Cytotoxic cardenolides from the root bark of Calotropis gigantea

•Six new cardenolides were isolated from the root bark of Calotropis gigantea.•Cardenolides were evaluated for their cytotoxicity against A549 and Hela cell lines.•Some cardenolides displayed potent cytotoxicity. Six new cardenolides (1, 2 and 11–14), along with ten known ones, were isolated from the root bark of Calotropis gigantea. The structural determination was accomplished by the 1D- and 2D-NMR spectrum as well as ESIMS analysis. The isolated compounds were evaluated for their in vitro growth inhibitory activity against human A549 and Hela cell lines. The results suggested that some of these cardenolides (compounds 1, 6, and 8) displayed potent cytotoxicities.