Microbial transformations of natural antitumor agents. 23. Conversion of withaferin-A to 12 beta- and 15 beta-hydroxy derivatives of withaferin-A.

Microbial transformation experiments were conducted with the antitumor lactone withaferin-A. Cunninghamella elegans NRRL 1393 transformed withaferin-A (1a) to 15 beta-hydroxywithaferin-A (2a) and 12 beta-hydroxy-withaferin-A (3a). The hydroxylated metabolites were isolated by solvent extraction and were purified by column and thin-layer chromatography. Structures of the hydroxylated metabolites were determined by proton-and carbon-13 NMR, IR and mass spectral analyses, and by the preparation of acylated derivatives. Compounds 2a and 3a inhibited the growth and biochemical functions of in vitro grown P-388 lymphocytic leukemic cells.