Investigation of the ethanol extract of the whole plant of Ainsliaea yunnanensis led to the isolation of four new dimeric sesquiterpene lactones, ainsliadimer F–I (1–4), together with seven known dimeric sesquiterpene lactones (5–11) and ten sesquiterpenes (12–21). Their structures were elucidated by spectroscopic methods. The relative stereochemistry of ainsliadimer F was further confirmed by single crystal X-ray diffraction analysis. Compounds 1–21 were tested for the inhibition of nuclear factor kappa B (NF-κB) in the 293-NF-κB-luciferase reporter cell line induced by lipopolysaccharide (LPS), and Compounds 5, 18, 20 and 21 were further tested for the production of TNF-α, IL-1β, IL-6 and IL-10 in RAW 264.7 macrophages induced by LPS. Compounds 5, 18, 20 and 21 exhibited significant activity in anti-inflammatory activity assays.
