Triterpenoid Saponins from Maesa argentea Leaves

Within an ongoing research program on saponins with potential antileishmanial activity, four previously undescribed saponins were isolated from Maesa argentea leaves and identified by LC-MS/MS, GC-MS, and 1D and 2D NMR spectroscopy as 3β-O-{([β-D-glucopyranosyl-(1 → 2)-α-L-rhamnopyranosyl-(1 → 2)-β-D-galactopyranosyl-(1 → 3)]-[β-D-galactopyranosyl-(1 → 2)]-β-D-glucuronopyranosyl)}-21β-angeloyloxy-22α-butanoyloxy-13β,28-oxidoolean-16α,28α-diol (1), 3β-O-{([β-D-glucopyranosyl-(1 → 2)-α-L-rhamnopyranosyl-(1 → 2)-β-D-galactopyranosyl-(1 → 3)]-[β-D-galactopyranosyl-(1 → 2)]-β-D-glucuronopyranosyl)}-21β,22α-angeloyloxy-13β,28-oxidoolean-16α,28α-diol (2), 3β-O-{([β-D-glucopyranosyl-(1 → 2)-α-L-rhamnopyranosyl-(1 → 2)-β-D-galactopyranosyl-(1 → 3)]-[β-D-galactopyranosyl-(1 → 2)]-β-D-glucuronopyranosyl)}-21β-angeloyloxy-22α-(E)-cinnamoyloxy-13β,28-oxidoolean-16α,28α-diol (3), and 3β-O-{([α-L-rhamnopyranosyl-(1 → 2)-β-D-galactopyranosyl-(1 → 3)]-[β-D-galactopyranosyl-(1 → 2)]-β-D-glucuronopyranosyl)}-21β-angeloyloxy-22α-(E)-cinnamoyloxy-13β,28-oxidoolean-16α,28α-diol (4). Leaf material was obtained from a germinated seed that was clonally propagated using in vitro tissue culturing. Compounds 1-4 showed structural similarity with maesasaponins and maesabalides reported before from other Maesa spp. All four compounds showed in vitro activity against Plasmodium falciparum K1 and Leishmania infantum at micromolar concentrations. However, the observed inhibitory action must be considered nonspecific since they were also cytotoxic in the same concentration range.