In the present study, a series of 3-(8-hydroxyquinolin-5-yl)-5-oxo-5H-[1,3]thiazolo[3,2-a]pyrimidines (4a,b), (5a-c) and (7a-c) were synthesized by
the reaction of 7-metyhlthio-3-(8-hydroxyquinolin-5-yl)-5-oxo-5H-[1,3]thiazolo[3,2-a]pyrimidine-6-carbonitrile (3) with different N- and Onucleophiles,
such as hetaryl amines, aryl amines, substituted phenols in the presence of anhydrous potassium carbonate (K2CO3) and dimethyl
formamide (DMF). Also, other fused tetracyclic thiazolo[2′,3′:1,2]pyrimido[5,4-d]thiazolo[3,2-a]pyrimidines (8a,b) and (9) were synthesized on
treatment of 3 with substituted aminothiazoles and 2-aminobenzothiazole. The parent compound (3) was reacted with hydrazine hydrate to obtain
the corresponding aminopyrazole derivative (10) which was conducted to react with various reagents, such as acetic anhydride, acetyl acetone,
ethyl acetoacetate and diethyl malonate to yield thiazolo[2,3′:1,2]pyrimido[4,5-c]pyazolo[2,3-a]pyrimidine derivatives (12-14). On the other hand,
treatment of 10 with appropriate aromatic aldehydes afforded the corresponding arylidene derivatives (15a-c). Finally, reaction of 4-
chlorobenzylidine derivative (15b) with thioglycolic acid and chloroacetyl chloride furnished the thiazolidinone and azetidenone derivatives (16)
and (17), respectively. All the new title compounds were characterized by elemental and spectral data. The antimicrobial activity of some novel
products was evaluated by agar well-diffusion.