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.