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

The stereoselectivity of baker's yeast in the reduction of ethyl 3-oxopenta noate was shifted towards the corresponding (R)-hydroxy ester by sugar, hea t treatment and allyl alcohol. The highest enantiomeric excesses obtained w ith baker's yeast with a good reduction capacity, 92-97%, were achieved by combining allyl alcohol and sugar; heat treatment did not increase the ster eoselectivity further. With the use of this technique, ethyl (R)-3-hydroxyh exanoate, >99% ee, and ethyl (S)-4-chloro-3-hydroxybutanoate, 82-90% ee, we re produced from the corresponding esters, and for the first time an excess of the (R)-enantiomer of ethyl 3-hydroxybutanoate was obtained with ordina ry baker's yeast. (C) 1999 Elsevier Science Ltd. All rights reserved.