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

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-hydroxy-olean-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.