Home About us Contact
|
Home About us Contact | ||
|
|
||
Optical Purity (optical + purity)
Kinds of Optical Purity Selected AbstractsA Homogeneous Catalyst for Reduction of Optically Active Esters to the Corresponding Chiral Alcohols without Loss of Optical PuritiesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 1 2010Wataru Kuriyama Abstract A ruthenium complex was found to catalyze the hydrogen reduction of esters under mild and neutral conditions. A variety of optically active esters can be reduced to the corresponding alcohols in excellent yield without loss of their optical purity or causing undesirable side reactions. Hydrogen reduction needs such simple operations , reaction, concentration, and purification , that the violent quench step and extraction step, which accompany conventional sodium borohydride or lithium aluminum hydride reduction, can be omitted. [source] ChemInform Abstract: Organocatalytic Asymmetric Intramolecular [3 + 2] Cycloaddition: A Straightforward Approach to Access Multiply Substituted Hexahydrochromeno[4,3-b]pyrrolidine Derivatives in High Optical Purity.CHEMINFORM, Issue 38 2010Nan Li Abstract A chiral dinaphthyl-BINOL-derived phosphoric acid (NABIP) efficiently catalyzes the asymmetric intramolecular cycloaddition of formylphenoxybutenoates (I) and (IV) in the presence of ,-amino-,-aryl esters (II). [source] ChemInform Abstract: Organocatalytic Asymmetric Formal [4 + 2] Cycloaddition for the Synthesis of Spiro[4-cyclohexanone-1,3,-oxindoline] Derivatives in High Optical Purity.CHEMINFORM, Issue 29 2010Qiang Wei Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] A Convenient Synthesis of Optically Active Unhindered Aliphatic Alcohols with High Optical Purity from Non-racemic ,-Hydroxy Sulfides.CHEMINFORM, Issue 10 2005Byung Tae Cho Abstract For Abstract see ChemInform Abstract in Full Text. [source] A Novel Method for the Preparation of Benzylidenecyclohexanes with High Optical Purity.CHEMINFORM, Issue 25 2004Shuichi Nakamura Abstract For Abstract see ChemInform Abstract in Full Text. [source] Enantioselective Hydrogenation of N -Acetyldehydroamino Acids over Supported Palladium CatalystsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 3 2007György Szöll Abstract The enantioselective hydrogenation of two N -acetyldehydroamino acids over Cinchona alkaloid-modified, supported palladium catalysts has been studied. Moderate enantioselectivities, up to 36,%, were obtained in the hydrogenation of 2-acetamidocinnamic acid over cinchonidine-modified Pd/TiO2 under low hydrogen pressure. Increase in the pressure or use of benzylamine as additive led to a gradual decrease in the enantiomeric excess and eventually inversion of the sense of the enantioselectivity. On the contrary, the optical purity of the product resulting from the hydrogenation of 2-acetamidoacrylic acid was significantly increased by addition of benzylamine to the reaction mixture. Enantiomeric excess values up to 58,% and 60,% were obtained over Pd/Al2O3 modified by cinchonidine and cinchonine, respectively. These optical purities are the best obtained in the hydrogenation of dehydroamino acid derivatives over chirally modified heterogeneous metal catalysts. [source] Rhodium-Catalyzed Asymmetric Nitroallylation of Arylmetallics with Cyclic Nitroallyl Acetates and Applications in Organic SynthesisEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 18 2006Lin Dong Abstract Highly enantioselective rhodium-catalyzed nitroallylations of arylboronic acids and arylzinc chlorides with cyclic nitroallyl acetates are described. Catalyst screening indicated that the rhodium complex of [Rh(OH)(COD)]2 and optically pure binap is the optimal catalyst for the nitroallylation of arylboronic acids with 2-nitrocyclohex-2-enyl esters, providing good yields and high enantioselectivities of up to 99,% ee. The rhodium complex prepared from Rh(acac)(C2H4)2 and (R)-binap efficiently catalyzed the nitroallylation of arylzinc chlorides with 2-nitrocyclohex-2-enyl acetate at 0 °C in high yields of up to 93,% and with high enantioselectivities of up to 96,% ee. A number of synthetically useful intermediates with high optical purity were prepared with this reaction as starting point: concise total syntheses of optically pure (+)-,-lycorane in 53,% overall yield and of (+)-,-lycorane in 52,% overall yield were achieved by commencing with the asymmetric nitroallylation of 3,4-methylenedioxyphenylzinc chloride with 2-nitrocyclohex-2-enyl acetate. