Asymmetric Hydrogenation of α,β-Unsaturated Carboxylic Acids Catalyzed by Ruthenium(II) Complexes of Spirobifluorene Diphosphine (SFDP) Ligands
作者:Xu Cheng、Jian-Hua Xie、Sheng Li、Qi-Lin Zhou
DOI:10.1002/adsc.200606065
日期:2006.7
The ruthenium diacetate complexes ligated by chiral spirobifluorene diphosphines (SFDP) were very effective catalysts for the asymmetric hydrogenation of tiglic acid derivatives and α-methylcinnamic acid derivatives with high activities and excellent enantioselectivities (up to 98 % ee). The α-aryloxybutenoic acids can also be hydrogenated by these catalysts to provide the corresponding saturated α-aryloxybutanoic
Enantioselective Hydrolysis of Some 2-Aryloxyalkanoic Acid Methyl Esters and Isosteric Analogues Using a Penicillin G Acylase-Based HPLC Monolithic Silica Column
A technique based on liquid chromatography has been developed to facilitate studies of enantioselectivity in penicillin G acylase (PGA)-catalyzed hydrolysis of some 2-aryloxyalkanoic acid methyl esters and isosteric analogues. PGA was covalently immobilized on an aminopropyl monolithic silica support to create an immobilized HPLC-enzyme reactor. Two sets of experimental data were drawn to calculate the enantioselectivity (E) of the kinetically controlled enantiomer-differentiating reaction, the degree of substrate conversion and the enantiomeric excess of the product. The developed enzymatic reactor was coupled through a switching valve to an achiral analytical column for separation and quantitation of the hydrolysis products. The enantiomeric excess was determined off-line on a PGA-chiral stationary phase. In this way, highly precise E values were determined. A computational study related to the hydrolysis of the considered racemic esters was also carried out in order to unambiguously clarify both the substrate specificity and the enantioselectivity displayed by PGA.
This paper describes a simple procedure for the resolution of racemic alpha-monoalkyl alpha-aryloxyacetic acids, using the chromatographic separation of their covalent derivatives. (R)-Ethyl mandelate, (R)-pantolactone and (S)-4-(1-methylethyl)-2-oxazolidinone are the resolving agents involved in the formation of equimolecular diastereomeric mixtures of esters or imides. Chromatograpkic resolutions were performed by means of gas chromatography (GC), thin-layer chromatography (TLC) and flash chromatography. Successive hydrolysis of separated diastereomers provided optically pure aryloxyacetic acids. (C) 1998 Elsevier Science S.A.
Noya; Ferorelli; Franchini, Il Farmaco, 1996, vol. 51, # 4, p. 293 - 296