Stereoselective Enzymatic Reduction of Ethyl Secodione : Preparation of a Key Intermediate for the Total Synthesis of Steroids

Ethyl secodione (1) has been enantioselectively reduced using different biocatalysts for the preparation of (13R, 17S)-2a. The recombinant ketoreductase KRED1-Pglu converted the substrate with the highest reaction rate and stereoselectivity (ee > 98%), whereas whole cells of Pichia minuta CBS 1708 showed the highest productivity. Stereoselective reduction of 1 provides the key chiral precursor for the synthesis of a number of hormonal contraceptives (i.e., desogestrel, norgestrel, gestodene).