C21 steroidal glycosides from Cynanchum paniculatum (Bunge) Kitagawa: structural elucidation and biological evaluation.

Phytochemical investigation of the ethyl acetate-soluble fraction from the 95 % ethanol extract of Cynanchum paniculatum (Bunge) Kitagawa roots and rhizomes led to the isolation of eight previously undescribed C21 steroidal glycosides (1-8) designated cynapanosides H-O, alongside eighteen known analogues. The structures of the compounds were elucidated by comprehensive spectroscopic analysis using HRESIMS, 1D/2D NMR, and comparison with reported data. All isolated glycosides were evaluated for cytotoxic activity against HeLa and HepG2 cell lines. Among these, cynapanoside K (4) exhibited antiproliferative effects on HeLa cells by inducing apoptosis and S-phase cell cycle arrest. Mechanistic studies revealed that 4 downregulated Bcl-2, c-Myc, and Cyclin D1 protein expression while activating Caspase-9, suggesting mitochondria-mediated apoptotic pathways contribute to its cytotoxic activity. This study expands the chemical diversity of bioactive C21 steroidal glycosides and provides insights into their potential antitumor mechanisms.