Sesquiterpenoids and lignans from the roots of Syringa pinnatifolia

Two new sesquiterpenoids, pinnatifone A (1) and pinnatifone B (2), and two new lignans, pinnatifolin (3) and isopinnatifolin (4), along with six known lignans (5-10), were isolated from the roots of Syringa pinnatifolia. The structures of the new compounds were elucidated by extensive spectroscopic methods, including NMR, MS, UV, and IR spectra. The lignans were screened for their anti-oxidant activity (2,2-diphenyl-1-picrylhydrazyl (DPPH) assay). Most of them showed potent anti-oxidant activity, especially compound 5, whose potent anti-oxidant activity had an SC50 value higher than that of the positive control vitamin C.