Abstract: The asymmetric reduction of ethyl 4-chloro-3-oxobutanoate (COBE) to optically active ethyl 4-chloro-3-hydroxybutanoate (CHBE) directly catalyzed by yeast fermentation broth and the influence of chiral additives and reaction conditions on this reaction were studied. The concentrations of COBE and (S)-CHBE, and the optical purity of the product were determined by gas chromatography and high-performance liquid chromatography with a Chiralcel OB column, respectively. In the yeast fermentation broth without any chiral additive, the substrate was decomposed and the pH value of the reaction mixture decreased sharply. When β-cyclodextrin was used as the chiral additive, the yield and enantiomeric excess of (S)-CHBE reached as high as 76% and 92%, respectively. Under specified conditions, high β-cyclodextrin concentration favored (S)-CHBE formation. The optimum reaction conditions are 29～31 ℃, pH 7.2, and yeast cultivation time of 16～18 h.

Key words: yeast, fermentation broth, ethyl 4-chloro-3-oxobutanoate, asymmetric reduction, ethyl 4-chloro-3-hydroxybutanoate, β-cyclodextrin