both groups. Data were analyzed using Statistical Package for the Social Sciences (SPSS version 16. Results: More than 50% females in both groups were had body mass index > 25. Group A achieved high rate of regular cycles, ovulation success, and conception than group B (71.4% vs. 38.1%; P = 0.03, (76.2% vs. 38.1%; P = 0.021, and (66.6% vs. 28.6%; P = 0.01, respectively. Conclusion: Management with metformin + CC increased the ovulation and conception rates.

  9. Production of technical-grade sodium citrate from glycerol-containing biodiesel waste by Yarrowia lipolytica.

    Science.gov (United States)

    Kamzolova, Svetlana V; Vinokurova, Natalia G; Lunina, Julia N; Zelenkova, Nina F; Morgunov, Igor G

    2015-10-01

    The production of technical-grade sodium citrate from the glycerol-containing biodiesel waste by Yarrowia lipolytica was studied. Batch experiments showed that citrate was actively produced within 144 h, then citrate formation decreased presumably due to inhibition of enzymes involved in this process. In contrast, when the method of repeated batch cultivation was used, the formation of citrate continued for more than 500 h. In this case, the final concentration of citrate in the culture liquid reached 79-82 g/L. Trisodium citrate was isolated from the culture liquid filtrate by the addition of a small amount of NaOH, so that the pH of the filtrate increased to 7-8. This simple and economic isolation procedure gave the yield of crude preparation containing trisodium citrate 5.5-hydrate up to 82-86%. PMID:26141285

  10. Evidence for the effect of sorption enantioselectivity on the availability of chiral pesticide enantiomers in soil.

    Science.gov (United States)

    Gámiz, Beatriz; Facenda, Gracia; Celis, Rafael

    2016-06-01

    Although enantioselective sorption to soil particles has been proposed as a mechanism that can potentially influence the availability of individual chiral pesticide enantiomers in the environment, environmental fate studies generally overlook this possibility and assume that only biotic processes can be enantioselective, whereas abiotic processes, such as sorption, are non-enantioselective. In this work, we present direct evidence for the effect of the enantioselective sorption of a chiral pesticide in a natural soil on the availability of the single pesticide enantiomers for transport. Batch sorption experiments, with direct determination of the sorbed amounts, combined with column leaching tests confirmed previous observations that from non-racemic aqueous solutions the sorption of the chiral fungicide metalaxyl on the soil appeared to be enantioselective, and further demonstrated that the enantiomer that was sorbed to a greater extent (R-metalaxyl, Kd = 1.73 L/kg) exhibited retarded leaching compared to its optical isomer (S-metalaxyl, Kd = 1.15 L/kg). Interconversion and degradation of the pesticide enantiomers, which are potential experimental artifacts that can lead to erroneous estimates of sorption and its enantioselectivity, were discarded as possible causes of the observed enantioselective behavior. The results presented here may have very important implications for a correct assessment of the environmental fate of chiral pesticides that are incorporated into the environment as non-racemic mixtures, and also of aged chiral pesticide residues that have been transformed from racemic to non-racemic by biologically-mediated processes. PMID:27060281

  11. Iridium-Catalyzed Selective Isomerization of Primary Allylic Alcohols.

    Science.gov (United States)

    Li, Houhua; Mazet, Clément

    2016-06-21

    This Account presents the development of the iridium-catalyzed isomerization of primary allylic alcohols in our laboratory over the past 8 years. Our initial interest was driven by the long-standing challenge associated with the development of a general catalyst even for the nonasymmetric version of this seemingly simple chemical transformation. The added value of the aldehyde products and the possibility to rapidly generate molecular complexity from readily accessible allylic alcohols upon a redox-economical isomerization reaction were additional sources of motivation. Certainly influenced by the success story of the related isomerization of allylic amines, most catalysts developed for the selective isomerization of allylic alcohols were focused on rhodium as a transition metal of choice. Our approach has been based on the commonly accepted precept that hydrogenation and isomerization are often competing processes, with the latter being usually suppressed in favor of the former. The cationic iridium complexes [(Cy3P)(pyridine)Ir(cod)]X developed by Crabtree (X = PF6) and Pfaltz (X = BArF) are usually considered as the most versatile catalysts for the hydrogenation of allylic alcohols. Using molecular hydrogen to generate controlled amounts of the active form of these complexes but performing the reaction in the absence of molecular hydrogen enabled deviation from the typical hydrogenation manifold and favored exclusively the isomerization of allylic alcohols into aldehydes. Isotopic labeling and crossover experiments revealed the intermolecular nature of the process. Systematic variation of the ligand on the iridium center allowed us to identify the structural features beneficial for catalytic activity. Subsequently, three generations of chiral catalysts have been investigated and enabled us to reach excellent levels of enantioselectivity for a wide range of 3,3-disubstituted aryl/alkyl and alkyl/alkyl primary allylic alcohols leading to β-chiral aldehydes. The

  12. ATP citrate lyase knockdown impacts cancer stem cells in vitro

    OpenAIRE

    Hanai, J-i; Doro, N; Seth, P; Sukhatme, V P

    2013-01-01

    ATP citrate lyase (ACL) knockdown (KD) causes tumor suppression and induces differentiation. We have previously reported that ACL KD reverses epithelial–mesenchymal transition (EMT) in lung cancer cells. Because EMT is often associated with processes that induce stemness, we hypothesized that ACL KD impacts cancer stem cells. By assessing tumorsphere formation and expression of stem cell markers, we showed this to be the case in A549 cells, which harbor a Ras mutation, and in two other non-sm...

  13. Subclinical abortions in patients treated with clomiphene citrate

    International Nuclear Information System (INIS)

    Using radioimmunoassay for human chorionic gonadotrophin beta-subunit, 39 treatment cycles of clomiphene citrate therapy were studied prospectively for incidence of subclinical abortions. Eight treatment cycles resulted in clinically recognizable pregnancies and three other treatment cycles ended up with subclinical abortions. The plasma progesterone levels in patients with subclinical abortions at the 13th day after ovulation were lower than those in patients with normal pregnancies. (author)

  14. Studies on Ga-67 citrate uptake in various experimental tumors

    International Nuclear Information System (INIS)

    Ga-67 citrate uptake was autoradiographically studied in Ehrlich's tumor and sarcoma 180 in mice and 3'-Me-DAB hepatoma in rats with a histological comparison. In order to evaluate the relationship between tumor growth and degree of Ga-67 citrate uptake, animals were sacrificed 3, 5, 7 and 10 days after transplantation of tumor cells of Ehrlich's tumor and sarcoma 180. The results were as follows. 1) When Ga-67 citrate was administered to mice having Ehrlich's tumor, sarcoma 180 and to rats having 3'-Me-DAB hepatoma, varying degrees of accumulation of Ga-67 were seen in all experimental tumors. 2) In Ehrlich's tumor and sarcoma 180, RI uptake ratio (Tumor/Normal tissue uptake ratio; T/N ratio) was increased in accordance with tumor growth and was about 5 in these tumors 10 days after transplantation of tumor cells. On the other hand, RI uptake ratio (Tumor/Normal Liver tissue uptake ratio; T/NL ratio) ranged from 1.62 to 3.31 in 3'-Me-DAB hepatoma. 3) In all tumors, remarkable accumulation of Ga-67 was demonstrated in the highly cellular sites of tumors without degeneration and necrosis. 4) In Ehrlich's tumor and sarcoma 180, an accumulation of Ga-67 citrate was also observed in granulation tissues consisting of fibroblasts, fibrocyte, neutrophils and a small number of lymphocytes around the tumor, and it was more intense than that of tumorous tissue in many cases. 5) In 3'-Me-DAB hepatoma, Ga-67 uptake was seen in hepatocellular carcinoma with little fibrous stroma, but not in cholangiocarcinoma with dense fibrous stroma. (author)

  15. Citrate Root Exudation under Zn and P Deficiency

    OpenAIRE

    Bless Aplena Elen Siane

    2012-01-01

    Zinc and phosphorus are essential nutrients with low bioavailability in calcareous soils. Some plants exude organic acids to increase the solubility of these two nutrients. The objective of this study was to examine citrate exudation rates of different lupin (Feodora and Energy) and rapeseed (Dunkeld, Yickadee and Rainbow) cultivars underdeficiencies of Zn and P. The plants were cultivated into three different nutrient solutions (complete, -Zn, and -P)with pH around 7. Under Zn deficiency, ra...

  16. Silver-YBCO composite through citrate gel decomposition

    International Nuclear Information System (INIS)

    Silver-YBCO composite containing upto 75% silver has been prepared by thermal decomposition of citrate gel. In this paper the morphological and structural changes taking place during the decomposition of the gel in the range 100--900 degrees C are presented. Heat treatment at 915 degrees C of the composite powder containing Ag2O above a critical limit has been found to impart superconductivity without any external oxygen annealing. The mechanical and microstructural features of the sintered composite are presented

  17. Electrodeposition of iron-molybdenum coatings from citrate electrolyte

    OpenAIRE

    Ved, M. V.; Sakhnenko, N. D.; Karakurkchi, A. V.; Zyubanova, S. I.

    2014-01-01

    Specifi c features of the electrodeposition of iron–molybdenum coatings from a citrate electrolyte based on iron(III) sulfate and sodium molybdate in dc and unipolar pulsed modes were studied. It was demonstrated that bright compact coatings with varied content of molybdenum can be produced by varying the relative concentrations of salts of the alloy-forming components and the solution pH. The current density ranges providing the high efficiency of the galvanostastic electrolysis were determi...

  18. Electrodeposition of iron-molybdenum-tungsten coatings from citrate electrolytes

    OpenAIRE

    Karakurkchi, A. V.; Ved, M. V.; Sakhnenko, N. D.; Yermolenko, I. Yu.

    2015-01-01

    Specific features of the electrodeposition of iron–molybdenum–tungsten coatings from citrate electrolytes based on iron(III) sulfate in the dc mode and with a unipolar pulsed current were studied. It was shown that varying the relative concentrations of salts of alloy-forming metals and the solution pH makes it possible to obtain lustrous compact coatings with low porosity and various contents of high-melting components. The effect of temperature on the coating composition and current efficie...

  19. Renal Localization of {sup 67}Ga Citrate in Noninfectious Nephritis

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Kang Wook; Jeong, Min Soo; Rhee, Sunn Kgoo; Kim, Sam Yong; Shin, Young Tai; Ro, Heung Kyu [Chungnam University College of Medicine, Deajeon (Korea, Republic of)

    1992-07-15

    {sup 67}Ga citrate scan has been requested for detection or follow-up of inflammatory or neoplastic disease. Visualization of {sup 67}Ga citrate in the kidneys at 48 and 72 hr post injection is usually interpreted as evidence of renal pathology. But precise mechanisms of abnormal {sup 67}Ga uptake in kidneys were unknown. We undertook a study to determine the clinical value of {sup 67}Ga citrate imaging of the kidneys in 68 patients with primary or secondary nephropathy confirmed by renal biopsy and 66 control patients without renal disease. Renal uptake in 48 to 72 hr images was graded as follows: Grade 0=background activity;1=faint uptake greater than background; 2=definite uptake, but less than lumbar vertebrae;3 same uptake as lumbar vertebrae, but less than liver; 4=same or higher uptake than liver. The results were as follows. 1) 42 of 68(62%) patients with noninfectious nephritis showed grade 2 or higher {sup 67}Ga renal uptake but only 10 percent of control patients showed similar uptake. 2) In 14 patients with systemic lupus erythematosus, 8 of 9 (89%) patients with lupus nephritis exhibited marked renal uptake. 3) 36 of 41 patients (88%) with combined nephrotic syndrome showed Grade 2 or higher renal uptake. 4) Renal {sup 67}Ga uptake was correlated with clinical severity of nephrotic syndrome determined by serum albumin level, 24 hr urine protein excretion and serum lipid levels. 5) After complete remission of nephrotic syndrome, renal uptake in all 8 patients who were initially Grade 3 or 4, decreased to Grade 1 or 0. In conclusion, we think that the mechanism of renal {sup 67}Ga uptake in nephrotic syndrome might be related to the pathogenesis of nephrotic syndrome. In systemic lupus erythematosus, {sup 67}Ga citrate scan is useful in predicting renal involvement.

  20. PZ, PT and PZT formation from metal citrates

    International Nuclear Information System (INIS)

    Lead zirconate, lead titanate and lead titanate-zirconate were obtained by mechanical mixing of lead, titanium and zirconium citrates in ether and by calcination. The process was analyzed by DTA, TGA, IR, pore size distribution and surface area measurements. The results indicate that the decomposition reaction and formation of PZ, PT occur simultaneaously without formation of intermediate compounds. PZT was formed from 5000C. (author)

  1. Sildenafil citrate and uteroplacental perfusion in fetal growth restriction

    Directory of Open Access Journals (Sweden)

    Marzieh Vahid Dastjerdi

    2012-01-01

    Full Text Available Background: To determine whether the phosphodiesterase type 5 inhibitor, Sildenafil citrate, affects uteroplacental perfusion. Materials and Methods: Based on a randomized double-blinded and placebo-controlled trial, forty one pregnant women with documented intrauterine growth retardation at 24-37 weeks of gestation were evaluated for the effect of a single dose of Sildenafil citrate on uteroplacental circulation as determined by Doppler ultrasound study of the umbilical and middle cerebral arteries. Statistical analysis included χ2 -test to compare proportions, and independent-samples t-test and paired student′s t-test to compare continuous variables. Results: Sildenafil group fetuses demonstrated a significant decrease in systolic/diastolic ratios (0.60 [SD 0.40] [95% Cl 0.37-0.84], P=0.000, and pulsatility index (0.12 [SD 0.15] [95% Cl 0.02-0.22], P=0.019 for the umbilical artery and a significant increase in middle cerebral artery pulsatility index (MCA PI (0.51 [SD 0.60] [95% Cl 0.16-0.85], P=0.008. Conclusion: Doppler velocimetry index values reflect decreased placental bed vascular resistance after Sildenafil. Sildenafil citrate can improve fetoplacental perfusion in pregnancies complicated by intrauterine growth restriction. It could be a potential therapeutic strategy to improve uteroplacental blood flow in pregnancies with fetal growth restriction (FGR.

  2. Calcium citrate and vitamin D in the treatment of osteoporosis.

    Science.gov (United States)

    Quesada Gómez, José Manuel; Blanch Rubió, Josep; Díaz Curiel, Manuel; Díez Pérez, Adolfo

    2011-01-01

    The combination of calcium with vitamin D (vitamin D(3) [colecalciferol]) forms the basis of preventive and therapeutic regimens for osteoporosis. A number of studies have suggested that the combination of calcium and vitamin D is effective when administered at respective dosages of at least 1200 mg and 800 IU per day, although efficacy is, as expected, affected by patient compliance. Overall, treatment with this combination appears to be effective in reducing the incidence of non-vertebral and hip fractures. Also, in all drug studies (of antiresorptive and anabolic agents and strontium ranelate) that demonstrated a reduction in risk of osteoporotic fractures, patients also took calcium and vitamin D supplements. An important finding in this regard is that vitamin D levels have been demonstrated to be inadequate in more than half of women treated for osteoporosis in the US and Europe. The capacity of the small intestine to absorb calcium salts depends on the solubility and ionization of the salts. These properties vary for different salts, with fasting calcium citrate absorption being greater than that of calcium lactogluconate and calcium carbonate. Calcium citrate formulations taken between meals may help to prevent abdominal distension and flatulence, as well as minimize the risk of renal calculus formation, thus helping to optimize patient compliance. Therefore, calcium citrate combined with vitamin D is the combination of choice for the prevention or treatment of osteoporosis. PMID:21405146

  3. Design, Synthesis and Biological Activity of Novel Reversible Peptidyl FVIIa Inhibitors Rh-Catalyzed Enantioselective Synthesis of Diaryl Amines

    DEFF Research Database (Denmark)

    Storgaard, Morten

    This thesis describes two different projects. The first project deals with the design, synthesis and biological activity of novel reversible peptidyl FVIIa inhibitors (Chapter 1–3). FVIIa was launced as NovoSeven R over a decade ago by Novo Nordisk for the treatment of hemophilia A and B complica......This thesis describes two different projects. The first project deals with the design, synthesis and biological activity of novel reversible peptidyl FVIIa inhibitors (Chapter 1–3). FVIIa was launced as NovoSeven R over a decade ago by Novo Nordisk for the treatment of hemophilia A and B...... complicated by antibodies. FVIIa is a serine protease and hence liquid formulations are not stable due to autoproteolysis. A reversible inhibitor would stabilize FVIIa making a liquid formulation possible, representing an important follow-up product for Novo Nordisk. Peptidyl benzyl ketones was chosen...... as a new class of potential inhibitors, whose sequence was rationally selected from a previously reported FVIIa-TF specificity profile. Since arginine was found to be the most active P1-amino acid, a mild and efficient synthesis of the corresponding arginyl benzyl ketone building block was sought. Two...

  4. Transfer Hydrogenation of C= C Double Bonds Catalyzed by Ruthenium Amido-Complexes:Scopes, Limitation and Enantioselectivity

    Institute of Scientific and Technical Information of China (English)

    XUE,Dong; CHENG,Ying-Chun; CUI,Xin; WANG,Qi-Wei; ZHU,Jin; DENG,Jin-Gen

    2004-01-01

    @@ The reduction of C = C double bonds is one of the most fundamental synthetic transformations and plays a key role in the manufacturing of a wide variety of bulk and fine chemicals. Hydrogenation of olefinic substrates can be achieved readily with molecular hydrogen in many cases, but transfer hydrogenation methods using suitable donor molecules such as formic acid or alcohols are receiving increasing attention as possible synthetic alternatives because it requires no special equipment and avoids the handling of potentially hazardous gaseous hydrogen.

  5. Combined experimental and theoretical study of the mechanism and enantioselectivity of palladium-catalyzed intermolecular Heck coupling

    DEFF Research Database (Denmark)

    Henriksen, Signe Teuber; Norrby, Per-Ola; Kaukoranta, Päivi;

    2008-01-01

    -Pd(P,N) species prefers a geometry with the phenyl trans to N. However, the alternative form, with Ph trans to P, is much less stable but much more reactive. In the preferred transition state, the phenyl moiety is trans to P, but significant electron density has been transferred to the alkene carbon trans to N...... date....

  6. (Enantio)selective Hydrogen Autotransfer: Ruthenium-Catalyzed Synthesis of Oxazolidin-2-ones from Urea and Diols.

    Science.gov (United States)

    Peña-López, Miguel; Neumann, Helfried; Beller, Matthias

    2016-06-27

    A novel strategy for the synthesis of oxazolidin-2-ones from vicinal diols and urea is described. In this heterocycle synthesis, two different C-O and C-N bonds are sequentially formed in a domino process consisting of nucleophilic substitution and alcohol amination. The use of readily available starting materials and the good atom economy render this process environmentally benign. While this transformation is already highly chemo- and regioselective, we also developed the first asymmetric version of this method using (R)-(+)-MeO-BIPHEP as the chiral ligand. PMID:27072612

  7. Enantioselective addition of diethylzinc to aryl aldehydes catalyzed by 1,2,3,4-tetrahydroisoquinoline β-amino alcohol

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    A highly effective,new chiral 1,2,3,4-tetrahydroisoquinoline catalyst 1 for the diethylzinc addition to aryl aldehydes has been investigated.Using 10 mol%of this chiral catalyst,secondary alcohols can be obtained in up to 87%yield and 99.5%ee under mild conditions.

  8. Chiral Cu(II-catalyzed enantioselective β-borylation of α,β-unsaturated nitriles in water

    Directory of Open Access Journals (Sweden)

    Lei Zhu

    2015-10-01

    Full Text Available The promising performance of copper(II complexes was demonstrated for asymmetric boron conjugate addition to α,β-unsaturated nitriles in water. The catalyst system, which consisted of Cu(OAc2 and a chiral 2,2′-bipyridine ligand, enabled β-borylation and chiral induction in water. Subsequent protonation, which was accelerated in aqueous medium, led to high activity of this asymmetric catalysis. Both solid and liquid substrates were suitable despite being insoluble in water.

  9. A Multistep Organocatalysis Experiment for the Undergraduate Organic Laboratory: An Enantioselective Aldol Reaction Catalyzed by Methyl Prolinamide

    Science.gov (United States)

    Wade, Edmir O.; Walsh, Kenneth E.

    2011-01-01

    In recent years, there has been an explosion of research concerning the area of organocatalysis. A multistep capstone laboratory project that combines traditional reactions frequently found in organic laboratory curriculums with this new field of research is described. In this experiment, the students synthesize a prolinamide-based organocatalyst…

  10. Asymmetric azidation-cycloaddition with open-chain peptide-based catalysts. A sequential enantioselective route to triazoles.

    Science.gov (United States)

    Guerin, David J; Miller, Scott J

    2002-03-13

    A family of beta-substituted histidine-containing peptides has been synthesized to probe the effect of noncovalent conformational rigidification on catalyst enantioselectivity. Unambiguous enhancement of enantioselectivity in the conjugate addition of azide to alpha,beta-unsaturated carboxylate derivatives has been achieved, enabling application to a sequential asymmetric azidation/cycloaddition for the synthesis of optically enriched triazoles and triazolines. PMID:11878965

  11. Enantioselective separation and transformation of metalaxyl and its major metabolite metalaxyl acid in tomato and cucumber.

    Science.gov (United States)

    Li, Yuanbo; Dong, Fengshou; Liu, Xingang; Xu, Jun; Chen, Xiu; Han, Yongtao; Cheng, Youpu; Jian, Qiu; Zheng, Yongquan

    2013-11-01

    Many studies have shown the enantioselective transformation of metalaxyl in soil and animals, but little is known about the enantioselective biotransformation of metalaxyl in plants. In this study, a sensitive and convenient chiral liquid chromatography-tandem mass spectrometry method was developed for simultaneous measurement of the enantiomers of metalaxyl and its major metabolite, metalaxyl acid, in tomato and cucumber. Separation was by reversed-phase chromatography on a Chiralcel OD-RH column under isocratic conditions using acetonitrile-water (60/40, v/v) as mobile phase. The proposed method was successfully applied to investigate the possible enantioselective transformation of metalaxyl as well as the formation of metalaxyl acid in tomato and cucumber. In both vegetables, the (-)-R-enantiomer was preferentially degraded, resulting in relative enrichment of the (+)-S-enantiomer. Furthermore, formation of the metalaxyl acid enantiomers was also shown to be enantioselective, with the R-metalaxyl acid formed at a faster rate. This is the first evidence of enantioselective transformation of metalaxyl in vegetables, and the results should be considered in future environmental risk and food safety evaluations. PMID:23768319

  12. A Process-Based Model of TCA Cycle Functioning to Analyze Citrate Accumulation in Pre- and Post-Harvest Fruits

    OpenAIRE

    Etienne, Audrey; GÉNARD, MICHEL; Bugaud, Christophe

    2015-01-01

    Citrate is one of the most important organic acids in many fruits and its concentration plays a critical role in organoleptic properties. The regulation of citrate accumulation throughout fruit development, and the origins of the phenotypic variability of the citrate concentration within fruit species remain to be clarified. In the present study, we developed a process-based model of citrate accumulation based on a simplified representation of the TCA cycle to predict citrate concentration in...

  13. Differences between the effects of EDTA and citrate anticoagulants on platelet count and mean platelet volume.

    Science.gov (United States)

    McShine, R L; Sibinga, S; Brozovic, B

    1990-01-01

    Platelet counts on whole blood samples collected into tripotassium salt of EDTA, trisodium citrate (Na3 citr), citrate phosphate dextrose adenine formula 1 (CPDA-1) and acid citrate dextrose formula A (ACD-A), all showed a statistically significant drop (P less than 0.01) after 1 h standing at room temperature (RT) as compared with the immediate (within 30 min) counts. After 1 h the enumeration became stable in the EDTA samples but the drop continued up to 4-6 h in those samples taken into citrate. The decreases in citrate were significant (18-30%, P less than 0.001). The addition of EDTA (1.5 mg/ml) to the citrated samples after the sixth hour count created a significant rise (6-22%, P less than 0.01) in the counts between the sixth and the seventh hour. Our observations show that platelet counts in citrated blood samples are lower than those in EDTA and highlight the necessity to present citrated samples mixed wtih dried EDTA when characterization or quality control of blood and blood components is required. Analysis of the mean platelet volume (MPV) showed significantly lower values (6-13%, P less than 0.05) in the citrated samples as compared to the same samples in EDTA, and a significant increase (4-6%, P less than 0.01) on the addition of EDTA to the citrated samples after the sixth hour analysis. PMID:2125542

  14. Exogenous citrate impairs glucose tolerance and promotes visceral adipose tissue inflammation in mice.

    Science.gov (United States)

    Leandro, João G B; Espindola-Netto, Jair M; Vianna, Maria Carolina F; Gomez, Lilian S; DeMaria, Thaina M; Marinho-Carvalho, Monica M; Zancan, Patricia; Paula Neto, Heitor A; Sola-Penna, Mauro

    2016-03-01

    Overweight and obesity have become epidemic worldwide and are linked to sedentary lifestyle and the consumption of processed foods and drinks. Citrate is a metabolite that plays central roles in carbohydrate and lipid metabolism. In addition, citrate is the additive most commonly used by the food industry, and therefore is highly consumed. Extracellular citrate can freely enter the cells via the constitutively expressed plasma membrane citrate transporter. Within the cytosol, citrate is readily metabolised by ATP-citrate lyase into acetyl-CoA - the metabolic precursor of endogenously produced lipids and cholesterol. We therefore hypothesised that the citrate ingested from processed foods and drinks could contribute to increased postprandial fat production and weight gain. To test our hypothesis, we administered citrate to mice through their drinking water with or without sucrose and monitored their weight gain and other metabolic parameters. Our results showed that mice receiving citrate or citrate+sucrose did not show increased weight gain or an increase in the weight of the liver, skeletal muscles or adipose tissues (AT). Moreover, the plasma lipid profiles (TAG, total cholesterol, LDL and HDL) were similar across all groups. However, the group receiving citrate+sucrose showed augmented fasting glycaemia, glucose intolerance and the expression of pro-inflammatory cytokines (TNF-α, IL-1β, IL-6 and IL-10) in their AT. Therefore, our results suggest that citrate consumption contributes to increased AT inflammation and altered glucose metabolism, which is indicative of initial insulin resistance. Thus, citrate consumption could be a previously unknown causative agent for the complications associated with obesity. PMID:26863933

  15. Ferric citrate controls phosphorus and delivers iron in patients on dialysis.

    Science.gov (United States)

    Lewis, Julia B; Sika, Mohammed; Koury, Mark J; Chuang, Peale; Schulman, Gerald; Smith, Mark T; Whittier, Frederick C; Linfert, Douglas R; Galphin, Claude M; Athreya, Balaji P; Nossuli, A Kaldun Kaldun; Chang, Ingrid J; Blumenthal, Samuel S; Manley, John; Zeig, Steven; Kant, Kotagal S; Olivero, Juan Jose; Greene, Tom; Dwyer, Jamie P

    2015-02-01

    Patients on dialysis require phosphorus binders to prevent hyperphosphatemia and are iron deficient. We studied ferric citrate as a phosphorus binder and iron source. In this sequential, randomized trial, 441 subjects on dialysis were randomized to ferric citrate or active control in a 52-week active control period followed by a 4-week placebo control period, in which subjects on ferric citrate who completed the active control period were rerandomized to ferric citrate or placebo. The primary analysis compared the mean change in phosphorus between ferric citrate and placebo during the placebo control period. A sequential gatekeeping strategy controlled study-wise type 1 error for serum ferritin, transferrin saturation, and intravenous iron and erythropoietin-stimulating agent usage as prespecified secondary outcomes in the active control period. Ferric citrate controlled phosphorus compared with placebo, with a mean treatment difference of -2.2±0.2 mg/dl (mean±SEM) (P<0.001). Active control period phosphorus was similar between ferric citrate and active control, with comparable safety profiles. Subjects on ferric citrate achieved higher mean iron parameters (ferritin=899±488 ng/ml [mean±SD]; transferrin saturation=39%±17%) versus subjects on active control (ferritin=628±367 ng/ml [mean±SD]; transferrin saturation=30%±12%; P<0.001 for both). Subjects on ferric citrate received less intravenous elemental iron (median=12.95 mg/wk ferric citrate; 26.88 mg/wk active control; P<0.001) and less erythropoietin-stimulating agent (median epoetin-equivalent units per week: 5306 units/wk ferric citrate; 6951 units/wk active control; P=0.04). Hemoglobin levels were statistically higher on ferric citrate. Thus, ferric citrate is an efficacious and safe phosphate binder that increases iron stores and reduces intravenous iron and erythropoietin-stimulating agent use while maintaining hemoglobin. PMID:25060056

  16. Catalytic enantioselective addition of organoboron reagents to fluoroketones controlled by electrostatic interactions

    Science.gov (United States)

    Lee, Kyunga; Silverio, Daniel L.; Torker, Sebastian; Robbins, Daniel W.; Haeffner, Fredrik; van der Mei, Farid W.; Hoveyda, Amir H.

