Synthesis, Catalytic GPx-like Activity, and SET Reactions of Conformationally Constrained 2,7-Dialkoxy-Substituted Naphthalene-1,8-diselenides.

Several 2,7-dialkoxy-substituted naphthalene-1,8-diselenides were prepared and tested for catalytic antioxidant activity in an NMR-based assay employing the reduction of hydrogen peroxide with stoichiometric amounts of benzyl thiol. Acidic conditions enhanced their catalytic activity, whereas basic conditions suppressed it. The highest activity was observed with a 2,7-bis(triethyleneglycol) derivative. These compounds serve as mimetics of the antioxidant selenoenzyme glutathione peroxidase. Studies based on NMR peak-broadening effects and EPR spectroscopy indicated that a thiol-dependent SET reaction occurs under the conditions of the assay, which can be reversed by the addition of triethylamine. In contrast, peak broadening induced by proton-catalyzed electron transfer during the treatment of naphthalene-1,8--diselenides with trifluoroacetic acid can be suppressed by the addition of excess thiol. These observations provide new insights into the redox mechanisms of these processes.