Microbial transformations of 6 alpha- and 6 beta-eudesmanolides by Rhizopus nigricans cultures

Microbial transformations of 6 alpha-eudesmanolides and 6 beta-eudesmanolides were accomplished using the hydroxylating fungus Rhizopus nigricans. The eudesmane skeleton was functionalized principally at positions C-1, C-4 and C-8. Hydroxylation yields depended on the configuration of the hydroxyl group at C-3, the methyl group at C-4, and the lactone ring in the substrates. Several metabolites with hydroxylation at C-9 and C-11 were also obtained with 6 alpha-eudesmanolide substrates. An inversion of configuration at C-3 may occur when the substrates have an axial hydroxyl group at this carbon. Hydroxylation at C-4 was observed only when the substrate had a 4 beta-methyl group.