Synthesis and Antibacterial Activity of New Imidazo[1,2-a]pyridines Festooned with Pyridine, Thiazole or Pyrazole Moiety

A series of new 6,8-dichloro-imidazo[1,2-a]pyridine derivatives incorporating pyridine, thiazole, and pyrazole ring systems was synthesized. The synthetic strategy of imidazopyridinyl-pyridine hybrids 2 and 3 involves one pot reaction of the precursor 3-acetyl-6,8-dichloro-2-methylimidazo[1,2-a] pyridine (1) with aldehydes, malononitrile, and/or ethyl cyanoacetate. Treatment of 1 with thiosemicarbazide and/or bromine followed by subsequent cyclization with ethyl bromoacetate, chloroacetone, phenacyl chloride, and/or thiourea was applied as synthetic routes for accessing the imidazopyridinyl-thiazole hybrids 5, 6, and 8-10. The reaction of 1 with dimethylformamide-dimethylacetal followed by subsequent treatment with hydrazine was employed to prepare the imidazopyridinyl-pyrazole motif 12. The antibacterial potency of these imidazopyridine hybrids has been evaluated against some model bacteria. The results indicated that the imidazopyridine-thiazole hybrids revealed remarkable antibacterial activities.