Epikatonic acid from Austroplenckia populnea: Structure elucidation by 2D NMR spectroscopy and X-ray crystallography

Abstract

From the chloroform extract of Austroplenckia populnea, epikatonic acid, friedelin, populnonic acid, abruslactone A, salaspermic acid and 22β-epi-maytenfolic acid were isolated. The structure and stereochemistry of epikatonic acid were established by two-dimensional NMR spectroscopic techniques (HMQC, HMBC and NOESY) and later confirmed by single crystal X-ray diffraction as 3β-hydroxyolean-12-en-29-oic acid, which unambiguously established the configuration of the hydroxyl group at C-3 as 3β-OH and the carboxyl group at C-20 as 20α-COOH. The crystal structure shows two independent molecules in the asymmetric unit. The crystal packing is stabilized by four O-H⋯O intermolecular hydrogen bonds, which give rise to infinite double chains along the c axis. Copyright © 2002 John Wiley & Sons, Ltd.