    2016-08-01

    Organofluorine compounds are central to modern chemistry, and broadly applicable transformations that generate them efficiently and enantioselectively are in much demand. Here we introduce efficient catalytic methods for the addition of allyl and allenyl organoboron reagents to fluorine-substituted ketones. These reactions are facilitated by readily and inexpensively available catalysts and deliver versatile and otherwise difficult-to-access tertiary homoallylic alcohols in up to 98% yield and >99:1 enantiomeric ratio. Utility is highlighted by a concise enantioselective approach to the synthesis of the antiparasitic drug fluralaner (Bravecto, presently sold as the racemate). Different forms of ammonium–organofluorine interactions play a key role in the control of enantioselectivity. The greater understanding of various non-bonding interactions afforded by these studies should facilitate the future development of transformations that involve fluoroorganic entities.

  17. Enantioselective bioaccumulation and degradation of sediment-associated metalaxyl enantiomers in Tubifex tubifex.

    Science.gov (United States)

    Di, Shanshan; Liu, Tiantian; Diao, Jinling; Zhou, Zhiqiang

    2013-05-29

    Knowledge about the enantioselective bioavailability of chiral pesticides in aquatic organisms facilitates more accurate interpretation of their environmental behaviors. In this study, the enantioselective bioaccumulation of metalaxyl enantiomers in Tubifex tubifex was detected in two uptake pathways. For the spike water treatment, a 16 day exposure experiment was employed and the enantiomer fractions (EFs) in tubifex tissue were maintained approximately at 0.47 during the experiment. For the spike sediment treatment, a 14 day bioaccumulation period indicated the concentrations of (-)-(R)-metalaxyl were higher than those of (+)-(S)-metalaxyl. Therefore, the bioaccumulation of metalaxyl in worms was enantioselective for these treatments. With the presence of tubifex, higher concentrations of metalaxyl in overlying water and lower concentrations in sediment were detected than in worm-free treatments. This means that tubifex has positive functions in metalaxyl's diffusion from the sediment to overlying water and in the degradation of the sediment-associated metalaxyl. PMID:23635317

  18. 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.

  19. Catalytic enantioselective reductions and allylations of prochiral ketones

    CERN Document Server

    Cunningham, A

    2002-01-01

    The use of LiGaH sub 4 in combination with the S,O-chelate 2-hydroxy-2'-mercapto-1,1'-binaphthyl (monothiobinaphthol, MTBH sub 2), forms an active catalyst (2 mol %) for the asymmetric reduction of prochiral ketones, when using catecholborane as the hydride source. This catalyst has successfully been applied to the enantioselective reduction of aryl/n-alkyl ketones, providing the chiral sec-alcohols in yields of 82 - 96% and with enantiomeric excess values of 59 - 93%. Alkyl/methyl ketones are reduced in yields of 72 - 93% and in 46 - 79% enantiomeric excess. Enantioface differentiation is on the basis of the steric requirements of the ketone substituents. The X-ray structure of the pre-catalyst, Li(THF) sub 3 Ga(MTB) sub 2 has been determined and in solution is in equilibrium with a dimeric species of constitution Li sub 2 Ga sub 2 (MTB) sub 4. An indium analogue whose X-ray structure was determined as Li sub 2 (THF) sub 5 lnCI(MTB) sub 2 has also been prepared. The indium- based catalyst does not form an en...

  20. Robert Boyle's chiral crystal chemistry: computational re-evaluation of enantioselective adsorption on quartz.

    Science.gov (United States)

    Kahr, Bart; Chittenden, Brianne; Rohl, Andrew

    2006-02-01

    While searching for early examples of interactions of organic chromophores with minerals in the context of a systematic study of the process of dyeing crystals, we came across Robert Boyle's description of an experiment that may have been evidence of the enantioselective adsorption of a natural product, carminic acid (7-beta-D-glucopyranosyl-9,10-dihydro-3,5,6,8-tetrahydroxy-1-methyl-9,10-dioxo-2-anthracenecarboxylic acid), to the chiral surfaces of alpha-quartz, three centuries before such interactions became the subject of active chemical investigations. In order to determine whether Boyle did indeed observe enantioselective adsorption--albeit unbeknownst to him--we attempted to dye quartz with carminic acid according to his recipe. Quartz adsorbs carminic acid only because on heating it develops a network of microfissures that adsorb dye. This process depends on capillarity, not on specific non-covalent interactions; there is no evidence of enantioselectivity adsorption to heated crystals or enantioselective epitaxy to unheated crystals. These failures changed the focus of our inquiry: Why have almost all attempts to demonstrate the enantioselective adsorption of additives to quartz crystal surfaces been generally confounding and equivocal? In order to answer this question, we complement our experimental historical re-investigation with contemporary computational techniques for modeling crystal surface structure and the adsorption of additives. Minimizations of the energies associated with the adsorption of carminic acid to relaxed, hydrated d- and l-quartz {10(-)0} surfaces are analyzed in light of quartz's abysmal record as an enantioselective stationary phase. PMID:16385623

  1. 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

  2. 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.

  3. Ferric Citrate Hydrate as a Phosphate Binder and Risk of Aluminum Toxicity

    OpenAIRE

    Ajay Gupta

    2014-01-01

    Ferric citrate hydrate was recently approved in Japan as an oral phosphate binder to be taken with food for the control of hyperphosphatemia in patients with chronic kidney disease (CKD). The daily therapeutic dose is about 3 to 6 g, which comprises about 2 to 4 g of citrate. Oral citrate solubilizes aluminum that is present in food and drinking water, and opens the tight junctions in the intestinal epithelium, thereby increasing aluminum absorption and urinary excretion. In healthy animals d...

  4. Forsterite Carbonation in Wet Supercritical CO2 and Sodium Citrate

    Science.gov (United States)

    Qiu, L.; Schaef, T.; Wang, Z.; Miller, Q.; McGrail, P.

    2013-12-01

    Lin Qiu1*, Herbert T. Schaef2, Zhengrong Wang1, Quin R.S. Miller3, BP McGrail2 1. Yale University, New Haven, CT, USA 2. Pacific Northwest National Laboratory, Richland, WA, USA 3. University of Wyoming, Laramie, WY, USA Geologic reservoirs for managing carbon emissions (mostly CO2) have expanded over the last 5 years to include unconventional formations including basalts and fractured shales. Recently, ~1000 metric tons of CO2 was injected into the Columbia River Basalt (CRB) in Eastern Washington as part of the Wallula Pilot Project, Big Sky Regional Carbon Partnership. Based on reservoir conditions, the injected CO2 is present as a supercritical fluid that dissolves into the formation water over time, and reacts with basalt components to form carbonate minerals. In this paper, we discuss mineral transformation reactions occurring when the forsterite (Mg2SiO4) is exposed to wet scCO2 in equilibrium with pure water and sodium citrate solutions. Forsterite was selected as it is an important olivine group mineral present in igneous and mafic rocks. Citrate was selected as it has been shown to enhance mineral dissolution and organic ligands are possible degradation products of the microbial communities present in the formational waters of the CRB. For the supercritical phase, transformation reactions were examined by in situ high pressure x-ray diffraction (HXRD) in the presence of supercritical carbon dioxide (scCO2) in contact with water and sodium citrate solutions at conditions relevant to carbon sequestration. Experimental results show close-to-complete dissolution of forsterite in contact with scCO2 equilibrated with pure water for 90 hours (90 bar and 50°C). Under these conditions, thin films of water coated the mineral surface, providing a mechanism for silicate dissolution and transport of cations necessary for carbonate formation. The primary crystalline component initially detected with in situ HXRD was the hydrated magnesium carbonate, nesquehonite [Mg

  5. Engineering genetically encoded nanosensors for real-time in vivo measurements of citrate concentrations.

    Directory of Open Access Journals (Sweden)

    Jennifer C Ewald

    Full Text Available Citrate is an intermediate in catabolic as well as biosynthetic pathways and is an important regulatory molecule in the control of glycolysis and lipid metabolism. Mass spectrometric and NMR based metabolomics allow measuring citrate concentrations, but only with limited spatial and temporal resolution. Methods are so far lacking to monitor citrate levels in real-time in-vivo. Here, we present a series of genetically encoded citrate sensors based on Förster resonance energy transfer (FRET. We screened databases for citrate-binding proteins and tested three candidates in vitro. The citrate binding domain of the Klebsiella pneumoniae histidine sensor kinase CitA, inserted between the FRET pair Venus/CFP, yielded a sensor highly specific for citrate. We optimized the peptide linkers to achieve maximal FRET change upon citrate binding. By modifying residues in the citrate binding pocket, we were able to construct seven sensors with different affinities spanning a concentration range of three orders of magnitude without losing specificity. In a first in vivo application we show that E. coli maintains the capacity to take up glucose or acetate within seconds even after long-term starvation.

  6. Renal uptake of /sup 67/Ga-citrate in renal amyloidosis due to Familiar Mediterranean Fever

    Energy Technology Data Exchange (ETDEWEB)

    Banzo-Marraco, J.; Abos-Olivares, M.D.; Iribar-Ibabe, M.C.; Prats-Rivera, E.; Banzo-Marraco, J.I.; Teijeiro-Vidal, J.; Nerin-Mora, E.; Nerin de la Puerta, I.

    1981-06-01

    Renal uptake of /sup 67/Ga-citrate is described in a patient with biopsy-proven amyloidosis of the kidneys, due to Familiar Mediterranean Fever. After administration 150 MBq (4mCi) /sup 67/Ga-citrate, scans were done at 48, 72, and 120 h. Intense uptake was noted in both kidneys. A renal biopsy done 5 days after the /sup 67/Ga-citrate scan revealed a pattern typical of amyloidosis. Gallium scanning can be useful in patients with fever of unknown origin. Renal amyloidosis can be considered when renal uptake of /sup 67/Ga-citrate associated with nephrotic syndrome is observed.

  7. Comparison of the efficiency of clomiphene citrate and letrozole in combination with metformin in moderately obese clomiphene citrate - resistant polycystic ovarian syndrome patients

    Directory of Open Access Journals (Sweden)

    Bjelica Artur

    2016-01-01

    Full Text Available Introduction. Polycystic ovary syndrome is the most common endocrinopathy in women of reproductiveage. Therapy for those who want to get pregnant involves ovulation induction using clomiphene citrate, metformin, letrozole and gonadotropins. Objective. The aim of the study was to compare the efficacy of combinations of clomiphene citrate-metformin and letrozole-metformin in obese patients who are resistant to clomiphene citrate alone. Methods. The investigation was conducted as a retrospective study involving 60 moderately obese patients with polycystic ovary syndrome. Thirty-one of them received the clomiphene citrate-metformin, and 29 letrozole-metformin therapy. Stimulation was carried out for the procedures of intrauterine insemination (IUI. Results. The age of patients, duration of infertility, and body mass index in both groups were similar. There was statistically significant difference in the thickness of the endometrium in favor of the group having the letrozole-metformin therapy (8.9 ± 1.7 mm compared with the group receiving the clomiphene citrate-metformin treatment (6.3 ± 1.3 mm. The number of follicles was not statistically significantly different. Pregnancy rate in the first cycle of IUI in the clomiphene citrate group was 6.4%, and 17.2% in the letrozole group, which also was not statistically different. After the third IUI cycle, the pregnancy rate was significantly higher in the letrozole group (20.6%, while in the clomiphene citrate group it was (9.6%. Conclusion. This retrospective study demonstrated the advantages of the use of letrozole over clomiphene citrate in combination with metformin in moderately obese patients with polycystic ovary syndrome who are resistant to stimulation with clomiphene citrate alone.

  8. Citrate anticoagulation for continuous renal replacement therapy in small children

    OpenAIRE

    Soltysiak, Jolanta; Warzywoda, Alfred; Kociński, Bartłomiej; Ostalska-Nowicka, Danuta; Benedyk, Anna; Silska-Dittmar, Magdalena; Zachwieja, Jacek

    2013-01-01

    Background Regional citrate anticoagulation (RCA) is one of the methods used to prevent clotting in continuous renal replacement therapy (CRRT). The aim of this study was to describe the outcomes and complications of RCA-CRRT in comparison to heparin anticoagulation (HA)-CRRT in critically ill children. Methods This study was a retrospective review of 30 critically ill children (16 on RCA- and 14 on HA-CRRT) who underwent at least 24 h of CRRT. The mean body weight of the children was 8.69 ± ...

  9. Impact of Creatine on Coordination of Urea and Citrate Cycles

    Czech Academy of Sciences Publication Activity Database

    Kohlíková, E.; Petr, M.; Navrátil, Tomáš; Šenholdová, Z.; Přistoupilová, K.; Přistoupil, T. I.; Heyrovský, Michael; Pelclová, D.

    Praha: IV. interní klinika 1. LF UK Praha, 2006 - (Tvrzická, E.), s. 21-24 ISBN 80-239-7726-1. [Atherosklerosa 2006. Diagnostika, léčba, prevence v dětském i dospělém věku. Praha (CZ), 11.09.2006-13.09.2006] R&D Projects: GA MPO 1H-PK/42; GA MZd NR8107 Institutional research plan: CEZ:AV0Z40400503 Keywords : Atherosclerosis * Citrate cycle * Urea cycle * Blood Subject RIV: CF - Physical ; Theoretical Chemistry

  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. Formulation, Characterization and Physicochemical Evaluation of Potassium Citrate Effervescent Tablets

    Directory of Open Access Journals (Sweden)

    Fatemeh Fattahi

    2013-02-01

    Full Text Available Purpose: The aim of this study was to design and formulation of potassium citrate effervescent tablet for reduction of calcium oxalate and urate kidney stones in patients suffering from kidney stones. Methods: In this study, 13 formulations were prepared from potassium citrate and effervescent base in different concentration. The flowability of powders and granules was studied. Then effervescent tablets were prepared by direct compression, fusion and wet granulation methods. The prepared tablets were evaluated for hardness, friability, effervescent time, pH, content uniformity. To amend taste of formulations, different flavoring agents were used and then panel test was done by using Latin Square method by 30 volunteers. Results: Formulations obtained from direct compression and fusion methods had good flow but low hardness. Wet granulation improves flowability and other physicochemical properties such as acceptable hardness, effervescence time ≤3 minutes, pH<6, friability < 1%, water percentage < 0.5% and accurate content uniformity. In panel test, both of combination flavors; (orange - lemon and (strawberry - raspberry had good acceptability. Conclusion: The prepared tablets by wet granulation method using PVP solution had more tablet hardness. It is a reproducible process and suitable to produce granules that are compressed into effervescent tablets due to larger agglomerates.

  12. Trapping and release of citrate-capped gold nanoparticles

    International Nuclear Information System (INIS)

    An electrical method to trap and release charged gold nanoparticles onto and from the surface of gold electrodes modified by an alkanethiol self-assembled monolayer (SAM) is presented. To form electrodes coated with gold nanoparticles (GNPs), amine-terminated SAMs on gold electrodes were immersed in a solution of negatively charged citrate-capped GNPs. Accumulation of GNPs on the electrode surface was monitored by a decrease in the impedance of the SAM-modified electrode and by an increase in the electrochemical activity at the electrode as shown through cyclic voltammetry (CV). Electrostatic interactions between the GNPs and the amine-terminated SAM trap the GNPs on the electrode surface. Application of a subsequent negative bias to the electrode initiated a partial release of the GNPs from the electrode surface. Impedance spectroscopy, cyclic voltammetry, ultraviolet-visible (UV-Vis) spectroscopy and atomic force microscopy (AFM) were used to monitor and confirm the attraction of GNPs to and release from the aminealkanethiolated gold electrodes. This work describes a method of trapping and release for citrate-capped GNPs that could be used for on-demand nanoparticle delivery applications such as in assessing and modeling nanoparticle toxicology, as well as for monitoring the functionalization of gold nanoparticles.

  13. 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.

  14. Enantioselective Synthesis of the 5-6-7 Carbocyclic Core of the Gagunin Diterpenoids

    OpenAIRE

    Shibuya, Grant M.; Enquist, John A.; Stoltz, Brian M.

    2013-01-01

    A catalytic enantioselective double allylic alkylation reaction has been employed in the synthesis of the core of the gagunin diterpenoids. Enantioenriched material was advanced in 11 steps to afford the core of the highly oxygenated target, which includes two all-carbon quaternary stereocenters.

  15. Exploiting the enantioselectivity of Baeyer-Villiger monooxygenases via boron oxidation

    NARCIS (Netherlands)

    Brondani, Patricia B.; Dudek, Hanna; Reis, Joel S.; Fraaije, Marco W.; Andrade, Leandro H.

    2012-01-01

    The enantioselective carbon-boron bond oxidation of several chiral boron-containing compounds by Baeyer-Villiger monooxygenases was evaluated. PAMO and M446G PAMO conveniently oxidized 1-phenylethyl boronate into the corresponding 1-(phenyl)ethanol (ee = 82-91%). Cyclopropyl boronic esters were also

  16. The Enantioselectivity of Odor Sensation: Some Examples for Undergraduate Chemistry Courses

    Science.gov (United States)

    Kraft, Philip; Mannschreck, Albrecht

    2010-01-01

    This article discusses seven chiral odorants that demonstrate the enantioselectivity of odor sensation: carvone, Celery Ketone, camphor, Florhydral, 3-methyl-3-sulfanylhexan-1-ol, muscone, and methyl jasmonate. After a general introduction of the odorant-receptor interaction and the combinatorial code of olfaction, the olfactory properties of the…

  17. Enantioselective total synthesis of a novel polyketide natural product(+)-integrasone, an HIV-1 integrase inhibitor

    OpenAIRE

    Mehta, Goverdhan; Roy, Subhrangsu

    2005-01-01

    Enantioselective total synthesis of the recently isolated, novel polyketide natural product (+)-integrasone has been accomplished from the readily available Diels-Alder adduct of cyclopentadiene and p-benzoquinone. An enzymatically desymmetrized epoxyquinone building block has been elaborated through a series of regio-, chemo- and stereocontrolled steps to the final bicyclic framework of the natural product.

  18. Resolution of alpha/beta-amino acids by enantioselective penicillin G acylase from Achromobacter sp

    Czech Academy of Sciences Publication Activity Database

    Grulich, Michal; Brezovský, J.; Štěpánek, Václav; Palyzová, Andrea; Kyslíková, Eva; Kyslík, Pavel

    2015-01-01

    Roč. 122, DEC 2015 (2015), s. 240-247. ISSN 1381-1177 R&D Projects: GA MŠk(CZ) ED1.1.00/02.0109 Institutional support: RVO:61388971 Keywords : Penicillin G acylase * Enantioselectivity * Homologous model Subject RIV: CE - Biochemistry Impact factor: 2.128, year: 2014

  19. Enantioselective polymerization of epoxides using biaryl-linked bimetallic cobalt catalysts: A mechanistic study

    KAUST Repository

    Ahmed, Syud M.

    2013-12-18

    The enantioselective polymerization of propylene oxide (PO) using biaryl-linked bimetallic salen Co catalysts was investigated experimentally and theoretically. Five key aspects of this catalytic system were examined: (1) the structural features of the catalyst, (2) the regio- and stereoselectivity of the chain-growth step, (3) the probable oxidation and electronic state of Co during the polymerization, (4) the role of the cocatalyst, and (5) the mechanism of monomer enchainment. Several important insights were revealed. First, density functional theory (DFT) calculations provided detailed structural information regarding the regio- and stereoselective chain-growth step. Specifically, the absolute stereochemistry of the binaphthol linker determines the enantiomer preference in the polymerization, and the interaction between the salen ligand and the growing polymer chain is a fundamental aspect of enantioselectivity. Second, a new bimetallic catalyst with a conformationally flexible biphenol linker was synthesized and found to enantioselectively polymerize PO, though with lower enantioselectivity than the binaphthol linked catalysts. Third, DFT calculations revealed that the active form of the catalyst has two active exo anionic ligands (chloride or carboxylate) and an endo polymer alkoxide which can ring-open an adjacent cobalt-coordinated epoxide. Fourth, calculations showed that initiation is favored by an endo chloride ligand, while propagation is favored by the presence of two exo carboxylate ligands. © 2013 American Chemical Society.

  20. Understanding the endocrine disruption of chiral pesticides:The enantioselectivity in estrogenic activity of synthetic pyrethroids

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    Synthetic pyrethroids(SPs) ,a family of chiral insecticides consisting of multiple stereoismers,have been regarded as estrogenic endocrine-disrupting chemicals(EDCs) .In this study,we applied the yeast two-hybrid and molecular docking(MD) assay to assess the enantioselective estrogenic activities of three commonly used SPs,bifenthrin(cis-BF) ,permethrin(PM) and fenvalerate(Fen) .The β-galactosidase analyses indicated that all of the testing pyrethroids displayed significant(p<0.05) enantioselectivity.The results showed that the estrogenic potential of cis-BF was mainly attributed to 1S-cis-BF.Neither PM nor Fen showed estrogenic effects.However,two stereoisomers of PM possessed estrogenic potential activities.αR-2R-Fen and αS-2S-Fen also induced the β-galactosidase activity.The inability to initiate the reporter gene expression by the racemic chemicals may be due to the low ratios of these isomers or the antagonism among them.The strong hydrophobic interaction and the hydrogen bond between positive estrogenic isomers and ERα support our biological testing results.This research demonstrated that the enantioselective estrogenic activity of chiral SPs was due to selective binding between their isomers and the ERαreceptor.The data suggests that enantioselectivity of these chiral pesticides is significant to their estrogenic activities.

  1. Enantioselective Formation of a Dynamic Hydrogen-Bonded Assembly Based on the Chiral Memory Concept

    NARCIS (Netherlands)

    Ishi-i, Tsutomu; Crego Calama, Mercedes; Timmerman, Peter; Reinhoudt, David N.; Shinkai, Seiji

    2002-01-01

    In this paper, we report the enantioselective formation of a dynamic noncovalent double rosette assembly 1a3·(CYA)6 composed of three 2-pyridylcalix[4]arene dimelamines (1a) and six butylcyanuric acid molecules (BuCYA). The six 2-pyridyl functionalities of the assembly interact stereoselectively wit

  2. Simple Aziridino Alcohols as Chiral Ligands. Enantioselective Additions of Diethylzinc to N-Diphenylphosphinoylimines

    DEFF Research Database (Denmark)

    Tanner, David Ackland; Andersson, Pher G.; Guijarro, David

    Simple chiral aziridino alcohols 2-5, easily available from L-serine, L-threonine or L-allo-threonine, have been used as ligands to promote the addition of Et(2)Zn to the diphenylphosphinoylimine 1 (Ar=Ph). Enantioselectivities of up to 94% could be obtained by proper choice of the substituents on...

  3. Syntheses of a Flobufen Metabolite and Dapoxetine Based on Enantioselective Allylation of Aromatic Aldehydes

    Czech Academy of Sciences Publication Activity Database

    Hessler, F.; Korotvička, A.; Nečas, D.; Valterová, Irena; Kotora, M.

    2014-01-01

    Roč. 2014, č. 12 (2014), s. 2543-2548. ISSN 1434-193X Grant ostatní: GA ČR(CZ) GAP207/11/0587 Institutional support: RVO:61388963 Keywords : synthetic methods * asymmetric catalysis * organocatalysis * allylation * aldehydes * enantioselectivity Subject RIV: CC - Organic Chemistry Impact factor: 3.065, year: 2014

  4. A DFT exploration of the enantioselective rearrangement of cyclohexene oxide to cyclohexenol

    DEFF Research Database (Denmark)

    Brandt, Peter; Norrby, Per-Ola; Andersson, Pher G.

    2003-01-01

    In this paper, we present computational results for the (1S,3R,4R)-3-(pyrrolidinyl)-methyl-2-azabicyclo[2.2.1]heptane mediated rearrangement of cyclohexene oxide. The results nicely explain the differences in enantioselectivities between catalytic and stoichiometric mode between different ligands...

