Secoiridoid Glucosides and Anti-Inflammatory Constituents from the Stem Bark of Fraxinus chinensis .

Qin Pi ( Fraxinus chinensis Roxb.) is commercially used in healthcare products for the improvement of intestinal function and gouty arthritis in many countries. Three new secoiridoid glucosides, (8 E )-4''- O -methylligstroside ( 1 ), (8 E )-4''- O -methyldemethylligstroside ( 2 ), and 3'',4''-di- O -methyl-demethyloleuropein ( 3 ), have been isolated from the stem bark of Fraxinus chinensis , together with 23 known compounds ( 4 - 26 ). The structures of the new compounds were established by spectroscopic analyses (1D, 2D NMR, IR, UV, and HRESIMS). Among the isolated compounds, (8 E )-4''- O -methylligstroside ( 1 ), (8 E )-4''- O -methyldemethylligstroside ( 2 ), 3'',4''-di- O -methyldemethyloleuropein ( 3 ), oleuropein ( 6 ), aesculetin ( 9 ), isoscopoletin ( 11 ), aesculetin dimethyl ester ( 12 ), fraxetin ( 14 ), tyrosol ( 21 ), 4-hydroxyphenethyl acetate ( 22 ), and (+)-pinoresinol ( 24 ) exhibited inhibition (IC ₅₀ ≤ 7.65 μg/mL) of superoxide anion generation by human neutrophils in response to formyl-L-methionyl-L-leuckyl-L-phenylalanine/cytochalasin B (fMLP/CB). Compounds 1 , 9 , 11 , 14 , 21 , and 22 inhibited fMLP/CB-induced elastase release with IC ₅₀ ≤ 3.23 μg/mL. In addition, compounds 2 , 9 , 11 , 14 , and 21 showed potent inhibition with IC ₅₀ values ≤ 27.11 μM, against lipopolysaccharide (LPS)-induced nitric oxide (NO) generation. The well-known proinflammatory cytokines , tumor necrosis factor-alpha (TNF-α) and interleukin 6 (IL-6), were also inhibited by compounds 1 , 9 , and 14 . Compounds 1 , 9 , and 14 displayed an anti-inflammatory effect against NO, TNF-α, and IL-6 through the inhibition of activation of MAPKs and IκBα in LPS-activated macrophages. In addition, compounds 1 , 9 , and 14 stimulated anti-inflammatory M2 phenotype by elevating the expression of arginase 1 and Krüppel-like factor 4 (KLF4). The above results suggested that compounds 1 , 9 , and 14 could be considered as potential compounds for further development of NO production-targeted anti-inflammatory agents.