SYNTHESIS AND SOME BIOLOGICAL PROPERTIES OF DERIVATIVES OF 2,3-DISUBSTITUTED 5,5-DIMETHYL-BENZO[H]QUINAZOLIN-4(1H)-ONES.

A series of novel 5,5-dimethyl-benzo[h]quinazolin-4(1H)-one derivatives bearing thioalkynyl and amino substituents were synthesized starting from ethyl 1-amino-3,3-dimethyl-3,4-dihydronaphthalene-2-carboxylate. The synthetic pathway involved cyclization, alkylation, and condensation reactions leading to structurally diverse quinazolinone derivatives. The structures of the synthesized compounds were confirmed by IR, ^1H and ^13C NMR spectroscopy, mass spectrometry, and thin-layer chromatography. The antioxidant activity of selected compounds was evaluated using the DPPH free radical scavenging assay, and their IC₅₀ values were determined. All tested compounds exhibited concentration-dependent antioxidant activity with IC₅₀ values ranging from 0.388 to 0.521 mM. Among them, compound XIII showed the highest radical scavenging activity, although lower than that of the reference antioxidant, ascorbic acid. Structure-activity relationship analysis indicated that the presence of amino and methoxy-substituted aromatic moieties enhanced antioxidant potential. The obtained results suggest that the synthesized benzo[h]quinazolinone represent a useful basis for further structural optimization as antioxidant agents.