Asymmetric bioreduction of keto esters by immobilized baker's yeast entrapped in calcium alginate beads in both water and organic/water solvent systems.

Immobilized baker's yeast entrapped in calcium alginate beads, ca 1.5 mm diameter, was used more than 10 times in water and reduced ethyl 3-oxobutanoate and ethyl benzoylformate to the corresponding chiral hydroxy esters in good chemical yields and in high enantioselectivities. The biocatalyst was also successfully used in organic/water solvent systems such as hexane/water and acetonitrile/water, and in other systems, particularly in hexane, converted keto esters into their individual chiral hydroxy esters.