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 i mportant chiral starting material, by baker's yeast-mediated bioreduct ion of ethyl acetoacetate was investigated. In preliminary studies, we found that the procedure using ethanol as an energy source for the bi oreduction, which we developed recently, was better than that using ca rbohydrate 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-b atch operation to the yeast-mediated bioreduction using ethanol as an energy source. In this method, the concentrations of ethyl acetoacetat e and ethanol were maintained during the reaction at less than 1 mM an d 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 o n the use of ethanol as the energy source was devised for baker's yeas t-mediated bioreduction.