Synthesis of (4H)-Imidazol-4-ones from α-Amino Acids, and their Antioxidant Activities using Electron Transfer Methods

A novel series of (4H)-imidazol-4-ones, designated as compounds 5(a–l), were synthesized from phenylalanine and tyrosine. This synthesis involved derivatization of amino acids with phenylacetyl chloride, followed by cyclocondensation with aromatic amines using PCl₃ and a deep eutectic solvent as both catalyst and solvent. Amide intermediates were first produced via the Schotten-Baumann reaction. These intermediates then underwent cyclization in the presence of PCl₃ and deep-eutectic solvent, leading to the formation of imidazolones as potent antioxidants. The newly synthesized compounds were evaluated for their antioxidant activities using several electron transfer-based assays, including DPPH, ABTS, FRAP, and CUPRAC. Among the tested compounds, compound 5 i exhibited excellent antioxidant activity compared to the standard reference drugs, ascorbic acid and Trolox.