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] 7-Iodo-5-aza-7-deazaguanine: Syntheses of Anomeric D - and L -Configured 2-DeoxyribonucleosidesHELVETICA CHIMICA ACTA, Issue 9 2004Wenqing Lin Iodination of N2 -isobutyryl-5-aza-7-deazaguanine (7) with N -iodosuccinimide (NIS) gave 7-iodo- N2 -isobutyryl-5-aza-7-deazaguanine (8) in a regioselective reaction (Scheme,1). Nucleobase-anion glycosylation of 8 with 2-deoxy-3,5-di- O -toluoyl- , - D - or , - L - erythro -pentofuranosyl chloride furnished anomeric mixtures of D - and L -nucleosides. The anomeric D -nucleosides were separated by crystallization to give the , - D -anomer and , - D -anomer with excellent optical purity. Deprotection gave the 7-iodo-5-aza-7-deazaguanine 2,-deoxyribonucleosides 3 (, - D; ,99% de) and 4 (, - D; ,99% de). The reaction sequence performed with the D -series was also applied to L -nucleosides to furnish compounds 5 (, - L; ,99% de) and 6 (, - L; ,95% de). [source] Preparation, structure, and optical properties of chiral sulfoxides and disulfoxide with a trithiole ringHETEROATOM CHEMISTRY, Issue 1 2003Takeshi Kimura Optically active 4,9-diethyl[1,4]-dithiino[5,6- f]benzo[1,2,3]trithiole 5-oxide (3) and 4,9-diethyl[1,4]dithiino[5,6- f]benzo[1,2,3]trithiole 5,8-dioxide (4) were obtained by the asymmetric oxidation of 6,11-diethyl[1,4]dithiino[5,6- h]benzo[1,2,3,4,5]pentathiepin (1). The reaction was accompanied by desulfurization and ring-contraction reactions of the pentathiepin ring. Similarly, optically active 4,8-diethyl[1,3]dithiolo[4,5- f]benzo[1,2,3]trithiole 5-oxide (7) was produced by the analogous asymmetric oxidation of 6,10-diethyl[1,3]dithiolo[4,5- h]benzo[1,2,3,4,5]pentathiepin (2). The specific rotations of 3, 4, and 7 were measured in chloroform, and their optical purity was verified by 1H NMR with a shift reagent [Eu(hfc)3]. The structures of 4 and 7 were determined by X-ray crystallography using Cu K, radiation, and the absolute configuration of the sulfinyl group was examined based on the Flack parameter, which revealed that 4 has an RR configuration, while 7 has an S configuration. The circular dichroism spectra of 3, 4, and 7 were measured in chloroform. © 2003 Wiley Periodicals, Inc. Heteroatom Chem 14:88,94, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.10104 [source] Stereoselective Chemoenzymatic Preparation of ,-Amino Esters: Molecular Modelling Considerations in Lipase-Mediated Processes and Application to the Synthesis of (S)-DapoxetineADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 2-3 2010María Rodríguez-Mata Abstract A wide range of optically active 3-amino-3-arylpropanoic acid derivatives have been prepared by means of a stereoselective chemoenzymatic route. The key step is the kinetic resolution of the corresponding ,-amino esters. Although the enzymatic acylations of the amino group with ethyl methoxyacetate showed synthetically useful enantioselectivities, the hydrolyses of the ester group catalyzed by lipase from Pseudomonas cepacia have been identified as the optimal processes concerning both activity and enantioselectivity. The enantiopreference of this lipase in these reactions has been explained, at the molecular level, by using a fragment-based approach in which the most favoured binding site for a phenyl ring and the most stable conformation of the 3-aminopropanoate core nicely match the (S)-configuration of the major products. The conversion and enantioselectivity values of the enzymatic reactions have been compared in order to understand the influence of the different substitution patterns present in the phenyl ring. This chemoenzymatic route has been successfully applied to the preparation of a valuable intermediate in the synthesis of (S)-dapoxetine, which has been chemically synthesised in excellent optical purity. [source] A Homogeneous Catalyst for Reduction of Optically Active Esters to the Corresponding Chiral Alcohols without Loss of Optical PuritiesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 1 2010Wataru Kuriyama Abstract A ruthenium complex was found to catalyze the hydrogen reduction of esters under mild and neutral conditions. A variety of optically active esters can be reduced to the corresponding alcohols in excellent yield without loss of their optical purity or causing undesirable side reactions. Hydrogen reduction needs such simple operations , reaction, concentration, and purification , that the violent quench step and extraction step, which accompany conventional sodium borohydride or lithium aluminum hydride reduction, can be omitted. [source] Asymmetric