Two novel C21 steroidal glycosides from Cynanchum auriculatum.

Two new C21 steroidal glycosides, metaplexigenin TC1 (1) and cynanchogenin TC2 (2), were isolated from the roots of Cynanchum auriculatum. Their structures were determined to be meta--plexigenin 3-O-α-L-cymaropyranosyl-(1→4)-β-D-cymaropyranosyl-(1→4)-α-L-cymaropyr-anosyl-(1→4)-β-D-digitoxopyranoside (1) and cynanchogenin 3-O-β-D-cymaropyranos-yl-(1→4)-α-L-diginopyranosyl-(1→4)-β-D-oleandropyranosyl-(1→4)-β-D-cymaropyr-anoside (2) by IR, HRESIMS and NMR experiments. The in vitro NO release inhibition assays gave IC50 values of 76.5 and 53.0 μmol/L, respectively.