New Triterpenoid Saponins from Glochidion eriocarpum and Their Cytotoxic Activity

Combined chromatographic methods led to the isolation of two new triterpenoid saponins, glochieriosides A and B (1,2), from the aerial parts of Glochidion eriocarpum, along with three known triterpenes, glochidone (3), lup-20(29)-en-3β,23-diol (4), and lup-20(29)-en-1β,3β-diol (5). The structures of the new saponins were determined to be 22β-benzoyloxy-3β,16β,28-trihydroxyolean-12-ene 3-O-[β-D-glucopyranosyl-(1→3)-α-L-arabinopyranoside] (1) and 22β-benzoyloxy-3β,16β,28-trihydroxyolean-12-ene 3-O-[β-D-glucopyranosyl-(1→3)-β-D-xylopyranoside] (2). The structural elucidation was accomplished by using a combination of the 1D-NMR (1H-, 13C-NMR, distortionless enhancement by polarization transfer (DEPT) 90°, and DEPT 135°), 2D-NMR (1H-1H correlation spectroscopy, heteronuclear multiple quantum correlation, heteronuclear multiple bond correlation, and rotating frame Overhouser effect spectroscopy), ESI-MS, and HR-FAB-MS experiments. Glochieriosides A and B exhibited significant cytotoxic activity against HL-60, HT-29, MCF-7 and SK-OV-3 human cancer cell lines with the IC50 values of 5.5, 6.8, 29.1, and 22.7 μM for glochierioside A, respectively, and 6.6, 18.6, 36.1, and 16.0 μM for glochierioside B. Glochidone was less active with IC50 values greater than 100 μM while lup-20(29)-en-1β,3β-diol was moderately active with IC50 values of 43.3, 67.0, 66.1, and 48.0 μM, respectively.