Reduction of Activated Alkenes by Pentaerythritol Tetranitrate Reductase: Specificity and Control of Stereochemical Outcome by Reaction OptimisationADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 17 2009Anna Fryszkowska Abstract We show that pentaerythritol tetranitrate reductase (PETNR), a member of the ,ene' reductase old yellow enzyme family, catalyses the asymmetric reduction of a variety of industrially relevant activated ,,,-unsaturated alkenes including enones, enals, maleimides and nitroalkenes. We have rationalised the broad substrate specificity and stereochemical outcome of these reductions by reference to molecular models of enzyme-substrate complexes based on the crystal complex of the PETNR with 2-cyclohexenone 4a. The optical purity of products is variable (49,99% ee), depending on the substrate type and nature of substituents. Generally, high enantioselectivity was observed for reaction products with stereogenic centres at C, (>99% ee). However, for the substrates existing in two isomeric forms (e.g., citral 11a or nitroalkenes 18,19a), an enantiodivergent course of the reduction of E/Z -forms may lead to lower enantiopurities of the products. We also demonstrate that the poor optical purity obtained for products with stereogenic centres at C, is due to non-enzymatic racemisation. In reactions with ketoisophorone 3a we show that product racemisation is prevented through reaction optimisation, specifically by shortening reaction time and through control of solution pH. We suggest this as a general strategy for improved recovery of optically pure products with other biocatalytic conversions where there is potential for product racemisation. [source] Enzymatic Production of l -Menthol by a High Substrate Concentration Tolerable Esterase from Newly Isolated Bacillus subtilis ECU0554ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 3 2009Gao-Wei Zheng Abstract Enzymatic preparation of l -menthol has been attracting much attention in the flavor and fragrance industry. A new ideal strain, Bacillus subtilis ECU0554, which exhibited high hydrolytic activity and excellent enantioselectivity towards l -menthyl ester, has been successfully isolated from soil samples through enrichment culture and identified as Bacillus subtilis by 16S rDNA gene sequencing. The esterase extracted from B. subtilis ECU0554 (BSE) showed the best catalytic properties (E>200) for dl -menthyl acetate among the five menthyl esters examined. Enantioselective hydrolysis of 100,mM dl -menthyl acetate at 30°C and pH,7.0, using crude BSE as biocatalyst and 10% ethanol (v/v) as cosolvent, resulted in 49.0% conversion (3,h) and 98.0% ee for the l -menthol produced, which were much better than those using commercial enzymes tested. Moreover, BSE exhibited strong tolerance against high substrate concentration (up to 500,mM), and the concentration of l -menthol produced could reach as high as 182,mM, and more importantly, the optical purity of l -menthol produced was kept above 97% ee, which were not found in previous reports. These results imply that BSE is a potentially promising biocatalyst for the large-scale enzymatic preparation of l -menthol. Using this excellent biocatalyst, the enzymatic production of l -menthol will become a mild, efficient, inexpensive and easy-to-use "green chemistry" methodology. [source] On the Resolution of Chiral Substrates by a retro- Claisenase Enzyme: Biotransformations of Heteroannular Bicyclic ,-Diketones by 6-Oxocamphor HydrolaseADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 8-9 2007Cheryl Abstract The enzyme 6-oxocamphor hydrolase (OCH) from Rhodococcus sp. NCIMB 9784 catalyses the cleavage of a carbon-carbon bond between two carbonyl groups in both mono- and bicyclic non-enolisable ,-diketone substrates. In this mode OCH has been shown to effect the desymmetrisation of both bridged symmetrical bicyclic [2.2.1] and [2.2.2] systems and a series of 1-alkylbicyclo[3.3.0]octane-2,8-diones, yielding chiral substituted cyclopentanone and cyclohexanone products in high optical purity. In the present study, OCH has been challenged with a series of heteroannular substrates including 1-methylbicyclo[4.3.0]nonane-2,9-dione (7a-methylhexahydroindene-1,7-dione) in an effort to assess the competence of the enzyme for kinetic resolutions of asymmetric, racemic substrates. OCH was shown to catalyse the resolution of 1-methylbicyclo[4.3.0]nonane-2,9-dione with an E value of 2.9. The effect of increasing the length of the alkyl chain in the 1-position, or enlarging one of the rings, was to increase the enantioselectivity of the enzyme to 5.7 and 3.1 for the substrates 1-allylbicyclo[4.3.0]nonane-2,9-dione (7a-allylhexahydroindene-1,7-dione) and 1-methylbicyclo[5.3.0]decane-2,10-dione (8a-methyloctahydroazulene-1,8-dione), respectively. 