New Fused Imidazo-Pyrimidine and Imidazo-Purine Derived From Maleimide and Nucleobases: One Pot Synthesis, Structure Elucidation, Antioxidant and Antimicrobial Evaluation

Abstract

A series of novel quinoxalinones, (2,5-dioxoimidazo[1,2-f]pyrimidin-3-yl)acetamide, 8-oxo-3H-imidazo[1,2-g]purin-7-yl)acetamide, and 4,7-dioxo-3H-imidazo[2,1-e]purin-8-yl)acetamide, were synthesized by reaction of maleimide with substituted orthophenylenediamine or nucleobases. The analytical methods such as FT-IR, ¹H and ¹³C NMR spectroscopy, mass spectrometry, and microanalyses (C, H, N) were utilized to elucidate the structures of the target compounds. These products were tested for their ability to scavenge DPPH^• (1,1-diphenyl-1-picrylhydrazyl) and ABTS^+• (2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) free radicals, as well as for their total antioxidant capacity (TAC). Additionally, antimicrobial activity was screened against four bacterial strains and fungi using the well diffusion method. The results demonstrated that quinoxalinone 1f exhibited potent free radical scavenging activities against DPPH and ABTS radicals, with IC₅₀ values of 1.67 μg mL^-1 and 20.76 μg mL^-1, respectively, compared to the standard antioxidant ascorbic acid (IC₅₀ values of 2.82 and 74.22 μg mL^-1, respectively). Compound 1f also displayed the highest TAC with a value of 1303 mg (AAE)/g of dry compound. Furthermore, (2,5-dioxoimidazo[1,2-f]pyrimidin-3-yl)acetamide (2a) demonstrated superior antioxidant activity against ABTS radical, with an IC₅₀ value of 73.89 μg mL^-1, which is lower than that of the ascorbic acid (74.22 μg mL^-1). The antimicrobial assay revealed that compound 1f exhibited potent inhibitory effects against all tested bacterial and fungal strains.