Two new cytotoxic triterpenoid saponins from the roots of Clematis argentilucida

Bioassay-guided fractionation of the n-BuOH extract of the roots of Clematis argentilucida led to the isolation of two new triterpenoid saponins along with a known one, cussonside B (3). By extensive spectral analysis and chemical evidences, the structures of the two new saponins were determined to be 3β-O-[β-d-ribopyranosyl-(1 → 3)-α-l-rhamnopyranosyl-(1 → 2)-α-l-arabinopyranosyl] hederagenin-11,13-dien-28-oic acid (1) and 3β-O-{β-d-ribopyranosyl-(1 → 3)-α-l-rhamnopyranosyl-(1 → 2)-[β-d-glucopyranosyl-(1 → 4)]-β-d-xylopyranosyl} oleanolic acid (2), respectively. Saponin 1 is the first example of triterpenoid saponins with two double bonds located at C-11 and C-13 in the aglycone from the genus Clematis. The two new saponins exhibited significant cytotoxicity against human leukemia HL-60 cell lines, human hepatocellular carcinoma Hep-G2 cell lines and human glioblastoma U251MG cell lines with a range of IC50 values from 2.74 to 25.40 μM, while 3 showed inactivity against all of the three cancer cell lines.

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