Stereoselective reduction of keto esters with marine micro algae

It was found that α- and β-keto esters were converted to the corresponding hydroxy esters by marine micro algae. Ethyl 2-methyl-3-oxobutanoate was reduced by Nannochloropsis sp. to the anti-hydroxy ester with excellent diastereo- (syn/anti=1:99) and high enantioselectivity (anti >99%, syn 98%). The stereocontrolled reduction of ethyl 3-methyl-2-oxobutanoate was accomplished by Nannochloropsis sp. or Chaetoceros gracilis in the presence of l-lactic acid as an additive.