Syringenes A-L: Bioactive dimeric eremophilane sesquiterpenoids from Syringa pinnatifolia

A phytochemical investigation guided by ¹H NMR and LC-MS data on the ethanol extract of Syringa pinnatifolia stems led to the isolation of 11 new dimeric eremophilane sesquiterpenoids, namely, syringenes A-K (1-11) and one known analog (12, syringene L). These structures were elucidated by extensive analysis of spectroscopic data, single-crystal X-ray diffraction, and computational methods. Biological assays revealed that 1-12 exhibited different degrees of anti-inflammatory effects, and 5 and 6 showed significant cytotoxicity against human hepatoma HepG2 cells with IC₅₀ values of 12.3 and 12.9 μM, respectively. Furthermore, flow cytometry assays and western blot analysis revealed that 5 and 6 promoted the apoptosis of HepG2 cells by activating ERK. Finally, the molecular docking analysis implied that the carbonyl and hydroxy groups at the C-11/C-6' of 5 and 6 had a good binding affinity with ERK.