Biotransformation of two stemodane diterpenes by Mucor plumbeus

The microbiological transformation of 13α,17-dihydroxy-stemodane () by the fungus Mucor plumbeus afforded 13α,17,19-trihydroxy-stemodane (), 3β,13α,17-trihydroxy-stemodane (), 3-oxo-13α,17-dihydroxy-stemodane (), 7α,13α,17,19-tetrahydroxy-stemodane (), 3β,11α,13α,17-tetrahydroxy-stemodane (), 3β,7α,13α,17-tetrahydroxy-stemodane (), 3β,8β,13α,17-tetrahydroxy-stemodane (), 2α,13α,17-trihydroxy-stemodane (), 2α,13α,17,19-tetrahydroxy-stemodane (), 2α,3β,13α,17-tetrahydroxy-stemodane () and 3β,11β,13α,17-tetrahydroxy-stemodane (), whilst the incubation of 13α,14-dihydroxy-stemodane () gave 3β,13α,14-trihydroxy-stemodane (), 2α,13α,14-trihydroxy-stemodane () and 13α,14,19-trihydroxy-stemodane (). Preference for hydroxylations of ring A at C-2(α), C-3(β) and C-19 were observed in both incubations. An interesting rearrangement of 13α,14α-dihydroxy-stemodanes to 14-oxo derivatives with an unusual carbon framework has been observed under acetylation conditions. We have named this skeleton prestemodane, which, as a hydrocarbon ion, had been postulated as a biogenetic precursor of stemodane.