Carbon-13 nuclear magnetic resonance structural and biosynthetic studies on deoxyherqueinone and herqueichrysin, phenalenone metabolites of Penicillium herquei

Abstract

A detailed analysis of the ¹³C–¹H couplings observed in the fully ¹H-coupled ¹³C n.m.r. spectrum of deoxyherqueinone diacetate allow its structure to be defined as (3) and a full assignment of the ¹³C n.m.r. spectrum to be made. The structure of herqueichrysin triacetate (8) is established by analysis of ¹³C–¹H couplings in the fully ¹H-coupled, natural abundance ¹³C n.m.r. spectrum, and ¹³C–¹³C couplings in the [1,2-¹³C₂] acetate enriched ¹³C n.m.r. spectrum. Further chemical and spectral studies allow structure (9) to be proposed for herqueichrysin. Incorporations of sodium [1-¹³C]-, [2-¹³C]-, and [1,2-¹³C₂]-acetate, and diethyl [2-¹³C]malonate indicate formation of the phenalenone ring system via a specific folding of a single heptaketide chain.