Antioxidant, antibacterial and antigiardial activities of Walsura robusta Roxb

Walsura robusta Roxb. (Family: Meliaceae) is a well-known multi-purpose medicinal plant, and has been employed for a wide range of disease conditions without documented scientific data. In the current study, four pure isolated compounds, 3,4,5-trimethoxyphenyl beta-D-glucopyranoside (1), turpinionoside A (2), (+)-lyoniresinol 3alpha-O-beta-D-glucopyranoside (3) and (-)-lyoniresinol 3alpha-O-beta-D-glucopyranoside (4), were isolated from the leaves and twigs of W. robusta. Biological evaluation for free radical scavenging, antibacterial and antigiardial activities was performed. We investigated antioxidant effects of the crude extracts as well as the isolated compounds using 1,1-diphenyl-2-picrylhydrazyl radical (DPPH), hydroxyl radical (OH), and superoxide anion (O(2)) scavenging assays. Three phenolic glucosides (1, 3 and 4) were found to possess strong antioxidant activity. They scavenged DPPH(*) with IC(50) values in the range of 51.5-86.6 microM. We also detected the superoxide dismutase-like activities in compounds 3 and 4 which are lignan glucosides, demonstrating potent superoxide scavenging activity with IC(50) values in the range of 0.8 and 0.7 microM, respectively. Other biological activities including antibacterial and antigiardial assays were carried out. Preliminary results demonstrated that most extracts, except the diethyl ether extract, exhibited inhibition zones against all Gram-positive bacteria including Bacillus cereus, Staphylococcus aureus, Streptococcus mutans, and S. pyogenes. Aqueous extracts of this plant species could inhibit Gram-positive and some Gram-negative bacteria such as Escherichia coli, Salmonella typhi and Shigella sonnei. However, the determination of minimum inhibitory concentrations (MICs) and minimum bactericidal concentrations (MBCs) of W. robusta on all tested bacterial strains showed only weak activity, and their MBCs were greater than 25 mg mL(-1). For antigiardial activity, incubation with 2 x 10(5) trophozoites mL(-1) of the culture medium with the crude extracts at concentration ranged from 31.25 to 1000 microg mL(-1) demonstrated no activity (MIC > 1000 microg mL(-1)).