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

Abstract

A new furofuran lignan, styraxlignolide B (1), and four new dibenzyl-γ-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 2α-(4′-hydroxy-3′-methoxyphenyl)-6α-(3″, 4″-methylenedioxyphenyl)-8-oxo-3,7-dioxabicyclo[3.3.0]octane 4′-O-(β-D-glucopyranoside)(1), (2S,3S)-2α-(3″-hydroxy- 4″-methoxybenzyl)-3β-(4′-hydroxy-3′-methoxybenzyl) -γ-butyrolactone 4′-O-(β-D-glucopyranoside)(2), (2S,3S)-2α-(4″-hydroxy-3″-methoxybenzyl)-3β-(4′- hydroxy-3′-methoxybenzyl)-γ-butyrolactone 4′-O-(β-D- glucopyranoside) (3), (2S,3S)-2α-(4″-hydroxy-3″-methoxybenzyl) -3β-(4′-hydroxy-3′-methoxybenzyl)-γ-butyrolactone 4″-O-(β-D-glucopyranoside) (4), and (2S,3S)-2α-(3″, 4″-dimethoxybenzyl)-3β-(4″-hydroxy-3′-methoxybenzyl) -γ-butyrolactone 4′-O-(β-D-glucopyranoside) (5) by spectroscopic means including 2D NMR. Compounds 1-8 were tested in vitro for antioxidant activity against 1,1-diphenyl-2-picrylhydrazyl (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 μM, respectively.