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Electrochemical oxidation and superoxide radical scavenging activity of 2-hydroxy/methoxy phenylbenzothiazole derivatives

Benzothiazoles are among the most important nitrogen heterocyclic compounds, frequently found in many molecules of interest in medicinal chemistry. Their derivatives are possessing diverse biological activities such as anticancer, cardio-protective, anti-inflammatory, anticonvulsant, antifungal, antibacterial, antiprotozoal activities, etc. Recently, amidino- substituted benzothiazole derivatives substituted with the variable number of hydroxyl and methoxy groups have shown to possess antioxidant activity, by using DPPH, ABTS and FRAP spectrophotometric methods [1, 2]. As a continuation of the study reported by Racané et al., the present study was aimed to elucidate the redox chemistry behind the antioxidant activity of amino/amidino- substituted 2-hydroxy/methoxy phenylbenzothiazoles. The kinetics and mechanism of electrochemical oxidation of compounds of interest (compounds 1-4, Fig.1) were studied by means of square-wave voltammetry (SWV) in aqueous electrolyte solution (0.1 mol/L KNO3) at a glassy-carbon electrode (GCE) over a wide range of pHs (pH 1–11) and SW frequencies (8-1000 Hz). We have shown that the studied compounds incorporate electron-transfer (ET) moieties which may play important role in their antioxidant activities. The oxidation mechanism of compounds 1-3 is related to an oxidation process taking place on the hydroxyl groups located at 2-phenyl ring. The electrochemical behaviour of compound 4 (without – OH groups on the phenyl ring) proved more complex and further studies are in progress to elucidate the functional groups responsible for electroactivity and antioxidant activity of 4. Furthermore, we studied the reactivity of compounds 1 -4 against electrochemically generated superoxide anion radical by the means of cyclic voltammetry. The superoxide radical scavenging activities of compounds 1 -4, determined by measuring the anodic current decay of the radical in the presence of increasing concentrations of compounds of interest, were expressed in terms of EC50 values, i.e. the concentration of compound needed to consume 50% of a superoxide radical. All four compounds showed a more or less pronounced superoxide radical scavenging activity, depending on their structural features. Superoxide radical scavenging activities of compounds correlated well with their electrochemical oxidation potentials, implying that the scavenging activity of investigated compounds is mainly governed by their redox properties.

2-hydroxy/methoxy phenylbenzothiazole derivatives ; electrochemistry ; oxidation potential ; superoxide radical scavenging activity ; antioxidant activity

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