Naturally occurring compounds related to phenalenone. Part III. The structure of herqueinone and norherqueinone and their relationships with isoherqueinone and isonorherqueinone

Abstract

Herqueinone extracted from the mycelium of P. herquei has been found to be invariably contaminated with isoherqueinone, from which it has so far not been possible to separate it. By means of chemical degradation and spectral interpretation herqueinone has been shown to possess structure (2; R¹= Me, R²= H) and to differ from isoherqueinone only in the configuration of the carbon atom carrying the secondary methyl group in the ether ring. Mild base treatment results in epimerisation of the tertiary asymmetric centre of herqueinone to produce enantio-isoherqueinone, and in those cases where the starting material contains a significant amount of isoherqueinone of natural configuration, the crystalline product obtained is (±)-isoherqueinone. Norherqueinone and isonorherqueinone have been shown to be the de-O-methyl analogues of herqueinone and isoherqueinone respectively.