  5. Enantioselective determination of triazole fungicide epoxiconazole bioaccumulation in tubifex based on HPLC-MS/MS.

    Science.gov (United States)

    Liu, Chunxiao; Wang, Bo; Xu, Peng; Liu, Tiantian; Di, Shanshan; Diao, Jinling

    2014-01-15

    In this study, the enantioselective bioaccumulation of epoxiconazole enantiomers in tubifex (Oligochaeta, Tubificida) was investigated in two uptake pathways. A sensitive and rapid chiral method was developed for the determination of epoxiconazole enantiomers in tubifex and soil based on high-performance liquid chromatography coupled with triple-quadrupole mass spectrometry (HPLC-MS/MS). In the spiked-water or spiked-soil treatments, enantioselective bioaccumulation of epoxiconazole in tubifex was obersved. For spiked-water treatment, (-)-epoxiconazole accumulated in tubifex to a greater extent than (+)-epoxiconazole, leading to enrichments with a composition (-) > (+). However, for spiked-soil treatment, the enantioselectivity in tubifex was reversed with a preferential accumulation of (+)-epoxiconazole. Calculated accumulation factors (AFs) indicated that epoxiconazole in spiked-water treatment had higher bioaccumulation potential than that in spiked-soil treatment. The results from the spiked-soil treatment also revealed that the dissipation of epoxiconazole in soil was enantioselective, and tubifex has positive effects on epoxiconazole diffusion from soil to overlying water. PMID:24364671

  6. Enantioselective bioaccumulation of soil-associated fipronil enantiomers in Tubifex tubifex.

    Science.gov (United States)

    Liu, Tiantian; Wang, Peng; Lu, Yuele; Zhou, Gaoxin; Diao, Jinling; Zhou, Zhiqiang

    2012-06-15

    Enantioselective behavior of chiral pesticides in the aquatic environment has been a subject of growing interest. In this study, the enantioselective bioaccumulation of fipronil enantiomers in Tubifex tubifex (Oligochaeta, Tubificida) was detected in both spike-water and spike-soil systems, respectively. For the spike-water treatment, a 9-day exposure experiment was employed and the enantiomer fraction in tubifex tissue was maintained approximately at 0.58 during the experiment. In addition, a 14-day bioaccumulation period was chosen for the spike-soil treatment and a more significant deviation of enantiomer fraction from 0.5 in tubifex tissue was detected, with concentrations of the R-form higher than that of the S-form. Therefore, the bioaccumulation of fipronil was enantioselective in tubifex tissue for the two treatments and the magnitude of enantioselectivity may be influenced by different exposure conditions. For the spike-soil treatment, the concentrations of fipronil in verlying water and soil were also determined. With the presence of tubifex worms, higher concentrations of fipronil in overlying water and lower concentrations in soil were detected than that in the absence of tubifex treatment during the whole 14-day exposure period. This means that tubifex has positive functions in fipronil's diffusion from soil to overlying water and in the degradation of the soil-associated fipronil. PMID:22502899

  7. Efficient and highly enantioselective formation of the all-carbon quaternary stereocentre of lyngbyatoxin A

    DEFF Research Database (Denmark)

    Vital, Paulo J.V.; Tanner, David

    2006-01-01

    Indole 25, an advanced intermediate in a projected enantioselective total synthesis of lyngbyatoxin A 1, was prepared from allylic alcohol 11 in 9 steps and >95% ee, key transformations being the enantiospecific rearrangement of vinyl epoxide 14 and the Hemetsberger-Knittel reaction of azide 24....

  8. Enantioselective synthesis of tertiary α-chloro esters by non-covalent catalysis

    Science.gov (United States)

    Liu, Richard Y.; Wasa, Masayuki; Jacobsen, Eric N.

    2015-01-01

    We report an enantioselective approach to tertiary α-chloro esters through the reaction of silyl ketene acetals and N-chlorosuccinimide. The reaction is promoted by a chiral squaramide catalyst, which is proposed to engage both reagents exclusively through non-covalent interactions. Application of the tertiary chloride products in stereospecific substitution reactions is demonstrated. PMID:26085694

  9. Directed evolution of metagenome-derived epoxide hydrolase for improved enantioselectivity and enantioconvergence

    Czech Academy of Sciences Publication Activity Database

    Kotík, Michael; Zhao, W.; Lacazio, G.; Archelas, A.

    2013-01-01

    Roč. 91, JUL 2013 (2013), s. 44-51. ISSN 1381-1177 R&D Projects: GA ČR GAP207/10/0135 Institutional support: RVO:61388971 Keywords : Regioselectivity * Enantioselectivity * Chiral building block Subject RIV: CE - Biochemistry Impact factor: 2.745, year: 2013

  10. 1,2-Ferrocenediylazaphosphinines 3: a new class of planar chiral ligands for Cu-catalyzed cyclopropanation

    International Nuclear Information System (INIS)

    The synthesis and catalytic application of a new class of planar chiral ferrocenes, 1,2-ferrocenediylazaphos-phinines (1 and 2) are described. They are powerful ligands for the copper(I)-catalyzed asymmetric cyclopropanation of a range of alkenes with diazo esters to exhibit an exceptionally high degree of diastereoselectivity (∼100%) in favor of trans isomers, regardless the structure of the olefins and the diazo compounds. Comparative studies between 1 and 2 reveal that the former works better in terms of diastereocontrol. In contrast, however, enantioselectivity is low with both 1 and 2 as a whole although, in certain cases with a proper combination of the olefin and the diazo ester, high optical yields (up to 100% ee) can be achieved. Other reaction parameters such as the reaction temperature and the structure of the ligand do exhibit some influence, although infinitesimal, on both chemical and optical yields

  11. Bioavailability of zinc and phosphorus in calcareous soils as affected by citrate exudation

    NARCIS (Netherlands)

    Duffner, A.; Hoffland, E.; Temminghoff, E.J.M.

    2012-01-01

    Aims Zinc (Zn) and phosphorus (P) deficiency often occurs at the same time and limits crop production in many soils. It has been suggested that citrate root exudation is a response of plants to both deficiencies. We used white lupin (Lupinus albus L.) as a model plant to clarify if citrate exuded by

  12. PREPARATION OF SORBITOL CITRATE POLYESTERS BY REACTIVE EXTRUSION AND APPLICATION AS INHIBITIORS OF CALCIUM CARBONATE PRECIPITATION

    Science.gov (United States)

    Sorbitol citrates were prepared using a vented ZSK-30-twin-screw extruder as part of a program to develop bio-based, water soluble polycarboxylates. A Box-Behnken experimental design was used and included the variables sorbitol, citric acid, sodium citrate, temperature and feed rate. Extent of est...

  13. MECHANISM AND ENERGETICS OF A CITRATE-TRANSPORT SYSTEM OF KLEBSIELLA-PNEUMONIAE

    NARCIS (Netherlands)

    VANDERREST, ME; ABEE, T; MOLENAAR, D; KONINGS, WN

    1991-01-01

    The citrate-transport determinant of plasmid pES1 from Klebsiella pneumoniae [Schwarz, E. & Oesterhelt, D. (1985) EMBO J. 4, 1599 - 1603] has been subcloned in Escherichia coli DH1. Uptake of citrate in E. coli membrane vesicles via this uptake system is an electrogenic process, although the pH grad

  14. 21 CFR 520.763c - Dithiazanine iodide and piperazine citrate suspension.

    Science.gov (United States)

    2010-04-01

    ... 21 Food and Drugs 6 2010-04-01 2010-04-01 false Dithiazanine iodide and piperazine citrate... § 520.763c Dithiazanine iodide and piperazine citrate suspension. (a) Specifications. Each milliliter of the drug contains 69 milligrams of dithiazanine iodide and 83 milligrams of piperazine base...

  15. Mechanism of Citrate Metabolism by an Oxaloacetate Decarboxylase-Deficient Mutant of Lactococcus lactis IL1403

    NARCIS (Netherlands)

    Pudlik, Agata M.; Lolkema, Juke S.

    2011-01-01

    Citrate metabolism in resting cells of Lactococcus lactis IL1403(pFL3) results in the formation of two end products from the intermediate pyruvate, acetoin and acetate (A. M. Pudlik and J. S. Lolkema, J. Bacteriol. 193:706-714, 2011). Pyruvate is formed from citrate following uptake by the transport

  16. Addition of senna improves quality of colonoscopy preparation with magnesium citrate

    Institute of Scientific and Technical Information of China (English)

    Stergios Vradelis; Evangelos Kalaitzakis; Yalda Sharifi; Otto Buchel; Satish Keshav; Roger W Chapman; Barbara Braden

    2009-01-01

    AIM: To prospectively investigate the effectiveness and patient's tolerance of two low-cost bowel cleansing preparation protocols based on magnesium citrate only or the combination of magnesium citrate and senna. METHODS: A total of 342 patients who were referred for colonoscopy underwent a colon cleansing protocol with magnesium citrate alone ( n = 160) or magnesium citrate and senna granules ( n = 182). The colonoscopist rated the overall efficacy of colon cleansing using an established score on a 4-point scale. Patients were questioned before undergoing colonoscopy for side effects and symptoms during bowel preparation. RESULTS: The percentage of procedures rescheduled because of insufficient colon cleansing was 7% in the magnesium citrate group and 4% in the magnesium citrate/senna group ( P = 0.44). Adequate visualization of the colonic mucosa was rated superior under the citramag/senna regimen ( P = 0.004). Both regimens were well tolerated, and did not significantly differ in the occurrence of nausea, bloating or headache. However, abdominal cramps were observed more often under the senna protocol (29.2%) compared to the magnesium citrate only protocol (9.9%, P < 0.0003). CONCLUSION: The addition of senna to the bowel preparation protocol with magnesium citrate significantly improves the cleansing outcome.

  17. Standardization of the biological control of 67 Ga-citrate in rats and mice

    International Nuclear Information System (INIS)

    67Ga-citrate is frequently used in Nuclear Medicine for tumor diagnosis. This study established the biological distribution parameters in rats with experimental abscesses in the left thigh. The biological model choosen made possible the routine control of 67Ga-citrate giving a realiable result in a relative short-time (60 min.) after the radionuclide administration. (author)

  18. Characterization of citrate utilization in Corynebacterium glutamicum by transcriptome and proteome analysis.

    Science.gov (United States)

    Polen, Tino; Schluesener, Daniela; Poetsch, Ansgar; Bott, Michael; Wendisch, Volker F

    2007-08-01

    Corynebacterium glutamicum grows aerobically on a variety of carbohydrates and organic acids as single or combined sources of carbon and energy. To characterize the citrate utilization in C. glutamicum on a genomewide scale, a comparative analysis was carried out by combining transcriptome and proteome analysis. In cells grown on citrate, transcriptome analysis revealed highest expression changes for two different citrate-uptake systems encoded by citM and tctCBA, whereas genes encoding uptake systems for the glucose- (ptsG), sucrose- (ptsS) and fructose- (ptsF) specific PTS components and permeases for gluconate (gntP) and glutamate (gluC) displayed decreased mRNA levels in citrate-grown cells. This pattern was also observed when cells grown in Luria-Bertani (LB) medium plus citrate were compared with cells grown in LB medium, indicating some kind of catabolite repression. Genes encoding enzymes of the tricarboxylic acid cycle (aconitase, succinyl-CoA synthetase, succinate dehydrogenase and fumarase), malic enzyme, PEP carboxykinase, gluconeogenic glyceraldehyde-3-phosphate dehydrogenase and ATP synthase displayed increased expression in cells grown on citrate. Accordingly, proteome analysis revealed elevated protein levels of these enzymes and showed a good correlation with the mRNA levels. In conclusion, this study revealed the citrate stimulon in C. glutamicum and the regulated central metabolic genes when grown on citrate. PMID:17559405

  19. Iodine-catalyzed coal liquefaction

    Energy Technology Data Exchange (ETDEWEB)

    Joseph, J.T.; Duffield, J.E.; Davidson, M.G. (Amoco Oil Company, Naperville, IL (USA). Research and Development Dept.)

    Coals of two different ranks were liquefied in high yields using catalytic quantities of elemental iodine or iodine compounds. Iodine monochloride was found to be especially effective for enhancing both coal conversion and product quality. It appears that enhancement in coal conversion is due to the unique ability of iodine to catalyze radical-induced bond scission and hydrogen addition to the coal macromolecule or coal-derived free radicals. The starting iodine can be fully accounted for in the reaction products as both organic-bound and water-soluble forms. Unconverted coal and the heavy product fractions contain the majority of the organic-bound iodine. The results of iodine-catalyzed coal reactions emphasize the need for efficient hydrogen atom transfer along with bond scission to achieve high conversion and product quality. 22 refs., 12 tabs.

  20. Radiolabeled porphyrin versus gallium-67 citrate for the detection of human melanoma in athymic mice

    International Nuclear Information System (INIS)

    We performed the biodistribution and imaging studies of 111In and 67Ga labeled tetra(4-N-methylpyridyl) porphine, (T4NMPYP), and compared it to that of 67Ga citrate in athymic mice bearing a human melanoma xenograft. The biodistribution results of both 111In and 67Ga labeled T4NMPYP (3, 6, 24, and 48 hours) were similar but differed from that of 67Ga citrate (48 hours). The optimum tumor uptake of both radiolabeled porphyrins was at 6 hours postinjection and was lower than the tumor uptake of 67Ga citrate at 48 hours postinjection. Kidney was the only organ showing higher uptake of radiolabeled porphyrin compared to that of 67Ga citrate. The imaging studies performed with 111In T4NMPYP and 67Ga citrate correspond to the biodistribution results. Osteomyelitis present in one mouse showed good localization of 111In T4NMPYP. 15 refs., 3 figs., 5 tabs

  1. Enantioselective total synthesis of the novel tricyclic sesquiterpene (−)-sulcatine G. Absolute configuration of the natural product

    OpenAIRE

    Mehta, Goverdhan; Sreenivas, K.

    2002-01-01

    An enantioselective total synthesis of (−)-sulcatine G 4 from the readily available (+)-diquinane diol 6 has been accomplished. This leads to the establishment of the absolute configuration of the natural product (+)-sulcatine G as 1.

  2. Enantioselective Bio-Hydrolysis of Various Racemic and meso Aromatic Epoxides Using the Recombinant Epoxide Hydrolase Kau2

    Czech Academy of Sciences Publication Activity Database

    Zhao, W.; Kotík, Michael; Iacazio, G.; Archelas, A.

    2015-01-01

    Roč. 357, č. 8 (2015), s. 1895-1908. ISSN 1615-4150 Institutional support: RVO:61388971 Keywords : biotransformations * chiral resolution * enantioselectivity Subject RIV: CE - Biochemistry Impact factor: 5.663, year: 2014

  3. Enantioselective Pinacol Coupling of Aromatic Aldehydes Mediated by TiCl4(THF)2/Zn with Tartaric Ester

    Institute of Scientific and Technical Information of China (English)

    LI You-Gui李有桂; JIANG Chen江辰; ZHAO Jun赵俊; TIAN Qing-Shan田青杉; YOU Tian-Pa尤田耙

    2004-01-01

    Asymmetric pinacol coupling of aromatic aldehydes mediated by low valent titanium complexes of chiral ligands derived from natural tartaric acid provided corresponding pinacols in good yields with excellent diastereoselectivities and moderate enantioselectivities.

  4. Ruthenium and rhodium complexes with chiral P-donor ligands as catalysts of enantioselective hydrogenation of ketoesters

    International Nuclear Information System (INIS)

    The use of ruthenium(II) and rhodium(III) complexes with chiral P-donor ligands as catalysts of asymmetric hydrogenation of α-, β- and γ-ketoesters is considered. The attention is focused on highly enantioselective processes.

  5. 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.

  6. Synthesis of chiral N-ferrocenylmethylaminoalcohols and their applica-tion in enantioselective addition of diethylzinc to aldehydes

    Institute of Scientific and Technical Information of China (English)

    Jian Feng GE; Zong Xuan SHEN; Ya Wen ZHANG

    2004-01-01

    Three chiral N-ferrocenylmethylaminoalcohols were synthesized from readily available natural L-valine, leucine and phenylanine, and used as chiral ligands in the enantioselective addition of diethylzinc to aldehydes.

  7. PREPARATION, CHRACTERIZATION AND EVALUATION OF STARCH CITRATE- A NEW MODIFIED STARCH AS A DISINTEGRANT IN TABLET FORMULATIONS

    OpenAIRE

    K. P. R. Chowdary

    2011-01-01

    Starch citrate prepared by reacting potato starch with citric acid at elevated temperatures was found to be a white, crystalline, non-hygroscopic powder. Starch citrate prepared exhibited excellent flow characteristics. Starch citrate was insoluble in water and aqueous fluids of acidic and alkaline pHs. It also exhibited good swelling (1500%) in water. It has no pasting or gelling property when heated at 1000C in water for 30 min. As starch citrate exhibited good swelling in water it is consi...

  8. Model‐Based Assessment of Plasma Citrate Flux Into the Liver: Implications for NaCT as a Therapeutic Target

    OpenAIRE

    Z. Li; Erion, DM; Maurer, TS

    2016-01-01

    Cytoplasmic citrate serves as an important regulator of gluconeogenesis and carbon source for de novo lipogenesis in the liver. For this reason, the sodium‐coupled citrate transporter (NaCT), a plasma membrane transporter that governs hepatic influx of plasma citrate in human, is being explored as a potential therapeutic target for metabolic disorders. As cytoplasmic citrate also originates from intracellular mitochondria, the relative contribution of these two pathways represents critical in...

  9. Bidirectional enantioselective effects of the GABAB receptor agonist baclofen in two mouse models of excessive ethanol consumption

    OpenAIRE

    Kasten, Chelsea R.; Blasingame, Shelby N.; Boehm, Stephen L.

    2014-01-01

    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 separ...

  10. 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.

  11. 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.

  12. Use of Blemaren citrate formula in gout patients with nephrolithiasis

    Directory of Open Access Journals (Sweden)

    M S Eliseev

    2008-01-01

    Results. After completion of a course of Blemaren therapy, there was an 8% reduction in the mean serum UA levels, which correlated with an increase in its daily excretion (by an average of 20%. The highest increase in UA excretion was observed in 20 patients with baseline hypoex-cretion (<700 mg/day: from 226,3 (range 201,6-436,8 to 635,0 (range 272,2-705,6 mg/day (p = 0,01. UA excretion substantially unchanged in patients with normal uricosuria (>700 mg/day. Side effects that could cause the agent to be discontinued were absent. Conclusion. The Blemaren citrate formula used in gout patients with nephrolithiasis causes a significant increase in the renal excretion of UA (p = 0,01, normalizes its metabolic parameters, and shows a high safety, without worsening hepatic and renal functions and electrolyte metabolism.

  13. Response of patients with indolent systemic mastocytosis to tamoxifen citrate.

    Science.gov (United States)

    Butterfield, Joseph H; Chen, Dong

    2016-01-01

    We examined whether tamoxifen citrate at 20mg/day for 1 year had a beneficial effect on laboratory findings, bone marrow mastocytosis, common clinical symptoms, or quality-of-life assessment for 5 women and 2 men with indolent systemic mastocytosis. Tamoxifen was well tolerated. We found significant reductions in the platelet count, serum alkaline phosphatase, and 24-h urinary excretion of N-methylhistamine and significant increases in serum lactate dehydrogenase and (excluding 2 patients taking aspirin) in 24-h urinary excretion of 11β-prostaglandin F2α. Overall, no change occurred in percent involvement of bone marrow by mastocytosis. Symptom scores were mild and did not change during the treatment. The 36-Item Short Form Health Survey scores for quality of life physical and mental components showed no marked changes. Tamoxifen, an older, nonhematotoxic medication, has limited activity in systemic mastocytosis at the dosage used in this study. PMID:26612479

  14. Effect of Nb on barium titanate prepared from citrate solutions

    Directory of Open Access Journals (Sweden)

    Stojanović Biljana D.

    2002-01-01

    Full Text Available The influence of the addition of dopants on the microstructure development and electrical properties of BaTiO3 doped with 0.2, 0.4, 0.6, 0.8 mol% of Nb and 0.01 mol% of Mn based compounds was studied. Doped barium titanate was prepared using the polymeric precursor method from citrate solutions. The powders calcined at 700°C for 4 hours were analysed by infrared (IR spectroscopy to verify the presence of carbonates, and by X-ray diffraction (XRD for phase formation. The phase composition, microstructure and dielectric properties show a strong dependence on the amount of added niobium.

  15. Lipase Catalyzed Kinetic Resolution of rac-2-(3-Methoxy-4-methylphenyl) propan-1-ol and rac-2-(3-Hydroxy-4-methylphenyl)propyl propanoate for S-(+)-Xanthorrhizol

    Energy Technology Data Exchange (ETDEWEB)

    Shafioul, Azam Sharif Mohammed [University of Science and Technology, Daejeon (Korea, Republic of); Cheong, Chan Seong [Korea Institute of Science and Technology, Seoul (Korea, Republic of)

    2012-02-15

    Xanthorrhizol is a bisabolane type of natural sesquiterpene, the major component of essential oils of Curcuma xanthorrhiza. 2-(3-Methoxy-4-methylphenyl)propan-1-ol and 2-(3-hydroxy-4-methyl phenyl)propan-1-ol could be essential building block for enantioselective synthesis of xanthorrhizol. Enantioselective (c = 53%, E = 80 ± 3) for R-(+)-2-(3-hydroxy-4-methylphenyl) propan-1-ol and (c = 58%, E = 27 ± 1) for R-(+)-2-(3- methoxy-4-methylphenyl) propan-1-ol resolution processes were developed via lipase-catalyzed reaction. We found lipase Aspergillus oryzae (AOL) and Porcine pancreas (PPL) are selective to transesterification and hydrolysis in organic and aqueous phase. Modified demethylated substrate is appropriate for enantioselective hydrolysis reaction without any additives. Enantiopure chiral alcohol was crystallized from ethyl acetate/ n-hexane co-solvent system. Gram scale resolved chiral intermediate will facilitate the synthesis of the unnatural S-(+)-xanthorrhizol, the corresponding isomer of the natural one.

  16. Lipase Catalyzed Kinetic Resolution of rac-2-(3-Methoxy-4-methylphenyl) propan-1-ol and rac-2-(3-Hydroxy-4-methylphenyl)propyl propanoate for S-(+)-Xanthorrhizol

    International Nuclear Information System (INIS)

    Xanthorrhizol is a bisabolane type of natural sesquiterpene, the major component of essential oils of Curcuma xanthorrhiza. 2-(3-Methoxy-4-methylphenyl)propan-1-ol and 2-(3-hydroxy-4-methyl phenyl)propan-1-ol could be essential building block for enantioselective synthesis of xanthorrhizol. Enantioselective (c = 53%, E = 80 ± 3) for R-(+)-2-(3-hydroxy-4-methylphenyl) propan-1-ol and (c = 58%, E = 27 ± 1) for R-(+)-2-(3- methoxy-4-methylphenyl) propan-1-ol resolution processes were developed via lipase-catalyzed reaction. We found lipase Aspergillus oryzae (AOL) and Porcine pancreas (PPL) are selective to transesterification and hydrolysis in organic and aqueous phase. Modified demethylated substrate is appropriate for enantioselective hydrolysis reaction without any additives. Enantiopure chiral alcohol was crystallized from ethyl acetate/ n-hexane co-solvent system. Gram scale resolved chiral intermediate will facilitate the synthesis of the unnatural S-(+)-xanthorrhizol, the corresponding isomer of the natural one

  17. Inkjet printing of silver citrate conductive ink on PET substrate

    International Nuclear Information System (INIS)

    Highlights: ► A direct synthesis method of silver conductive film on PET substrate was presented. ► A stable particle-free conductive ink was prepared. ► Formation of silver-amine complex reduced the thermal decomposition temperature. ► Conductive patterns for flexible electronics were fabricated by inkjet printing. ► Silver film on PET substrate possessed highest adhesion rating even without polymer. - Abstract: Direct synthesis of silver conductive film on PET substrate by inkjet printing silver citrate conductive ink was presented in this paper. This kind of conductive ink contained silver citrate as silver precursor, 1,2-diaminopropane as complex agent dissolving the silver salt and methanol and isopropanol as a media adjusting the viscosity and surface tension. The formation of silver-amine complex reduced the decomposition temperature from 180 °C to 135 °C, thus the ink could be cured at relatively low temperature. The film reached the lowest resistivity of 17 μΩ cm after cured at 150 °C for 50 min, 3.1 μΩ cm at 230 °C and possessed high reflection and excellent adhesive property. Electrical conductivity, surface morphology and composition were investigated by four-point probe method, scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDS). It is demonstrated how the cured condition affects the silver film. Moreover, radio-frequency identification (RFID) antenna was fabricated by inkjet printing, which opens up routes for the flexible electronics fabrication.

  18. Inkjet printing of silver citrate conductive ink on PET substrate

    Energy Technology Data Exchange (ETDEWEB)

    Nie Xiaolei [Key Laboratory for Green Chemical Technology of Ministry of Education, School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072 (China); Wang Hong, E-mail: hongwang@tju.edu.cn [Key Laboratory for Green Chemical Technology of Ministry of Education, School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072 (China); Zou Jing [Key Laboratory for Green Chemical Technology of Ministry of Education, School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072 (China)

    2012-11-15

    Highlights: Black-Right-Pointing-Pointer A direct synthesis method of silver conductive film on PET substrate was presented. Black-Right-Pointing-Pointer A stable particle-free conductive ink was prepared. Black-Right-Pointing-Pointer Formation of silver-amine complex reduced the thermal decomposition temperature. Black-Right-Pointing-Pointer Conductive patterns for flexible electronics were fabricated by inkjet printing. Black-Right-Pointing-Pointer Silver film on PET substrate possessed highest adhesion rating even without polymer. - Abstract: Direct synthesis of silver conductive film on PET substrate by inkjet printing silver citrate conductive ink was presented in this paper. This kind of conductive ink contained silver citrate as silver precursor, 1,2-diaminopropane as complex agent dissolving the silver salt and methanol and isopropanol as a media adjusting the viscosity and surface tension. The formation of silver-amine complex reduced the decomposition temperature from 180 Degree-Sign C to 135 Degree-Sign C, thus the ink could be cured at relatively low temperature. The film reached the lowest resistivity of 17 {mu}{Omega} cm after cured at 150 Degree-Sign C for 50 min, 3.1 {mu}{Omega} cm at 230 Degree-Sign C and possessed high reflection and excellent adhesive property. Electrical conductivity, surface morphology and composition were investigated by four-point probe method, scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDS). It is demonstrated how the cured condition affects the silver film. Moreover, radio-frequency identification (RFID) antenna was fabricated by inkjet printing, which opens up routes for the flexible electronics fabrication.

