Stigmastane-type steroid saponins from the leaves of Vernonia amygdalina Del

Vernoramyosides A-F ( 1 – 6 ), six new Δ 7,9(11) stigmastane-type steroid saponins , along with four known analogues ( 7 – 10 ) were isolated from the leaves of Vernonia amygdalina Delile (Compositae). Their structures were determined by the combination of NMR, ECD and HR-ESI-MS data. These compounds all possessed highly oxidized side chain and a γ-lactam or α , β -unsaturated five-membered lactone ring. All isolates were screened for their activities in reversing resistance in MCF/DOX cells.