Na+,K(+)-ATPase inhibiting activity of cardiac glycosides from Erysimum cheiranthoides

We previously reported the isolation of eleven new cardiac glycosides called cheiranthosides I-XI together with two known ones (olitoriside and erysimoside) from the seeds of Erysimum cheiranthoides L. The glycosides were evaluated for their inhibitory activity against Na+,K(+)-ATPase by comparing with typical cardiac glycosides. Two of them, cheiranthoside III and VIII, showed high inhibiting activity which was equivalent to that of digitoxin. Cheiranthoside XI containing a rhamnopyranosyl digitoxopyranosyl moiety and a carboxyl group showed the lowest activity which was similar to that of the inactive aglycone, strophanthidin. Some characteristics in the structure-activity relationship are also discussed.