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Mandelic Acid (mandelic + acid)

Distribution by Scientific Domains

Chemistry	94%

Selected Abstracts

Deracemisation of Mandelic Acid to Optically Pure Non-Natural L -Phenylglycine via a Redox-Neutral Biocatalytic Cascade

ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 6 2010
Verena Resch
Abstract A biocatalytic redox-neutral reaction cascade was designed for the deracemisation of racemic mandelic acid to yield optically pure L -phenylglycine employing three enzymes. The cascade consisted of three steps: a racemisation, an enantioselective oxidation and a stereoselective reductive amination. The enantioselective oxidation of D -mandelic acid to the corresponding oxo acid was coupled with the stereoselective reductive amination of the latter; thus the oxidation as well as the reduction reactions were performed simultaneously. The formal hydrogen abstracted in the first step , the oxidation , was consumed in the reductive amination allowing a redox-neutral cascade due to a cascade-internal cofactor recycling. The enantiomers of the starting material were interconverted by a racemase (mandelate racemase) ensuring that in theory 100% of the starting material can be transformed. Using this set-up racemic mandelic acid was transformed to optically pure L -phenylglycine (ee >97%) at 94% conversion without the requirement of any additional redox reagents in stoichiometric amounts. [source]

Construction of Recombinant Escherichia coli Catalysts which Simultaneously Express an (S)-Oxynitrilase and Different Nitrilase Variants for the Synthesis of (S)-Mandelic Acid and (S)-Mandelic Amide from Benzaldehyde and Cyanide

ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 10 2009
Olga Sosedov
Abstract Recombinant Escherichia coli strains were constructed which simultaneously expressed the genes encoding the (S)-oxynitrilase from cassava (Manihot esculenta) together with the wild-type or a mutant variant of the arylacetonitrilase from Pseudomonas fluorescens EBC191 in a single organism under the control of a rhamnose-inducible promoter. The whole cell catalysts obtained converted benzaldehyde and potassium cyanide in aqueous media at pH,5.2 mainly to (S)-mandelic acid and/or (S)-mandelic amide and synthesized only low amounts of the corresponding (R)-enantiomers. The conversion of benzaldehyde and potassium cyanide (KCN) by a whole-cell catalyst simultaneously expressing the (S)-oxynitrilase and the wild-type nitrilase resulted in a ratio of (S)-mandelic acid to (S)-mandelic amide of about 4:3. This could be explained by the strong nitrile hydratase activity of the wild-type nitrilase with (S)-mandelonitrile as substrate. The relative proportion of (S)-mandelic amide formed in this system was significantly increased by coexpressing the (S)-oxynitrilase with a carboxy-terminally truncated variant of the nitrilase. This whole-cell catalyst converted benzaldehyde and KCN to mandelic amide and mandelic acid in a ratio of about 9:1. The ee of the (S)-mandelic amide formed was calculated to be >95%. [source]

New Chiral Ligands Derived from Mandelic Acid: Synthesis and Application in the Asymmetric Phenyl Transfer Reaction to an Aromatic Aldehyde.

CHEMINFORM, Issue 4 2005
Carsten Bolm
Abstract For Abstract see ChemInform Abstract in Full Text. [source]

Deracemisation of Mandelic Acid to Optically Pure Non-Natural L -Phenylglycine via a Redox-Neutral Biocatalytic Cascade

Construction of Recombinant Escherichia coli Catalysts which Simultaneously Express an (S)-Oxynitrilase and Different Nitrilase Variants for the Synthesis of (S)-Mandelic Acid and (S)-Mandelic Amide from Benzaldehyde and Cyanide

Analysis of urinary biomarkers for exposure to alkyl benzenes by isotope dilution gas chromatography-mass spectrometry

JOURNAL OF SEPARATION SCIENCE, JSS, Issue 18 2005
Adriaan A. S. Marais
Abstract A validated GC-MS method for the analysis of urinary metabolites of alkyl benzenes is reported. Metabolites for exposure to toluene, xylene and ethylbenzene were analyzed simultaneously using stable isotope substituted internal standards. The method entailed acidic deconjugation of urine samples followed by extractive alkylation with pentafluorobenzyl bromide as alkylating agent. The resulting pentafluorobenzyl derivatives of ortho -, meta -, para -cresol, mandelic acid (MA), hippuric acid (HA) and ortho -, meta -, para -methylhippuric acid (MHA) were then quantified by SIM. Optimized reaction conditions for the extractive alkylation step are reported. The derivatives were found to be sufficiently stable for overnight batch analysis. The LODs were below 0.1 ,mol/L for the cresols and below 1 ,mol/L for MA and the HAs. Within-batch precision for o -MHA was 7%, for m -MHA 5%, for p -MHA 5.2% and below 5% for the rest of the analytes. [source]

Influence of steric hindrance on enantioseparation of Dns-amino acids and pesticides on terguride based chiral selectors in capillary electrophoresis