1-Methylbicyclo[5.4.0]undecane-2,10-dione (9a-methyloctahydrobenzocycloheptene-1,9-dione) was not a substrate for OCH. These experiments constitute the first description of the resolution behaviour of such a retro -Claisenase enzyme, and suggest a maximum steric limit for substrate recognition by OCH. [source] Enantioselective Hydrogenation of N -Acetyldehydroamino Acids over Supported Palladium CatalystsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 3 2007György Szöll Abstract The enantioselective hydrogenation of two N -acetyldehydroamino acids over Cinchona alkaloid-modified, supported palladium catalysts has been studied. Moderate enantioselectivities, up to 36,%, were obtained in the hydrogenation of 2-acetamidocinnamic acid over cinchonidine-modified Pd/TiO2 under low hydrogen pressure. Increase in the pressure or use of benzylamine as additive led to a gradual decrease in the enantiomeric excess and eventually inversion of the sense of the enantioselectivity. On the contrary, the optical purity of the product resulting from the hydrogenation of 2-acetamidoacrylic acid was significantly increased by addition of benzylamine to the reaction mixture. Enantiomeric excess values up to 58,% and 60,% were obtained over Pd/Al2O3 modified by cinchonidine and cinchonine, respectively. These optical purities are the best obtained in the hydrogenation of dehydroamino acid derivatives over chirally modified heterogeneous metal catalysts. [source] Efficient, Enantioselective Organocatalytic Synthesis of Trichostatin AADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 10-11 2006Shilei Zhang Abstract An efficient, highly stereocontrolled total synthesis of trichostatin A (1) has been achieved in 9 steps with 17.4,% overall yield and >99,% optical purity from readily available achiral starting materials. The key features of this synthesis include the L -proline-promoted, highly enantioselective cross-aldol reaction as a crucial step for the construction of the C-6 chiral center and the minimization of racemization by final step oxidation of the OH group to a ketone at position 7. [source] Chemo-Enzymatic Approach to Statin Side-Chain Building BlocksADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 6-7 2003R. Öhrlein Abstract A versatile statin side-chain building block is obtained by an enzymatic desymmetrisation of the symmetrical glutaric acid diethyl ester. The monoacid is produced in almost quantitative yield in the desired high optical purity. The monoacid is easily converted to the corresponding acid chloride, which is a key compound to be elaborated to some statin side-chain derivatives. The optically active C-5 chain is subsequently elongated by two carbon atoms and syn -reduced to the final diol fragment. [source] Enantioseparation via EIC-OSN: Process design and improvement of enantiomers resolvability and separation performanceAICHE JOURNAL, Issue 4 2010Issara Sereewatthanawut Abstract This article presents a mathematical model to assess and optimize the separation performance of an enantioselective inclusion complexation-organic solvent nanofiltration process. Enantiomer solubilities, feed concentrations, solvent compositions, permeate solvent volumes, and numbers of nanofiltrations were identified as key factors for process efficiency. The model was first tested by comparing calculated and experimental results for a nonoptimized process, and then, calculations were carried out to select the best operating conditions. An important finding was that the optimal configuration varied with the objective function selected, e.g., resolvability versus yield, with a boundary on product optical purity. The model also suggested that the process efficiency could benefit from diafiltration of the distomer and from the use of higher feed concentrations. However, the latter strategy would result in higher losses of eutomer. To address this drawback, a multistage process was evaluated using the verified process model. