Hysterolides A-I, dimeric or monomeric sesquiterpene lactones from Parthenium hysterophorus L.

Nine undescribed sesquiterpene lactones, including two pseudoguaianolide dimers (1 and 2), a pseudoguaiac dilactone (3), and six pseudoguaianolides (4-9), along with 13 known analogues (10-22) were isolated from Parthenium hysterophorus. Among them, hysterolide A (1) possesses an unusual carbon skeleton with a unique cyclobutane ring connecting two pseudoguaianolides. Hysterolide C (3) is a sesquiterpene dilactone incorporating a bicyclo[5.1.0]octane core. Spectroscopic analyses, 13C NMR and ECD calculations, and X-ray diffraction elucidated their structures and absolute configurations. Moreover, all the isolates were assayed for their antiinflammatory activities by inhibiting LPS-induced nitric oxide production in BV -2 microglia cells, wherein, nine compounds displayed significant inhibitory activities with IC50 of 0.52-6.32 mu M. Furthermore, the preliminary structure-activity relationship was also established.