Phytotoxic compounds produced by Fusarium equiseti. Part 8. Acid catalysed rearrangement of 12,13-epoxytrichothec-9-enes

The acid catalysed rearrangement of 12,13-epoxytrichothec-9-enes to give biologically inactive 10,13-cyclotrichothecane or apotrichothec-9-ene products depends on the substitution pattern of both rings A and C. The former rearrangement is adversely affected by 8α-substitution and by the presence of a 4,15-macrolide ring; the latter rearrangement by 7α- and by 3α-substitution. Compared with the trichothecene, the greater flexibility of the apotrichothecene skeleton is reflected in the range of values for the ring C vicinal coupling constants in the 1H n.m.r. spectra.