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] High-performance liquid chromatographic resolution of 1-(1,4-benzodioxane-2-formyl)- piperazine enantiomers after chiral derivatizationJOURNAL OF SEPARATION SCIENCE, JSS, Issue 2 2005Zhiqiong Chen Abstract Chiral separation of racemic mixtures is of the greatest importance to the pharmaceutical industry, as the isomers of a given racemate may exhibit substantially different pharmacological effects, not to mention possibly differing toxicity behaviour. A novel chiral separation method is developed for the determination of 1-(1,4-benzodioxane-2-formyl)piperazine (BFP) enantiomers. The indirect resolution is performed by applying precolumn derivatization with the chiral reagent 2,3,4,6-tetra- O -acetyl-,-D-glucopyranosyl isothiocyanate (GITC). The resulting diastereoisomers are separated on a reversed-phase ODS column with methanol-potassium dihydrogen phosphate (0.02mol/L, 50:50) as mobile phase. UV detection is at 250 nm. The effect of mobile phase composition upon resolution and analysis time is investigated. Two diastereoisomers show nearly base-line separation under optimal chromatographic conditions. The presented study provides a simple and accurate method for the enantiomeric quality control and the optical purity assay of BFP. [source] Microwave-assisted synthesis and characterization of heterocyclic, and optically active poly(amide-imide)s incorporating L -amino acidsPOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 12 2008Abdol R. Hajipour Abstract N,N,-Pyromelliticdiimido-di- L -alanine (1), N,N,-pyromelliticdiimido-di- L -phenylalanine (2), and N,N,-pyromelliticdiimido-di- L -leucine (3) were prepared from the reaction of pyromellitic dianhydride with corresponding L -amino acids in a mixture of glacial acetic acid and pyridine solution (3/2 ratio) under refluxing conditions. The microwave-assisted polycondensation of the corresponding diimide-diacyl chloride monomers (5,7) with 4-phenyl-2,6-bis(4-aminophenyl) pyridine (10) or 4-(p -methylthiophenyl)-2,6-bis(4-aminophenyl) pyridine (12) were carried out in a laboratory microwave oven. The resulting poly(amide-imide)s were obtained in quantitative yields, and they showed admirable inherent viscosities (0.12,0.55 dlg,1), were soluble in polar aprotic solvents, showed good thermal stability and high optical purity. The synthetic compounds were characterized by IR, MS, 1H NMR, and 13C NMR spectroscopy, elemental analysis, and specific rotation. Copyright © 2008 John Wiley & Sons, Ltd. [source] Simultaneous Saccharification and Co-Fermentation of Crystalline Cellulose and Sugar Cane Bagasse Hemicellulose Hydrolysate to Lactate by a Thermotolerant Acidophilic Bacillus sp.BIOTECHNOLOGY PROGRESS, Issue 5 2005Milind A. Patel Polylactides produced from renewable feedstocks, such as corn starch, are being developed as alternatives to plastics derived from petroleum. In addition to corn, other less expensive biomass resources can be readily converted to component sugars (glucose, xylose, etc.) by enzyme and/or chemical treatment for fermentation to optically pure lactic acid to reduce the cost of lactic acid. Lactic acid bacteria used by the industry lack the ability to ferment pentoses (hemicellulose-derived xylose and arabinose), and their growth and fermentation optima also differ from the optimal conditions for the activity of fungal cellulases required for depolymerization of cellulose. To reduce the overall cost of simultaneous saccharification and fermentation (SSF) of cellulose, we have isolated bacterial biocatalysts that can grow and ferment all sugars in the biomass at conditions that are also optimal for fungal cellulases. SSF of Solka Floc cellulose by one such isolate, Bacillus sp. strain 36D1, yielded l(+)-lactic acid at an optical purity higher than 95% with cellulase (Spezyme CE; Genencor International) added at about 10 FPU/g cellulose, with a product yield of about 90% of the expected maximum. Volumetric productivity of SSF to lactic acid was optimal between culture pH values of 4.5 and 5.5 at 50 °C. At a constant pH of 5.0, volumetric productivity of lactic acid was maximal at 55 °C. Strain 36D1 also co-fermented cellulose-derived glucose and sugar cane bagasse hemicellulose-derived xylose simultaneously (SSCF). In a batch SSCF of 40% acid-treated hemicellulose hydrolysate (over-limed) and 20 g/L Solka Floc cellulose, strain 36D1 produced about 35 g/L lactic acid in about 144 h with 15 FPU of Spezyme CE/g cellulose. The maximum volumetric productivity of lactic acid in this SSCF was 6.7 mmol/L (h). Cellulose-derived lactic acid contributed to about 30% of this total lactic acid. These results show that Bacillus sp. strain 36D1 is well-suited for simultaneous saccharification and co-fermentation of all of the biomass-derived sugars