Antioxidative Effects of 6-Methoxysorigenin and Its Derivatives from Rhamnus nakaharai

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In the search for potential antioxidants, the naphthalenic compounds, 6-methoxysorigenin (2) and its glvcosides [i.e. 6-methoxysorigenin-8-0-gIucoside (3), α-sorinin (4), and 6-methoxysorigenin-8-rutinoside (5)] isolated from Rhamnus nakaharai together with two acylates (peracetate and perpropionate) of 2 were evaluated for antioxidant activities using 2, 2-diphenyl-1-picrylhydrazyl (DPPH), metal chelating, and electron spin resonance (ESR) assays as well as anti-lipid peroxidation assay. The results showed that 2 possesses the most potent DPPH radical scavenging, metal chelating, and anti-lipid peroxidation activities with IC_<50> values of 3.48, 615.90, and 5.95μg/ml, respectively. The glycosides 3, 4, and 5 showed decreasing antioxidant activity that was related to an increased substitution at 1 ,8-dihydroxyl with sugar molecules. This suggests the importance of 1, 8-dihydroxyl of 2 in the antioxidative effect. The iron chelation result could further explain the main cause of increasing antioxidant activity in 2. The acylates of 2 (2a peracetate and 2b perpropionate), although lacking a free hydroxyl, also exhibited significant anti-lipid peroxidation effect. ESR results further demonstrated that 2 possesses strong antioxidant activities. Taken together, this study shows that 2 is a potent antioxidant and may also be used for designing new iron chelators for clinical applications.
2007-03-01