Pseudoguanolide Sesquiterpene Lactones fromVernoniopsiscaudataand Their in Vitro Antiplasmodial Activities

Two new helenanolide sesquiterpene lactones, 1 and 2, as well as one known related structure, 11 alpha,13-dihydrohelenalin- [2-(1-hydroxyethyl)acrylate] (3), together with 4'-beta-D-O-glueopyranosyl-luteolin and ethyl 2,5-dihydroxycinnamate were isolated from an ethyl acetate extract of leaves of Vernoniopsis caudata with potent antiplasmodial activity (IC50 1.6 mu g/mL) in a preliminary biological screen. The structures of the new compounds were determined by spectroscopic techniques. The three sesquiterpene lactones 1-3 displayed strong in vitro antiplasmodial activity, with IC50 values of 1, 0.19, and 0.41 mu M, respectively. However, these compounds also exhibited considerable cytotoxicity on KB cells (IC50 < 1 mu M in each case).