Targeted isolation of dimeric sesquiterpene lactones and sesquiterpene derivatives from the roots of Inula helenium

LC-HRMS/MS-based molecular networking was applied to investigate the bioactive sesquiterpene lactones and their analogs contained in Inula helenium, , enabling the isolation of four undescribed eudesmane-eudesmane sesquiterpene dimers (1-4), 1 - 4 ), a sesquiterpene-amino acid adduct (5), 5 ), and 17 known sesquiterpenes (6-22). 6 - 22 ). The structures were determined based on 1D, 2D NMR, and HRESIMS data analysis, as well as DP4+ + probability analyses and ECD calculations. The biosynthetic pathway of the sesquiterpene dimers is postulated to proceed via the Diels-Alder reaction as the key step. The inhibitory activity of all isolates on LPS-induced nitric oxide (NO) production in RAW 264.7 macrophages was evaluated. Compounds 4 , 17 , and 20 exhibited significant inhibitory activity against NO production, with IC50 50 values of 8.4, 5.5, and 9.1 mu M, respectively.