Triterpenoid saponin anthranilates from Albizia grandibracteata leaves ingested by primates in Uganda

Three new oleanane-type triterpene saponins (1-3), named grandibracteosides A-C, were isolated from the methanolic extract of leaves of Albizia grandibracteata, a species consumed by primates in the Kibale National Park, Uganda. The structures of the saponins were established using 1D and 2D NMR experiments and mass spectrometry and confirmed by acid and alkaline hydrolysis. The crude extract and the pure compounds showed significant inhibitory activity against KB and MCF7 tumoral cell lines in vitro. The compounds are glycosides of acacic acid acylated by an o-aminobenzoyl unit. This is the first report of such ester saponins in dicotyledonous plants. Studies of the primate diet may provide a useful method for finding naturally occurring compounds of medicinal significance.