In Vitro Study of the Effect of 2,6-Substituents at the New 4-Ethoxy-Phenols as Antioxidants

The antioxidant effect of the different groups in the 2,6-positions of the new 4-ethoxy-phenols were evaluated. To address our research, 2,2-diphenyl-1-picrylhydrazyl (DPPH), 2,2’-azino-bis-3-ethylbenzothiazoline-6-sulfonic acid (ABTS) and reducing power capacity, were employed to analyze the antioxidant activity. The results of the antioxidant test indicated that most of the new molecules 6a–l presented high antioxidant activity. Compound 6f had the highest activity (1.47 ± 0.39 µg/mL) when it was compared with 2,6 di-tert-butyl hydroxytoluene (BHT, 6.72 ± 0.47 µg/mL) and trolox (2.81 ± 0.31 µg/mL) as standards using DPPH assay. ABTS method confirmed that 6f was the most active antioxidant molecule. Theoretical analysis showed that phenyl group in 6f has a similar effect in the O-H energy that t-butyl in BHA, but the steric hindrance is different. In the three tests, compound 6i turned out to be the one with the least antioxidant effect; it demonstrated the main role of hydroxyl group on the topology of the species to achieve the desired antioxidant effect, which was completely lost when this group was absent.