Interaction of Phenolic Schiff Bases Bearing Sulfhydryl Moieties with DPPH Radical: Structure-Activity Relationship Study

Phenolic compounds are extensively studied due to their antioxidant properties. Naturally occurring polyphenols, including flavonoids, are mainly secondary metabolites of plants produced to resist ultraviolet irradiation and pathogenic microorganisms [1]. Moreover, cellular response to oxidative stress in aerobic organisms is mediated by phenolic antioxidants that inactivate reactive oxygen species (ROS). In the event of ROS overproduction endogenous enzymatic and non-enzymatic defense mechanisms fail to scavenge ROS, so the damage to DNA, protein and lipid molecules may occur as a result of oxidative stress. This poses a risk of the development of cancer, Alzheimer’s and Parkinson’s diseases, atherosclerosis, hypertension, type I diabetes [2]. Phenolic antioxidants have been found to exhibit biological activity in their treatment. Synthetic phenolic antioxidants are added to processed foods to preserve their organoleptic properties by preventing lipid peroxidation, whereas sterically hindered phenols are applied for the stabilization of polymers. Investigation of antioxidant activity mechanisms of phenols is a challenging problem for the discovery of novel compounds possessing antimicrobial, antiproliferative, and anti-inflammatory activity.

Sterically hindered phenolic Schiff bases were synthesized by the condensation of 4,6-di-tert-butyl-2,3-dihydroxybenzaldehyde with o-, m-, p-mercaptoanilines and 2,2’-, 4,4’-disulfanediyldianilines. Their antioxidant properties were further evaluated in vitro by studying their ability to scavenge a stable nitrogen-centered radical, 2,2-diphenyl-1-picrylhydrazyl (DPPH). The results obtained are discussed in the context of presumed interrelationship of their antioxidant activity and chemical structure. Bearing hydroxyl and sulfhydryl groups bonded to aromatic rings, these compounds could work as hydrogen donors, singlet oxygen and superoxide radical scavengers, reducing agents, and metal-chelating agents [3].