  19. The Metal Chelators, Trientine and Citrate, Inhibit the Development of Cardiac Pathology in the Zucker Diabetic Rat

    Directory of Open Access Journals (Sweden)

    John W. Baynes

    2009-01-01

    Full Text Available Purpose. The objective of this study was to determine the efficacy of dietary supplementation with the metal chelators, trientine or citric acid, in preventing the development of cardiomyopathy in the Zucker diabetic rat. Hypothesis. We hypothesized that dietary chelators would attenuate metal-catalyzed oxidative stress and damage in tissues and protect against pathological changes in ventricular structure and function in type II diabetes. Methods. Animals (10 weeks old included lean control (LC, fa/+, untreated Zucker diabetic fatty (ZDF, fa/fa, and ZDF rats treated with either trientine (triethylenetetramine or citrate at 20 mg/d in drinking water, starting when rats were frankly diabetic. Cardiac functional assessment was determined using a Millar pressure/volume catheter placed in the left ventricle at 32 weeks of age. Results. End diastolic volume for the ZDF animals increased by 36% indicating LV dilatation (P<.05 and was accompanied by a 30% increase in the end diastolic pressure (P≤.05. Both trientine and citric acid prevented the increases in EDV and EDP (P<.05. Ejection fraction and myocardial relaxation were also significantly improved with chelator treatment. Conclusion. Dietary supplementation with trientine and citric acid significantly prevented structural and functional changes in the diabetic heart, supporting the merits of mild chelators for prevention of cardiovascular disease in diabetes.

  20. Effect of sodium citrate on preparation of nano-sized cobalt particles by organic colloidal process

    Institute of Scientific and Technical Information of China (English)

    Huaping ZHU; Hao LI; Huiyu SONG; Shijun LIAO

    2009-01-01

    Nano-sized cobalt particles with the diameter of 2 nm were prepared via an organic colloidal process with sodium formate, ethylene glycol and sodium citrate as the reducing agent, the solvent and the complexing agent, respectively. The effects of sodium citrate on the yield, crystal structure, particle size and size distribution of the prepared nano-sized cobalt particles were then investigated. The results show that the average particle diameter decreases from 200 nm to 2 nm when the molar ratio of sodium citrate to cobalt chloride changes from 0 to 6. Furthermore, sodium citrate plays a crucial role in the controlling of size distribution of the nano-sized particles. The size distribution of the particle without sodium citrate addition is in range from tens of nanometers to 300 or 400 nm, while that with sodium citrate addition is limited in the range of (2±0.25) nm. Moreover, it is found that the addition of sodium citrate as a complex agent could decrease the yield of the nano-sized cobalt particle.

  1. Stau-catalyzed Nuclear Fusion

    OpenAIRE

    Hamaguchi, K.; Hatsuda, T.(Theoretical Research Division, Nishina Center, RIKEN, Saitama, 351-0198, Japan); Yanagida, T. T.

    2006-01-01

    We point out that the stau may play a role of a catalyst for nuclear fusions if the stau is a long-lived particle as in the scenario of gravitino dark matter. In this letter, we consider d d fusion under the influence of stau where the fusion is enhanced because of a short distance between the two deuterons. We find that one chain of the d d fusion may release an energy of O(10) GeV per stau. We discuss problems of making the stau-catalyzed nuclear fusion of practical use with the present tec...

  2. Gold-catalyzed naphthalene functionalization

    OpenAIRE

    Iván Rivilla; M. Mar Díaz-Requejo; Pedro J. Pérez

    2011-01-01

    The complexes IPrMCl (IPr = 1,3-bis(diisopropylphenyl)imidazol-2-ylidene, M = Cu, 1a; M = Au, 1b), in the presence of one equiv of NaBAr'4 (Ar' = 3,5-bis(trifluoromethyl)phenyl), catalyze the transfer of carbene groups: C(R)CO2Et (R = H, Me) from N2C(R)CO2Et to afford products that depend on the nature of the metal center. The copper-based catalyst yields exclusively a cycloheptatriene derivative from the Buchner reaction, whereas the gold analog affords a mixture of products derived either f...

  3. Thermodynamics of Enzyme-Catalyzed Reactions Database

    Science.gov (United States)

    SRD 74 Thermodynamics of Enzyme-Catalyzed Reactions Database (Web, free access)   The Thermodynamics of Enzyme-Catalyzed Reactions Database contains thermodynamic data on enzyme-catalyzed reactions that have been recently published in the Journal of Physical and Chemical Reference Data (JPCRD). For each reaction the following information is provided: the reference for the data, the reaction studied, the name of the enzyme used and its Enzyme Commission number, the method of measurement, the data and an evaluation thereof.

  4. Citrate-selective electrochemical μ-sensor for early stage detection of prostate cancer

    OpenAIRE

    Azzouzi, Sawsen; Patra, Hirak K.; Ben Ali, Mounir; Abbas, Mohammed Nooredeen; Dridi, Cherif; Errachid, Abdelhamid; Turner, Anthony P. F.

    2016-01-01

    The extremely specialised anatomical function of citrate inside the prostate, make it one of the preferred biomarkers for early stage detection of prostate cancer. However, current detection methods are seriously limited due to the very low citrate concentrations that need to be measured in order to follow disease progression. In the present work, we report a novel citrate-selective μ-sensor based on iron (III) phthalocyanine chloride-C-monoamido-Poly-n-Butyl Acrylate (Fe(III)MAPcCl-P-n-BA) m...

  5. Ferric Citrate Transport of Escherichia coli: Functional Regions of the FecR Transmembrane Regulatory Protein

    OpenAIRE

    Welz, Dietrich; Braun, Volkmar

    1998-01-01

    Transcription of the ferric citrate transport genes of Escherichia coli is induced by ferric citrate bound to the outer membrane receptor FecA. Additional ferric citrate-specific regulatory proteins are FecR in the cytoplasmic membrane and the FecI sigma factor in the cytoplasm. To further understand the assumed FecR-mediated signal transduction across the cytoplasmic membrane, the transmembrane topology of FecR (317 amino acids) was determined with hybrid proteins containing portions of FecR...

  6. A Process-Based Model of TCA Cycle Functioning to Analyze Citrate Accumulation in Pre- and Post-Harvest Fruits.

    Science.gov (United States)

    Etienne, Audrey; Génard, Michel; Bugaud, Christophe

    2015-01-01

    Citrate is one of the most important organic acids in many fruits and its concentration plays a critical role in organoleptic properties. The regulation of citrate accumulation throughout fruit development, and the origins of the phenotypic variability of the citrate concentration within fruit species remain to be clarified. In the present study, we developed a process-based model of citrate accumulation based on a simplified representation of the TCA cycle to predict citrate concentration in fruit pulp during the pre- and post-harvest stages. Banana fruit was taken as a reference because it has the particularity of having post-harvest ripening, during which citrate concentration undergoes substantial changes. The model was calibrated and validated on the two stages, using data sets from three contrasting cultivars in terms of citrate accumulation, and incorporated different fruit load, potassium supply, and harvest dates. The model predicted the pre and post-harvest dynamics of citrate concentration with fairly good accuracy for the three cultivars. The model suggested major differences in TCA cycle functioning among cultivars during post-harvest ripening of banana, and pointed to a potential role for NAD-malic enzyme and mitochondrial malate carriers in the genotypic variability of citrate concentration. The sensitivity of citrate accumulation to growth parameters and temperature differed among cultivars during post-harvest ripening. Finally, the model can be used as a conceptual basis to study citrate accumulation in fleshy fruits and may be a powerful tool to improve our understanding of fruit acidity. PMID:26042830

  7. Model‐Based Assessment of Plasma Citrate Flux Into the Liver: Implications for NaCT as a Therapeutic Target

    Science.gov (United States)

    Erion, DM; Maurer, TS

    2016-01-01

    Cytoplasmic citrate serves as an important regulator of gluconeogenesis and carbon source for de novo lipogenesis in the liver. For this reason, the sodium‐coupled citrate transporter (NaCT), a plasma membrane transporter that governs hepatic influx of plasma citrate in human, is being explored as a potential therapeutic target for metabolic disorders. As cytoplasmic citrate also originates from intracellular mitochondria, the relative contribution of these two pathways represents critical information necessary to underwrite confidence in this target. In this work, hepatic influx of plasma citrate was quantified via pharmacokinetic modeling of published clinical data. The influx was then compared to independent literature estimates of intracellular citrate flux in human liver. The results indicate that, under normal conditions, NaCT inhibition will have a limited impact on hepatic citrate concentrations across species. PMID:27069776

  8. Model-Based Assessment of Plasma Citrate Flux Into the Liver: Implications for NaCT as a Therapeutic Target.

    Science.gov (United States)

    Li, Z; Erion, D M; Maurer, T S

    2016-03-01

    Cytoplasmic citrate serves as an important regulator of gluconeogenesis and carbon source for de novo lipogenesis in the liver. For this reason, the sodium-coupled citrate transporter (NaCT), a plasma membrane transporter that governs hepatic influx of plasma citrate in human, is being explored as a potential therapeutic target for metabolic disorders. As cytoplasmic citrate also originates from intracellular mitochondria, the relative contribution of these two pathways represents critical information necessary to underwrite confidence in this target. In this work, hepatic influx of plasma citrate was quantified via pharmacokinetic modeling of published clinical data. The influx was then compared to independent literature estimates of intracellular citrate flux in human liver. The results indicate that, under normal conditions, NaCT inhibition will have a limited impact on hepatic citrate concentrations across species. PMID:27069776

  9. 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.

  10. Enantioselective [4 + 1] Annulation Reactions of α-Substituted Ammonium Ylides To Construct Spirocyclic Oxindoles.

    Science.gov (United States)

    Zheng, Peng-Fei; Ouyang, Qin; Niu, Sheng-Li; Shuai, Li; Yuan, Yi; Jiang, Kun; Liu, Tian-Yu; Chen, Ying-Chun

    2015-07-29

    Ammonium ylides have a long history in organic synthesis, but their application in asymmetric catalysis is still underdeveloped in regard to both substrate scope and reaction pathways compared with phosphorus and sulfur ylides. Here a previously unreported asymmetric [4 + 1] annulation reaction of 3-bromooxindoles and electron-deficient 1-azadienes has been developed through ammonium ylide catalysis of a newly designed 2'-methyl α-isocupreine (α-MeIC), efficiently delivering spirocyclic oxindole compounds incorporating a dihydropyrrole motif in excellent enantioselectivity (up to 99% ee). To the best of our knowledge, this work represents the first example of asymmetric catalysis of ammonium ylides bearing α-substitutions, and the catalytic [4 + 1] annulation pathway of ammonium ylides is also unprecedented. Moreover, (1)H NMR, mass spectroscopy, and computational calculation studies were conducted, and the catalytic cycle and a tentative explanation of the enantioselective mechanism have been successfully elucidated. PMID:26151623

  11. Enantioselective desymmetrization of prochiral cyclohexanones by organocatalytic intramolecular Michael additions to α,β-unsaturated esters.

    Science.gov (United States)

    Gammack Yamagata, Adam D; Datta, Swarup; Jackson, Kelvin E; Stegbauer, Linus; Paton, Robert S; Dixon, Darren J

    2015-04-13

    A new catalytic asymmetric desymmetrization reaction for the synthesis of enantioenriched derivatives of 2-azabicyclo[3.3.1]nonane, a key motif common to many alkaloids, has been developed. Employing a cyclohexanediamine-derived primary amine organocatalyst, a range of prochiral cyclohexanone derivatives possessing an α,β-unsaturated ester moiety linked to the 4-position afforded the bicyclic products, which possess three stereogenic centers, as single diastereoisomers in high enantioselectivity (83-99% ee) and in good yields (60-90%). Calculations revealed that stepwise C-C bond formation and proton transfer via a chair-shaped transition state dictate the exclusive endo selectivity and enabled the development of a highly enantioselective primary amine catalyst. PMID:25727215

  12. 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. PMID:23716265

  13. Catalytic enantioselective OFF ↔ ON activation processes initiated by hydrogen transfer: concepts and challenges.

    Science.gov (United States)

    Quintard, Adrien; Rodriguez, Jean

    2016-08-18

    Hydrogen transfer initiated processes are eco-compatible transformations allowing the reversible OFF ↔ ON activation of otherwise unreactive substrates. The minimization of stoichiometric waste as well as the unique activation modes provided by these transformations make them key players for a greener future for organic synthesis. Long limited to catalytic reactions that form racemic products, considerable progress on the development of strategies for controlling diastereo- and enantioselectivity has been made in the last decade. The aim of this review is to present the different strategies that enable enantioselective transformations of this type and to highlight how they can be used to construct key synthetic building blocks in fewer operations with less waste generation. PMID:27381644

  14. 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.

  15. Enantioselective analysis of ibuprofen and its biotransformation products in water/sediment systems,

    DEFF Research Database (Denmark)

    Sundström, Maria; Escola, Monica; Radke, Michael;

    2015-01-01

    As ibuprofen degrades enantioselectively in activated sludge, the same process is assumed to occur in surface lake-water and in river-water based biofilms. Yet, the effects of the wastewater inflow, containing non-racemic ibuprofen, into natural systems have never been studied. The role of the...... sediments in the aquatic systems has neither been taken in account previously. In this study, four water-sediment systems were chosen according to anthropogenic exposure and sediment conditions. A low anthropogenic impact lake (Largen), a river receiving wastewater (Fyrisån) and two sediments (anoxic and...... equipped with an enantioselective HPLC-column. The detection was performed by MS/MS. Single first-order kinetics and Weibull distribution models were fitted to the data. Both models indicated that ibuprofen degraded with half-lives around 4-5 and 5-6 days in Largen and Fyrisån respectively and 3-4 and 5...

  16. Removal of polycyclic musks by anaerobic membrane bioreactor: biodegradation, biosorption, and enantioselectivity.

    Science.gov (United States)

    Wang, Lili; Wijekoon, Kaushalya C; Nghiem, Long D; Khan, Stuart J

    2014-12-01

    This study aims to investigate the performance of anaerobic membrane bioreactor (AnMBR) for removing five polycyclic musks (PCMs), which are common active ingredients of personal care and household cleaning products. A laboratory scale AnMBR system was used in this investigation. Concentrations of the PCMs in both the liquid and biosolids phase were measured to conduct a mass balance analysis and elucidate their fate during AnMBR treatment. The AnMBR was effective for removing PCMs from the aqueous phase by a combination of biotransformation and sorption onto the biosolids. However, biotransformation was observed to be the dominant removal mechanism for all five PCMs. Enantioselective analysis of the PCMs in influent, effluent and biomass samples indicated that there was negligible enantioselectivity in the removal of these PCMs. Accordingly, all enantiomers of these PCMs can be expected to be removed by AnMBR with similar efficiency. PMID:25461940

  17. Enantioselective cytotoxicity of the insecticide bifenthrin on a human amnion epithelial (FL) cell line

    International Nuclear Information System (INIS)

    Synthetic pyrethroids (SPs) are used in preference to organochlorines and organophosphates due to their high efficiency, low toxicity to mammals, and ready biodegradability. Previous studies reported that enantioselective toxicity of SPs occurs in aquatic toxicity. Several studies have indicated that SPs could lead to oxidative damage in humans or animals which was associated with their toxic effects. Little is known about the differences in the effects of chronic toxicity induced by individual stereoisomers of chiral SPs. The present study was therefore undertaken to evaluate the enantioselectivity in cytotoxicity, genotoxicity caused by bifenthrin (BF) on human amnion epithelial (FL) cell lines and pesticidal activity on target organism. The cell proliferation and cytoflow analysis indicated that 1S-cis-BF presented more toxic effects than 1R-cis-BF above the concentration of 7.5 mg L-1 (p > 0.05). FL cells incubated with 1S-cis-BF exhibited a dose-dependent accumulation of intracellular reactive oxygen species (ROS). In the comet assay, the number of cells with damaged DNA incubated with 1S-cis-BF was more than that with 1R-cis-BF (p 50 values of enantiomer to the target pest on Pieris rapae L. show that 1R-cis-BF was 300 times more active than 1S-cis-BF. These results indicate that the enantioselective toxicity and activity of BF between non-target organism and target organism was reversal. These implications together suggest that assessment of the environmental safety and new pesticides development with chiral centers should consider enantioselectivity

  18. L-Proline Derived Bifunctional Organocatalysts: Enantioselective Michael Addition of Dithiomalonates to trans-β-Nitroolefins.

    Science.gov (United States)

    Jin, Hui; Kim, Seung Tae; Hwang, Geum-Sook; Ryu, Do Hyun

    2016-04-15

    A series of novel L-proline derived tertiary amine bifunctional organocatalysts 9 are reported, which were applied to the asymmetric Michael addition of dithiomalonates 2 to trans-β-nitroolefins 1. The reaction proceeded in high yields (up to 99%) with high enantioselectivities (up to 97% ee). The synthetic utility of this methodology was demonstrated in the short synthesis of (R)-phenibut in high yield. PMID:26989804

  19. Enantioselective Determination of Polycyclic Musks in River and Wastewater by GC/MS/MS

    OpenAIRE

    Injung Lee; Anantha-Iyengar Gopalan; Kwang-Pill Lee

    2016-01-01

    The separation of chiral compounds is an interesting and challenging topic in analytical chemistry, especially in environmental fields. Enantioselective degradation or bioaccumulation has been observed for several chiral pollutants. Polycyclic musks are chiral and are widely used as fragrances in a variety of personal care products such as soaps, shampoos, cosmetics and perfumes. In this study, the gas chromatographic separation of chiral polycyclic musks, 1,3,4,6,7,8-hexahydro-4,6,6,7,8,8-he...

  20. An enantioselective organocatalyzed aza-Morita-Baylis-Hillman reaction of isatin-derived ketimines with acrolein.

    Science.gov (United States)

    Yoshida, Yasushi; Sako, Makoto; Kishi, Kenta; Sasai, Hiroaki; Hatakeyama, Susumi; Takizawa, Shinobu

    2015-09-14

    A highly enantioselective aza-Morita-Baylis-Hillman (aza-MBH) reaction of isatin-derived ketimines with acrolein was established using β-isocupreidine (β-ICD) or α-isocupreine (α-ICPN) as a chiral acid-base organocatalyst. The present protocol readily furnished (S) or (R)-aza-MBH adducts with a chiral tetrasubstituted carbon stereogenic center in up to 98% ee. PMID:26214279

  1. Investigations into surface-confined covalent organic frameworks : towards developing novel enantioselective heterogeneous catalysts

    OpenAIRE

    Greenwood, John

    2013-01-01

    There is an increasing necessity for the pharmaceutical industry to develop enantiomerically pure drugs. Up till now, production of enantiomerically pure molecules has been provided by harvesting them from plants or utilising homogeneous catalysis and biocatalysis. None of these methods are efficient means of production, and attention is now being directed towards heterogeneous enantioselective catalysis as the preferred technique. This is on account of the high product yield a...

  2. Enantioselective Synthesis of Isoquinolines: Merging Chiral-Phosphine and Gold Catalysis.

    Science.gov (United States)

    Gao, Yu-Ning; Shi, Feng-Chen; Xu, Qin; Shi, Min

    2016-05-10

    The highly enantioselective synthesis of dihydroisoquinoline derivatives from aromatic sulfonated imines tethered with an alkyne moiety, through a one-pot asymmetric relay catalysis of chiral-phosphine and gold catalysts, is reported. Enantiomerically enriched dihydroisoquinoline derivatives were afforded in good yields and good-to-excellent ee values under mild conditions, based on the asymmetric aza-Morita-Baylis-Hillman reaction. Dihydroisoquinoline derivatives containing two chiral centers were also synthesized through further transformations. PMID:26990120

  3. Enantioselective Total Syntheses of (−)-Palau’amine, (−)- Axinellamines, and (−)-Massadines

    OpenAIRE

    Seiple, Ian B.; Su, Shun; Young, Ian S.; Nakamura, Akifumi; Yamaguchi, Junichiro; Jørgensen, Lars; Rodriguez, Rodrigo A.; O’Malley, Daniel P.; Gaich, Tanja; Köck, Matthias; Baran, Phil S.

    2011-01-01

    Dimeric pyrrole-imidazole alkaloids represent a rich and topologically unique class of marine natural products. This full account will follow the progression of efforts that culminated in the enantioselective total syntheses of the most structurally ornate members of this family: the axinellamines, the massadines, and palau’amine. A bio-inspired approach capitalizing on the pseudo-symmetry of the members of this class is recounted, delivering a deschloro derivative of the natural product core...

  4. Primary Amine–2-Aminopyrimidine Chiral Organocatalysts for the Enantioselective Conjugate Addition of Branched Aldehydes to Maleimides

    OpenAIRE

    Vizcaíno-Milla, Pascuala; Sansano Gil, José Miguel; Nájera Domingo, Carmen; Fiser, Béla; Gómez Bengoa, Enrique

    2015-01-01

    Chiral primary amines containing the (R,R)- and (S,S)-trans-cyclohexane-1,2-diamine scaffold and a pyrimidin-2-yl unit are synthesized and used as general organocatalysts for the Michael reaction of α-branched aldehydes to maleimides. The reaction takes place with 10 mol% organocatalyst loading and hexanedioic acid as cocatalyst in aqueous N,N-dimethylformamide at 10 °C affording the corresponding succinimides in good yields and enantioselectivities. DFT calculations support the stereochemica...

  5. Synthesis of 3-fluoro-3-aryl oxindoles: Direct enantioselective α arylation of amides

    KAUST Repository

    Wu, Linglin

    2012-02-06

    Modus operandi: Catalytic access to the title compounds through a new asymmetric α-arylation protocol is reported (see scheme). These products are formed in good yields and excellent enantioselectivities by using a new and easily synthesized chiral N-heterocyclic carbene (NHC) ligand. Advanced DFT calculations reveal the properties of the NHC ligand and the mode of operation of the catalyst. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  6. Carbamate-directed benzylic lithiation for the diastereo- and enantioselective synthesis of diaryl ether atropisomers

    Directory of Open Access Journals (Sweden)

    Abigail Page

    2011-09-01

    Full Text Available Diaryl ethers carrying carbamoyloxymethyl groups may be desymmetrised enantio- and diastereoselectively by the use of the sec-BuLi–(−-sparteine complex in diethyl ether. Enantioselective deprotonation of one of the two benzylic positions leads to atropisomeric products with ca. 80:20 e.r.; an electrophilic quench typically provides functionalised atropisomeric diastereoisomers in up to 97:3 d.r.

  7. Enantioselectivity Induced by Oxazaborolidine Supported on Mesoporous Silica or by Its Analog in Homogeneous Phase

    Directory of Open Access Journals (Sweden)

    Jeremy H. Yune

    2010-05-01

    Full Text Available The impact of immobilization of oxazaborolidines supported on silica via different substituents on the boron and nitrogen atoms is evaluated in the enantioselective reduction of acetophenone. The performances of the homogeneous analog oxazaborolidines and silica supported-ones are compared by varying different parameters. This article deals with the synthesis, characterization and catalytic evaluation of silica-supported oxazaborolidines, their recycling capabilities and regeneration limitations.

  8. The impact of citrate introduction at UK syringe exchange programmes: a retrospective cohort study in Cheshire and Merseyside, UK

    Directory of Open Access Journals (Sweden)

    Wareing Michelle

    2007-12-01

    Full Text Available Abstract Background In 2003, it became legal in the UK for syringe exchange programmes (SEPs to provide citrate to injecting drug users to solubilise heroin. Little work has been undertaken on the effect of policy change on SEP function. Here, we examine whether the introduction of citrate in Cheshire and Merseyside SEPs has altered the number of heroin/crack injectors accessing SEPs, the frequency at which heroin/crack injectors visited SEPs and the number of syringes dispensed. Methods Eleven SEPs in Cheshire and Merseyside commenced citrate provision in 2003. SEP-specific data for the six months before and six months after citrate was introduced were extracted from routine monitoring systems relating to heroin and crack injectors. Analyses compared all individuals attending pre and post citrate and matched analyses only those individuals attending in both periods (defined as 'longitudinal attenders'. Non-parametric tests were used throughout. Results Neither new (first seen in either six months period nor established clients visited SEPs more frequently post citrate. New clients collected significantly less syringes per visit post citrate, than pre citrate (14.5,10.0; z = 1.992, P Conclusion The introduction of citrate did not negatively affect SEP attendance. 'Longitudinal attenders' visited SEPs more frequently post citrate, providing staff with greater opportunity for intervention and referral. As the number of syringes they collected each visit remained unchanged the total number of clean syringes made available to this group of injectors increased very slightly between the pre and post citrate periods. However, new clients collected significantly less syringes post citrate than pre citrate, possibly due to staff concerns regarding the amount of citrate (and thus syringes to dispense safely to new clients. These concerns should not be allowed to negatively impact on the number of syringes dispensed.

  9. Modelling substrate specificity and enantioselectivity for lipases and esterases by substrate-imprinted docking

    Directory of Open Access Journals (Sweden)

    Tyagi Sadhna

    2009-06-01

    Full Text Available Abstract Background Previously, ways to adapt docking programs that were developed for modelling inhibitor-receptor interaction have been explored. Two main issues were discussed. First, when trying to model catalysis a reaction intermediate of the substrate is expected to provide more valid information than the ground state of the substrate. Second, the incorporation of protein flexibility is essential for reliable predictions. Results Here we present a predictive and robust method to model substrate specificity and enantioselectivity of lipases and esterases that uses reaction intermediates and incorporates protein flexibility. Substrate-imprinted docking starts with covalent docking of reaction intermediates, followed by geometry optimisation of the resulting enzyme-substrate complex. After a second round of docking the same substrate into the geometry-optimised structures, productive poses are identified by geometric filter criteria and ranked by their docking scores. Substrate-imprinted docking was applied in order to model (i enantioselectivity of Candida antarctica lipase B and a W104A mutant, (ii enantioselectivity and substrate specificity of Candida rugosa lipase and Burkholderia cepacia lipase, and (iii substrate specificity of an acetyl- and a butyrylcholine esterase toward the substrates acetyl- and butyrylcholine. Conclusion The experimentally observed differences in selectivity and specificity of the enzymes were reproduced with an accuracy of 81%. The method was robust toward small differences in initial structures (different crystallisation conditions or a co-crystallised ligand, although large displacements of catalytic residues often resulted in substrate poses that did not pass the geometric filter criteria.

