Stereocontrolled reduction of α-keto esters with thermophilic actinomycete, Streptomyces thermocyaneoviolaceus IFO 14271

The reduction of aliphatic and aromatic α-keto esters was carried out using a thermophilic actinomycete, Streptomyces thermocyaneoviolaceus IFO 14271, as a biocatalyst. Ethyl 3-methyl-2-oxobutanoate, methyl benzoylformate, and ethyl benzoylformate were reduced to the corresponding (R)-alcohols with >98% enantiomeric excess (ee) at 37°C, while the reduction in the presence of glutamic acid gave the (S)-hydroxy esters in excellent ee (>99%). Ethyl 2-oxopropanoate and ethyl 2-oxobutanoate were also reduced to the corresponding (S)-alcohols with >99% ee in the presence of an amino acid such as asparagine or aspartic acid.