JOURNAL OF SEPARATION SCIENCE, JSS, Issue 7 2005
Honzátko
Abstract Three urea derivatives of ergoline-based chiral selectors (CSs), differing in the size of the urea side chain, i. e. dimethyl- (CSI), diethyl- (CSII), and diisopropylurea (CSIII), were used to study the effect of steric hindrance on the enantioseparation of dansyl amino acids (Dns-AAs), pesticides, and mandelic acid under condition of capillary electrophoresis (CE) in linear polyacrylamide coated capillaries. A mixture of organic modifiers (MeOH/THF, 4 : 1 v/v) in a BGE consisting of 100 mM ,-alanine-acetate was used to increase the solubility of CSs up to 25 mM. The capillary was filled with CS (high UV absorption), and the inlet and outlet vials contained buffer solutions only. The best enantioseparation of Dns-AAs was achieved on CSI. Increased steric hindrance of the chiral binding site led to reduction of both enantioselectivity and resolution. The opposite pattern was observed for the separation of mandelic acid enantiomers, where the best enantioseparation and resolution was obtained with CSIII. Most of the pesticides studied reached maximum selectivity on the diethylurea ergoline derivative (CSII). Enantioseparation of fenoxaprop was found to be independent of steric hindrance. [source]

Determination of organic acids in urine by solid-phase microextraction and gas chromatography,ion trap tandem mass spectrometry previous ,in sample' derivatization with trimethyloxonium tetrafluoroborate

BIOMEDICAL CHROMATOGRAPHY, Issue 10 2008
Marco Pacenti
Abstract A method for the determination of the organic acids directly in the urine employing derivatization with trimethyloxonium tetrafluoroborate as a methylating agent and sequential extraction by head space and direct immersion/solid phase microextraction is reported. Furoic acid, hippuric acid, methylhippuric acid, mandelic acid, phenylglyoxylic acid and trans, trans muconic acid contained in urine and proposed by the American Conference of Governmental Industrial Hygienists as biological exposure indices were determined after a fast and economically convenient preparation step and sensitive gas chromatography,ion trap,mass spectrometry/tandem mass spectrometry analysis. Urine is rather a complex sample and hence the acquisition method required specific GC-MS instrumentation capable of supporting the changeover, fully automated during a single chromatographic separation, from mass to tandem mass spectrometry and both chemical and electron ionization modes. The automation of the analytical method provides a number of advantages, including reduced analysis time for both routine analysis and method development, and greater reproducibility. The equilibrium and kinetics of this substances vs head space/direct immersion-solid phase microextraction were investigated and evaluated theoretically. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Direct TLC resolution of atenolol and propranolol into their enantiomers using three different chiral selectors as impregnating reagents

BIOMEDICAL CHROMATOGRAPHY, Issue 9 2008
Ravi Bhushan
Abstract Direct resolution of racemic atenolol and propranolol into their enantiomers was achieved by normal phase TLC on silica gel plates impregnated with optically pure l -tartaric acid, (R)-mandelic acid and (,)-erythromycin as chiral selectors. Different solvent systems were worked out to resolve the enantiomers. Spots were detected using iodine vapour. The TLC method was validated for linearity, limit of detection and limit of quantification. The influence of pH, temperature and concentration of chiral selector was studied. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Non-invasive assessment of cardioregulatory autonomic functions in children with epilepsy

ACTA NEUROLOGICA SCANDINAVICA, Issue 6 2007
H. L. El-Sayed
Objectives ,, We aimed to evaluate the interictal cardiovascular autonomic functions in pediatric patients with idiopathic epilepsy, both partial and generalized. Materials and methods ,, The study included 25 patients with idiopathic epilepsy and 50 control subjects. Patients underwent five standardized clinical cardiovascular reflex autonomic tests [resting heart rate (HR), HR response to deep breathing and to Valsalva maneuver, the 30:15 ratio of HR response to standing, and blood pressure response to standing], as well as a 12 lead surface electrocardiogram. Heart rate variability (HRV) was tested via 24-h Holter monitoring and the time domain parameters (SDNN, PNN50, rMSDD) were assessed. Excretion of vanillyl mandelic acid and metanephrine was measured in 24-h urine collection. Results ,, Clinical reflex autonomic tests showed mild dysfunction in 8%, moderate dysfunction in 44% and severe dysfunction in 4% of patients. The HRV parameter, SDNN, was reduced in all age groups, while rMSDD and PNN50 were reduced only in the older age group. Metanephrine levels were significantly reduced in the patients group. Patients with uncontrolled epilepsy had a significantly higher frequency of autonomic dysfunction as assessed by clinical scoring. Conclusion ,, Cardiac autonomic dysfunction is not uncommon in pediatric patients with epilepsy. Altered cardiovascular regulation seems to be related to the epilepsy itself rather than to the characteristics of the disorder. [source]

Production and Characteristics of an Enantioselective Lipase from Burkholderia sp.

CHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 2 2008
GXU5
Abstract The lipase production of Burkholderia sp. GXU56 was influenced by carbon and nitrogen sources, inorganic salts, initial pH of the medium and cultivation temperature. The maximum lipase production was 580.52,U/mL and reached 5,times the level of the basic medium in the optimum medium at pH 8.0, 32,°C, 200,rpm and 40,48,h. The lipase was purified 53.6,fold to homogeneity and the molecular weight was 35,KDa on SDS-PAGE. The optimum pH and temperature of the lipase were 8.0 and 40,°C, respectively, and it was stable in the range of pH 7,8.5 and at temperatures below 45,°C. The lipase activity was strongly inhibited by Zn2+, Cu2+, Co2+, Fe2+, Fe3+ ions and SDS, while it was stimulated by Li+ and Ca2+ ions and in presence of 0.1,% CTAB, 0.1,% Triton X-100 and 10,% DMSO. Km and Vmax of the lipase were calculated to be 0.038,mmol/L, and 0.029,mmol/L min,1, respectively, with PNPB as the substrate. The GXU56 lipase showed enantioselective hydrolysis of (R,S)-methyl mandelate to (R)-mandelic acid, which is an important intermediate in the pharmaceutical industry. [source]

Chiral Recognition of Carboxylic Acids by Chiral Nitrogen Containing Calix[4]arene

CHINESE JOURNAL OF CHEMISTRY, Issue 10 2005
Yan-Song Zheng
Abstract Chiral nitrogen-containing calix[4]arene was easily synthesized by the reaction of 25,27-di(2-bromoethoxy)-26,28-dihydroxy-5,11,17,23-tetrakis(t -butyl)calix[4]arene with S -((,)-1-phenylethylamine in excellent yield, and showed good ability to recognize the enantiomers of mandelic acid and 2,3-dibenzoyltartaric acid. This finding has potential application to assay and separation of enantiomers of the carboxylic acids. [source]

Electrochemical reduction of benzoylformic acid in ionic liquid

CHINESE JOURNAL OF CHEMISTRY, Issue 9 2003
Jia-Xing Lu
Abstract Ionic liquids possess a number of unique properties that make them ideal electrolytes. Electrochemical reduction of benzoylformic acid in room temperature ionic liquids as reaction media could be conducted with excellent performances without any additional supporting electrolyte. Electrolysis at glassy carbon electrode results in the formation of mandelic acid in 91% yield. And the electrochemical behavior of benzoylformic acid was investigated with the technique of cyclic voltammetry. [source]

High-performance liquid chromatography separation of enantiomers of mandelic acid and its analogs on a chiral stationary phase

CHIRALITY, Issue 5 2010
Ritu Aneja
Abstract The enantiomers of mandelic acid and its analogs have been chromatographically separated on a chiral stationary phase (CSP) derived from 4-(3,5-dinitrobenzamido) tetrahydrophenanthrene. The rationale of separations of these compounds is discussed with respect to the method development for determining enantiomeric purity and possibility of obtaining enantiomerically pure materials by high-pressure liquid chromatography. The relationship of analyte structure to the extent of enantiomeric separation has been examined and separation factors (,) are presented for various groups of structurally related compounds. Chiral recognition models have been suggested to account for the observed separations. These models provide mechanistic insights into the chiral recognition process. Chirality 2010. © 2009 Wiley-Liss, Inc. [source]

Potential of different techniques of preferential crystallization for enantioseparation of racemic compound forming systems

CHIRALITY, Issue 8 2009
Daniel Polenske
Abstract Recently the feasibility of preferential crystallization for enantioseparation of racemic compound forming systems has been demonstrated (Lorenz et al., Application of preferential crystallization to resolve racemic compounds in a hybrid process. Chirality 2006;18:828,840; Polenske et al., Separation of the propranolol hydrochloride enantiomers by preferential crystallization: thermodynamic basis and experimental verification. Cryst Growth Des 2007;7:1628,1634). Here, the development and the potential of an efficient separation process operated via two different techniques of preferential crystallization are studied: (1) seeded isothermal preferential crystallization and (2) auto-seeded polythermal preferential crystallization. Both techniques were investigated in the batch and in the cyclic operation mode. On the example of mandelic acid as a typical racemic compound forming system, it is demonstrated that a cyclic auto-seeded polythermal process is feasible and significantly more efficient than the seeded isothermal one. Chirality, 2009. © 2008 Wiley-Liss, Inc. [source]

Kinetics and mechanism of the oxidation of some ,-hydroxy acids by 2,2,-bipyridinium chlorochromate

INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 4 2002
Vinita Kumbhat
The oxidation of glycolic, lactic, malic, and a few substituted mandelic acids by 2,2,-bipyridinium chlorochromate (BPCC) in dimethylsulphoxide leads to the formation of corresponding oxoacids. The reaction is first order each in BPCC and the hydroxy acids. The reaction is catalyzed by the hydrogen ions. The hydrogen ion dependence has the form: kobs = a + b [H+]. The oxidation of ,-deuteriomandelic acid exhibited a substantial primary kinetic isotope effect (kH/kd = 5.29 at 303 K). Oxidation of p -methylmandelic acid was studied in 19 different organic solvents. The solvent effect has been analyzed by using Kamlet's and Swain's multiparametric equations. A mechanism involving a hydride ion transfer via a chromate ester is proposed. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 248,254, 2002 [source]