Antioxidant hydroquinones substituted by beta-1,6-linked oligosaccharides in wheat germ.

Seven new compounds that demonstrate antioxidant properties, 4-hydroxy-3-methoxyphenyl beta-d-glucopyranosyl-(1-->6)-beta-D-glucopyranosyl-(1-->6)-beta-D-glucopyranoside (1), 4-hydroxyphenyl beta-D-glucopyranosyl-(1-->6)-beta-D-glucopyranosyl-(1-->6)-beta-D-glucopyranoside (2), 4-hydroxy-3-methoxyphenyl beta-D-glucopyranosyl-(1-->6)-beta-D-glucopyranosyl-(1-->6)-beta-D-glucopyranosyl-(1-->6)beta-D-glucopyranoside (3), 4-hydroxy-3-methoxyphenyl beta-D-glucopyranosyl-(1-->6)-beta-D-glucopyranoside (4), 4-hydroxy-3,5-dimethoxyphenyl beta-D-glucopyranosyl-(1-->6)-beta-D-glucopyranoside (5), 4-hydroxy-3,5-dimethoxyphenyl beta-D-glucopyranosyl-(1-->6)-beta-D-glucopyranosyl-(1-->6)-beta-D-glucopyranoside (6), and 4-hydroxy-2-methoxyphenyl beta-d-glucopyranosyl-(1-->6)-beta-D-glucopyranosyl-(1-->6)-beta-D-glucopyranoside (7), were isolated from wheat germ. The structures were determined by spectroscopic and chemical methods. Compound 1 was the most abundant, approximately 2 mg isolated from each gram of wheat germ. The antioxidant activity of compounds 1-7 was determined by the Trolox equivalent antioxidant capacity assay, and 2 and 7 showed higher values than the other compounds. Compounds 1 and 3-6 reacted with the radical cation reagent within a few seconds, whereas 2 and 7 required several minutes for complete reaction. Compound 1 was shown to protect plasmid DNA from oxidative stress damage caused by hydrogen peroxide; this effect was concentration-dependent.