Biotransformation of 20(S)-protopanaxadiol by Mucor spinosus.

Biotransformation of 20(S)-protopanaxadiol (1) by the fungus Mucor spinosus AS 3.3450 yielded eight metabolites (2-9). On the basis of NMR and MS analyses, the metabolites were identified as 12-oxo-15alpha,27-dihydroxyl-20(S)-protopanaxadiol (2), 12-oxo-7beta,11alpha,28-trihydroxyl-20(S)-protopanaxadiol (3), 12-oxo-7beta,28-dihydroxyl-20(S)-protopanaxadiol (4), 12-oxo-15alpha,29-dihydroxyl-20(S)-protopanaxadiol (5), 12-oxo-7beta,15alpha-dihydroxyl-20(S)-protopanaxadiol (6), 12-oxo-7beta,11beta-dihydroxyl-20(S)-protopanaxadiol (7), 12-oxo-15alpha-hydroxyl-20(S)-protopanaxadiol (8), and 12-oxo-7beta-hydroxyl-20(S)-protopanaxadiol (9), respectively. Among them, 2-5, 7, and 8 are new compounds. These results indicated that M. spinosus could catalyze the specific C-12 dehydrogenation of 20(S)-protopanaxadiol, as well hydroxylation at different positions. These biocatalytic reactions may be difficult for chemical synthesis. The biotransformed products showed weak in vitro cytotoxic activities.