Microbial transformation of sesquiterpene lactones by the fungi Cunninghamella echinulata and Rhizopus oryzae

Incubations of the fungi Cunninghamella echinulata and Rhizopus oryzae with the sesquiterpene lactones (+)-costunolide (1), (+)-cnicin (2), (+)-salonitenolide (3), (-)-dehydrocostuslactone (4), (-)-lychnopholide (5), and (-)-eremantholide C (6) were performed. Incubation of 1 with C. echinulata afforded Delta(11(13))-dihydrogenation and Delta(1(10))-epoxidation products (7-10). C. echinulata also hydrolyzed the side chain of 2, and transformed 4 into (+)-11 alpha,13-dihydrodehydrocostuslactone (12), a new natural product. R, oryzae converted 4 into both Delta(11(13))-dihydrogenation and Delta(10(14))-epoxidation products (16 and 17). Both fungi transformed 5 into (-)-16-(1-methyl-1-propenyl)eremantholanolide (13), providing experimental evidence for the biosynthesis of the eremantholide hemiketal unit. Compounds 3 and 6 were not metabolized by either fungus under the test conditions.