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.