  10. CcpA-independent regulation of expression of the Mg2+-citrate transporter gene citM by arginine metabolism in Bacillus subtilis

    NARCIS (Netherlands)

    Warner, JB; Magni, C; Lolkema, JS; Warner, Jessica B.

    2003-01-01

    Transcriptional regulation of the Mg2+ -citrate transporter, CitM, the main citrate uptake system of Bacillus subtilis, was studied during growth in rich medium. Citrate in the growth medium was required for induction under all growth conditions. In Luria-Bertani medium containing citrate, citM expr

  11. Electrodeposition and characterisation of Ni/Cu nanostructured multilayers from citrate solutions

    CERN Document Server

    Meuleman, W R A

    2002-01-01

    A study of the effect of chemical and electrochemical parameters such as solution composition, pH, and current and potential waveforms on magnetic metal multi-layers plated from citrate electrolytes was carried out. Until now, magnetic multilayers have usually been electrodeposited mainly form sulfamate electrolytes; far less information is available on Cu-Ni multilayers obtained from citrate electrolytes. Since copper is deposited at its diffusion limiting current during multilayer deposition from citrate electrolytes, a rotating disc electrode study was carried out. It was found that the apparent diffusion coefficient changes significantly depending on the citrate ion concentration and pH, indicating the importance of metal speciation. In order to identify the rate controlling species, speciation calculations were carried out in order to model the dependence of the limiting current on the solution composition. The model is based on the assumption that complexes in solution are either labile or inert. A vert...

  12. USE OF TRANSDERMAL GEL OF SILDENAFIL CITRATE IN SEXUAL DYSFUNCTION

    Directory of Open Access Journals (Sweden)

    Harshid Patel , Amit Maniyar and Hiren Patel*

    2012-11-01

    Full Text Available Premature Ejaculation (PE is one of the most common forms of Sexual Dysfunction and is thought to affect up to 30 % of men. This is the most frequently encountered sexual complaint of men and couples. The physical problem associated with premature ejaculation can be simply described as “over-sensitivity” of the penis. Psychological causes of PE are often associated with “performance anxiety” – anxiety relating to sexual intercourse. The most common treatment today is the oral treatment with phosphodiesterase -5 (PDE-5 inhibitors. There are currently three different inhibitors available Sildenafil, Vardenafil, and Tadalafil. Sildenafil citrate is a drug of choice used in the treatment of premature ejaculation disorder. It was licensed for use in the United States in 1998; Sildenafil has shown in studies that it improves ED in men regardless of disease etiology, severity of disease, or even age. Transdermal gel has gained more and more importance because the gel based formulations are better percutaneously absorbed than creams and ointment bases. Transdermal drug delivery systems are defined as self-contained, discrete dosage forms which, when applied to the intact skin, deliver the drug, through the skin, at a controlled rate to the systemic circulation. Present Status - A review by Barry in 2001 showed, the transdermal route has vied with oral treatment as the most successful innovative research area in drug delivery.

  13. Assembly of citrate gold nanoparticles on hydrophilic monolayers

    Science.gov (United States)

    Vikholm-Lundin, Inger; Rosqvist, Emil; Ihalainen, Petri; Munter, Tony; Honkimaa, Anni; Marjomäki, Varpu; Albers, Willem M.; Peltonen, Jouko

    2016-08-01

    Self-assembled monolayers (SAMs) as model surfaces were linked onto planar gold films thorough lipoic acid or disulfide groups. The molecules used were polyethylene glycol (EG-S-S), N-[tris-(hydroxymethyl)methyl]acrylamide polymers with and without lipoic acid (Lipa-pTHMMAA and pTHMMAA) and a lipoic acid triazine derivative (Lipa-MF). All the layers, but Lipa-MF with a primary amino group were hydroxyl terminated. The layers were characterized by contact angle measurements and atomic force microscopy, AFM. Citrate stabilized nanoparticles, AuNPs in water and phosphate buffer were allowed to assemble on the layers for 10 min and the binding was followed in real-time with surface plasmon resonance, SPR. The SPR resonance curves were observed to shift to higher angles and become increasingly damped, while also the peaks strongly broaden when large nanoparticles assembled on the surface. Both the angular shift and the damping of the curve was largest for nanoparticles assembling on the EG-S-S monolayer. High amounts of particles were also assembled on the pTHMMAA layer without the lipoic acid group, but the damping of the curve was considerably lower with a more even distribution of the particles. Topographical images confirmed that the highest number of particles were assembled on the polyethylene glycol monolayer. By increasing the interaction time more particles could be assembled on the surface.

  14. Pseudohypernatremia secondary to trisodium citrate (Citra-LockTM)

    Science.gov (United States)

    Milliere, Janice; Corriveau, Daryl; Parmar, Malvinder S.

    2016-01-01

    Introduction Hypernatremia is common among hospitalized patients especially in the intensive care units and presents an independent risk factor for mortality. Mild hypernatremia is often asymptomatic but severe hypernatremia causes central nervous system dysfunction with initial non-specific symptoms of encephalopathy that may progress to seizures, coma and death, if left untreated. Severe hypernatremia is a medical emergency and requires emergent medical attention. Materials and methods A haemodialysis patient who arrived for his scheduled haemodialysis treatment had monthly blood work drawn and was reported to have severe hypernatremia with serum sodium concentration of 183 mmol/L. The possibility of technique or laboratory error was considered and systematically evaluated. Results The serum sodium measurement using another analyser showed similar value of 182 mmolL. A repeat serum sodium level on a sample drawn 2 h later showed normal value of 139–140 mmol/L. A step-wise evaluation of the complete procedure from blood collection to analysis of the sample revealed this to be spuriously elevated serum sodium concentration secondary to contamination of the sample during sample collection with trisodium citrate, a catheter-lock solution, commonly used in dialysis units to maintain patency of dialysis catheters. Conclusions Spuriously elevated plasma sodium concentration (pseudohypernatremia) of mild degree is common but severe pseudohypernatremia is rare and the possibility of sample contaminations or laboratory error should be considered. Vigilance is required by both the medical and the laboratory staff to resolve such issues in a timely fashion to avoid unintended consequences. PMID:27346973

  15. Anticaries effect of dentifrices with calcium citrate and sodium trimetaphosphate

    Directory of Open Access Journals (Sweden)

    Alberto Carlos Botazzo Delbem

    2012-02-01

    Full Text Available Because of the growing concerns regarding fluoride ingestion by young children and dental fluorosis, it is necessary to develop new dentifrices. OBJECTIVE: The aim of this study was to evaluate the effect of dentifrices with calcium citrate (Cacit and sodium trimetaphosphate (TMP on enamel demineralization. MATERIAL AND METHODS: Enamel blocks (n=70, previously selected through surface hardness analysis, were submitted to daily treatment with dentifrices diluted in artificial saliva and to a pH-cycling model. The fluoride concentration in dentifrices was 0, 250, 450, 550, 1,000 and 1,100 µg F/g. CrestTM was used as a positive control (1,100 mg F/g. Cacit (0.25% and TMP (0.25% were added to dentifrices with 450 and 1,000 µg F/g. Surface hardness was measured again and integrated loss of subsurface hardness and fluoride concentration in enamel were calculated. Parametric and correlation tests were used to determine difference (p0.05. CONCLUSIONS: Dentifrices with 450 and 1,000 µg F/g, Cacit and TMP were as effective as a gold standard one.

  16. Triplet heterotopic pregnancy following ovulation induction with clomiphene citrate: a case report and review of literature

    OpenAIRE

    Maheswari S; Seetha Panicker

    2013-01-01

    Heterotopic pregnancy, though rare is a combined pregnancy in which synchronous intrauterine and extra uterine pregnancy occur. An estimated incidence of between 1/8000 to 1/30,000 has been reported following spontaneous conception. After artificial reproductive techniques, the incidence is as high as 1/100 and after ovulation induction with clomiphene citrate, it is around 1/900. We are reporting a case of 26 year old gravida 2 who conceived after ovulation induction with clomiphene citrate ...

  17. Preparation of association compound between rhodium(II) citrate and β-cyclodextrin

    International Nuclear Information System (INIS)

    Inclusion compound of rhodium(II) citrate withβ-cyclodextrin in a 1:1 molar ratio was prepared using freeze-drying method. X-ray diffractometry, thermal analysis (TG/DTG/DSC), infrared and 1H-NMR with 1H spin lattice relaxation (1H T1) measurements and 13C techniques were used to characterize the system prepared. The results indicated the formation of inclusion or association compounds between rhodium(II) citrate and β-cyclodextrin. (author)

  18. Can laccases catalyze bond cleavage in lignin?

    DEFF Research Database (Denmark)

    Munk, Line; Sitarz, Anna Katarzyna; Kalyani, Dayanand;

    2015-01-01

    these enzymes may help degrading lignin, using oxygen as the oxidant. Laccases can catalyze polymerization of lignin, but the question is whether and how laccases can directly catalyze modification of lignin via catalytic bond cleavage. Via a thorough review of the available literature and detailed...

  19. Enantioselectivity of hydroxylation of racemic piperitone by fungi.

    Science.gov (United States)

    Grudniewska, Aleksandra; Gniłka, Radosław; Wawrzeńczyk, Czesław

    2010-11-01

    The biotransformation of racemic piperitone ((±)-1) was investigated using four strains of fungi selected in the screening procedure. The substrate was transformed by Botrytis cinerea AM235, Absidia cylindrospora AM336, Absidia coerulea AM93, and Absidia glauca AM177 into more polar metabolites. The transformation of racemic piperitone ((±)-1) catalyzed by B. cinerea AM235 gave 7-hydroxypiperitone (2) as the only product. The biotransformation of (±)-1 by A. cylindrospora AM336 afforded mixture of three products: (-)-(R)-7-hydroxypiperitone ((-)-2), (+)-(4S,6R)-trans-6-hydroxypiperitone ((+)-3), and (+)-(4R,6R)-cis-6-hydroxypiperitone ((+)-4). The transformation of this substrate ((±)-1) by A. coerulea AM93 gave (±)-7-hydroxypiperitone ((±)-2), (-)-(4R,6S)-trans-6-hydroxypiperitone (-)-3), and (-)-(4S,6S)-cis-6-hydroxypiperitone ((-)-4). The last strain studied, A. glauca AM177, converted racemic piperitone ((±)-1) to four products: (+)-(S)-7-hydroxypiperitone (2), (+)-(4S,6R)-trans-6-hydroxypiperitone ((+)-3), (±)-cis-6-hydroxypiperitone ((±)-4), and 8-hydroxypiperitone (5). PMID:20872669

  20. Branching Out: Rhodium-Catalyzed Allylation with Alkynes and Allenes.

    Science.gov (United States)

    Koschker, Philipp; Breit, Bernhard

    2016-08-16

    We present a new and efficient strategy for the atom-economic transformation of both alkynes and allenes to allylic functionalized structures via a Rh-catalyzed isomerization/addition reaction which has been developed in our working group. Our methodology thus grants access to an important structural class valued in modern organic chemistry for both its versatility for further functionalization and the potential for asymmetric synthesis with the construction of a new stereogenic center. This new methodology, inspired by mechanistic investigations by Werner in the late 1980s and based on preliminary work by Yamamoto and Trost, offers an attractive alternative to other established methods for allylic functionalization such as allylic substitution or allylic oxidation. The main advantage of our methodology consists of the inherent atom economy in comparison to allylic oxidation or substitution, which both produce stoichiometric amounts of waste and, in case of the substitution reaction, require prefunctionalization of the starting material. Starting out with the discovery of a highly branched-selective coupling reaction of carboxylic acids with terminal alkynes using a Rh(I)/DPEphos complex as the catalyst system, over the past 5 years we were able to continuously expand upon this chemistry, introducing various (pro)nucleophiles for the selective C-O, C-S, C-N, and C-C functionalization of both alkynes and the double-bond isomeric allenes by choosing the appropriate rhodium/bidentate phosphine catalyst. Thus, valuable compounds such as branched allylic ethers, sulfones, amines, or γ,δ-unsaturated ketones were successfully synthesized in high yields and with a broad substrate scope. Beyond the branched selectivity inherent to rhodium, many of the presented methodologies display additional degrees of selectivity in regard to regio-, diastereo-, and enantioselective transformations, with one example even proceeding via a dynamic kinetic resolution. Many advances

  1. Preparation of 153Sm-citrate-HA for radioactive synovectomy of rheumatoid arthritis

    International Nuclear Information System (INIS)

    A new kind of labelled radiopharmaceutical hydroxyapatite (HA) by means of transfer complexing for the treatment of rheumatoid arthritis is described. HA with partials of 2-10 μm is labelled with 153Sm by a citrate transfer ligand. 153Sm-citrate-HA is obtained in high yield and is extremely stable in vitro. The complexing capability of HA is about 5 mg Sm2O3/g HA, the decomposition rates of 153Sm-citrate-HA both in saline of 0.9% and in human plasma (37 +- 0.5 degree C) are less than 2.0% for a period of 3 half lives. Biodistribution studies in rabbits demonstrated long term retention of nearly 99% of injected 153Sm-Citrate-HA in arthritis joint. Extra-articular leakage of radioactivity in both blood and urine accounted for 0.5% of injected dose, and few retained in other major tissues after about 14.8 MBq of 153Sm-Citrate-HA has injected into the left knee joint of normal rabbits. 153Sm-citrate-HA could be potentially useful in radio-synovectomy treatment of rheumatism arthritis

  2. Is it safe to prescribe clomiphene citrate without ultrasound monitoring facilities?

    LENUS (Irish Health Repository)

    Coughlan, C

    2010-05-01

    The majority of triplet and higher order multiple pregnancies now result from ovulation induction\\/superovulation rather than in vitro fertilisation. However, clomiphene citrate is still widely prescribed by gynaecologists and general practitioners who do not have access to ultrasound monitoring. The objective of our study was to determine the prevalence of multifollicular development with different doses of clomiphene citrate. A retrospective review of transvaginal ultrasound monitoring of 425 cycles in 182 women receiving clomiphene citrate from January 2002 to December 2003, was studied. Three or more follicles of >or= 14 mm were identified in 58 cycles (14%). Patients received 50 mg of clomiphene citrate in 52 of these 58 cycles and 25 mg in the remaining six. One patient was noted to have developed five follicles and 10 patients developed four follicles. One patient developed six follicles, despite receiving only 25 mg clomiphene citrate daily. It was concluded that a significant number of women (14%) developed three or more follicles, despite receiving low doses of clomiphene citrate.

  3. Catalytic enantioselective 1,3-dipolar cycloadditions of azomethine ylides for biology-oriented synthesis.

    Science.gov (United States)

    Narayan, Rishikesh; Potowski, Marco; Jia, Zhi-Jun; Antonchick, Andrey P; Waldmann, Herbert

    2014-04-15

    Cycloaddition reactions are among the most powerful methods for the synthesis of complex compounds. In particular, the development and application of the 1,3-dipolar cycloaddition, an important member of this reaction class, has grown immensely due to its powerful ability to efficiently build various five-membered heterocycles. Azomethine ylides are commonly used as dipoles for the synthesis of the pyrrolidine scaffold, which is an important motif in natural products, pharmaceuticals, and biological probes. The reaction between azomethine ylides and cyclic dipolarophiles allows access to polycyclic products with considerable complexity. The extensive application of the 1,3-dipolar cycloaddition is based on the fact that the desired products can be obtained with high yield in a regio- and stereocontrolled manner. The most attractive feature of the 1,3-dipolar cycloaddition of azomethine ylides is the possibility to generate pyrrolidines with multiple stereocenters in a single step. The development of enantioselective cycloadditions became a subject of intensive and impressive studies in recent years. Among many modes of stereoinduction, the application of chiral metal-ligand complexes has emerged as the most viable option for control of enantioselectivity. In chemical biology research based on the principle of biology-oriented synthesis (BIOS), compound collections are prepared inspired by natural product scaffolds. In BIOS, biological relevance is employed as the key criterion to generate hypotheses for the design and synthesis of focused compound libraries. In particular, the underlying scaffolds of natural product classes provide inspiration for BIOS because they define the areas of chemical space explored by nature, and therefore, they can be regarded as "privileged". The scaffolds of natural products are frequently complex and rich in stereocenters, which necessitates the development of efficient enantioselective methodologies. This Account highlights examples

  4. Catalyzed electrolytic plutonium oxide dissolution

    International Nuclear Information System (INIS)

    Catalyzed electrolytic plutonium oxide dissolution (CEPOD) was first demonstrated at Pacific Northwest Laboratory (PNL) in early 1974 in work funded by the Exxon Corporation. The work, aimed at dissolution of Pu-containing residues remaining after the dissolution of spent mixed-oxide reactor fuels, was first publicly disclosed in 1981. The process dissolves PuO2 in an anolyte containing small (catalytic) amounts of elements that form kinetically fast, strongly oxidizing ions. These are continuously regenerated at the anode. Catalysts used, in their oxidized form, include Ag2+, Ce4+, Co3+, and AmO22+. This paper reviews the chemistry involved in CEPOD and the results of its application to the dissolution of the Pu content of a variety of PuO2-containing materials such as off-standard oxide, fuels dissolution residues, incinerator ash, contaminated soils, and other scraps or wastes. Results are presented for both laboratory-scale and plant-scale dissolves

  5. Gold-catalyzed naphthalene functionalization

    Directory of Open Access Journals (Sweden)

    Iván Rivilla

    2011-05-01

    Full Text Available The complexes IPrMCl (IPr = 1,3-bis(diisopropylphenylimidazol-2-ylidene, M = Cu, 1a; M = Au, 1b, in the presence of one equiv of NaBAr'4 (Ar' = 3,5-bis(trifluoromethylphenyl, catalyze the transfer of carbene groups: C(RCO2Et (R = H, Me from N2C(RCO2Et to afford products that depend on the nature of the metal center. The copper-based catalyst yields exclusively a cycloheptatriene derivative from the Buchner reaction, whereas the gold analog affords a mixture of products derived either from the formal insertion of the carbene unit into the aromatic C–H bond or from its addition to a double bond. In addition, no byproducts derived from carbene coupling were observed.

  6. Hydrogen evolution catalyzed by cobaloximes.

    Science.gov (United States)

    Dempsey, Jillian L; Brunschwig, Bruce S; Winkler, Jay R; Gray, Harry B

    2009-12-21

    Natural photosynthesis uses sunlight to drive the conversion of energy-poor molecules (H(2)O, CO(2)) to energy-rich ones (O(2), (CH(2)O)(n)). Scientists are working hard to develop efficient artificial photosynthetic systems toward the "Holy Grail" of solar-driven water splitting. High on the list of challenges is the discovery of molecules that efficiently catalyze the reduction of protons to H(2). In this Account, we report on one promising class of molecules: cobalt complexes with diglyoxime ligands (cobaloximes). Chemical, electrochemical, and photochemical methods all have been utilized to explore proton reduction catalysis by cobaloxime complexes. Reduction of a Co(II)-diglyoxime generates a Co(I) species that reacts with a proton source to produce a Co(III)-hydride. Then, in a homolytic pathway, two Co(III)-hydrides react in a bimolecular step to eliminate H(2). Alternatively, in a heterolytic pathway, protonation of the Co(III)-hydride produces H(2) and Co(III). A thermodynamic analysis of H(2) evolution pathways sheds new light on the barriers and driving forces of the elementary reaction steps involved in proton reduction by Co(I)-diglyoximes. In combination with experimental results, this analysis shows that the barriers to H(2) evolution along the heterolytic pathway are, in most cases, substantially greater than those of the homolytic route. In particular, a formidable barrier is associated with Co(III)-diglyoxime formation along the heterolytic pathway. Our investigations of cobaloxime-catalyzed H(2) evolution, coupled with the thermodynamic preference for a homolytic route, suggest that the rate-limiting step is associated with formation of the hydride. An efficient water splitting device may require the tethering of catalysts to an electrode surface in a fashion that does not inhibit association of Co(III)-hydrides. PMID:19928840

  7. Michael Addition of Thiols to á,(a)-Unsaturated Carbonyl Compounds Catalyzed by Bifunctional Organocatalysts:Asymmetric Michael Addition and Asymmetric Protonation

    Institute of Scientific and Technical Information of China (English)

    LI Bang-Jing; JIANG Lin; LIU Min; DING Li-Sheng; CHEN Ying-Chun

    2004-01-01

    Recently the hydrogen-bond activated reactions have attracted much attention.1 Takemoto2 reported a highly enantioselective Michael addition of manolate to nitroolefins catalyzed by a bifunctional organocatalyst with tertiary amine and thiourea moiety. As we known,stereoselective conjugate additions of thiols are interesting due to the standpoint of biological and synthetic importance, however, only very limited good results have been obtained except for the works of Shibasaki3, Kanemasa4 and Deng5 et al.In this letter, we report an efficient catalytic asymmetric Michael reactions of thiols to a,a-unsaturated carbonyl compounds promoted by bifunctional organocatalysts. A series of organocatalysts with chiral amine and thiourea structures were designed and synthesized and have been successfully applied in the conjugated additions of thiols to a,a-unsaturated imides and enones.The reactions got quantitative yields and the ee values were up to 84%. It is noteworthy that the a-asymmetric protonation (up to 43% ee) also could be achieved.The Michael addition between aromatic thiols and a,a-unsaturated carbonyl compounds isdescribed as follows:Works to further increase the enantioselectivity is under investigation in our laboratory.

  8. Theoretical Studies on the Asymmetric Baeyer-Villiger Oxidation Reaction of 4-Phenylcyclohexanone with m-Chloroperoxobenzoic Acid Catalyzed by Chiral Scandium(III)-N,N'-Dioxide Complexes.

    Science.gov (United States)

    Yang, Na; Su, Zhishan; Feng, Xiaoming; Hu, Changwei

    2015-05-01

    The mechanism and enantioselectivity of the asymmetric Baeyer-Villiger oxidation reaction between 4-phenylcyclohexanone and m-chloroperoxobenzoic acid (m-CPBA) catalyzed by Sc(III) -N,N'-dioxide complexes were investigated theoretically. The calculations indicated that the first step, corresponding to the addition of m-CPBA to the carbonyl group of 4-phenylcyclohexanone, is the rate-determining step (RDS) for all the pathways studied. The activation barrier of the RDS for the uncatalyzed reaction was predicted to be 189.8 kJ mol(-1) . The combination of an Sc(III) -N,N'-dioxide complex and the m-CBA molecule can construct a bifunctional catalyst in which the Lewis acidic Sc(III) center activates the carbonyl group of 4-phenylcyclohexanone while m-CBA transfers a proton, which lowers the activation barrier of the addition step (RDS) to 86.7 kJ mol(-1) . The repulsion between the m-chlorophenyl group of m-CPBA and the 2,4,6-iPr3 C6 H2 group of the N,N'-dioxide ligand, as well as the steric hindrance between the phenyl group of 4-phenylcyclohexanone and the amino acid skeleton of the N,N'-dioxide ligand, play important roles in the control of the enantioselectivity. PMID:25809412

  9. A COMPARISON OF CLOMIPHENE CITRATE AND SEQUENTIAL CLOMIPHENE CITRATE PLUS HUMAN MENOPAUSAL GONADOTROPIN FOR USE IN CONJUNCTION WITH INTRAUTERINE INSEMINATION

    Directory of Open Access Journals (Sweden)

    B. H. Rashidi

    2005-06-01

    Full Text Available There are currently ‎many different protocols in use for controlled ovarian hyperstimulation (COH, but the optimal method has ‎not yet been determined. To compare the outcome of COH using ‎clomiphene citrate (CC versus CC plus human menopausal gonadotropin (hMG in conjunction with intrauterine insemination (IUI, we studied 117 infertile couples‎. IUI with CC was used in 92 cycles ‎(group A and IUI with CC plus hMG was used in 66 cycles (group B. ‎Data analysis demonstrated no significant difference between the two ‎groups with respect to patients’ age, duration and type of infertility, prior COH and endometrial thickness and pattern. Group A had a little ‎longer follicular phase length than group B. ‎Pregnancy rate for group A and B were 6.52% and 12.12%, respectively (P= 0.22. ‎Endometrial pattern and thickness had no impact on pregnancy rate. ‎There were no multiple gestation and obvious hyperstimulation syndrome. ‎For patients undergoing controlled ovarian hyperstimulation with IUI, ‎CC plus hMG protocol yields higher pregnancy rate than one using CC, although this ‎difference was not statistically significant because of limitation of number of ‎cycles.

