Stereocontrolled reduction of alpha- and beta-keto esters with micro greenalgae, Chlorella strains

The stereocontrolled reduction of alpha- and beta -keto esters using micro green algae was accomplished by a combination of the cultivation method and the introduction of an additive. The reduction of ethyl pyruvate and ethyl benzoylformate by the photoautotrophically cultivated Chlorella sorokinian a gave the corresponding alcohol in high e.e. (>99% e.e. (S) and >99% e.e. (R), respectively). In the presence of glucose as an additive, the reductio n of ethyl 3-methyl-2-oxobutanoate by the heterotrophically cultivated C. s orokiniana afforded the corresponding (R)-alcohol. On the other hand, the r eduction in the presence of ethyl propionate gave the (S)-alcohol. Ethyl 2- methyl-3-oxobutanoate was reduced in the presence of glycerol by the photoa utotrophically cultivated C. sorokiniana or the heterotrophically cultivate d C. sorokiniana to the corresponding syn-(2R,3S)-hydroxy ester with high d iastereo- and enantiomeric excess (e.e.). Some additives altered the stereo chemical course in the reduction of alpha- and beta -keto esters.