Oleanane-type Saponins from Glochidion hirsutum and Their Cytotoxic Activities

Five new oleanane-type saponins, hirsutosides A - E, were isolated from the leaves of Glochidion hirsutum (Roxb.) Voigt. Their structures were elucidated as 21β-benzoyloxy-3β,16β,23,28-tetrahydroxyolean-12-ene 3-O-β-d-glucopyranoside (1), 21β-benzoyloxy-3β,16β,23,28-tetrahydroxyolean-12-ene 3-O-β-d-glucopyranosyl-(1 → 3)-β-d-glucopyranoside (2), 21β-benzoyloxy-3β,16β,23,28-tetrahydroxyolean-12-ene 3-O-6-acetyl-[β-d-glucopyranosyl-(1 → 3)]-β-d-glucopyranoside (3), 21β-benzoyloxy-3β,16β,23,28-tetrahydroxyolean-12-ene 3-O-β-d-glucopyranosyl-(1 → 3)-〈-l-arabinopyranoside (4), and 21β-benzoyloxy-3β,16β,23-trihydroxyolean-12-ene-28-al 3-O-β-d-glucopyranosyl-(1 → 3)-α-l-arabinopyranoside (5). All isolated compounds were evaluated for cytotoxic activities on four human cancer cell lines, HepG-2, A-549, MCF-7, and SW-626 using the SRB assay. Compounds 1, 2, 4, and 5 showed significant cytotoxic activities against all human cancer cell lines with IC₅₀ values ranging from 3.4 to 10.2 μm. Compound 3 containing acetyl group at glc C(6″) exhibited weak cytotoxic activity with IC₅₀ values ranging from 47.0 to 54.4 μm.