Sporidesmins. Part XIII. Ovine III-thrift in Nova Scotia. Part III. The characterisation of chetomin a toxic metabolite of Chaetomium cochliodes and Chaetomium globosum

Chetomin, one of the antibiotic metabolites of Chaetomium cochliodes and C. globosum has been isolated as an amorphous, glass-like solid. Elemental analysis of chetomin, its diacetate, and its bistrimethylsilyl ether, mass spectroscopy of its tetrathiomethyl derivative, and n.m.r. spectroscopy indicate the molecular formula to be C₃₁H₃₀N₆O ₆S₄. The formation of a tetra-S-methyl derivative and a bismonosulphide indicated the presence of two epidithiodioxopiperazine ring systems like those present in chaetocin, a metabolite of C. minutum, a conclusion supported by the close similarity of the c.d. of the two metabolites. The u.v. spectrum of chetomin was the same as that of echinulin. These facts, and an interpretation of the n.m.r. spectra of chetomin and its derivatives, lead us to believe that the molecule contains an indole, an indoline, and two epidithiodioxopiperazine systems. A biogenetically plausible assembly of these structural features is shown [formula (XIII)], but other formulae are possible.