Abstract

Aims: The synthesis of bioactive compounds has antioxidant potential.

Background: All aerobic bodies including human beings, have antioxidant defense systems that protect them from oxidative damage, and many enzymes to remove or heal damaged molecules. However, this normal antioxidant mechanism can be incompetent, and hence dietary intakes of antioxidant compounds are important.

Objective: This study aimed to synthesize isophthalate Schiff base derivatives 1-14 and screen them for their antioxidant activities (DPPH, ferrous ion Fe²⁺ chelating, and ferric Fe³⁺ reducing activities).

Methods: Schiff bases 1-14 were synthesized by a two-step reaction scheme. The first step was the esterification reaction of isophthalic acid followed by the hydrazinolysis of methyl isophthalate to afford isophthalic dihydrazide. The second step was the condensation reaction of isophthalic dihydrazide with various benzaldehydes to afford Schiff bases 1-14. Synthetic compounds were characterized by spectroscopic techniques such as ¹ H-NMR and EI-MS.

Results: Compounds were screened for their antioxidant activities (DPPH, ferrous ion Fe²⁺ chelating, and ferric Fe³⁺ reducing activities). Most of the compounds showed significant antioxidant activities. A structure- activity relationship has also been discussed.

Conclusion: Most of the synthetic isophthalate Schiff bases were found to be moderately active when screened for their antioxidant activities by three assays such as DPPH radical scavenging, ferrous ionchelating, and ferric reducing activities. These moderately active compounds can serve as lead molecules to further modify the structure and identify more powerful antioxidant agents.

Keywords: Isophthalic acid, Schiff base, DPPH, ferric ion reducing activity, ferrous ion chelating activity.

Graphical Abstract