Enantioselective bio-reduction of prochiral ketones by the non-conventional yeast Kluyveromyces marxianus

Optically active molecules are important building blocks for the synthesis of many chemicals and biologically active compounds. Among the known catalysts, isolated enzymes have some advantages over conventional methods in the asymmetric synthesis, such as chemo-, regio-, and stereo-selectivity, together with very mild reaction conditions [1]. The asymmetric synthesis accomplished by using whole-cells has also further advantages [2, 3] because all the necessary cofactors and all required substances for their regeneration are present in their natural environment, thus making the catalytic system more efficient [4]. Many research groups have focused their attention on looking for non-conventional yeasts, to study in comparison to the deeply investigated Saccharomyces cerevisiae [5]. For several years our interests focused on using non-conventional yeasts to prepare new EPCs: among these, thermotolerant Kluyveromyces marxianus CBS 6556, not widely investigated in asymmetric synthesis, was preliminarly and successfully used by us for the stereoselective bioreduction of prostereogenic keto-esters to prepare optically active building-blocks in the synthesis of pharmacologically active compounds [6, 7]. These studies allowed also the isolation of an unkown ADH from this yeast [8], able to mediate the highly stereoselective bioreduction of prostereogenic 3-oxo esters. Herein, we report the continuation of such studies, in which the Kluyveromyces marxianus CBS 6556 is used in the bioreduction of various prochiral ketones, with the aim to deepen its substrate specificity, turnover rate, regio- chemo- and enantioselectivity.