MICROBIAL TRANSFORMATIONS OF THE SESQUITERPENE LACTONE COSTUNOLIDE

The microbial transformation of the sesquiterpene lactone costunolide has been studied. Preliminary screening experiments indicated a large number of fungi were capable of biotransforming costunolide. In preparative-scale fermentations, Aspergillus niger converted costunolide into dihydrocostunolide (5) and into four eudesmanolide derivatives, colartin (2), 11,13- dihydrosantamarine (6), 11,13-dihydroreynosin (7), and tetrahydrovulgarin (8) formed by a sequence in which costunolide was reduced, epoxidized, and then cyclized. Cunninghamella echinulata produced 1β-hydroxyarbusculin A (10) and Fusarium oxysporum produced dihydrocostunolide (5). A proposal of the sequence of events in the conversion of costunolide to the eudesmanolide metabolites is discussed.