Anti-inflammatory lignans from peeled stems of Syringa pinnatifolia

Three new lignans namely alashanenols H₁-J₁ (1-3) and one dimeric lignan namely bisyringol A (4) together with 15 known analogues (5-19) were isolated from the peeled stems of Syringa pinnatifolia Hemsl. with the aid of an in vitro anti-inflammation guided fractionation. The structures were elucidated by analysis of spectroscopic data, including IR, UV, MS, and NMR, and their absolute configurations were resolved by X-ray single crystal diffraction analysis and comparison of experimental and calculated ¹³C NMR and ECD data. Compound 2 possesses a cage-like motif in lignan family and 4 owns a rare framework composed of one lignan and one norlignan fragments. The bioassay results showed that 4, 13, and 18 significantly inhibit the NO production in LPS-induced RAW264.7 cells with IC₅₀ values of 5.90 ± 0.28, 53.26 ± 9.96 and 53.25 ± 6.84 μM, compared with the positive control indomethacin (IC₅₀ 33.6).