Hemistepsins with cytotoxic activity from Hemisteptia lyrata

Two sesquiterpene lactones were isolated from Hemisteptia lyrata Bunge (Com positae). Their structures were elucidated by spectroscopic methods as rece ntly known hemistepsin and the new 6-O-(2-methylpropenoyl)-3-hydroxy-4(15), 10(14),11(13)-guaiatrien-12,8-olide. The two hemistepsin derivatives were examined for their in vitro cytotoxic activity against human cell lines suc h as UACC 62, HCT 15, UO-31, PC-3 and A549. Growth inhibitory property was determined by in vitro treatment of the respective cell lines using the sul forhodamine B assay (SRB). Both compounds exhibited significant cytotoxic a ctivity (IC50 < 4.3 mu g/ml) on all five human cell lines tested.