Carpedilactones A-D, four new isomeric sesquiterpene lactone dimers with potent cytotoxicity from Carpesium faberi.

Four new isomeric sesquiterpene lactone dimers, carpedilactones A-D (1-4), were isolated from the acetonic extract of Carpesium faberi. Among them, 1-3 are the first three 2,4-linked exo-Diels-Alder adducts between a eudesmanolide dienophile and a guaianolide diene. The absolute configurations of 1-4 were unambiguously established by Cu Kα X-ray crystallographic analyses. Compounds 1-4 exhibited potent cytotoxicities against human leukemia (CCRF-CEM) cells with IC50 value of 0.14, 0.32, 0.35, and 0.16 μM, respectively.