Alashanoids K-M, bioactive eremophilane sesquiterpenoids from Syringa pinnatifolia

Three new eremophilane-type sesquiterpenoids, alashanoids K-M (1-3), and one known analogue (4) were isolated from the peeled stems of Syringa pinnatifolia. All the compounds were isolated from the genus Syringa for the first time. Structures of these compounds were established using 1D and 2D NMR and MS data. The absolute configurations were determined by experimental and calculated electronic circular dichroism analysis, a modification of Mosher's method, and X-ray diffraction. Compounds 2 and 3 inhibited NO production in LPS-induced RAW264.7 macrophage cells with IC₅₀ values of 14.23 and 12.20 μM, respectively, and showed cytotoxic activities against HepG2 cells with the IC₅₀ values of 34.41 and 40.86 μM, respectively.