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 C18H20ClN3O6S4. 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.
The structure of sporidesmin E suggests that it is biosynthesised from sporidesmin by a sulphurising enzyme analogous to a peroxidase. Accordingly, the reaction of dihydrogen disulphide with sporidesmin, dehydrogliotoxin, and other disulphides, has been studied. Polysulphides were obtained in all cases, but the reaction of dibenzyl disulphide with dihydrogen disulphide was slow. By contrast phenylmethanethiol reacted smoothly with the reagent to give di-, tri-, tetra-, and penta-sulphides, and this oxidation appears to be general. The epitrithiadioxopiperazines were light-sensitive and were converted photolytically into equimolecular mixtures of di-, and tetra-sulphides. By use of 35S-labelled polysulphides it was shown that the photolysed sulphur was that inserted by the dihydrogen disulphide.
The isolation, mass spectral fragmentation, and 100 Mc./sec. nuclear magnetic resonance spectrum of the hexaacetate of 2-O-α-D-galactopyranosylglycerol, the major methanol soluble constituent of the red seaweed Laurencia pinnatifida, is described.
The structure of the polyacetylenic keto-aldehyde {H2CCH·CO·[CC]2·CH2·CH[graphic omitted]CH·[CH2]7·CHO} has been determined. It is the first C18 polyacetylene to be isolated from a plant (Pastinaca sativa L.) of the main polyacetylene-producing families. Its occurrence almost certainly establishes the derivation of the C17 falcarinone and related compounds and is in harmony with Bu'Lock's hypothesis for the biogenesis of the natural acetylenes.
