Bioactive Sesquiterpenoids from the Peeled Stems of Syringa pinnatifolia

Fourteen new sesquiterpenoids, alashanoids A-H (1, 2, and 4-9), (+)-2,9-humuladien-6-ol-8-one (3b), and five pairs of enantiomers (1 and 4-7), along with eight known analogues (3a and 10-16) were isolated from the stems of Syringa pinnatifolia. The structures were established using IR, UV, MS, and NMR data. The absolute configurations of the new compounds were resolved by X-ray diffraction, a modification of Mosher's method, and experimental and calculated ECD data analysis. The new sesquiterpenoids represent three skeletons: a rare 2,2,5,9-tetramethylbicyclo[6.3.0]-undecane (1), a humulane-type (2-8), and a caryophyllene-type (9) skeleton. Compounds 6a, 7, and 11 showed protective effects against hypoxia-induced injury to H9c2 cells at a concentration of 40 μM, and 5-7, 11, and 13 inhibited NO production in LPS-induced RAW264.7 macrophage cells with IC₅₀ values ranging from 13.6 to 70.6 μM. These compounds decreased the TNF-α and IL-6 levels in RAW264.7 cells in a concentration-dependent manner at 20-80 μM.