Preparation of enantiomerically enriched aromatic β-hydroxynitriles and halohydrins by ketone reduction with recombinant ketoreductase KRED1-Pglu

A NADPH-dependent benzil reductase (KRED1-Pglu) was used as recombinant enzyme for catalysing the reduction of different functionalised ketones. The reactions were carried out in the presence of a catalytic amount of NADP+and an enzyme-coupled transformation (oxidation of glucose catalysed by glucose dehydrogenase), for regenerating the cofactor and thus driving the reaction to completion. KRED1-Pglu showed remarkable versatility, being able to reduce different β-ketonitriles and α-haloketones at different pHs; notably, depending on the nature of the substrate, KRED1-Pglu can be used for efficient and clean enzymatic reduction, avoiding side-reactions due to the pH of the medium. The reduction generally occurred with high enantioselectivity, allowing the preparation of enantiomerically enriched β-hydroxynitriles and halohydrins in high yields; the stereochemical outcome of the reduction followed in all the cases the so-called Prelog's rule.