LARGE-SCALE PREPARATION OF (S)-ETHYL 3-HYDROXYBUTANOATE WITH A HIGH ENANTIOMERIC EXCESS THROUGH BAKERS YEAST-MEDIATED BIOREDUCTION

Large-scale preparation of (S)-ethyl 3-hydroxybutanoate (E 3-HB), an important chiral starting material, by baker's yeast-mediated bioreduction of ethyl acetoacetate was investigated. In preliminary studies, we found that the procedure using ethanol as an energy source for the bioreduction, which we developed recently, was better than that using carbohydrate for large-scale preparation, as the cells were inactivated faster with carbohydrate than ethanol. Both the yield and the optical purity of the product were considerably improved by applying the fed-batch operation to the yeast-mediated bioreduction using ethanol as an energy source. In this method, the concentrations of ethyl acetoacetate and ethanol were maintained during the reaction at less than 1 mM and about 200 mM, respectively. Finally, large-scale preparation of (S)-E 3-HB was effectively performed using a bubble-column reactor with 10 l of medium, and the final reaction medium contained 6%(w/w) (S)-E 3-HB with >99% enantiomeric excess. Thus, a new scaled-up method based on the use of ethanol as the energy source was devised for baker's yeast-mediated bioreduction.