Insights in the antioxidant activity of diarylamines from the 2,3-dimethylbenzo[b]thiophene through the redox profile

Cyclic voltammetry was used to evaluate the antioxidant activity of 7-aryl or 7-heteroarylamino-2,3-dimethylbenzo[b]thiophenes previously synthesized by some of us, comparing their oxidation potentials with those of the well-known synthetic standards (BHA, BHT). Compounds with electron-donating groups on the arylamine moiety have lower Ep/2 than compounds with electron-withdrawing groups or electron-deficient rings (pyridines). The position of the methoxy group on the arylamine moiety also changes the oxidation potential: lower Ep/2 for the diarylamines with methoxy groups in the para position. Comparing the first peak potential with the ones of BHA and BHT, the diarylamine compounds show lower oxidation potential, and therefore higher reducing power. A reasonable inverse correlation was also observed between the Ep/2 values and the pEC50 values obtained in antioxidant activity chemical assays. It can be generalized that compounds with lower Ep/2 values have better antioxidant activity (DPPH assay) and higher reducing power.