Triterpenoids and triterpenoid saponins from Dipsacus asper and their cytotoxic and antibacterial activities

Phytochemical investigation of the ethyl acetate soluble part, generated from the ethanol extract of the roots of Dipsacus asper, led to the separation and identification of three undescribed triterpenoids including one arborinane type, one ursane type and one oleanane type, two unreported oleanane type triterpenoid arabinoglycosides, and 18 known analogues. Structures of these compounds were determined by comprehensive spectroscopic analyses, with the absolute configurations of 25-acetoxy-28-dehydroxyrubiarbonone E and 2α,3β-dihydroxy-23-norurs-4(24),11,13(18)-trien-28-oic acid being established by evaluation of their experimental and calculated ECD spectra. 25-Acetoxy-28-dehydroxyrubiarbonone E features an oxygenated C-25 that is the first case among arborinane type triterpenoids, while 2α,3β,24-trihydroxy-23-norurs-12-en-28-oic acid incorporates a sp3 C-24 that is a rare structural feature of 23-norursane type triterpenoids. Of these isolates, 2′,4′-O-diacetyl-3-O-α-l-arabinopyranosyl-23-hydroxyolea-12-en-28-oic acid and hederagonic acid exhibited moderate antibacterial activity against Staphylococcus aureus with IC50 values of 12.3 and 10.3 μM, respectively, while those with either a feruloyloxy group or an arabinosyl moiety at C-3 displayed potent cytotoxic activities against four tumor cell lines A549, H157, HepG2 and MCF-7.