Baker's yeast: improving the d-stereoselectivity in reduction of 3-oxo esters

Abstract The stereoselectivity of baker's yeast in the reduction of ethyl 3-oxopentanoate was shifted towards the corresponding ( R )-hydroxy ester by sugar, heat treatment and allyl alcohol. The highest enantiomeric excesses obtained with baker's yeast with a good reduction capacity, 92–97%, were achieved by combining allyl alcohol and sugar; heat treatment did not increase the stereoselectivity further. With the use of this technique, ethyl ( R )-3-hydroxyhexanoate, >99% ee , and ethyl ( S )-4-chloro-3-hydroxybutanoate, 82–90% ee , were produced from the corresponding esters, and for the first time an excess of the ( R )-enantiomer of ethyl 3-hydroxybutanoate was obtained with ordinary baker's yeast.