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Insights into the antioxidant activity of phenolic compounds: Synthesis and electrochemical study of new series of hydroxycoumarins
1 , 1 , 2 , 2 , 3 , 3 , * 2, 3
1  Departamento de Química Inorgánica y analítica, Laboratorio de radicales libres y antioxidantes, Facultad de Ciencias Químicas y Farmacéuticas, Universidad de Chile, Chile
2  CIQUP/Departamento de Química e Bioquímica, Faculdade de Ciências, Universidade do Porto, Portugal
3  Departmento de Química Orgánica, Facultad de Farmacia, Universidad de Santiago de Compostela, Spain

Abstract: Phenolic compounds are bioactive substances widely distributed in the vegetable kingdom. They act as natural antioxidants, and their presence contributes to the color, flavor and aroma of food. This group of micronutrients is composed of one or more aromatic benzene rings with one or more hydroxyl groups and their redox properties are related with their chemical structure characteristics. The knowledge of their redox potentials may help the food industry, because when phenolic compounds are oxidized they could affect the quality of the wines, beers, grape juices, etc. Coumarins are a large family of compounds, of natural and synthetic origin, that show important biological activities. Therefore, they occupy an important place in the study of natural products and synthetic organic chemistry. Recent studies pay special attention to their antioxidative, anticarcinogenic and enzymatic inhibition properties. Their preparation, and the versatility of the synthetic methodology, allowed us obtaining a wide family of compounds with substituent in different positions in the molecule. The election of these derivatives has considered the later pharmacological evaluation. The investigation of the properties of these compounds, the study of the structural pattern and the elucidation of their biological role is of great interest for further development of coumarin-like antioxidant drugs. The electrochemical behaviour of a group of differently substituted hydroxycoumarins was investigated using cyclic, differential pulse and square wave voltammetry, in aqueous media at a glassy carbon electrode over the whole pH range. The antioxidant reactivity and capacity were also evaluated through a competition assay with hydroxyl radical (OH•) and DMPO like ORAC-FL methodology. Number and positions of the hydroxyl groups were important factors in the antioxidant activities against peroxyl radical of both types of coumarins derivatives.
Keywords: Hydroxycoumarins, Perkin reaction, hydrolysis reaction, Electrochemical study, ORAC-FL, voltametry