  10. Origins of stereoselectivities in chiral phosphoric acid catalyzed allylborations and propargylations of aldehydes.

    Science.gov (United States)

    Wang, Hao; Jain, Pankaj; Antilla, Jon C; Houk, K N

    2013-02-01

    The chiral BINOL-phosphoric acid catalyzed allylboration and propargylation reactions are studied with density functional theory (B3LYP and B3LYP-D3). Two different models were recently proposed for these reactions by Goodman and our group, respectively. In Goodman's model for allylborations, the catalyst interacts with the boronate pseudoaxial oxygen. By contrast, our model for propargylations predicts that the catalyst interacts with the boronate pseudoequatorial oxygen. In both models, the phosphoric acid stabilizes the transition state by forming a strong hydrogen bond with the oxygen of the boronate and is oriented by a formyl hydrogen bond (Goodman model) and by other electrostatic attractions in our model. Both of these models have now been reinvestigated for both allylborations and propargylations. For the most effective catalyst for these reactions, the lowest energy transition state corresponds to Goodman's axial model, while the best transition state leading to the minor enantiomer involves the equatorial model. The high enantioselectivity observed with only the bulkiest catalyst arises from the steric interactions between the substrates and the bulky groups on the catalyst, and the resulting necessity for distortion of the catalyst in the disfavored transition state. PMID:23298338

  11. Redox properties and activity of iron-citrate complexes: evidence for redox cycling.

    Science.gov (United States)

    Adam, Fatima I; Bounds, Patricia L; Kissner, Reinhard; Koppenol, Willem H

    2015-04-20

    Iron in iron overload disease is present as non-transferrin-bound iron, consisting of iron, citrate, and albumin. We investigated the redox properties of iron citrate by electrochemistry, by the kinetics of its reaction with ascorbate, by ESR, and by analyzing the products of reactions of ascorbate with iron citrate complexes in the presence of H2O2 with 4-hydroxybenzoic acid as a reporter molecule for hydroxylation. We report -0.03 V +0.01 V for the (Fe(3+)-cit/Fe(2+)-cit) couple. The first step in the reaction of iron citrate with ascorbate is the rapid formation of mixed complexes of iron with citrate and ascorbate, followed by slow reduction to Fe(2+)-citrate with k = ca. 3 M(-1) s(-1). The ascorbyl radical is formed by iron citrate oxidation of Hasc(-) with k = ca. 0.02 M(-1) s(-1); the majority of the ascorbyl radical formed is sequestered by complexation with iron and remains EPR silent. The hydroxylation of 4-hydroxybenzoic acid driven by the Fenton reduction of iron citrate by ascorbate in the presence of H2O2 proceeds in three phases: the first phase, which is independent of the presence of O2, is revealed as a nonzero intercept that reflects the rapid reaction of accumulated Fe(2+) with H2O2; the intermediate oxygen-dependent phase fits a first-order accumulation of product with k = 5 M(-1) s(-1) under aerobic and k = 13 M(-1) s(-1) under anaerobic conditions; the slope of the final linear phase is ca. k = 5 × 10(-2) M(-1) s(-1) under both aerobic and anaerobic conditions. Product yields under aerobic conditions are greater than predicted from the initial concentration of iron, but they are less than predicted for continuous redox cycling in the presence of excess ascorbate. The ongoing formation of hydroxylated product supports slow redox cycling by iron citrate. Thus, when H2O2 is available, iron-citrate complexes may contribute to pathophysiological manifestations of iron overload diseases. PMID:25654270

  12. Mitochondrial aconitase and citrate metabolism in malignant and nonmalignant human prostate tissues

    Directory of Open Access Journals (Sweden)

    Franklin Renty B

    2006-04-01

    Full Text Available Abstract Background In prostate cancer, normal citrate-producing glandular secretory epithelial cells undergo a metabolic transformation to malignant citrate-oxidizing cells. m-Aconitase is the critical step involved in this altered citrate metabolism that is essential to prostate malignancy. The limiting m-aconitase activity in prostate epithelial cells could be the result of a decreased level of m-aconitase enzyme and/or the inhibition of existing m-aconitase. Earlier studies identified zinc as an inhibitor of m-aconitase activity in prostate cells; and that the depletion of zinc in malignant cells is an important factor in this metabolic transformation. However, a possibility remains that an altered expression and level of m-aconitase enzyme might also be involved in this metabolic transformation. To address this issue, the in situ level of m-aconitase enzyme was determined by immunohistochemical analysis of prostate cancer tissue sections and malignant prostate cell lines. Results The immunocytochemical procedure successfully identified the presence of m-aconitase localized in the mitochondrial compartment in PC-3, LNCaP, and DU-145 malignant prostate cell lines. The examination of prostate tissue sections from prostate cancer subjects demonstrated that m-aconitase enzyme is present in the glandular epithelium of normal glands, hyperplastic glands, adenocrcinomatous glands, and prostatic intraepithelial neoplastic foci. Quantitative analysis of the relative level of m-aconitase in the glandular epithelium of citrate-producing adenomatous glands versus the citrate-oxidizing adenocarcinomatous glands revealed no significant difference in m-aconitase enzyme levels. This is in contrast to the down-regulation of ZIP1 zinc transporter in the malignant glands versus hyperplastic glands that exists in the same tissue samples. Conclusion The results demonstrate the existence of m-aconitase enzyme in the citrate-producing glandular epithelial cells

  13. Transport of citrate-coated silver nanoparticles in unsaturated sand

    Energy Technology Data Exchange (ETDEWEB)

    Kumahor, Samuel K., E-mail: samuel.kumahor@ufz.de [Department of Soil Physics, Helmholtz Centre for Environmental Research–UFZ, Theodor-Lieser-Strasse 4, 06120 Halle-Saale (Germany); Hron, Pavel, E-mail: pavel.hron@iwr.uni-heidelberg.de [Interdisciplinary Center for Scientific Computing, University of Heidelberg, Im Neuenheimer Feld 368, Raum 422, 69120 Heidelberg (Germany); Metreveli, George, E-mail: metreveli@uni-landau.de [Universität Koblenz-Landau, Institute for Environmental Sciences, Group of Environmental and Soil Chemistry, Fortstr. 7, D-76829 Landau (Germany); Schaumann, Gabriele E., E-mail: schaumann@uni-landau.de [Universität Koblenz-Landau, Institute for Environmental Sciences, Group of Environmental and Soil Chemistry, Fortstr. 7, D-76829 Landau (Germany); Vogel, Hans-Jörg, E-mail: hans-joerg.vogel@ufz.de [Department of Soil Physics, Helmholtz Centre for Environmental Research–UFZ, Theodor-Lieser-Strasse 4, 06120 Halle-Saale (Germany); Institute of Soil Science and Plant Nutrition, Martin-Luther-University Halle-Wittenberg, Von-Seckendorff-Platz 3, 06120 Halle-Saale (Germany)

    2015-12-01

    Chemical factors and physical constraints lead to coupled effects during particle transport in unsaturated porous media. Studies on unsaturated transport as typical for soils are currently scarce. In unsaturated porous media, particle mobility is determined by the existence of an air–water interface in addition to a solid–water interface. To this end, we measured breakthrough curves and retention profiles of citrate-coated Ag nanoparticles in unsaturated sand at two pH values (5 and 9) and three different flow rates corresponding to different water contents with 1 mM KNO{sub 3} as background electrolyte. The classical DLVO theory suggests unfavorable deposition conditions at the air–water and solid–water interfaces. The breakthrough curves indicate modification in curve shapes and retardation of nanoparticles compared to inert solute. Retention profiles show sensitivity to flow rate and pH and this ranged from almost no retention for the highest flow rate at pH = 9 to almost complete retention for the lowest flow rate at pH = 5. Modeling of the breakthrough curves, thus, required coupling two parallel processes: a kinetically controlled attachment process far from equilibrium, responsible for the shape modification, and an equilibrium sorption, responsible for particle retardation. The non-equilibrium process and equilibrium sorption are suggested to relate to the solid–water and air–water interfaces, respectively. This is supported by the DLVO model extended for hydrophobic interactions which suggests reversible attachment, characterized by a secondary minimum (depth 3–5 kT) and a repulsive barrier at the air–water interface. In contrast, the solid–water interface is characterized by a significant repulsive barrier and the absence of a secondary minimum suggesting kinetically controlled and non-equilibrium interaction. This study provides new insights into particle transport in unsaturated porous media and offers a model concept representing the

  14. Transport of citrate-coated silver nanoparticles in unsaturated sand

    International Nuclear Information System (INIS)

    Chemical factors and physical constraints lead to coupled effects during particle transport in unsaturated porous media. Studies on unsaturated transport as typical for soils are currently scarce. In unsaturated porous media, particle mobility is determined by the existence of an air–water interface in addition to a solid–water interface. To this end, we measured breakthrough curves and retention profiles of citrate-coated Ag nanoparticles in unsaturated sand at two pH values (5 and 9) and three different flow rates corresponding to different water contents with 1 mM KNO3 as background electrolyte. The classical DLVO theory suggests unfavorable deposition conditions at the air–water and solid–water interfaces. The breakthrough curves indicate modification in curve shapes and retardation of nanoparticles compared to inert solute. Retention profiles show sensitivity to flow rate and pH and this ranged from almost no retention for the highest flow rate at pH = 9 to almost complete retention for the lowest flow rate at pH = 5. Modeling of the breakthrough curves, thus, required coupling two parallel processes: a kinetically controlled attachment process far from equilibrium, responsible for the shape modification, and an equilibrium sorption, responsible for particle retardation. The non-equilibrium process and equilibrium sorption are suggested to relate to the solid–water and air–water interfaces, respectively. This is supported by the DLVO model extended for hydrophobic interactions which suggests reversible attachment, characterized by a secondary minimum (depth 3–5 kT) and a repulsive barrier at the air–water interface. In contrast, the solid–water interface is characterized by a significant repulsive barrier and the absence of a secondary minimum suggesting kinetically controlled and non-equilibrium interaction. This study provides new insights into particle transport in unsaturated porous media and offers a model concept representing the

  15. A direct approach to amines with remote stereocentres by enantioselective CuH-catalysed reductive relay hydroamination

    Science.gov (United States)

    Zhu, Shaolin; Niljianskul, Nootaree; Buchwald, Stephen L.

    2016-02-01

    Amines with remote stereocentres (stereocentres that are three or more bonds away from the C-N bond) are important structural elements in many pharmaceutical agents and natural products. However, previously reported methods to prepare these compounds in an enantioselective manner are indirect and require multistep synthesis. Here, we report a copper-hydride-catalysed, enantioselective synthesis of γ- or δ-chiral amines from readily available allylic alcohols, esters and ethers using a reductive relay hydroamination strategy (a net reductive process in which an amino group is installed at a site remote from the original carbon-carbon double bond). The protocol was suitable for substrates containing a wide range of functional groups and provided remote chiral amine products with high levels of regio- and enantioselectivity. Sequential amination of substrates containing several carbon-carbon double bonds could be achieved, demonstrating the high chemoselectivity of this process.

  16. Dissolution kinetics and biodurability of tremolite particles in mimicked lung fluids: Effect of citrate and oxalate

    Science.gov (United States)

    Rozalen, Marisa; Ramos, M. Elena; Huertas, F. Javier; Fiore, Saverio; Gervilla, Fernando

    2013-11-01

    The effect of citrate and oxalate on tremolite dissolution rate was measured at 37 °C in non-stirred flow-through reactors, using modified Gamble's solutions at pH 4 (macrophages), 7.4 (interstitial fluids) and 5.5 (intermediate check point) containing 0, 0.15, 1.5 and 15 mmol L-1 of citrate or oxalate. The dissolution rates calculated from Si concentration in the output solutions without organic ligands depend on pH, decreasing when the pH increases from -13.00 (pH 4) to -13.35 (pH 7.4) mol g-1 s-1 and following a proton-promoted mechanism. The presence of both ligands enhances dissolution rates at every pH, increasing this effect when the ligand concentration increases. Citrate produces a stronger effect as a catalyst than oxalate, mainly at more acidic pHs and enhances dissolution rates until 20 times for solutions with 15 mmol L-1 citrate. However, at pH 7.4 the effect is lighter and oxalate solutions (15 mmol L-1) only enhances dissolution rates eight times respect to free organic ligand solutions. Dissolution is promoted by the attack to protons and organic ligands to the tremolite surface. Magnesium speciation in oxalate and citrate solutions shows that Mg citrate complexes are more effective than oxalate ones during the alteration of tremolite in magrophages, but this tendency is the opposite for interstitial fluids, being oxalate magnesium complexes stronger. The biodurability estimations show that the destruction of the fibers is faster in acidic conditions (macrophages) than in the neutral solutions (interstitial fluid). At pH 4, both ligands oxalate and citrate reduce the residence time of the fibers with respect to that calculated in absence of ligands. Nevertheless, at pH 7.4 the presence of ligands does not reduce significantly the lifetime of the fibers.

  17. Effects and mechanisms of action of sildenafil citrate in human chorionic arteries.

    LENUS (Irish Health Repository)

    Maharaj, Chrisen H

    2009-01-01

    OBJECTIVES: Sildenafil citrate, a specific phosphodiesterase-5 inhibitor, is increasingly used for pulmonary hypertension in pregnancy. Sildenafil is also emerging as a potential candidate for the treatment of intra-uterine growth retardation and for premature labor. Its effects in the feto-placental circulation are not known. Our objectives were to determine whether phosphodiesterase-5 is present in the human feto-placental circulation, and to characterize the effects and mechanisms of action of sildenafil citrate in this circulation. STUDY DESIGN: Ex vivo human chorionic plate arterial rings were used in all experiments. The presence of phosphodiesterase-5 in the feto-placental circulation was determined by western blotting and immunohistochemical staining. In a subsequent series of pharmacologic studies, the effects of sildenafil citrate in pre-constricted chorionic plate arterial rings were determined. Additional studies examined the role of cGMP and nitric oxide in mediating the effects of sildenafil. RESULTS: Phosphodiesterase-5 mRNA and protein was demonstrated in human chorionic plate arteries. Immunohistochemistry demonstrated phosphodiesterase-5 within the arterial muscle layer. Sildenafil citrate produced dose dependent vasodilatation at concentrations at and greater than 10 nM. Both the direct cGMP inhibitor methylene blue and the cGMP-dependent protein kinase inhibitor Rp-8-Br-PET-cGMPS significantly attenuated the vasodilation produced by sildenafil citrate. Inhibition of NO production with L-NAME did not attenuate the vasodilator effects of sildenafil. In contrast, sildenafil citrate significantly enhanced the vasodilation produced by the NO donor sodium nitroprusside. CONCLUSION: Phosphodiesterase-5 is present in the feto-placental circulation. Sildenafil citrate vasodilates the feto-placental circulation via a cGMP dependent mechanism involving increased responsiveness to NO.

  18. 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. PMID:23722178

  19. Exploration of Cocatalyst Effects on a Bimetallic Cobalt Catalyst System: Enhanced Activity and Enantioselectivity in Epoxide Polymerization

    KAUST Repository

    Widger, Peter C. B.

    2011-07-26

    Organic ionic compounds were synthesized and investigated as cocatalysts with a bimetallic cobalt complex for enantioselective epoxide polymerization. The identities of both the cation and the anion were systematically varied, and the subsequent reactivity was studied. The nature of the ionic cocatalyst dramatically impacted the rate and enantioselectivity of the catalyst system. The ionic cocatalyst [P(N=P(N(CH2)4)3) 4 +][tBuCO2 -] in combination with a bimetallic cobalt complex produced a catalyst system that exhibited the greatest activity and selectivity for a variety of monosubstituted epoxides. © 2011 American Chemical Society.

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

    DEFF Research Database (Denmark)

    Revunov, Evgeny V.

    The purpose of this PhD project was to develop an enantioselective cobalt-mediated radiofluorination of epoxides and apply this methodology for radiosynthesis of the PET radiopharmaceutical [18F]FMISO. The developed procedure utilizes [18F]HF-gas (as an efficient source of nucleophilic 18F......(salen)-mediated no-carrier-added radiofluorination of epoxides has been achieved for the first time. A number of model meso-epoxides were successfully radiofluorinated producing 18F-fluorohidrines in high RCC and RCY, and modest enantioselectivity. The developed procedure is simple, rapid and lends itself to easy...

  1. Application of citrate as a tricarboxylic acid (TCA cycle intermediate, prevents diabetic-induced heart damages in mice

    Directory of Open Access Journals (Sweden)

    Qianqian Liang

    2016-01-01

    Conclusion: Results indicate that application of citrate, a tricarboxylic acid (TCA cycle intermediate, might alleviate cardiac dysfunction by reducing cardiac inflammation, apoptosis, and increasing cardiac EC.

  2. Concave Urinary Crystallines: Direct Evidence of Calcium Oxalate Crystals Dissolution by Citrate In Vivo

    Directory of Open Access Journals (Sweden)

    Yun-Feng Shang

    2013-01-01

    Full Text Available The changes in urinary crystal properties in patients with calcium oxalate (CaOx calculi after oral administration of potassium citrate (K3cit were investigated via atomic force microscopy (AFM, scanning electron microscopy (SEM, X-ray powder diffractometry (XRD, and zeta potential analyzer. The AFM and SEM results showed that the surface of urinary crystals became concave, the edges and corners of crystals became blunt, the average size of urinary crystallines decreased significantly, and aggregation of urinary crystals was reduced. These changes were attributed to the significant increase in concentration of excreted citrate to  mg/L after K3cit intake from  mg/L before K3cit intake. After the amount of urinary citrate was increased, it complexed with Ca2+ ions on urinary crystals, which dissolved these crystals. Thus, the appearance of concave urinary crystals was a direct evidence of CaOx dissolution by citrate in vivo. The XRD results showed that the quantities and species of urinary crystals decreased after K3cit intake. The mechanism of inhibition of formation of CaOx stones by K3cit was possibly due to the complexation of Ca2+ with citrate, increase in urine pH, concentration of urinary inhibitor glycosaminoglycans (GAGs, and the absolute value of zeta potential after K3cit intake.

  3. Bio-inspired citrate functionalized apatite coating on rapid prototyped titanium scaffold

    International Nuclear Information System (INIS)

    Highlights: • Designed and reproducible porous titanium scaffolds were produced. • Hydrophilic nanoporous film was built on scaffold. • Apatite coating was deposited on scaffold under the modulation of citrate ions. • Citrate ions could affect CO32− incorporation in apatite coatings. - Abstract: Scaffold functionalized with appropriate osteogenic coatings can significantly improve implant-bone response. In this study, with designed model and optimized manufacture parameters, reproducible and precise titanium scaffolds were produced. Reconstructed three-dimensional image and sectional structure of the scaffold were examined by micro-computed tomography and relative software. Alkali treatment was carried out on these manufactured porous scaffolds to produce nanoporous hydrophilic film. After 6 days deposition in simulated body fluid (SBF) containing sodium citrate (SC-SBF), plate-like amorphous calcium phosphate (ACP) coating was deposited on scaffold surface. Ultrasonication tests qualitatively indicated an enhanced adhesion force of apatite coatings deposited in SC-SBF compared to that deposited in SBF. And the effect of citrate ions on the CO32− incorporation rate in apatite coating was quantitatively examined by bending vibration of CO32− at ∼874 cm−1. Results indicated the highest carbonate content was obtained at the citrate ion concentration of 6 × 10−5 mol/L in SC-SBF. These three-dimensional porous titanium-apatite hybrid scaffolds are expected to find application in bone tissue regeneration

  4. Films based on neutralized chitosan citrate as innovative composition for cosmetic application.

    Science.gov (United States)

    Libio, Illen C; Demori, Renan; Ferrão, Marco F; Lionzo, Maria I Z; da Silveira, Nádya P

    2016-10-01

    In this work, citrate and acetate buffers, were investigated as neutralizers to chitosan salts in order to provide biocompatible and stable films. To choose the appropriate film composition for this study, neutralized chitosan citrate and acetate films, with and without the plasticizer glycerol, were prepared and characterized by thickness, moisture content, degree of swelling, total soluble matter in acid medium, simultaneous thermal analysis and differential scanning calorimetry. Chitosan films neutralized in citrate buffer showed greater physical integrity resulted from greater thicknesses, lower moisture absorbance, lower tendency to solubility in the acid medium, and better swelling capacities. According to thermal analyses, these films had higher interaction with water which is considered an important feature for cosmetic application. Since the composition prepared in citrate buffer without glycerol was considered to present better physical integrity, it was applied to investigate hyaluronic acid release in a skin model. Skins treated with those films, with or without hyaluronic acid, show stratum corneum desquamation and hydration within 10min. The results suggest that the neutralized chitosan citrate film prepared without glycerol promotes a cosmetic effect for skin exfoliation in the presence or absence of hyaluronic acid. PMID:27287105

  5. Artificial citrate operon confers mineral phosphate solubilization ability to diverse fluorescent pseudomonads.

    Science.gov (United States)

    Adhikary, Hemanta; Sanghavi, Paulomi B; Macwan, Silviya R; Archana, Gattupalli; Naresh Kumar, G

    2014-01-01

    Citric acid is a strong acid with good cation chelating ability and can be very efficient in solubilizing mineral phosphates. Only a few phosphate solubilizing bacteria and fungi are known to secrete citric acids. In this work, we incorporated artificial citrate operon containing NADH insensitive citrate synthase (gltA1) and citrate transporter (citC) genes into the genome of six-plant growth promoting P. fluorescens strains viz., PfO-1, Pf5, CHAO1, P109, ATCC13525 and Fp315 using MiniTn7 transposon gene delivery system. Comprehensive biochemical characterization of the genomic integrants and their comparison with plasmid transformants of the same operon in M9 minimal medium reveals the highest amount of ∼7.6±0.41 mM citric and 29.95±2.8 mM gluconic acid secretion along with ∼43.2±3.24 mM intracellular citrate without affecting the growth of these P. fluorescens strains. All genomic integrants showed enhanced citric and gluconic acid secretion on Tris-Cl rock phosphate (TRP) buffered medium, which was sufficient to release 200-1000 µM Pi in TRP medium. This study demonstrates that MPS ability could be achieved in natural fluorescent pseudomonads by incorporation of artificial citrate operon not only as plasmid but also by genomic integration. PMID:25259527

  6. Artificial citrate operon confers mineral phosphate solubilization ability to diverse fluorescent pseudomonads.

    Directory of Open Access Journals (Sweden)

    Hemanta Adhikary

    Full Text Available Citric acid is a strong acid with good cation chelating ability and can be very efficient in solubilizing mineral phosphates. Only a few phosphate solubilizing bacteria and fungi are known to secrete citric acids. In this work, we incorporated artificial citrate operon containing NADH insensitive citrate synthase (gltA1 and citrate transporter (citC genes into the genome of six-plant growth promoting P. fluorescens strains viz., PfO-1, Pf5, CHAO1, P109, ATCC13525 and Fp315 using MiniTn7 transposon gene delivery system. Comprehensive biochemical characterization of the genomic integrants and their comparison with plasmid transformants of the same operon in M9 minimal medium reveals the highest amount of ∼7.6±0.41 mM citric and 29.95±2.8 mM gluconic acid secretion along with ∼43.2±3.24 mM intracellular citrate without affecting the growth of these P. fluorescens strains. All genomic integrants showed enhanced citric and gluconic acid secretion on Tris-Cl rock phosphate (TRP buffered medium, which was sufficient to release 200-1000 µM Pi in TRP medium. This study demonstrates that MPS ability could be achieved in natural fluorescent pseudomonads by incorporation of artificial citrate operon not only as plasmid but also by genomic integration.

  7. Nitrate Protects Cucumber Plants Against Fusarium oxysporum by Regulating Citrate Exudation.

    Science.gov (United States)

    Wang, Min; Sun, Yuming; Gu, Zechen; Wang, Ruirui; Sun, Guomei; Zhu, Chen; Guo, Shiwei; Shen, Qirong

    2016-09-01

    Fusarium wilt causes severe yield losses in cash crops. Nitrogen plays a critical role in the management of plant disease; however, the regulating mechanism is poorly understood. Using biochemical, physiological, bioinformatic and transcriptome approaches, we analyzed how nitrogen forms regulate the interactions between cucumber plants and Fusarium oxysporum f. sp. cucumerinum (FOC). Nitrate significantly suppressed Fusarium wilt compared with ammonium in both pot and hydroponic experiments. Fewer FOC colonized the roots and stems under nitrate compared with ammonium supply. Cucumber grown with nitrate accumulated less fusaric acid (FA) after FOC infection and exhibited increased tolerance to chemical FA by decreasing FA absorption and transportation in shoots. A lower citrate concentration was observed in nitrate-grown cucumbers, which was associated with lower MATE (multidrug and toxin compound extrusion) family gene and citrate synthase (CS) gene expression, as well as lower CS activity. Citrate enhanced FOC spore germination and infection, and increased disease incidence and the FOC population in ammonium-treated plants. Our study provides evidence that nitrate protects cucumber plants against F. oxysporum by decreasing root citrate exudation and FOC infection. Citrate exudation is essential for regulating disease development of Fusarium wilt in cucumber plants. PMID:27481896

  8. Direct separation of 67Ga citrate from zinc and copper target materials by an ion exchange

    International Nuclear Information System (INIS)

    The separation of 67Ga from zinc and copper target materials using an anion- f:exchanger (Dowex21K) and 0.1 M citrate buffer at pH 6 is described. The gallium-67 was separated in citrate solution and can be directly used for medical applications. Gallium-67 with a half-life of 78.3 h and gamma-rays with energies of 93, 185 and 300 keV is a cyclotron produced radioisotope for which a considerable demand exists. 67Ga is frequently produced through proton or deuteron bombardment of natural or enriched Zn targets (Helus and Maier-Borst, 1973). It is usually separated from Zn by ion exchange chromatography (Helus and Maier-Borst, 1973; van der Walt and Strelow, 1983) or by liquid extraction Helus and Maier-Borst, 1973; Hupf and Beaver, 1970). The isotope is usually supplied in citrate solution which is widely used as 67Ga Gallium citrate which is a well-established radiopharmaceutical for imaging soft tissue tumors and abscesses. Several routes for large scale production of 67Ga and the development of medical applications have been reported (Silvester and Thakur, 1970; Dahl and Tilbury, 1972; Steyn and Meyer,1973; Vlatkovic et al., 1975; Neirinckx, 1976; Thakur, 1977). Various attempts were carried out to separate gallium-67 by using different ion exchange methods (Strelow et al., 1971; Das and Ramamoorthy, 1995; Boothe et al.,1991) through the labelling of citrate by using 67Ga was carried out for medical applications

  9. Radiolabeled porphyrin versus gallium-67 citrate for the detection of human melanoma in athymic mice

    Energy Technology Data Exchange (ETDEWEB)

    Maric, N.; Chan, S. Ming; Hoffer, P.B.; Duray, P.

    1987-01-01

    We performed the biodistribution and imaging studies of /sup 111/In and /sup 67/Ga labeled tetra(4-N-methylpyridyl) porphine, (T4NMPYP), and compared it to that of /sup 67/Ga citrate in athymic mice bearing a human melanoma xenograft. The biodistribution results of both /sup 111/In and /sup 67/Ga labeled T4NMPYP (3, 6, 24, and 48 hours) were similar but differed from that of /sup 67/Ga citrate (48 hours). The optimum tumor uptake of both radiolabeled porphyrins was at 6 hours postinjection and was lower than the tumor uptake of /sup 67/Ga citrate at 48 hours postinjection. Kidney was the only organ showing higher uptake of radiolabeled porphyrin compared to that of /sup 67/Ga citrate. The imaging studies performed with /sup 111/In T4NMPYP and /sup 67/Ga citrate correspond to the biodistribution results. Osteomyelitis present in one mouse showed good localization of /sup 111/In T4NMPYP. 15 refs., 3 figs., 5 tabs.

  10. Muon catalyzed fusion under compressive conditions

    International Nuclear Information System (INIS)

    The viability of a symbiotic combination of Muon Catalyzed Fusion (μCF) and high density generation processes has been investigated. The muon catalyzed fusion reaction rates are formulated in the temperature and density range found under moderate compressive conditions. Simplified energy gain and power balance calculations indicate that significant energy gain occurs only if standard type deuterium-tritium (dt) fusion is ignited. A computer simulation of the hydrodynamics and fusion kinetics of a spherical deuterium-tritium pellet implosion including muons is performed. Using the muon catalyzed fusion reaction rates formulated and under ideal conditions, the pellet ignites (and thus has a significant energy gain) only if the initial muon concentration is approximately 1017 cm-3. The muons need to be delivered to the pellet within a very short-time (≅ 1 ns). The muon pulse required in order to make the high density and temperature muon catalyzed fusion scheme viable is beyond the present technology for muon production. (orig.)

