Antimicrobial activity of pentacyclic triterpenes isolated from African Combretaceae

Four pentacyclic tritepenes were isolated from Combretum imberbe Engl. & Diels, of which two are novel glycosidic derivatives of 1α,3β,23-trihydroxyolean-12-en-29-oic acid (hydroxyimberbic acid). Terminalia stuhlmannii Engl. & Diels stem bark yielded two glycosides of hydroxyimberbic acid, one of which is reported for the first time. The structures of the isolated compounds were elucidated by spectroscopic methods. Several of the compounds had antibacterial activity, imberbic acid showing particularly potent activity against Mycobacterium fortuitum and Staphylococcus aureus. Imberbic acid and four rhamnosides, three of which are new, have been isolated from two species of Combretaceae. Imberbic acid has potent activity against Mycobacterium fortuitum.