Synthesis and antibacterial activity of some quinazolin-containing oxadiazolin-5-thione moieties

Several new quinazolin-4-one containing oxadiazolin-5-thione moieties were synthesized and evaluated for their antibacterial activity. Esterification of 2-substituted phenyl-3-carboxyalkyl-methyl-3,4-dihydroquinazolin-4-ones (I) with absolute ethyl alcohol in the presence of sulfuric acid afforded the corresponding esters (II). Hydrazinolysis of (II) with hydrazine hydrate in ethanol gave the acid hydrazides (III). Refluxing (III) with equimolar amounts of potassium hydroxide and slight excess of carbon disulfide afforded the corresponding oxadiazolin-5-thione derivatives (IV). The thiones undergo Mannich reaction using a formaldehyde/secondary amines mixture whereby the 4-substituted amino-methyl derivatives (V) were obtained. Microanalysis, IR, NMR spectra were used to elucidate the structures of the newly synthesized compounds. All the designed compounds were tested for their antibacterial activity. The morpholino derivatives showed an encouraging antibacterial activity.