Novel microbial transformation of resibufogenin by Absidia coerules.

Resibufogenin is one of the major active components of the Chinese medicine ChanSu. In this paper, microbial transformation of resibufogenin by Absidia coerules AS 3.3382 was investigated and five metabolites were isolated and identified as 5beta-hydroxy-resibufogenin (2), 3-epi-resibufogenin (3), 3alpha-hydroxy-15-oxo-14alphaH-bufa-20, 22-dienolide (4), 3alpha,14alpha,15beta-trihydroxy-bufa-20, 22-dienolide (5) and 3-epi-15beta-hydroxy-bufalin (6). Among them, 4-6 are novel compounds, and compound 3 is a major transformed product. The cytotoxicities of the compounds against Bel-7402 and Hela cells were investigated, and our result suggested that 14,15-OH configuration was directly related to the cytotoxicities of bufadienolides.