  11. Palladium-Catalyzed Carbonylation and Arylation Reactions

    OpenAIRE

    Sävmarker, Jonas

    2012-01-01

    Palladium-catalyzed reactions have found widespread use in contemporary organic chemistry due to their impressive range of functional group tolerance and high chemo- and regioselectivity. The pioneering contributions to the development of the Pd-catalyzed C-C bond forming cross-coupling reaction were rewarded with the Nobel Prize in Chemistry in 2010. Today, this is a rapidly growing field, and the development of novel methods, as well as the theoretical understanding of the various processes...

  12. Enantioselective developmental toxicity and immunotoxicity of pyraclofos toward zebrafish (Danio rerio)

    International Nuclear Information System (INIS)

    Highlights: • Pyraclofos has significant enantioselective aquatic toxicities to zebrafish. • Pyraclofos induces time- and concentration-dependent developmental toxicity and immunotoxicity. • The mRNA level of IL-1β gene was significantly up-regulated by pyraclofos. • Pyraclofos binds potently to IL-1β, potentially affecting IL-1β-dependent proinflammatory signal transduction. • Our in vitro and in silico studies help to understand the molecular basis for aquatic toxicity of pyraclofos. - Abstract: Pyraclofos, a relatively new organophosphorus pesticide, has shown potential ecotoxicities, however, its aquatic toxicity, especially enantioselective aquatic toxicity, remains largely unknown. Using zebrafish (Danio rerio) as a preeminent vertebrate aquatic model, the enantioselective differences in the developmental toxicity and immunotoxicity of pyraclofos were evaluated. Following 96-h exposure, pyraclofos enantiomers exhibited acute toxicity and showed lethal concentration 50 of 2.23 and 3.99 mg/L for (R)-Pyraclofos and (S)-Pyraclofos, respectively. Exposure to pyraclofos caused time- and concentration-dependent malformations such as pericardial edema, yolk sac edema, crooked bodies and hatching during the embryonic development, with markedly higher percentages of malformation at higher concentrations. The concentration-dependent immunotoxicity to zebrafish embryo exposed to low level pyraclofos was induced with significant up-regulation of mRNA levels of immune-related interleukin-1β (IL-1β) gene. (R)-Pyraclofos was consistently more toxic than (S)-Pyraclofos for the acute toxicity, developmental toxicity and immunotoxicity to zebrafish. Molecular dynamics simulations revealed that at the atomic level, (R)-Pyraclofos binds more potently to IL-1β protein than (S)-Pyraclofos. This enantioselective binding is mainly contributed by the distinct binding mode of pyraclofos enantiomers and their electrostatic interactions with IL-1β, which potentially

  13. Enzymatic Kinetic Resolution of 2-Piperidineethanol for the Enantioselective Targeted and Diversity Oriented Synthesis

    Directory of Open Access Journals (Sweden)

    Dario Perdicchia

    2015-12-01

    Full Text Available 2-Piperidineethanol (1 and its corresponding N-protected aldehyde (2 were used for the synthesis of several natural and synthetic compounds. The existence of a stereocenter at position 2 of the piperidine skeleton and the presence of an easily-functionalized group, such as the alcohol, set 1 as a valuable starting material for enantioselective synthesis. Herein, are presented both synthetic and enzymatic methods for the resolution of the racemic 1, as well as an overview of synthesized natural products starting from the enantiopure 1.

  14. Diastereoselective and enantioselective conjugate addition reactions utilizing α,β-unsaturated amides and lactams

    Directory of Open Access Journals (Sweden)

    Katherine M. Byrd

    2015-04-01

    Full Text Available The conjugate addition reaction has been a useful tool in the formation of carbon–carbon bonds. The utility of this reaction has been demonstrated in the synthesis of many natural products, materials, and pharmacological agents. In the last three decades, there has been a significant increase in the development of asymmetric variants of this reaction. Unfortunately, conjugate addition reactions using α,β-unsaturated amides and lactams remain underdeveloped due to their inherently low reactivity. This review highlights the work that has been done on both diastereoselective and enantioselective conjugate addition reactions utilizing α,β-unsaturated amides and lactams.

  15. Application of 7-azaisatins in enantioselective Morita–Baylis–Hillman reaction

    Science.gov (United States)

    He, Qing; Zhan, Gu; Du, Wei

    2016-01-01

    Summary 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. PMID:26977190

  16. Enantioselective reduction of ketoimines promoted by easily available (S)-proline derivatives

    Science.gov (United States)

    Bonsignore, Martina; Raimondi, Laura; Orlandi, Manuel; Celentano, Giuseppe

    2013-01-01

    Summary The behavior of readily synthesized and even commercially available (S)-proline derivatives, was studied in the trichlorosilane-mediated reduction of ketoimines. A small library of structurally and electronically modified chiral Lewis bases was considered; such compounds were shown to promote the enantioselective reduction of different substrates in good chemical yields. In the HSiCl3 addition to the model substrate N-phenylacetophenone imine, the organocatalyst of choice led to the formation of the corresponding amine with good stereoselectivity, up to 75% ee. Theoretical studies were also performed in order to elucidate the origin of the stereoselection. PMID:23616807

  17. Enantioselective reduction of ketoimines promoted by easily available (S-proline derivatives

    Directory of Open Access Journals (Sweden)

    Martina Bonsignore

    2013-04-01

    Full Text Available The behavior of readily synthesized and even commercially available (S-proline derivatives, was studied in the trichlorosilane-mediated reduction of ketoimines. A small library of structurally and electronically modified chiral Lewis bases was considered; such compounds were shown to promote the enantioselective reduction of different substrates in good chemical yields. In the HSiCl3 addition to the model substrate N-phenylacetophenone imine, the organocatalyst of choice led to the formation of the corresponding amine with good stereoselectivity, up to 75% ee. Theoretical studies were also performed in order to elucidate the origin of the stereoselection.

  18. Enantioselective developmental toxicity and immunotoxicity of pyraclofos toward zebrafish (Danio rerio)

    Energy Technology Data Exchange (ETDEWEB)

    Zhuang, Shulin, E-mail: shulin@zju.edu.cn [Institute of Environmental Science, College of Environmental and Resource Sciences, Zhejiang University, Hangzhou 310058 (China); Zhejiang Provincial Key Laboratory of Organic Pollution Process and Control, Hangzhou 310058 (China); Zhang, Zhisheng [Institute of Environmental Science, College of Environmental and Resource Sciences, Zhejiang University, Hangzhou 310058 (China); Zhang, Wenjing; Bao, Lingling [Institute of Environmental Science, College of Environmental and Resource Sciences, Zhejiang University, Hangzhou 310058 (China); Zhejiang Provincial Key Laboratory of Organic Pollution Process and Control, Hangzhou 310058 (China); Xu, Chao, E-mail: chaoxu@zjut.edu.cn [Research Center of Environmental Science, College of Biological and Environmental Engineering, Zhejiang University of Technology, Hangzhou 310032 (China); Zhang, Hu [Institute of Quality and Standard for Agro-products, Zhejiang Academy of Agricultural Sciences, Hangzhou 210021 (China)

    2015-02-15

    Highlights: • Pyraclofos has significant enantioselective aquatic toxicities to zebrafish. • Pyraclofos induces time- and concentration-dependent developmental toxicity and immunotoxicity. • The mRNA level of IL-1β gene was significantly up-regulated by pyraclofos. • Pyraclofos binds potently to IL-1β, potentially affecting IL-1β-dependent proinflammatory signal transduction. • Our in vitro and in silico studies help to understand the molecular basis for aquatic toxicity of pyraclofos. - Abstract: Pyraclofos, a relatively new organophosphorus pesticide, has shown potential ecotoxicities, however, its aquatic toxicity, especially enantioselective aquatic toxicity, remains largely unknown. Using zebrafish (Danio rerio) as a preeminent vertebrate aquatic model, the enantioselective differences in the developmental toxicity and immunotoxicity of pyraclofos were evaluated. Following 96-h exposure, pyraclofos enantiomers exhibited acute toxicity and showed lethal concentration 50 of 2.23 and 3.99 mg/L for (R)-Pyraclofos and (S)-Pyraclofos, respectively. Exposure to pyraclofos caused time- and concentration-dependent malformations such as pericardial edema, yolk sac edema, crooked bodies and hatching during the embryonic development, with markedly higher percentages of malformation at higher concentrations. The concentration-dependent immunotoxicity to zebrafish embryo exposed to low level pyraclofos was induced with significant up-regulation of mRNA levels of immune-related interleukin-1β (IL-1β) gene. (R)-Pyraclofos was consistently more toxic than (S)-Pyraclofos for the acute toxicity, developmental toxicity and immunotoxicity to zebrafish. Molecular dynamics simulations revealed that at the atomic level, (R)-Pyraclofos binds more potently to IL-1β protein than (S)-Pyraclofos. This enantioselective binding is mainly contributed by the distinct binding mode of pyraclofos enantiomers and their electrostatic interactions with IL-1β, which potentially

  19. Nitrate Removal from Drinking Water with Sodium Citrate as Sole Carbon Source

    Institute of Scientific and Technical Information of China (English)

    YAN Bo; ZHAO Lin; TAN Xin

    2005-01-01

    This paper investigates the effect of using sodium citrate(NaC6H5O6*2H2O)as sole carbon source for nitrate removal from drinking water.With sodium citrate as sole carbon source, batch experiments have been conducted to study the law of denitrification influenced by pH, C/N and temperature. Results show that a denitrification rate reaching 1.32 g NO-3-N /(g Biomass*d) was obtained when pH was at 7.5,C/N at 1.7(atom ratio), and temperature from 20 ℃ to 30 ℃. The results also show that denitrification rate with sodium citrate as carbon source approaches to that with methanol as carbon source.

  20. Tamoxifen citrate loaded ethosomes for transdermal drug delivery system: preparation and characterization.

    Science.gov (United States)

    Sarwa, Khomendra Kumar; Suresh, Preeti K; Debnath, Manabendra; Ahmad, Mohammad Zaki

    2013-08-01

    Long term tamoxifen citrate therapy is imperative to treat several dermatological and hormonal sensitive disorders. Successful oral and parenteral administration of tamoxifen citrate has been challenging since it undergoes enzymatic degradation and has poor aqueous solubility issues. In the present work, tamoxifen citrate loaded ethosomes were prepared and characterized for transdermal applications. The prepared formulations were characterized for morphological features, particle size distribution, calorimetric attributes, zeta potential and drug entrapment. Permeation profile of prepared ethosomes was compared with liposomes and hydroethonalic solution across cellophane membrane and human cadaver skin. Results of the permeation studies indicate that ethosomes were able to deliver >90% drug within 24 hours of application, while liposomes and hydroethanolic solution delivered only 39.04% and 36.55% respectively. Skin deposition and stability studies are also reported. PMID:23656399

  1. Preparation and evaluation of 99m Tc-Sn-citrate freeze dried kits

    International Nuclear Information System (INIS)

    A method for preparing 99m Tc-Sn-citrate freeze dried kits is established. The method is based on the use of Sn(II), HCl and citrate concentrations which give the final pH 5.1 without pH adjustment. The obtained Sn-citrate solution is sterilized by filtration through 0.22 μm membrane filter. A 1.0 ml aliquots are transferred into pre sterilized 10 ml serum vials, quickly frozen by liquid nitrogen and lyophilized. The determined formulation was applied in the kit preparation in aseptic and pyrogen free conditions. The freeze dried kits were checked radio chromatographic ally and assayed biologically in normal mice. Under optimum conditions more than 97% labelling yield was obtained and more than 56% of the injected dose was found in urine 2 hours after injection. 1 fig. 6 tab

  2. Effect on the citrate secretion of soybean seedling under aluminum stress

    International Nuclear Information System (INIS)

    Aluminum toxicity is one of the most significant constaints limiting plant growth and crop production in acid soils.The root growth is hurted by Al stress and absorbability of water and nutrient decreased, so the growth and development of plant is limited. In the present study, with solution culture, Jilin70 was selected as the Al-tolerant cultivars for the research of effect of Al on the citrate secretion of soybean seedling. The results were as follows: Exclusion of citrate acid from soybean roots be used to chelating Al and thus minimising the impact of Al toxicity. We found that large quantities of citrate secretion from soybean roots occurred after 6-h Al stress. Therefore, the former was classified to pattern II; results of root manipulation experiments revealed that only the Al-treated root portions were hurted.This injury was not observed in the roots of the same plant, which received only calcium solution without Al. (authors)

  3. Aluminum resistance in common bean (Phaseolus vulgaris) involves induction and maintenance of citrate exudation from root apices.

    Science.gov (United States)

    Rangel, Andrés Felipe; Rao, Idupulapati Madhusudana; Braun, Hans-Peter; Horst, Walter Johannes

    2010-02-01

    Two common bean (Phaseolus vulgaris L.) genotypes differing in aluminum (Al) resistance, Quimbaya (Al-resistant) and VAX-1 (Al-sensitive) were grown in hydroponics for up to 25 h with or without Al, and several parameters related to the exudation of organic acids anions from the root apex were investigated. Al treatment enhanced the exudation of citrate from the root tips of both genotypes. However, its dynamic offers the most consistent relationship between Al-induced inhibition of root elongation and Al accumulation in and exclusion from the root apices. Initially, in both genotypes the short-term (4 h) Al-injury period was characterized by the absence of citrate efflux independent of the citrate content of the root apices, and reduction of cytosolic turnover of citrate conferred by a reduced Nicotinamide adenine dinucleotide phosphate-isocitrate dehydrogenase (EC 1.1.1.42) activity. Transient recovery from initial Al stress (4-12 h) was found to be dependent mainly on the capacity to utilize internal citrate pools (Al-resistant genotype Quimbaya) or enhanced citrate synthesis [increased activities of NAD-malate dehydrogenase (EC 1.1.1.37) and ATP-phosphofructokinase (EC 2.7.1.11) in Al-sensitive VAX-1]. Sustained recovery from Al stress through citrate exudation in genotype Quimbaya after 24 h Al treatment relied on restoring the internal citrate pool and the constitutive high activity of citrate synthase (CS) (EC 4.1.3.7) fuelled by high phosphoenolpyruvate carboxylase (EC 4.1.1.31) activity. In the Al-sensitive genotype VAX-1 the citrate exudation and thus Al exclusion and root elongation could not be maintained coinciding with an exhaustion of the internal citrate pool and decreased CS activity. PMID:20053183

  4. Enhancing radium solubilization in soils by citrate, EDTA, and EDDS chelating amendments

    International Nuclear Information System (INIS)

    Highlights: ► The aim was to optimize radium solubilization for the purposes of remediation. ► The most important factor in radium solubilization was found to be the pH. ► Radium release increases with the reagent concentration. ► The largest release of radium is obtained with 50 mmol kg−1 of citrate, at pH acid, and 4 days after incubation. ► The best conditions for the release of radium are the same as for uranium. -- Abstract: The effect of three chelating agents (citrate, EDTA, and EDDS) on the solubilization of radium from a granitic soil was studied systematically, considering different soil pH values, chelating agent concentrations, and leaching times. For all the chelating agents tested, the amount of radium leached proved to be strongly dependent on the pH of the substrate: only for acidic conditions did the amount of radium released increase significantly relative to the controls. Under the best conditions, the radium released from the amended soil was greater by factors of 20 in the case of citrate, 18 for EDTA, and 14 for EDDS. The greatest improvement in the release of radium was obtained for the citrate amendment at the highest concentration tested (50 mmol kg−1). A slightly lower amount of radium was leached with EDTA at 5 mmol kg−1 soil, but the solubilization over time was very different from that observed with citrate or EDDS. With EDTA, a maximum in radium leaching was reached on the first day after amendment, while with citrate, the maximum was attained on the fourth day. With EDDS, radium leaching increased slightly but steadily with time (until the sixth day), but the net effect for the period tested was the lowest of the three reagents

  5. Endometrial Receptivity Markers in Mice Stimulated With Raloxifene Versus Clomiphene Citrate and Natural Cycles.

    Science.gov (United States)

    Chen, Cairong; Yan, Qiuxia; Liu, Kunping; Zhou, Xiuqin; Xian, Yingjie; Liang, Dali; Zhao, Xiaoying; Guo, Xiaoyan; Quan, Song

    2016-06-01

    Ovulation induction therapy with clomiphene citrate can suppress endometrial receptivity. Raloxifene may be an alternative therapeutic for women with ovulatory disorders. This study aimed to compare the expression of endometrial receptivity markers, including homeobox gene 10 (HOXA10), integrin β3, and leukemia inhibitory factor (LIF), as well as pinopode production during the implantation window in mice stimulated with raloxifene and clomiphene citrate and natural cycles. Thirty-six 8-week-old female Kunming mice were randomly divided into 3 groups (n = 12) and administered daily raloxifene (22 mg/kg), clomiphene citrate (18 mg/kg), and normal saline (1 mL), respectively, by gavage. Two days later, mice were injected with 5 IU human chorionic gonadotropin and mated. Successfully mated female animals were identified with vaginal plugs designated gestation day 1. At day 4.5, pregnant donor mice were euthanized, and uterus samples were collected for immunohistochemistry, quantitative polymerase chain reaction, Western blot, and scanning electron microscopy analyses. Homeobox gene 10, integrin β3, and LIF messenger RNA (mRNA) and protein levels were significantly higher in the raloxifene-treated animals compared with the clomiphene citrate group (all P raloxifene and saline groups; however, in the clomiphene citrate-treated mice, fewer and poorly developed pinopodes were obtained. In mice, raloxifene had no effect on HOXA10, integrin β3, and LIF expression as well as pinopode production, suggesting it has no adverse effects on endometrial receptivity. Raloxifene may provide a viable alternative oral ovulation induction agent to clomiphene citrate. PMID:26603317

  6. Modulation of calcium oxalate monohydrate crystallization by citrate through selective binding to atomic steps

    Energy Technology Data Exchange (ETDEWEB)

    Qiu, S R; Wierzbicki, A; Salter, E A; Zepeda, S; Orme, C A; Hoyer, J R; Nancollas, G H; Cody, A M; De Yoreo, J J

    2004-10-19

    The majority of human kidney stones are composed primarily of calcium oxalate monohydrate (COM) crystals. Thus, determining the molecular mechanisms by which urinary constituents modulate calcium oxalate crystallization is crucial for understanding and controlling urolithiassis in humans. A comprehensive molecular-scale view of COM shape modification by citrate, a common urinary constituent, obtained through a combination of in situ atomic force microscopy (AFM) and molecular modeling is now presented. We show that citrate strongly influences the growth morphology and kinetics on the (-101) face but has much lower effect on the (010) face. Moreover, binding energy calculations show that the strength of the citrate-COM interaction is much greater at steps than on terraces and is highly step-specific. The maximum binding energy, -166.5 kJ {center_dot} mol{sup -1}, occurs for the [101] step on the (-101) face. In contrast, the value is only -56.9 kJ {center_dot} mol-1 for the [012] step on the (010) face. The binding energies on the (-101) and (010) terraces are also much smaller, -65.4 and -48.9 kJ {center_dot} mol{sup -1} respectively. All other binding energies lie between these extremes. This high selectivity leads to preferential binding of citrate to the acute [101] atomic steps on the (-101) face. The strong citrate-step interactions on this face leads to pinning of all steps, but the anisotropy in interaction strength results in anisotropic reductions in step kinetics. These anisotropic changes in step kinetics are, in turn, responsible for changes in the shape of macroscopic COM crystals. Thus, the molecular scale growth morphology and the bulk crystal habit in the presence of citrate are similar, and the predictions of molecular simulations are fully consistent with the experimental observations.

  7. Use of Potassium Citrate to Reduce the Risk of Renal Stone Formation During Spaceflight

    Science.gov (United States)

    Whitson, P. A.; Pietrzyk, R. A.; Sams, C. F.; Jones, J. A.; Nelman-Gonzalez, M.; Hudson, E. K.

    2008-01-01

    Introduction: NASA s Vision for Space Exploration centers on exploration class missions including the goals of returning to the moon and landing on Mars. One of NASA s objectives is to focus research on astronaut health and the development of countermeasures that will protect crewmembers during long duration voyages. Exposure to microgravity affects human physiology and results in changes in the urinary chemical composition favoring urinary supersaturation and an increased risk of stone formation. Nephrolithiasis is a multifactorial disease and development of a renal stone is significantly influenced by both dietary and environmental factors. Previous results from long duration Mir and short duration Shuttle missions have shown decreased urine volume, pH, and citrate levels and increased calcium. Citrate, an important inhibitor of calcium-containing stones, binds with urinary calcium reducing the amount of calcium available to form stones. Citrate inhibits renal stone recurrence by preventing crystal growth, aggregation, and nucleation and is one of the most common therapeutic agents used to prevent stone formation. Methods: Thirty long duration crewmembers (29 male, 1 female) participated in this study. 24-hour urines were collected and dietary monitoring was performed pre, in, and postflight. Crewmembers in the treatment group received two potassium citrate (KCIT) pills, 10 mEq/pill, ingested daily beginning 3 days before launch, all inflight days and through 14 days postflight. Urinary biochemical and dietary analyses were completed. Results: KCIT treated subjects exhibited decreased urinary calcium excretion and maintained the levels of calcium oxalate supersaturation risk at their preflight levels. The increased urinary pH levels in these subjects reduced the risk of uric acid stones. Discussion: The current study investigated the use of potassium citrate as a countermeasure to minimize the risk of stone formation during ISS missions. Results suggest that

  8. Enhancing radium solubilization in soils by citrate, EDTA, and EDDS chelating amendments

    Energy Technology Data Exchange (ETDEWEB)

    Prieto, C.; Lozano, J.C. [Departamento de Física Fundamental, Universidad de Salamanca, 37008 Salamanca (Spain); Rodríguez, P. Blanco [Natural Radioactivity Group, Universidad de Extremadura, Avda. Elvas s/n, 06071 Badajoz (Spain); Tomé, F. Vera, E-mail: fvt@unex.es [Natural Radioactivity Group, Universidad de Extremadura, Avda. Elvas s/n, 06071 Badajoz (Spain)

    2013-04-15

    Highlights: ► The aim was to optimize radium solubilization for the purposes of remediation. ► The most important factor in radium solubilization was found to be the pH. ► Radium release increases with the reagent concentration. ► The largest release of radium is obtained with 50 mmol kg{sup −1} of citrate, at pH acid, and 4 days after incubation. ► The best conditions for the release of radium are the same as for uranium. -- Abstract: The effect of three chelating agents (citrate, EDTA, and EDDS) on the solubilization of radium from a granitic soil was studied systematically, considering different soil pH values, chelating agent concentrations, and leaching times. For all the chelating agents tested, the amount of radium leached proved to be strongly dependent on the pH of the substrate: only for acidic conditions did the amount of radium released increase significantly relative to the controls. Under the best conditions, the radium released from the amended soil was greater by factors of 20 in the case of citrate, 18 for EDTA, and 14 for EDDS. The greatest improvement in the release of radium was obtained for the citrate amendment at the highest concentration tested (50 mmol kg{sup −1}). A slightly lower amount of radium was leached with EDTA at 5 mmol kg{sup −1} soil, but the solubilization over time was very different from that observed with citrate or EDDS. With EDTA, a maximum in radium leaching was reached on the first day after amendment, while with citrate, the maximum was attained on the fourth day. With EDDS, radium leaching increased slightly but steadily with time (until the sixth day), but the net effect for the period tested was the lowest of the three reagents.

  9. Clinical and biochemical studies on the mechanism of gallium-67 citrate accumulation in tumor tissues

    International Nuclear Information System (INIS)

    A series of 67Ga scintigraphies, taken at Kobe University Hospital and Tenri Hospital from 1970 to 1974, were investigated statistically and histologically. Positive imaging of the lesion was obtained in 87% of 196 cases of primary lung cancer; 94%, 83% and 82% were positive in squamous cell carcinoma, undifferentiated carcinoma, and adenocarcinoma. In a comparative study on inflammatory lesions such as pneumonia or lung abcess, positive imaging was also obtained frequently during the active state but no positive image was noted in the inactive state. Since cyclic AMP is reported to play a role as a potent growth regulator, the effect of cyclic AMP as well as that of theophylline on 67Ga citrate binding in vitro was examined using a Millipore filter. Although cyclic AMP released 67Ga citrate bound to the cytosols of a rat liver, theophylline stimulated 67Ga citrate binding. In order to prove the working hypothesis that cyclic AMP phosphodiesterase binds 67Ga citrate, this enzyme was purified to a specific activity of 2330 mU/mg by an elaborate method such as ammonium sulfate treatment (30 - 50%) and stepwise Hydroxyapatite fractionation. The specific radioactivity of 67Ga citrate bound to this enzyme preparation (500 mM potassium phosphate buffer, pH 7.5) was 70-fold greater than that of transferrin and 240-fold more than that of cyclic AMP-binding protein purified as 50 mM potassium phosphate buffer, pH 7.5 eluted through Hydroxyapatite. It was also confirmed that the lysosome purified from the more rapidly growing hepatoma (7316 A) had a radioactivity two-fold higher than that of the slower growing hepatoma (7794 A) using an in vitro 67Ga citrate binding method. (auth.)

  10. Effect of titanium (III) citrate as reducing agent on growth of rumen bacteria.

    OpenAIRE

    Jones, G A; Pickard, M D

    1980-01-01

    We compared the growth of 10 strains of rumen bacteria in an anaerobic medium reduced with cysteine hydrochloride, dithiothreitol, or titanium (III) citrate. The redox potential of medium reduced with cysteine hydrochloride was -167.8 mV; with dithiothreitol it was -175.8 mV; and with titanium(III) citrate it was -302.4 mV at a concentration of 5 X 10(-4) M titanium and -403.9 mV at 2 X 10(-3) M titanium. Maximum growth of the strains was generally lower with dithiothreitol or titanium(III) c...

  11. Bioavailability of zinc and phosphorus in calcareous soils as affected by citrate exudation

    OpenAIRE

    Duffner, A.; Hoffland, E.; Temminghoff, E.J.M.

