Asymmetric Reduction of Ethyl (S)-4-chloro-3-hydroxy butanoate in an Aqueous-Organic Solvent Biphasic System Using Dried Baker's Yeast

Abstract

A process of highly stereoselective reduction of ethyl 4-chloro-3-oxobutanoate (ECOB) to ethyl (S)-4-chloro-3-hydroxy butanoate [(S)-ECHB] with Baker's yeast was established. The influence of volumetric phase ratio, substrate concentration, the amount of dried yeast cells and glucose on the yield of ethyl (S)-4-chloro-3-hydroxybutanoate and the enantiomeric excess (e.e.) (S) value were also investigated. A high yield and e.e. of ethyl (S)-4-chloro-3-hydroxybutanoate were observed in a biphasic system composed of phosphate buffer (0.05 mol/L, pH 7.0) and isooctane. Under the optimum conditions (in the water/isooctane biphasic system, Vaq/Vorg 3/1, dried yeast cells 50 g/L, glucose 0.6 mol/L, 30 ºC, pH 7.0, substrate concentration 0.08 mol/L), the yield of ethyl (S)-4-chloro-3-hydroxybutanoate and the e.e. value of (S)-ECHB reached 93.9 % and 91.4 %, respectively, after 24 h reaction.