CHEMISTRY OF HOP CONSTITUENTS: XXII. PROTON MAGNETIC RESONANCE SPECTROSCOPY OFISOHUMULONE A

Abstract

Knowledge of the structure of isohumulone A is reviewed. Its proton magnetic resonance spectrum has been interpreted with the aid of the spectra of the two isomers of humulinic acid. It is concluded that isohumulone A consists of a mixture of stereoisomers, trans and cis with respect to the 4-isohexenoyl and 5-isopentenyl chains, in the ratio of about 60% trans (i.e., with the stereochemistry of humulinic acid B) to 40% cis (i.e., humulinic acid A stereochemistry). Humulone has been isomerized into isohumulone A in deuterium oxide, and unlabelled isohumulone A has been hydrolysed into humulinic acid A using sodium deuteroxide in deuterium oxide. The modified spectra assisted some of the assignments.