Synthesis, Biological, and Computational Studies of Novel Isoxazolone-Coupled Azo Moieties and Their Photophysical Interactions

Abstract

Objective: In this study, we report the synthesis of new heterocyclic azo dyes (IIIa–IIId) via diazo-coupling reactions of sulfonamides with isoxazolone as the coupling component. The synthesized compounds (IIIa–IIId) were thoroughly characterized, and their biological activities were evaluated through antioxidant and α-amylase inhibition assays. Methods: The target compounds were synthesized by diazo-coupling reactions of different heterocyclic amines (Ia–Id) with 3-phenyl-5-isoxazolone (II). Density Functional Theory (DFT) calculations were performed using the B3LYP functional with the 6-31G(d,p) basis set. Furthermore, in silico molecular docking studies of the target ligands were conducted against the α-amylase receptor. Results and Discussion: The synthesized azo compounds were characterized by various spectroscopic techniques, including FT-IR, ¹H, ¹³C NMR, and HR-MS. DFT studies provided insight into quantum chemical parameters such as the HOMO–LUMO energy gap, electrophilicity index (ω), chemical potential (μ), global hardness (η), softness (S), and molecular electrostatic potential (MEP) surfaces. UV-Vis absorption spectra of the azo dyes were recorded in 5 different solvents, revealing distinct solvatochromic behavior. Antioxidant and α-amylase inhibition assays were employed to assess the pharmacological potential of the synthesized azo dyes. Antioxidant activity results indicated that compound (IIIa) exhibited strong activity with an IC₅₀ value of 21.581 µg/mL, comparable to the reference standard ascorbic acid. In α-amylase inhibition studies, compounds (IIIc) and (IIId) demonstrated significant activity relative to the standard drug acarbose. Molecular docking results further supported these findings, with compounds (IIIc) and (IIId) exhibiting the lowest binding energies of –6.4 and –6.3 kcal/mol, respectively, forming two and four hydrogen bonds with key amino acid residues in the active site of α-amylase. Conclusions: The synthesized isoxazolone-based azo dyes showed promising biological activities and photophysical properties. The combined experimental and computational data suggest their potential for further development as bioactive agents.