Chlorine Position Governs the Multitarget Bioactivity of Phenylhydrazines: In Vitro Antioxidant, Anti‐Inflammatory, Anti‐Tyrosinase and Antibacterial Evaluation Supported by DFT and Molecular Docking

ABSTRACT

Phenylhydrazine is a common medicinal‐chemistry scaffold, but the effect of halogen ring position on its biological activity is not established. This work compares, under identical conditions, how one chlorine atom and its position modify antioxidant, anti‐inflammatory, anti‐tyrosinase, and antibacterial behavior. Phenylhydrazine (H1), 2‐chlorophenylhydrazine (H2, ortho) and 4‐chlorophenylhydrazine (H3, para) were tested in triplicate by five antioxidant assays, thermal bovine serum albumin BSA denaturation, L‐DOPA oxidation and broth microdilution against four bacterial strains. DFT (B3LYP/6‐31+G(d,p), docking against albumin, COX‐2, and TYRP1, and ADMET predictions supported the interpretation. H2 showed the strongest overall antioxidant profile. H3 produced the lowest IC ₅₀ in the BSA‐denaturation assay. H1 was the most active test compound in the tyrosinase assay (IC ₅₀ = 42.74 ± 1.75 µM), compared with kojic acid (IC ₅₀ = 32.02 ± 0.52 µM). H3 showed the strongest antibacterial effect against Salmonella Typhi (MIC = 19.531 mg L−1). Chlorine position redirects bioactivity rather than raising it uniformly: ortho favors radical scavenging, para favors protein stabilization and antibacterial action, and the unsubstituted scaffold remains the best tyrosinase inhibitor. The compounds are structural probes, not drug candidates, given predicted CYP3A4 inhibition, a moderate Ames signal, and the scaffold's known hematological liability.