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.