Cytotoxic Pregnane Steroidal Glycosides from Chonemorpha megacalyx

Three new C₂₁ pregnane steroids, chonemorphols A–C (1, 3, and 4), 11 new C₂₁ steroidal glycosides, chonemorphosides A–K (2 and 5–14), and 11 known compounds (15–25) were obtained from the vines and leaves of Chonemorpha megacalyx Pierre. Their structures were established using extensive spectroscopic data. The X-ray crystallographic data of 1 and 3 permitted definition of their absolute configurations. Notably, 1 and 2 possessed an uncommon 6/5/6/5/5-fused steroidal ring system. Compound 7 displayed significant cytotoxicity against several cancer cell lines with IC₅₀ values of 2.0–3.6 μM.