New furofuran and butyrolactone lignans with antioxidant activity from the stem bark of Styrax japonica

A new furofuran lignan, styraxlignolide B (1), and four new dibenzyl-gamma-butyrolactone lignans, styraxlignolides C-F (2-5), were isolated from the EtOAc-soluble fraction of stem bark of Styrax japonica. Known compounds, taraxerol (6), syringin (7), and (-)-pinoresinol glucoside (8), were also obtained. The structures of styraxligonolides B-F were determined as 2alpha-(4'-hydroxy-3'-methoxyphenyl)-6alpha-(3",4"-methylene-dioxyphenyl)-8-oxo-3,7-dioxabicyclo [3.3.0]octane 4'-O-(beta-D-glucopyranoside) (1), (2S,3S)-2alpha-(3"-hydroxy-4"-methoxybenzyl)-3 -(4'-hydroxy-3'-methoxybenzyl)-gamma-butyrolactone 4'-O-(beta-D-glucopyranoside) (2), (2S,3S)2(alpha-(4"-hydroxy-3"-methoxybenzyl)-3beta-(4'-hydroxy-3'-methoxybenzyl)-gamma-butyrolactone 4'-O-(fi-Dglucopyranoside) (3), (2S,3S)-2(alpha-(4"-hydroxy-3"-methoxybenzyl)-3beta-(4'-hydroxy-3'-methoxybenzyl)-gamma-butyrolactone 4"-O-(beta-D-glucopyranoside) (4), and (2S,3S)-2alpha-(3",4"-dimethoxybenzyl)-3 -(4'-hydroxy-3'-methoxybenzyl)-gamma-butyrolactone 4'-beta4-D-glucopyranoside) (5) by spectroscopic means including 2D NMR. Compounds 1-8 were tested in vitro for antioxidant activity against 1,1-diphenyl-2-pierylhydrazyl (DPPH) radicals. Styraxlignolide C (2), styraxlignolide D (3), styraxlignolide E (4), and (-)-pinoresinol glucoside (8) exhibited weak radical-scavenging activity in the DPPH assay, with IC50 values of 380, 278, 194, and 260 muM, respectively.