Biosynthesis of illudosin, a fomannosane-type sesquiterpene, by the Basidiomycete Omphalotus nidiformis

Sites of incorporation of C-13-labelled acetates and [1-C-13,2-H-2(3)]acetate into illudosin 1, a fomannosane type sesquiterpene produced by Omphalotus nidiformis, have been determined by C-13 NMR spectroscopy. The biosynthesis of illudosin was as expected, apart from the presence of some labelled species with two deuteriums attached to C-6 in illudosin which is also labelled at C-5 with C-13. This unusual rearrangement was also observed in the co-metabolite illudin M. A mechanism is proposed which involves the formation of a series of carbocations at the active site of the cyclase enzyme that can be reprotonated (or deuterated) non-stereospecifically.