Isolation and synthesis of a dimeric dihydrochalcone from Agapanthus africanus

A new dimeric dihydrochalcone, rel-(1beta,2alpha)-di-(2,4-dihydroxybenzoyl)-rel-(3beta,4alpha)-di-(4-hydroxyphenyl)-cyclobutane, accompanied by its apparent precursor, the known chalcone isoliquiritigenin, have been isolated from the roots of Agapanthus africanus (Liliaceae). The structure is based on spectroscopic methods including extensive NMR analyses, mass spectrometry and circular dichroism. Conclusions regarding the structure and relative configuration are supported by synthesis of the dimeric dihydrochalcone via a pericyclic [(pi)2s + (pi)2s] photocyclo-addition of the corresponding chalcone and consideration of the molecular symmetry involved.