Asymmetric Carbonyl Reductions with Microbial Ketoreductases

The biocatalytic reduction of β‐keto esters and some aromatic ketones in the presence of a variety of ketoreductases from different microbial origins was investigated. The prochiral selectivity was generally high and both product enantiomers could be obtained by a proper choice of enzyme. Aromatic ketones reacted slower than the esters but the prochiral selectivity was often high. The organic cosolvent tolerance of these enzymes was rather variable but useful activity could be maintained in a number of cases. Reduction of the oxidized cofactors NAD and NADP, employing 2‐propanol as a sacrificial reductant, was catalyzed by the ketoreductases from Rhodococcus erythropolis and Lactobacillus kefir, respectively.