A New Saponin with Anti-HIV-1 Protease Activity from Acacia pennata

We investigated the phytochemicals from an ethanol extract of Acacia pennata (L.) Willd stems, a Vietnam medicinal plant, which led to the isolation of a new saponin termed 21 beta-O-[(2E)-6-hydroxyl-2,6-dimethy1-2,7-octadienoyl] pitheduloside G (1), as well as pitheduloside G (2), a known saponin. The structures of compounds 1 and 2 were elucidated via spectroscopy and compared with those reported in the literature. The isolates (1 and 2) were tested for their inhibitory effects on human immunodeficiency virus type 1 (HIV-1) protease (PR). We found that the new compound, 21 beta-O-[(2E)-6-hydroxy1-2,6-dimethyl-2,7-octadienoyl] pitheduloside G (1), possessed potent anti-HIV-1 PR activity, with a half-maximum inhibitory concentration (IC50) value of 2.0 +/- 0.2 mu M. In contrast, pitheduloside G (2) exhibited much less inhibition, with an IC50 value of 18 +/- 0.5 mu M. Both compounds were nontoxic in human embryonic kidney 293T cells at concentrations effective against HIV-1 PR. This is the first report regarding the isolation of an anti-HIV-1 PR compound (1) from an Acacia plant species.