New sesquiterpene dimers from Inula britannica inhibit NF-kappaB activation and NO and TNF-alpha production in LPS-stimulated RAW264.7 cells.

A bioassay-guided isolation of an ethyl acetate-soluble extract of the aerial parts of Inula britannica var. chinensis (Rupr.) Regel, using an in vitro NF-kappaB reporter gene assay, led to the isolation of four new sesquiterpene dimers bearing a norbornene moiety, inulanolides A-D, and three known sesquiterpenes, 1,6alpha-dihydroxyeriolanolide, 1-acetoxy-6alpha-hydroxyeriolanolide, and eupatolide. The structures of the new compounds were elucidated by spectroscopic methods. Among these compounds, inulanolides B and D and eupatolide, exhibited potent inhibitory activity on the LPS-induced NF-kappaB activation with IC50 values of 0.49 microM, 0.48 microM, and 1.54 microM, respectively. Consistent with their inhibitory effect on NF-kappaB activation, compounds and also strongly inhibited the production of NO and TNF-alpha in the LPS-stimulated RAW264.7 cells with IC50 values in the range of 2 microM.