Lineariifolianoids M-O, three rare sesquiterpene lactone dimers inhibiting NO production from Inula lineariifolia

Abstract Three rare squiterpene lactone dimers lineariifolianoids M-O (1–3) were isolated from Inula lineariifolia for the first time. Their structures and absolute configuration were established on the basis of by NMR and MS spectroscopic data and X-ray crystallography. Furthermore, those three compounds exhibited significant inhibitory activity against LPS-induced NO production in RAW 264.7 macrophages with IC50 values of 1.421, 1.087 and 1.243 μM, respectively.