Synthesis, Identification, and Evaluation of New Pyrimidine and Pyrazole Derivatives Bearing a Quinazolin-4(3H)-one Moiety, Including Antibacterial, Antifungal, and Antioxidant Effects

New azo pyrimidine and pyrazole derivatives containing a quinazolin-4(3H)-one moiety were synthesized, and their antioxidant and antimicrobial effects were studied. The target compounds were obtained starting from ethyl 2-[2-(4-methoxyphenyl)-4-oxo-3,4-dihydroquinazolin-3-yl]acetate which was reacted with p-phenylenediamine, followed by diazotization, coupling with acetylacetone, and condensation with urea, thiourea, and substituted hydrazines. The synthesized compounds were characterized by melting points, FT-IR and ¹H and ¹³C NMR spectra, and elemental analyses. Some of them showed high antioxidant activity compared to ascorbic acid as standard drug, while the others exhibited moderate to low activity. The title compounds were also evaluated for antimicrobial activity by the well diffusion method and were found to be effective against Gram-positive and Gram-negative bacteria such as Escherichia coli, Bacillus cereus, and Staphylo­coccus aureus, as well as against the fungi Candida albicans and Rhizopus microsporum, at a concentration of 80 µg/mL.