Novel Oxidation Products of Two Sponge-Derived Sesquiterpenes, 4α-Formamedo- and 4α-Isocyanogorgon-11-Ene

Oxidation of two sesquiterpenoids, 4 alpha-formamido- and 4 alpha-isocyanogorgon-11-ene (1 and 2), isolated from the sponge Axinyssa terpnis, with m-chloroperbenzoic acid yielded unexpected cyclization products 3 and 4, respectively, instead of epoxides. Their structures were determined from spectral data and X-ray analysis. Possible mechanisms are proposed.