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.