Microbial Hydroxylation of Pregnenolone Derivatives

Pregnenolone (1) and pregnenolone acetate (2) were incubated with the fungi Cunninghamella elegans, Rhizopus stolonifer and Gibberella fujikuroi. Incubation of 1 with C. elegans yielded metabolites, 3β,7β,11α-trihydroxypreg-5-en-20-one (3), 3β,6α,11α,12β,15β-pentahydroxypreg-4-en-20-one (4) and 3β,6β,11α-trihydroxypreg-4-en-20-one (5), while incubation with G. fujikuroi yielded two known metabolites, 3β,7β-dihydroxypregn-5-en-20-one (6) and 6β,15β-dihydroxypreg-4-ene-3,20-dione (7). Metabolites 4 and 5 were found to be new. Fermentation of 2 by C. elegans yielded four known oxidative metabolites, 1, androsta-1,4-diene-3,17-dione (8), 6β,15β-dihydroxyandrost-4-ene-3,17-dione (9) and 11α,15β-dihydroxypreg-4-ene-3,20-dione (10). Fermentation of 2 with R. stolonifer yielded two known metabolites, 11α-hydroxypreg-4-ene-3,20-dione (11) and 7. Compounds 1—11 were screened for their cholinesterase inhibitory activity in a mechanism-based assay.