STEREOSELECTIVE REDUCTION OF 2 ZERANOLE PRECURSORS BY BAKERS-YEAST

Two macrocyclic keto-lactones, zeralenone (1) and zeralanone (2), are reduced by fresh Bakers' yeast at various substrate-to-cell ratios and pH values and under both aerobic and anaerobic conditions. Two substrates are reduced with opposite diastereoselectivity, resulting in alpha/beta-diastereomers 3/4 and 5/6, respectively. Zeralenone (1) produces 3/4 at ratios of approximately 1:3-4 and 6%-10% total yield (as determined by HPLC), while zeralanone (2) produces 5/6 at approximately 2:1 ratio and 15%-25% yield. The highest conversion (ca. 28%) was achieved with zeralanone (2) at pH 7.5-8, under aerobic conditions. The opposite diastereoselectivity for reduction of zeralenone (1) and zeralanone (2) is ascribed to different conformations of the macrocyclic ring in solution.