Triterpene saponins from Silphium radula

Nine triterpene saponins (1-9) were isolated from leaves and stems of Silphium radula Nutt. (Asteraceae). Their structures were determined by extensive 1D ((13)C, (1)H, DEPT, TOCSY) and 2D NMR (NOESY, HSQC, HMBC) and ESI-MS studies. The compounds were identified as 3beta,6beta,16beta-trihydroxyolean-12-en-23-al-3-O-beta-glucopyranosyl-16-O-beta-glucopyranoside (1), urs-12-ene-3beta,6beta,16beta-triol-3-O-beta-galactopyranosyl-(1-->2)-beta-glucopyranoside (2), 3beta,6beta,16beta-trihydroxyolean-12-en-23-oic acid-3-O-beta-glucopyranosyl-16-O-beta-glucopyranoside (3), urs-12-ene-3beta,6beta,16beta,21beta-tetraol-3-O-beta-glucopyranoside (4), olean-12-ene-3beta,6beta,16beta,21beta-tetraol-3-O-beta-glucopyranoside (5), olean-12-ene-3beta,6beta,16beta,21beta,23-pentaol-3-O-beta-glucopyranosyl-16-O-beta-glucopyranoside (6), olean-12-ene-3beta,6beta,16beta-triol-3-O-beta-glucopyranosyl-16-O-alpha-arabinopyranosyl-(1-->2)-beta-glucopyranoside (7), olean-12-ene-3beta,6beta,16beta,23-tetraol-3-O-beta-glucopyranosyl-16-O-alpha-arabinopyranosyl-(1-->2)-beta-glucopyranoside (8), 3beta,6beta,16beta,21beta-tetrahydroxyolean-12-en-23-al-3-O-beta-glucopyranoside (9). The presence of a 6beta-hydroxyl function was not common in the oleanene or ursene class and the aglycones of these compounds were not found previously in the literature. Moreover, the cytotoxic activities of the isolated compounds were tested against human breast cancer cell line MDA-MB-231. Results showed that compound 2 decreased cell proliferation in a statistically significant manner at 25 microg/ml.