Sporidesmins. Part XII. Isolation and structure of sporidesmin G, a naturally-occurring 3,6-epitetrathiopiperazine-2,5-dione

When the tail fractions from chromatograms of sporidesmin E(I; n = 3) were rechromatographed, a new crystalline metabolite of Pithomyces chartarum was isolated with molecular formula C₁₈H₂₀ClN ₃O₆S₄. The new compound, named, sporidesmin G (I; n = 4), gave sporidesmin (I; n = 2) on irradiation or treatment with triphenylphosphine, and sporidesmin D (V) after reduction and methylation. It was shown that the model compound, 1,4-dimethyl-3,6-epidithiopiperazine-2,5- dione, gave the cyclic tetrasulphide on treatment with dihydrogen disulphide. Similarly, sporidesmin and sporidesmin E when treated with dihydrogen disulphide gave the new metabolite.