Cytotoxic 20,22-Dihydrodigitoxigenin Glycosides and Other Constituents of Vallaris glabra Stems

Ten cardiac glycosides (1–10) including six 20,22-dihydrodigitoxigenin and four gitoxigenin glycosides were isolated from the stems of Vallaris glabra together with six known triterpenoid cinnamates. Spectroscopic data of these previously undescribed compounds are reported. All isolates were evaluated for their growth inhibitory activities against three cancer cell lines, and compound 2 was the most active against KB cells with an IC₅₀ value of 0.03 ± 0.001 μM. Also, compounds 1, 3, 5, and 6 and the triterpenoid cinnamates 11–13 showed inhibitory activity (IC₅₀ < 10 μM) for one or more of the cell lines used.