Triterpenoids and a sterol from the bark of Entandrophragma angolense

Abstract

Entandrophragma angolense (Welw) C. DC. is a large tree belonging to the family Meliaceae, distributed mainly in Africa. The wood is highly valued for exterior and interior joinery and ship building. The tree is used in folk medicine for the treatment of colds, fever, malaria, stomach pain, peptic ulcers, swellings, earache, arthritic or rheumatic pain and ophthalmia. Limonoids, triterpenoids, steroids and fatty acids have been found in the species. In this study, we report the results of the isolation and structure determination of four compounds from an n-hexane extract of the bark of the species collected in Trang Bom Botanical Garden, Dong Nai Province. Extraction was carried out using a Soxhlet extractor with n-hexane and ethyl acetate, respectively, as the solvents. Recovery of the solvents produced an n-hexane extract and an ethyl acetate extract. Repeated column chromatography over silica gel, RP-18 and Sephadex LH-20 on the n-hexane extract produced four compounds. Analysis of NMR spectra (¹H and ¹³C NMR, DEPT 90, DEPT 135, HSQC and HMBC) and comparison of the spectral data with those in literature revealed that the compounds comprising three triterpenoids, 3-oxoolean-12-en-30-oic acid (1), 3-oxoolean-12-en-29-oic acid (2) and 20-epibryonolic acid (3), together with a steroid, stigmas-4-en-3-one (4). This is the first time that all the compounds have been isolated from this species.