Isolation and structure of vaalens-1, -3, -5, and -7. Sesquiterpene esters of Catha transvaalensis Codd (Celastraceae): X-ray molecular structure of vaalens-5

Abstract

Four sesquiterpene esters are isolated from Catha transvaalensis, a rare relative of Catha edulis which is the source of the Middle Eastern drug Khat. The structure of one of these esters, vaalens-5, including its absolute configuration, is unequivocally determined by single-crystal X-ray analysis, correcting an earlier proposal: the lattice contains two distinct conformers, distortions being caused by hydrogen bonding. Vaalens-1, -3, and -7 are also assigned structures. Chemotaxonomic relationships between the two species are not close.