Lignans from the leaves of Styrax japonicus and their anti-inflammatory activity

Five novel lignans, namely styraxjaponica A-E (1–5), together with eight known compounds (6–13) were isolated from the leaves of Styrax japonicus Siebold & Zucc. Their chemical structures were characterized by extensive analysis of 1D and 2D NMR, UV, IR, HRESIMS spectroscopic analysis as well as by comparison to the literature. The absolute configurations of the new compounds were further determined by quantum chemical electronic circular dichroism (ECD) calculations powered by time-dependent density functional theory (TDDFT). Moreover, the anti-inflammatory effects of compounds 1–5 in lipopolysaccharide (LPS)-induced RAW 264.7 cells were also evaluated by measuring nitric oxide (NO) concentrations. All compounds displayed significant anti-inflammatory activity without affecting cell viability in vitro.