Immunosuppressive C21 steroidal glycosides from the root of Cynanchum atratum

Six new C21 steroidal glycosides (1-6) and one dideoxysaccharide (7), named atratcynosides A-F and atratcynose A, were isolated from the 80% ethanol extract of the root of Cynanchum atratum, together with three known compounds (8-10). The structures of the new compounds were determined on the basis of extensive spectral analyses and qualitative chemical methods. All compounds were subjected to detect the immunosuppressive activities by an in vitro model of concanavalin A-induced proliferation of T-lymphocytes from mice. Compounds 1-3 showed significant immunosuppressive activities in dose-dependent manners with the IC50 values from 3.3 to 7.0 μM. Moreover, the structure-activity relationship of the steroidal glycosides on the immunosuppression was analyzed.