Biosynthesis of illudosin, a fomannosane-type sesquiterpene, by the Basidiomycete Omphalotus nidiformis
Abstract
Sites of incorporation of 13C-labelled acetates and [1-13C,2-2H3]acetate into illudosin 1, a fomannosane type sesquiterpene produced by Omphalotus nidiformis, have been determined by 13C 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 13C. 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.