Asymmetric reduction of ketones via whole cell bioconversions and transferhydrogenation: complementary approaches

Prochiral aryl and dialkyl ketones were enantioselectively recduced to the corresponding alcohols using whole cells of the white-rot fungus Merulius t remellosus ono91 as a biocatalytic reduction system and ruthenium(II)amino alcohol and iridium(I)-amino sulfide complexes as metal catalysts in asymme tric transfer hydrogenation. Comparison of the results showed that the corr esponding chiral alcohols could be obtained with moderate to high enantiose lectivities (e.e.s of up to 98%). The biocatalytic and transfer hydrogenati on approaches appear to he complementary. The biocatalytic approach is the most suitable for the enantioselective reduction of chloro-substituted (ary l) ketones, whereas in the reduction of alpha,beta -unsaturated compounds e xcellent results were obtained using the catalytic hydrogenation protocol. (C) 2001 Elsevier Science Ltd. All rights reserved.