Cynanchinosides A−R, eighteen undescribed pregnane glycosides from Cynanchum auriculatum

Eighteen undescribed C21 pregnane glycosides, cynanchinosides A−R (1−18), together with sixteen known analogs (19−34) were isolated from the roots of Cynanchum auriculatum Royle ex Wight (Asclepiadaceae). Their structures were elucidated on the basis of various spectroscopic (NMR and HR-ESI-MS) analyses, combined with the comparison of their spectroscopic data with those of known ones from references. Every pregnane glycoside is a member of one of two fundamental C21 pregnane skeleton types, with changing substituents at C-12 and C-20 and saccharide chain lengths in distinct sequences of monosaccheride connection. The cytotoxicities of the isolated pregnane glycosides (1−34) against HCT-116 and HepG2 cell lines were evaluated. Compounds 2, 4, 25 and 27 exhibited significant cytotoxicity against HCT-116 cell line with IC₅₀ values in the range of 13.93 ± 3.22 to 19.21 ± 2.99 μmol·L⁻¹.