Low Molecular Weight Extractives from Green Husks of Juglans sigillata and Their Antioxidant Activities

Five low molecular weight phenolic compounds, (+)-catechin (1), (-)-epicatechin (2), (+)-catechin(4 -> 8 '')-(+)-catechin (3), 1,2,4,6-tetra-O-galloyl-beta-D-glucose (4) and 1,2,3,4,6-penta-O-galloyl-beta-D-glucose (5) were isolated from the 95% ethanolic extractives of green husks of Juglans sigillata Dode (Juglandaceae) by systematic Sephadex LH-20 open column chromatography and Thin Layer Chromatography (TLC). The structure elucidation and determination of the isolated extractives were based on physiochemical and spectroscopic methods, including H-1 and C-13 NMR, Positive FAG and MALDI-TOF MS analysis. The antioxidant activities of the subfractions derived from sequential fractionation by n-hexane, CH2Cl2, EtOAc, BuOH and H2O, and the isolated compounds 1-5 in the ethanolic extractives were evaluated by 2,2-diphenyl-1-picrylhydrazyl (DPPH) scavenging assay. The DPPH based assay results showed that EtOAc, BuOH and H2O soluble fractions and compounds 1-5 exhibited significant antioxidant effects comparing with alpha-tocopherol and BHT, which were used as positive controls. This was the first report of the isolation of the five low molecular weight phenolics from this species, and the antioxidant activities of this tree have never been investigated previously.