Stereocontrolled Reduction of Alpha-Methyl Beta-Ketoesters by Geotrichum Candidum

The conditions of the reduction of racemic ethyl 2-methyi-3-oxobutanoate by the mould Geotrichum candidum have been investigated in order to produce exclusively the corresponding (2S, 3S) anti hydroxyester. The alteration of the syn/anti hydroxyester ratio previously observed is the result of an interconversion equilibrium involving the oxoester. The syn ester formation is inhibited by ageing the biomass in water before use, or by effecting the reduction in the presence of sodium chloride. Optimized conditions are described allowing the production of the anti ester in high yield and high optical purity.