Cytotoxic triterpenoid saponins from the root of Olax subscorpioidea Oliv. (Olacaceae)

Bioactivity-guided phytochemical fractionation of the methanol extract of Olax subscorpioidea root has led to the isolation of six triterpenes. Three of these compounds are previously undescribed triterpenoid saponins: oleanolic acid 3-O-[α-L-rhamnopyranosyl-(1→3)-β-D-glucopyranosyl-(1→2)-6-O-methyl-β-D-glucuronopyranoside]-28-O-β-D-glucopyranosyl ester (2), oleanolic acid 3-O-[β-D-glucopyranosyl-(1→4)-β-D-glucopyranosyl-(1→3)-β-D-glucopyranoside] (3), and oleanolic acid 3-O-[β-D-glucopyranosyl-(1→4)-6-O-methyl-β-D-glucuronopyranoside] ester (5). Other reported known compounds include two triterpene glycosides: oleanolic acid 3-O-[β-D-glucopyranosyl-(1→4)-6-O-methyl-β-D-glucuronopyranoside]-28-O-β-D-glucopyranosyl ester (1) and oleanolic acid 3-O-[β-D-glucopyranosyl-(1→4)-β-D-glucuronopyranoside] (4); and a triterpene acid, oleanolic acid (6). The structures of these compounds were elucidated by spectroscopic means. The isolated compounds were tested against human cervical cancer (HeLa), colorectal cancer (Caco-2) and breast cancer (MCF-7) cell lines using the in vitro 3-[4,5-dimethylthiazole-2-yl] 3,5-diphenyltetrazolium bromide (MTT) assay, with vincristine as positive control. The cytotoxicity assay showed that compounds 3 and 5 exhibited significant inhibitory effects on the HeLa cell line, with IC50 values of 7.42±0.34 µM and 10.27±1.26 µM; and moderate effects on MCF-7 (IC50 values, 36.67±1.23 µM and 43.83±0.65 µM) and Caco-2 (IC50 values, 35.83±0.55 µM and 39.03±4.38 µM, respectively) cell lines. They were also more selectively cytotoxic than vincristine against the cancer cell lines, when compared with cytotoxicity against the normal lung cell line MRC5