Design, Synthesis, and In Vitro Antioxidant Evaluation of Novel Oxazole Derivatives

Abstract

Background: Oxazole derivatives represent an important class of heterocyclic compounds with diverse biological activities, including antioxidant potential. The present study aimed to synthesize and characterize a series of 2,4-disubstituted oxazole derivatives and evaluate their in vitro radical-scavenging activity.
Methods: A series of 24 oxazole derivatives comprising A1–A8, B1–B8, and C1–C8 was synthesized using Citrus limon juice as a natural catalyst. The synthesized compounds were further developed into Schiff-base and thiazole analogues and characterized using Fourier-transform infrared spectroscopy (FT-IR), ^1H-nuclear magnetic resonance (^1H-NMR), ^13C-nuclear magnetic resonance (^13C-NMR), and mass spectrometry. Antioxidant activity was evaluated using DPPH and ABTS radical-scavenging assays, with ascorbic acid used as the reference standard.
Results: Several derivatives demonstrated appreciable radical-scavenging activity in both assays. In the DPPH assay, compounds B5, B4, A6, C5, and C8 exhibited IC₅₀ values of 17.12, 19.89, 25.85, 29.54, and 33.61 μg/mL, respectively, compared with 28.47 μg/mL for ascorbic acid. In the ABTS assay, A2, B2, B6, A6, and C6 showed IC₅₀ values of 19.32, 21.05, 27.64, 2, and 28.52 μg/mL, respectively, compared with 26.18 μg/mL for ascorbic acid. The differing activity profiles across the two assays indicate that antioxidant activity was influenced by the structural characteristics of the individual derivatives.
Conclusion: The study demonstrates that the synthesized oxazole derivatives possess promising in vitro radical-scavenging activity, with B5 and B4 showing the strongest DPPH activity and A2 and B2 showing the strongest ABTS activity. The findings support further investigation of selected oxazole derivatives to elucidate their structure–activity relationships and biological potential.