Pergamon 0031-9422(95)00428-9 Phytochemistry, Vol. 40, No. 4, pp. 1311 1312, 1995 Copyright © 1995 Elsevier Science Ltd Printed in Great Britain. All rights reserved 0031-9422/95 $9.50 + 0.00 URSENE CARBOXYLIC ACIDS OF UNCARIA ELLIPTICA THUSHARA K. K. DIYABALANAGE, G. PERCY WANNIGAMA,* ARUNA WEERASURIYA,t LALITH JAYASINGHE~ a PETA SIMMONDS§ Department of Chemistry, University of Peradeniya, Sri Lanka; tRoyal Botanic Gardena, Peradeniya, Sri Lank Fundamental Studies, Kandy, Sri Lanka; §Research School of Chemistry, Australian National University, Canberra (Received 2 February 1995) Key Word Index--Uncaria elliptica; Rubiaceae; triterpenes; uncaric acid. Abstract--The structures of three triterpenoid acids isolated from Uncaria elliptica have been revised following a spectroscopic analysis of the major acid, uncaric acid. I N T R O D U C T I O N Uncaria elliptica R. Br. ex G. Don is a woody climber of the family Rubiaceae, growing mainly in the wet lowland forests of Sri Lanka. It is the only species of Uncaria to be found in the island. Plants described as U. thwaitesii are now classified as U. elliptica. In an earlier investigation, the plant, collected inthe lower montane zone near Kandy and described as U. thwaitesii, was examined for terpenoids. Three ursene carboxylic acids, named uncaric acid, diketouncaric acid and diacetyluncaric acid, were isolated [1]. Their structures were established by spectro- scopic methods as well as chemical interrelation. The alkaloids of the same sample of U. elliptica have also been investigated [2]. The present investigation was undertaken primarily because the attachment of the carboxyl group to C-20 in the three ursene carboxylic acids appeared biogeneti- cally unusual. Moreover, alternative structures with a CH3CH(CO2H) group attached to a five membered E- ring could not be excluded from the available spectro- scopic data. 19ct-Hydroxylated ursenes have been isolated from U. florida [3] and U. tomentosa [4]. Common to both species is an acid, identified as 3fl,6fl,19~t-trihydroxyurs- 12-en-28-oic acid (1). On the basis of 1H and '3C NMR spectroscopy, particularly connectivities obtained from two-dimensional ~H-1H and 1n-t3C correlation methods, the structure of uncaric acid has been revised as 1. R E S U L T S A N D D I S C U S S I O N The plant material for the present investigation was collected in the wet lowland forest zone. The woody part *Author to whom correspondence should be addressed. HO , ' u HO~,! =._ J OH ° ~CO2H was extracted successively with hot petrol and acetone, and the alkaloidal matter was removed from each extract by an acid wash. Chromatography of the petrol extract on silica gel gave sitosteroi in 0.016% yield along with traces of diketouncaric acid and diacetyluncaric acid. The identity of these acids was established by TLC com- parison with specimens obtained by oxidation and acetylation, respectively, of uncaric acid. Traces of ursolic acid were probably present in the petrol extract, but its presencecould not be establishedon TLC evidence alone. Chromatography of the acetone extract on silica gel gave sitosterol and uncaric acid in yields of 0.001 and 0.003%, respectively. Neither diketouncaric acid nor di- acetyluncaric acid were present in the acetone extract. It is noteworthy that the triterpenoid composition of the same Uncaria species collected at two sites differed con- siderably, indicating that these plants were probably eco- types/varieties of the same species. 1311