Epikatonic acid from Austroplenckia populnea : structure elucidation by nmr spectroscopy and x-ray crystallography.

Abstract

From the chloroform extract of Austroplenckia populnea, epikatonic acid, friedelin, populnonic acid, abruslactone A, salaspermic acid and 22b-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 3b-hydroxyolean- 12-en-29-oic acid, which unambiguously established the configuration of the hydroxyl group at C-3 as 3b-OH and the carboxyl group at C-20 as 20a-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.