Saponins with highly hydroxylated oleanane-type aglycones from Silphium asteriscus L.

Silphium asteriscus L., commonly known as starry rosinweed, is a plant found in prairies, glades, woodlands and savannas of the southeastern United States. The phytochemical investigation of the methanolic extract of S. asteriscus leaves led to the isolation of eighteen saponins with highly hydroxylated oleanane-type aglycones never reported before. Their structures were elucidated by extensive spectroscopic methods including 1D- ((1)H and (13)C) and 2D-NMR (DQF-COSY, HSQC, HMBC, TOCSY and ROESY) experiments as well as ESIMS analysis. The antiproliferative activity of the isolated compounds was evaluated against three cancer cell lines including Hela (human epitheloid cervix carcinoma), Jurkat cells (leukaemic T-cell line) and DLD-1 (colorectal adenocarcinoma). Compounds 1, 5 and 17 displayed weak activity with IC50 values ranging from 50 to 75 μM.