Biotransformation of the diterpene ribenone by Mucor plumbeus

The microbiological transformation of the diterpene ribenone (3-oxo-ent-13-epi-manoyl oxide) by the fungus Mucor plumbeus has been studied. Epoxidation of the vinyl group constitutes the main reaction and there exists a preference for hydroxylation at C-1(α), C-6(α or β) and C-12(β) and, to a lesser degree, at C-7(α) and C-11(β). Other observed reactions were the reduction of the 3-oxo group to a 3β-alcohol and the formation of metabolites with a 1,2-double bond. In this work the stereochemistry at C-14 of the diterpenes excoecarins A, B and C has been revised on the basis of X-ray data.