Pichia Glucozyma: a powerful biocatalyst for enantioselective reduction of ketones

The asymmetric reduction of prochiral ketones using isolated or cell-bound ketoreductases is a well-recognised method for the preparation of chiral alcohols. The major drawback encountered with enzymatic reduction using isolated enzymes is the necessity for cofactor recycling, which can be circumvented by two-enzyme or one-enzyme recycling methodologies. Whole cells exhibit as a major advantage that cofactors are already present and can be intrinsically recycled via the oxidation of a second substrate. Beside the easily available Saccharomyces cerevisiae, other microbial species have been widely employed for asymmetric reductions or more generally as sources for new selective ketoreductases, since there is still a need for new biocatalysts able to perform stereoselective reductions with different or ameliorated chemo-, regio- and stereoselectivity. Non-conventional yeasts are plentiful sources of different carbonyl reductases and during our past works on enantioselective carbonyl reduction we have found that whole cells of the yeast Pichia glucozyma CBS 5766 (now reclassified as Ogataea glucozyma) catalysed the stereoselective reduction of different ketones, often showing remarkable results in terms of activity and stereoselectivity. In this work, we have studied the potential of whole cells of Pichia glucozyma CBS 5766 for the reduction of various ketones with cells grown under optimised conditions. Enantioselective reduction of aromatic ketoesters and preparation of intermediates for chemo-enzymatic synthesis of steroids and prostaglandins are among the biotransformations studied. Purification and characterization of ketoreductases from P. glucozyma are under study.