    2012-01-01

    Aims Zinc (Zn) and phosphorus (P) deficiency often occurs at the same time and limits crop production in many soils. It has been suggested that citrate root exudation is a response of plants to both deficiencies. We used white lupin (Lupinus albus L.) as a model plant to clarify if citrate exuded by roots could increase the bioavailability of Zn and P in calcareous soils. Methods White lupin was grown in nutrient solution and in two calcareous soils in a rhizobox. Rhizosphere soil solution wa...

  12. Interfacial properties of asymmetrically functionalized citrate-stabilized gold and silver nanoparticles related to molecular adsorption

    Science.gov (United States)

    Park, Jong-Won

    A detailed understanding of the conformation of adsorbed molecules and regional surface functionalization of metal nanoparticles (MNPs) is challenging for nanometer-size (10 -- 100 m) materials and necessary for fundamental studies and applications. The studies are motivated by open questions related to surface chemistry of noble MNPs. Although citrate-stabilized gold NPs (AuNPs) have been widely used, the citrate layer is not well-understood. Thiols have been suggested to displace citrate anions adsorbed on metal surfaces due to strong gold-sulfur interaction, but quantitative experimental evidence of the extent of ligand-exchange has not been reported. Whereas asymmetrically-functionalized AuNPs are utilized for nanoparticle assembly due to the interparticle coupling of localized surface plasmons, the interface between asymmetric nanoparticles in single assemblies has not been studied. Noble MNPs with sizes smaller than citrate-stabilized AuNPs also need to be surface-modified for stability in water for biological applications. The dissertation presents investigations of the chemical and physical properties of gold and silver NPs (AgNPs) related to ligand adsorption at the metal surface. Firstly, self-assembled layers of citrate adsorbed on AuNP (111), (110), and (100) surfaces were proposed, based on geometric considerations and spectroscopic investigations by infrared (IR) and X-ray photoelectron spectroscopy (XPS). Adsorption characteristics of citrate are the unique structure of adsorbed species, intermolecular interactions through hydrogen bonds and van der Waals attractions, bilayer formation, surface coverage, nanoparticle-stabilization role, and chirality. Secondly, IR and XPS studies showed coadsorption of thiolate on the surface of citrate-stabilized AuNPs. Steric, chelating effects and intermolecular interactions are the origins of the strong adsorption of citrate on AuNP surfaces. Surface coverage was determined from XPS analyses. Thirdly, an

  13. Abnormal splenic uptake of gallium-67 citrate in a case of infectious mononucleosis

    International Nuclear Information System (INIS)

    A case of fever of undetermined origin (FUO) demonstrated abnormal intense concentration of Ga-67 citrate in the spleen. Initial workup demonstrated two negative mono spot tests for infectious mononucleosis (IM) but, on hospital day 2, a repeat mono test was positive. The diagnosis was subsequently confirmed by rising heterophilic antibody titers. Six weeks after hospital discharge, repeat Ga-67 citrate imaging demonstrated absence of abnormal splenic activity. To our knowledge, this phenomenon has not been previously described in IM. In the appropriate clinical setting, intense splenic uptake of Ga-67 should alert the clinician to include the possibility of IM in the differential diagnosis

  14. Morphology control of hydroxyapatite microcrystals: Synergistic effects of citrate and CTAB.

    Science.gov (United States)

    Yang, Hui; Wang, Yingjun

    2016-05-01

    Using hydrothermal treatment and with the synergistic regulating effects of citrate and CTAB, various 3D hierarchical superstructure of hydroxyapatite (HAp) microcrystals were synthesized by simply adjusting the Ct/CTAB ratio and calcium-citrate complex (CC) morphology. The resulting superstructure was characterized using X-ray diffraction (XRD), Fourier Transform infrared spectroscopy (FTIR), field-emission scanning electron microscopy (FESEM) etc. With the shape transformation of CC from sphere-like colloid, nano-needle to lamellar-like particles, the final products were hollow spheres, bunched-like microrods and nanorod clusters, respectively. A possible mechanism for the formation of HAp hierarchical microstructure was proposed. PMID:26952410

  15. Calcium citrate improves the epithelial-to-mesenchymal transition induced by acidosis in proximal tubular cells

    OpenAIRE

    Maria José Rodriguez Cabalgante; Liliana Gadola; Leonella Luzardo; María Márquez; José Boggia; Mirian Aparecida Boim

    2012-01-01

    INTRODUCTION: Epithelial-to-mesenchymal transition (EMT) is a key event in renal fibrosis. The aims of the study were to evaluate acidosis induced EMT, transforming-growth-factor (TGF) β1 role and citrate effect on it. METHODS: HK2 cells (ATCC 2290) were cultured in DMEM/HAM F12 medium, pH 7.4. At 80% confluence, after 24 hr under serum free conditions, cells were distributed in three groups (24 hours): A) Control: pH 7.4, B) Acidosis: pH 7.0 and C) Calcium citrate (0.2 mmol/L) + pH 7.0. Chan...

  16. Sodium-coupled dicarboxylate and citrate transporters from the SLC13 family

    OpenAIRE

    Pajor, AM

    2014-01-01

    The SLC13 family in humans and other mammals consists of sodium-coupled transporters for anionic substrates: three transporters for dicarboxylates/ citrate and two transporters for sulfate. This review will focus on the di- and tricarboxylate transporters: NaDC1 (SLC13A2), NaDC3 (SLC13A3), and NaCT (SLC13A5). The substrates of these transporters are metabolic intermediates of the citric acid cycle, including citrate, succinate, and α-ketoglutarate, which can exert signaling effects through sp...

  17. As a Bacterial Culture Medium, Citrated Sheep Blood Agar Is a Practical Alternative to Citrated Human Blood Agar in Laboratories of Developing Countries

    OpenAIRE

    Russell, F. M.; Biribo, S. S. N.; Selvaraj, G.; Oppedisano, F; Warren, S.; Seduadua, A.; Mulholland, E. K.; Carapetis, J.R.

    2006-01-01

    Human blood agar (HuBA) is widely used in developing countries for the isolation of bacteria from clinical specimens. This study compared citrated sheep blood agar (CSBA) and HuBA with defibrinated horse blood agar and defibrinated sheep blood agar (DSBA) for the isolation and antibiotic susceptibility testing of reference and clinical strains of Streptococcus pneumoniae, Streptococcus pyogenes, and Staphylococcus aureus. Reference and clinical strains of all organisms were diluted in brain h...

  18. Citrate-stabilized Q-CdSe seed-mediated synthesis of silver nanoparticles: The role of citrate moieties anchored to the Q-CdSe surface

    Science.gov (United States)

    Ingole, Pravin P.; Bhat, Mohsin A.

    2016-03-01

    Here, we try to explore a new dimension/role for citrate molecules in the bound state, i.e. anchored to the surface of cadmium selenide quantum dots (Q-CdSe), in the synthesis of metal nanoparticles (MNPs). Being labile, the citrate molecule is considered a good candidate for the stabilization of semiconductor quantum dots (QDs) such as Q-CdSe that can be used for further functionalization/modification of the surface properties of the QDs. In its free/ionic form (i.e. not bound to the surface), it is well known for its role as a reducing as well as a capping agent in the synthesis of silver and gold MNPs. A simple strategy for the preparation of silver MNPs following the chemical reduction of silver ions that is mediated by citrate-stabilized Q-CdSe seeds without addition of an external reducing agent is presented. The citrate moieties anchored to the surface of Q-CdSe are found to play an important role in the chemical reduction of silver ions. The obtained product was analysed by spectroscopic, microscopic and structural characterization techniques such as surface plasmon resonance (SPR), transmission electron microscopy (TEM) and cyclic voltammetry. The characteristic redox behaviour observed in cyclic voltammograms (CVs) also supports the formation of Ag MNPs in the samples. Further, the impact of the reaction solution pH on the feasibility of silver ion reduction by Q-CdSe seeds resulting into the formation of Ag MNPs is also briefly discussed.

  19. Synthesis and spectroscopic and structural studies of a new cadmium(II)-citrate aqueous complex. Potential relevance to cadmium(II)-citrate speciation and links to cadmium toxicity.

    Science.gov (United States)

    Dakanali, M; Kefalas, E T; Raptopoulou, C P; Terzis, A; Mavromoustakos, T; Salifoglou, A

    2003-04-21

    The presence of cadmium in the environment undoubtedly contributes to an increased risk of exposure and ultimate toxic influence on humans. In an effort to comprehend the chemical and biological interactions of Cd(II) with physiological ligands, like citric acid, we explored the requisite aqueous chemistry, which afforded the first aqueous Cd(II)-citrate complex [Cd(C(6)H(6)O(7))(H(2)O)](n)() (1). Compound 1 was characterized by elemental analysis, and spectroscopically by FT-IR and (113)Cd MAS NMR. Compound 1 crystallizes in the orthorhombic space group P2(1)2(1)2(1), with a = 6.166(2) A, b = 10.508(3) A, c = 13.599(5) A, V = 881.2(5) A(3), and Z = 4. The X-ray structure of 1 reveals the presence of octahedral Cd(II) ions bound to citrate ligands in a molecular crystal lattice. Citrate acts as a tridentate binder promoting coordination to one Cd(II) through the central alcoholic moiety, one terminal carboxylate group, and the central carboxylate group. In addition, the central carboxylate binds to three Cd(II) ions. Specifically, one of the oxygens of the central carboxylate serves as a bridge to two neighboring Cd(II) ions, while the other oxygen binds to a third Cd(II). A bound water molecule completes the coordination requirements of Cd(II). (113)Cd MAS NMR studies project the spectroscopic signature of the nature of the coordination environment around Cd(II) in 1, thus corroborating the X-ray findings. Collectively, the data at hand are in line with past solution studies. The latter predict that other similar low molecular mass Cd(II)-citrate complexes may exist in the acidic pH region, thus influencing the uptake of cadmium by living (micro)organisms, their ability to metabolize organic substrates, and possibly Cd(II) toxicity. PMID:12691558

  20. Pulmonary scintigraphy by citrate of Ga67 for HIV(+) patients or AIDS. Scintigraphie pulmonaire au citrate de Ga67 chez des patients VIH(+) ou sida

    Energy Technology Data Exchange (ETDEWEB)

    Daumal, J.; Pena, C.; Mata, F.; Paternostro, C.; Penafiel, A. (Hopital Son Dureta, Palma de Mallorca (Spain))

    1993-04-01

    Pulmonary scintigraphy with citrate of gallium 67 is useful when combined with a thorax radiography to establish the presence of an infection. When the two examinations are negative we can conclude there is no infection, but if the radiography is positive with a scintiscanning negative the most possible diagnosis is tuberculosis. If the scintiscanning is positive with a diffuse model we can envisage a pneumonia by Pneumocystis Carinii and if the model is ganglionic we can think to tuberculosis. 4 tabs.

  1. Enantioselective total synthesis of polyoxygenated cyclohexanoids:(+)-streptol, ent-RKTS-33 and putative '(+)-parasitenone'. Identity ofparasitenone with (+)-epoxydon

    OpenAIRE

    Mehta, Goverdhan; Pujar, Shashikant R; Ramesh, Senaiar S; Islam, Kabirul

    2005-01-01

    Short, simple and enantioselective syntheses of the natural product(+)-streptol, the non-peptide apoptosis inhibitor ent-RKTS-33 and theputative structure of 'parasitenone' have been accomplished from thereadily available chiral building block. 'Parasitenone' has been shownto be identical with the known natural product epoxydon.

  2. A Convergent Enantioselective Total Synthesis of (-)-Perhydrohistrionicotoxin with an Intramolecular Imino Ene-type Reaction as a Key Step

    DEFF Research Database (Denmark)

    Tanner, David Ackland; Hagberg, Lars

    1998-01-01

    A convergent enantioselective total synthesis of the neurotoxic spirocyclic alkaloid (-)-perhydrohistrionicotoxin (2) is described. A Lewis acid-mediated intramolecular imine ene-type reaction was used for the key spirocyclisation step (14 to 3, with 3 being obtained as a single diastereoisomer...

  3. Lewis base activation of Lewis acids. Catalytic enantioselective addition of silyl enol ethers of achiral methyl ketones to aldehydes.

    Science.gov (United States)

    Denmark, Scott E; Heemstra, John R

    2003-06-26

    A highly enantioselective addition of silyl enol ethers derived from simple methyl ketones is described. The catalyst system of silicon tetrachloride activated by a chiral bisphosphoramide (R,R)-7 effectively promotes the addition of a variety of unsubstituted silyl enol ethers to aromatic, olefinic, and heteroaromatic aldehydes in excellent yield. [reaction: see text] PMID:12816434

  4. Enantioselective Reduction by Crude Plant Parts: Reduction of Benzofuran-2-yl Methyl Ketone with Carrot ("Daucus carota") Bits

    Science.gov (United States)

    Ravia, Silvana; Gamenara, Daniela; Schapiro, Valeria; Bellomo, Ana; Adum, Jorge; Seoane, Gustavo; Gonzalez, David

    2006-01-01

    The use of biocatalysis and biotransformations are important tools in green chemistry. The enantioselective reduction of a ketone by crude plant parts, using carrot ("Daucus carota") as the reducing agent is presented. The experiment introduces an example of a green chemistry procedure that can be tailored to fit in a regular laboratory session.…

  5. Toward the Enantioselective Total Synthesis of Lyngbyatoxin A: On the Stereocontrolled Introduction of the Quaternary Stereogenic Centre

    DEFF Research Database (Denmark)

    Tønder, Janne Ejrnæs; Tanner, David Ackland

    2003-01-01

    This paper deals with an approach to the enantioselective total synthesis of Lyngbyatoxin A, with focus on the stereocontrolled introduction of the quaternary stereogenic centre. The key step in the synthesis involves an enantiospecific Lewis-acid mediated rearrangement of chiral vinyl epoxides...

  6. Lithium BINOL Phosphate Catalyzed Desymmetrization of meso-Epoxides with Aromatic Thiols

    OpenAIRE

    Ingle, Gajendrasingh; Mormino, Michael G.; Antilla, Jon C.

    2014-01-01

    A highly enantioselective method for desymmetrization of meso-epoxides using thiols is reported. This is the first example of epoxide activation achieved using metal BINOL phosphates. The reaction has a broad scope in terms of epoxide substrates and aromatic thiol nucleophiles. The resulting β-hydroxyl sulfides are obtained in excellent yield and enantioselectivity.

  7. Evaluating the enantioselective degradation and novel metabolites following a single oral dose of metalaxyl in mice.

    Science.gov (United States)

    Zhang, Ping; Zhu, Wentao; Qiu, Jing; Wang, Dezhen; Wang, Xinru; Wang, Yao; Zhou, Zhiqiang

    2014-11-01

    Metalaxyl [N-(2,6-dimethylphenyl)-N-(methoxyacetyl)-D,L-alaninemethylester] is a systemic fungicide widely used in agriculture. In this study, the enantioselective distribution, degradation and excretion of metalaxyl were investigated after oral gavage administration of rac-metalaxyl to mice. Concentration of metalaxyl and its enantiomers was determined by HPLC-MS/MS. The results showed that R-metalaxyl was much higher than S-metalaxyl in heart, liver, lung, urine and feces. As for the strong first pass effect, concentrations of metalaxyl in liver were much higher than those in other tissues. The total body clearance (CL) of metalaxyl in mice was 1.77 L h(-1 )kg(-1) and degradation half-lives of (t1/2) of S-metalaxyl and R-metalaxyl in liver were 2.2 h and 3.0 h, respectively. Such results indicated the enantioselectivity of metalaxyl lies in distribution, degradation and excretion processes in mice. Main metabolites were also determined and biotransformation reactions were hydroxylation, demethylation and didemethylation. Furthermore, metabolite concentrations in urine and feces were much higher than those in tissues. These results may have potential implications to predict toxicity and provide additional information associated with adverse health effects for risk assessment of metalaxyl. PMID:25454518

  8. Enantioselective approach to polycyclic polyprenylated acylphloroglucinols via catalytic asymmetric intramolecular cyclopropanation.

    Science.gov (United States)

    Uetake, Yuta; Uwamori, Masahiro; Nakada, Masahisa

    2015-02-01

    The formal enantioselective total synthesis of nemorosone, garsubellin A, clusianone, and hyperforin is described. The catalytic asymmetric intramolecular cyclopropanation (CAIMCP) of an α-diazo ketone, a common synthetic intermediate for the above four polycyclic polyprenylated acylphloroglucinols previously reported by us, exhibited low enantioselectivity. However, CAIMCP of the corresponding α-diazo β-keto sulfone afforded the desired product in 79% yield with 84% ee. Investigation of the CAIMCP of the α-diazo β-keto sulfone demonstrated the formation of a rearrangement product in the presence of molecular sieves 4 Å, whereas, in the presence of H2O, the byproduct derived from ring-opening of the desired cyclopropane was observed. X-ray crystallographic analysis suggested that the above two products are derived from the same chiral intermediate. The product derived from ring-opening of the cyclopropane was successfully transformed to the respective synthetic intermediates for the total syntheses of nemorosone, garsubellin A, clusianone, and hyperforin, which had previously been reported by us. PMID:25581002

  9. Enantioselective analysis and fate of polycyclic musks in a water recycling plant in Sydney (Australia).

    Science.gov (United States)

    Wang, L; Khan, S J

    2014-01-01

    Synthetic polycyclic musks (PCMs) Galaxolide (HHCB), Tonalide (AHTN), Phantolide (AHDI), Traseolide (ATII) and Cashmeran (DPMI) are chiral chemicals that are commonly used in washing product industries as racemic mixtures. The major source of PCMs in municipal wastewater is from personal care and household products. Recent studies have shown that PCMs may enhance the relative toxicity of other environmental chemicals by inhibiting cellular xenobiotic defence systems. High sensitivity enantioselective analysis of these compounds enables improved characterisation of the environmental persistence and fate of PCMs, distinguishing between individual enantiomers so that a more complete understanding of environmental risks tributed by individual enantiomers may be obtained. Concentrations of PCMs through the various treatment stages of an advanced water recycling plant in Sydney were investigated to assess the removal of these chemicals. Average concentrations of HHCB, AHTN, AHDI, ATII and DPMI in influent were: 2,545, 301, 2, 5 and 33 ng L(-1), respectively. In the final effluent, AHDI, ATII and DPMI were not detected, while HHCB and AHTN were still measured at concentrations of 21 and 2 ng L(-1). No significant enantioselective transformation was detected during biological or advanced treatment processes. PMID:24845313

  10. 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.

  11. The chiral separation and enantioselective degradation of the chiral herbicide napropamide.

    Science.gov (United States)

    Qi, Yanli; Liu, Donghui; Sun, Mingjing; Di, Shanshan; Wang, Peng; Zhou, Zhiqiang

    2014-02-01

    The chiral pesticide enantiomers often have different toxic effects and environmental behaviors, which suggests that the risk assessments should be on an enantiomeric level. In this work, the chiral separation of the napropamide enantiomers and the stereoselective degradation in tomato, cucumber, rape, cabbage, and soil were investigated. Napropamide enantiomers could be separated absolutely by high-performance liquid chromatography (HPLC) using a Chiralpak IC column with a resolution factor of 11.75 under the optimized condition. Solid phase extraction (SPE) was used for cleanup of the enantiomers in the vegetable samples. The residue analysis method was validated. Good linearities (R(2)  = 0.9997) and recoveries (71.43% -97.64%) were obtained. The limits of detection (LOD) were 0.05 mg/kg in soil and 0.20 mg/kg in vegetables. The results of degradation showed that napropamide dissipated rapidly in vegetables with half-lives of only 1.13-2.21 days, but much more slowly in soil, with a half-life of 11.95 d. Slight stereoselective degradation of the two enantiomers was only observed in cabbage, with enantiomeric fraction (EF) = 0.46, and there was no enantioselectivity in the other vegetables. The degradation of napropamide in the five matrixes was fast, and there was no enantioselectivity. PMID:24436218

  12. Enantioselective hydrolysis of epichlorohydrin using whole Aspergillus niger ZJB-09173 cells in organic solvents

    Indian Academy of Sciences (India)

    Huo-Xi Jin; Zhong-Ce Hu; Yu-Guo Zheng

    2012-09-01

    The enantioselective hydrolysis of racemic epichlorohydrin for the production of enantiopure ()-epichloro-hydrin using whole cells of Aspergillus niger ZJB-09173 in organic solvents was investigated. Cyclohexane was used as the reaction medium based on the excellent enantioselectivity of epoxide hydrolase from A. niger ZJB-09173 in cyclohexane. However, cyclohexane had a negative effect on the stability of epoxide hydrolase from A. niger ZJB-09173. In the cyclohexane medium, substrate inhibition, rather than product inhibition of catalysis, was observed in the hydrolysis of racemic epichlorohydrin using A. niger ZJB-09173. The racemic epichlorohydrin concentration was markedly increased by continuous feeding of substrate without significant decline of the yield. Ultimately, 18.5% of ()-epichlorohydrin with 98% enantiomeric excess from 153.6 mM of racemic epichlorohydrin was obtained by the dry cells of A. niger ZJB-09173, which was the highest substrate concentration in the production of enantiopure ()-epichlorohydrin by epoxide hydrolases using an organic solvent medium among the known reports.

  13. Evaluating the enantioselective distribution, degradation and excretion of epoxiconazole in mice following a single oral gavage.

    Science.gov (United States)

    Wang, Dezhen; Qiu, Jing; Zhu, Wentao; Zhang, Ping; Deng, Nian; Wang, Xinru; Wang, Yao; Zhou, Zhiqiang

    2015-01-01

    1. The enantiomeric enrichment or degradation of epoxiconazole has been reported in grape, soil, tubifex and mealworm beetle. But, little is known about its enantioselective behaviors in mammals. 2. To further understand differences in the distribution, degradation and excretion of epoxiconazole enantiomers in vivo, male CD-1 mice were selected as the test model to investigate the enantioselective behaviors after a single oral gavage. Mice were sacrificed after 1 h, 3 h, 7 h, 12 h, 24 h, 48 h, 72 h treatment, blood, tissues and excretions were collected for epoxiconazole analysis by LC-MS/MS. 3. On the Lux-Cellulose-1 chiral column, an enrichment of the second eluting (+)-epoxiconazole was generally observed, and feces and urine showed similar EF with major tissues. 4. To elucidate the potential role of intestinal bacterial flora in stereospecific degradation of epoxiconazole, mice fecal flora were cultured in vitro and incubated with epoxiconazole for 48 h. Results showed that (-)-epoxiconazole was preferentially degraded by intestinal bacterial. 5. These results may provide useful information for risk assessment of epoxiconazole on non-target animals. PMID:26108358

  14. Aluminum-activated citrate and malate transporters encoded by distinct Al tolerance genes function independently in Arabidopsis

    Science.gov (United States)

    Aluminum (Al) -activated malate and citrate exudation from roots plays an important role in conferring Al tolerance to many plant species. Here, we report on the identification and characterization of AtMATE, the gene encoding an Al-activated root citrate efflux transporter that functions in Arabid...

  15. Comparison of the influence of EDTA-K3 and sodium citrate on haematology analysis in healthy dogs.

    Science.gov (United States)

    Zmigrodzka, M; Winnicka, A; Guzera, M

    2012-01-01

    The study was carried out on 30 clinically healthy dogs of various breeds. Haemoglobin concentration, haematocrit, platelet count and platelet haematocrit were significantly lower in citrate blood than in tripotassium ethylenediaminetetraacetic acid (EDTA-K3) blood. The study confirmed the limited usage of sodium citrate in haematology analysis, unless canine EDTA-dependent thrombocytopenia is suspected. PMID:22844720

  16. 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.

    2014-01-01

    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 two hour period, three hours 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-hour 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. PMID:25557834

  17. Discovery and characterization of novel inhibitors of the sodium-coupled citrate transporter (NaCT or SLC13A5)

    OpenAIRE

    Kim Huard; Janice Brown; Jessica C. Jones; Shawn Cabral; Kentaro Futatsugi; Matthew Gorgoglione; Adhiraj Lanba; Nicholas B. Vera; Yimin Zhu; Qingyun Yan; Yingjiang Zhou; Cecile Vernochet; Keith Riccardi; Angela Wolford; David Pirman

    2015-01-01

    Citrate is a key regulatory metabolic intermediate as it facilitates the integration of the glycolysis and lipid synthesis pathways. Inhibition of hepatic extracellular citrate uptake, by blocking the sodium-coupled citrate transporter (NaCT or SLC13A5), has been suggested as a potential therapeutic approach to treat metabolic disorders. NaCT transports citrate from the blood into the cell coupled to the transport of sodium ions. The studies herein report the identification and characterizati...

  18. Synthesis of Ag Nanostructures by Photochemical Reduction Using Citrate-Capped Pt Seeds

    Directory of Open Access Journals (Sweden)

    Hyeong-Ho Park

    2011-01-01

    Full Text Available A simple synthesis of Ag nanostructures such as nanorods and nanowires has been demonstrated with citrate-capped Pt seeds. UV-visible spectra and photographs of the synthesized solutions at different UV exposure times showed that the citrate-capped Pt seed played a crucial role in the growth of Ag nanostructures. After UV exposure of the colloidal solution for 60 min, the average diameter, length, and aspect ratio of the Ag nanostructures were about 95 nm, 2.1 μm, and 22, respectively. The photochemical reduction is hypothesized to result from photoelectron transfer from adsorbed citrate to Pt nanoparticle seed allowing Ag ions to form Ag nanostructures. Based on X-ray diffraction spectra and transmission electron microscope images, the synthesized Ag nanostructures were a face-centered cubic single crystal with good purity. These results suggest that the photochemical reduction method can provide Ag nanostructures in the presence of citrate-capped Pt seeds at room temperature for anisotropic Ag products.

  19. Effect of bismuth citrate, lactose, and organic acid on necrotic enteritis in broilers

    Science.gov (United States)

    Clostridium perfringens – associated necrotic enteritis causes significant losses and increased morbidity in poultry. The objective of this study was to evaluate the effect of bismuth citrate and acidifiers on the development of necrotic enteritis in broilers. The first study was a dose response t...

  20. THE SURFACE PHOTOCHEMISTRY OF PROCYMIDONE IN PRESENCE OF AMMONIUM FERRIC CITRATE

    Directory of Open Access Journals (Sweden)

    Ivan Osipov

    2015-12-01

    Full Text Available Procymidone was chosen as the model compound and its phototransformation was followed under sunlight irradiation. The main photodegradation products on silica is 3,5-dichloroaniline and 3,5-diclorphenilisocyanate. The use of ammonium ferric citrate enhances the degradation of the procymidone.