Microbial transformation of 20(S)-protopanaxadiol by Absidia corymbifera. Cytotoxic activity of the metabolites against human prostate cancer cells

Biotransformation of 20(S)-protopanaxadiol (1) by the fungus Absidia corymbifera AS 3.3387 yielded five metabolites (2-6). On the basis of spectroscopic data analyses, the metabolites were identified as 26-hydroxyl-20(S)-protopanaxadiol (2), 23, 24-en-25-hydroxyl-20(S)-protopanaxadiol (3), 25-hydroxyl-20(S)-protopanaxadiol (4), 7β-hydroxyl-20(S)-protopanaxatriol (5), and 7-oxo-20(S)-protopanaxatriol (6), respectively. Among them, 5 and 6 are new compounds. These results indicated that A. corymbifera AS 3.3387 could catalyze the side-chain oxidation-reduction, 7β hydroxylation, and the specific C-7 dehydrogenation of derivatives of 20(S)-protopanaxadiol. The metabolites 2, 5, and 6 showed the more potent inhibitory effects against DU-145 and PC-3 cell lines than the substrate.