Improved production of ethyl-( R )-2-hydroxy-4-phenylbutyrate with pretreated Saccharomyces cerevisiae in water/organic solvent two-liquid phase systems
AbstractBaker's yeast pretreated with ॅ-phenacyl chloride was employed to improve the enantioselectivity of the asymmetric reduction of ethyl-2-oxo-4-phenylbutyrate (EOPB) to ethyl-( R )-2-hydroxy-4-phenylbutyrate (( R )-EHPB) and maintain a high activity of the yeast. A water/organic solvent two-liquid phase system was also introduced to overcome the strong substrate and product inhibition of the enzyme; the highest catalytic activity and enantioselectivity were obtained in a water/benzene two-liquid phase system. When the reduction was catalyzed with pretreated yeast (300 mg mL −1 buffer) in the water/benzene two-liquid phase system ( V aq / V ben =20:40), 41.9% molar conversion of EOPB and 87.5% e.e. of ( R )-EHPB were obtained in 48 h, using pH 8.0 phosphate buffer with 1.5% (v/v) of ethanol added as a co-substrate at 30°C, even with an initial EOPB concentration of 400 mM and a final EHPB concentration as high as 167.7 mM.