New C21-steroidal aglycones from the roots of Cynanchum otophyllum and their anticancer activity

Naturally occurring C21-steroidal aglycones from Cynanchum exhibit significant antitumor effects. To expand the chemical diversity and get large scale C21-steroidal aglycones, the extracts of the roots of Cynanchum otophyllum were treated with 5% HCl in aqueous and the resulting hydrolysate was investigated. Nine new C21-steroidal aglycones (1–9) namely cynotogenins A-I, along with seventeen known analogous (10–26), were isolated from the hydrolysate. The structures of compounds 1–9 were elucidated by spectroscopic analysis (IR, HR-ESI-MS, 1D and 2D NMR) and comparison of observed spectroscopic data with those of reported in the literature. Aglycones 2–5 with rare cis-cinnamoyl group as well as 8 and 9 with 5β,6β-epoxy group were found from the genus of Cynanchum for the first time. The cytotoxicities of compounds 1–26 toward human cancer HeLa, H1299, HepG2, and MCF-7 cells were evaluated and preliminary structure-activity relationship (SAR) was discussed. Moreover, compound 20 inhibits HepG2 cell apoptosis and induces of G0/G1 phase arrest in a dose dependent manner. [Display omitted] •Nine new C21-steroidal aglycones (1–9) were isolated from the hydrolytic extracts of Cynanchum otophyllum.•Compounds 20, 22, 24, and 26 showed strong cytotoxicities toward four human cancer cell lines.•SAR analysis showed that both trans-cinnamoyl at C-12 and phenolic group at C-20 were vital for their activities.•Compound 20 showed the strongest cytotoxicity with IC50 of 5.39–8.55 μM.•Compound 20 could induce apoptosis and cell cycle arrest at G0/G1 phase.