Patent ID: 8227208

Claim:
A process for the enantioselective enzymatic reduction of an oxosteroid compound to a hydroxysteroid compound, the process comprising: providing an oxosteroid compound having the following steroid structure (ABCD), wherein the ring of the steroid structure (ABCD) includes one or several heteroatoms, one or several double bonds and/or one aromatic component and has at least one oxo group at positions 3, 7, 11, 12 or 17 in the steroid structure or in the α-position at any carbon moiety attached to the steroid structure, reducing the oxosteroid compound with a hydroxysteroid dehydrogenase in the presence of a cofactor NADH or NADPH, characterized in that: (a) the oxosteroid compound is provided in the reaction at a concentration of 50 g/L, (b) the oxidized cofactor NAD or NADP formed by the hydroxysteroid dehydrogenase is regenerated continuously by oxidation of a secondary alcohol of formula R X R Y CHOH, wherein R X , R Y , independently represent a branched or unbranched C1-C8-alkyl and C total ≧3, or by oxidation of a C4-C6 cycloalkanol, and c) an additional oxidoreductase/alcohol dehydrogenase is used for the oxidation of the secondary alcohol of formula R x R y CHOH or of the cycloalkanol, respectively.