Four New Isomeric Sesquiterpene Lactone Dimers from Carpesium faberi.

Abstract Four new isomeric sesquiterpene lactone dimers (SLDs), guaianodilactones A–D ( 1 – 4 ), were isolated from Carpesium faberi . Among them, 1 – 3 were exo -1,3-linked, while 4 was the endo -2,4-linked, Diels–Alder adducts between two homo guaianolide units. Their exo / endo stereochemistry was established by both the characteristic chemical shift of Ha-2′ or Ha-3′ resulting from the deshielding effect of the carbonyl chromophore at C-12 and the diagnostic negative/positive cotton effect, as well as 1 was further confirmed by Cu-Kα X-ray crystallographic analysis. Compounds 1 – 4 exhibited potent cytotoxicity against human leukemia (CCRF-CEM) cells with IC 50 value of 9.13, 2.03, 4.74, and 13.72 μM, respectively.