Nine undescribed C₂₁-steroids with cytotoxic activity from the stems of Marsdenia tenacissima

Chemical investigation on the acid hydrolysate of Marsdenia tenacissima stems resulted in the isolation of nine previously undescribed C₂₁-steroids (1-9), along with six known analogues (10-15). The complete structures of these compounds were elucidated via comprehensive spectroscopic analyses (IR, UV, HR-ESI-MS, 1D and 2D NMR) and comparison with reference data, while their absolute stereochemistries were determined by quantum electronic circular dichroism (ECD) calculations. All isolates were evaluated for cytotoxicity against the MCF-7, HCT-116, HeLa, and HepG2 cancer cell lines, and their structure-activity relationships (SARs) were subsequently discussed. Notably, compound 3 exhibited the most potent cytotoxicity, with IC₅₀ values ranging from 15.81 to 22.88 μM, and it also induced apoptosis and arrested the cell cycle at the S phase in a dose-dependent manner against HepG2 cells.