Structure of Flavoglaucin and Auroglaucin

Abstract

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 others^4–6, 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.