Japonicones E-L, dimeric sesquiterpene lactones from Inula japonica Thunb.

Eight new dimeric sesquiterpene lactones (japonicones E-L, 1- 8), including a novel sesquiterpene dimer bearing a rare hydroperoxide group (japonicone E, 1), were isolated from the aerial part of Inula japonica Thunb. Their structures were determined mainly by the use of 1D and 2D NMR spectroscopic techniques including HSQC, (1)H-(1)H COSY, HMBC, and NOESY. All the isolates were tested for inhibitory effects against LPS-induced NO production in RAW264.7 macrophages. Among the compounds tested, japonicone F (2) showed the strongest activity with the IC(50) value of 4.1 microg/mL.