7.10 Reduction: Asymmetric Biocatalytic Reduction of Ketones

Abstract

The use of enzymes as catalysts in enantioselective ketone reduction has gained broad synthetic interest in organic chemistry since this biocatalytic methodology was found to be a versatile, robust, efficient, and industrially feasible synthetic approach toward enantiomerically pure alcohols. In such processes, which are based on the use of isolated enzymes, immobilized enzymes, and recombinant whole-cell catalysts, respectively, different types of cofactor regenerations based in particular on substrate- and enzyme-coupled methods have been successfully applied. The advantages of these types of alcohol dehydrogenase (ADH)-catalyzed ketone reductions are not only the well-known excellent enantio-, diastereo-, and regioselectivities of enzymes but also the high volumetric productivities and excellent substrate loadings that are tolerated by many (recombinant) biocatalyst systems. With respect to the search for suitable ADHs, a broad range of well-established screening tools have been developed. In addition, numerous recombinant ADHs are already available, and the known ADHs show a broad, often complementary substrate spectrum. Furthermore, biocatalytic ketone reductions have also demonstrated their suitability to be combined with other enzymatic or ‘classic’ chemical or chemocatalytic reaction steps toward chemoenzymatic one-pot multistep processes.