Stereoselective reduction of aromatic ketones by a new ketoreductase from Pichia glucozyma

The asymmetric reduction of ketones is one of the most important, practical reactions for producing chiral alcohols, which can be transformed into various functionalities, for the synthesis of many industrially important chemicals such as pharmaceuticals products. Bioreduction catalysed by NADPH- dependent benzil reductase (KRED1-Pglu) from Pichia glucozyma provides an attractive approach to selectively reducing a broad range of aromatic ketones. After protein identification, characterisation and over-expression in E. coli, we have established a procedure for the purification and storage of KRED1-Pglu. After optimisation of the reaction parameters, a thorough study of the substrate range of KRED1-Pglu was conducted. In contrast to most other known ketoreductase, KRED1-Pglu prefers space demading substrates which are often converted with high stereoselectivity. The observed activities and enantioselectivity, cannot be explained by simply assuming a model of the active site with two hydrophobic pockets differing size, where the large pocket accomodates the phenyl moiety while the small one determines whether the other substituent can be properly accomodated determining rates and enantioselectivitiy. Hence, a molecular modelling study was carried out for understanding the structura determinants involved in the stereorecognition experimentally observed and predictable on the basis of steric properties of the substrates.