to lactic acid. [source] Design of the pH Profile for Asymmetric Bioreduction of Ethyl 4-Chloro-3-oxobutyrate on the Basis of a Data-Driven MethodBIOTECHNOLOGY PROGRESS, Issue 6 2002Junghui Chen The goal of this paper was to design the optimal time-varying operating pH profile in the asymmetric reduction of ethyl 4-chloro-3-oxobutyrate by baker's yeast. Ethyl ( S)-4-chloro-3-hydroxybutyrate was produced to reach two important quality indices: reaction yield and product optical purity. The method integrated an orthogonal function approximation and an orthogonal array. The technique used a set of orthonormal functions as the basis for representing the possible profile. The optimal profile could be obtained if the orthogonal coefficients were properly adjusted. The orthogonal array was used to design and analyze the effect of each orthogonal coefficient in order to reach the optimal objective (quality) function. The performance based on the proposed strategy was significantly improved by over 10% compared with the traditional fixed pH or uncontrolled pH values during the reaction. The proposed method can be applied to the required dynamic profile in the bioreactor process to effectively improve the product quality, given good design directions and the advantage of the traditional statistical approach. [source] Lipases-Catalyzed Alcoholysis for the Preparation of Chiral 1- or 2-Hydroxyalkanephosphonates,CHINESE JOURNAL OF CHEMISTRY, Issue 1 2003Zhang Yong-Hui Abstract Enzymatic alcoholysis has been developed for the preparation of some chiral 1- and 2-hydroxyalkanephosphonates with high optical purity. This method ensures the convenient access to the optically pure phosphocarnitine, phosphogabob and phosphomycin. [source] Analysis of optical purity and impurity of synthetic d -phenylalanine products using sulfated ,-cyclodextrin as chiral selector by reversed-polarity capillary electrophoresisCHIRALITY, Issue 2 2006Yan Zhao Abstract A new capillary electrophoresis (CE) method has been achieved for simultaneous separation and quantification of phenylalanine, N -acetylphenylalanine enantiomers, and prochiral N -acetylaminocinnamic acid, possibly co-existent in reaction systems or synthesized products of d -phenylalanine. The separation was carried out in an uncoated capillary under reversed-electrophoretic mode. Among the diverse charged cyclodextrins (CDs) examined, highly sulfated (HS)-,-CD as the chiral selector exhibited the best enantioselectivity. The complete separation of the analytes was obtained under the optimum conditions of pH 2.5, 35 mM Tris buffer containing 4% HS-,-CD, applied voltage ,15 kV, and capillary temperature 25°C. Furthermore, the proposed method was applied to the determination of optical purity and trace impurities in three batches of the asymmetric synthetic samples of d -phenylalanine, and satisfactory results were obtained. The determination recoveries of the samples were in the range of 97.8,103.8%, and precisions fell within 2.3,5.0% (RSD). The results demonstrate that this CE method is a useful, simple technique and is applicable to purity assays of d -phenylalanine. © 2005 Wiley-Liss, Inc. Chirality 18:84,90, 2006. [source] Preparation of enantiomeric gossypol by crystallization,CHIRALITY, Issue 6 2003Michael K. Dowd Abstract Large enantiomorphic crystals of gossypol-acetone (1:3) were grown from acetone solutions of rac -gossypol-acetic acid (1:1) at 4°C. By controlling the initial gossypol concentration, crystallization time, and solution volume, single crystals were grown that weighed >50 mg, equivalent to >37 mg of enantiomeric gossypol. Even larger crystals were possible, but it was difficult to produce these reliably without contamination of the antipode. Essentially all of the acetone within the crystal form was removed by storing the crystals under vacuum for 3,4 days. By employing these techniques, gram quantities of enantiomeric gossypol were prepared in high chemical and optical purity. Based on measured and reported optical rotations, the optical purity of samples prepared by crystallization was greater than the optical purity of samples prepared by chromatographic separation of gossypol-amine diastereomers. The principal limitation of crystallization as a preparative method is the need to determine the chirality and purity of each product crystal. Nevertheless, the method competes favorably with preparative-scale chromatographic procedures. Chirality 15:486,493, 2003. Published 2003 Wiley-Liss, Inc. [source] | |||||||||||||||||||||||||