Structure of Flavoglaucin and Auroglaucin

FLAVOGLAUCIN, C19H28O3, m.p. 109–110°, and auroglaucin, C19H22O3, m.p. 152–153°, are two pigments, yellow and red respectively, isolated by Raistrick and his collaborators1 from Aspergillus glaucus, and later found by A. Quilico and L. Panizzi2 in the mycelium of Aspergillus echinulatus, where they are accompanied by a neutral colourless substance, C28H39O2N3 (echinulin)3. On the basis of detailed chemical investigations by Robinson, Raistrick, Todd, Cruickshank and others4–6, structures like () and () were ascribed to the pigments, the position and the structure of the chain (or chains) present in the residuo C5H10 (which contains a double bond) still being undetermined. The existence of the group (n)C7H15CO was inferred from the fact that n-octoic acid was obtained from () on oxidation with hydrogen peroxide and sodium hydroxide (by Dakin's reaction); the easy formation of a Schiff's base and phenylhydrazone derivatives both from () and () points to the presence of a free ortho position ciose to the carbonyl chain. The quinol structure was demonstrated by the absorption spectrum in the ultra-violet of tetrahydroflavoglaucin () dimethyl ether. As dihydroflavoglaucin, C19H30O3, proved to be identical with octohydroauroglaucin, the two pigments can differ only by the existence of three double bonds in the C8 side-chain, as formulæ () and () indicate.