Cardiotonic steroids with potent cytotoxicity from Streblus Asper

Four new and several known cardiotonic steroids were discovered from Streblus asper Lour. (Moraceae) collected in South Vietnam. The structures of the new compounds were established by analysis of their CD, IR, UV, NMR, and mass spectra, with those of the known compounds being determined by comparison of their spectroscopic data with the literature values. Several of these substances were cytotoxic toward the HT-29 human colon cancer cells, with a known compound, strebloside, found to be potently cytotoxic against the HT-29 cells, showing an IC₅₀ value of 170 nM. A preliminary structure-cytotoxicity-relationship study for strebloside showed that the glycose unit linked at the C-3 position and the C-19 aldehyde residue of this compound both play an important role in mediation of its cytotoxicity, and the activity was retained when the C-4′ hydroxy group of the glycose moiety is modified.