Cationic antiprotozoal drugs. Trypanocidal activity of 2-(4'-formylphenyl)imidazo[1,2-a]pyridinium guanylhydrazones and related derivatives of quaternary heteroaromatic compounds

Abstract
A series of quaternary 2-phenylimidazo[1,2-.alpha.]pyridinum salts has been prepared and evaluated for antiparasitic activity. Primary attention was focused on derivatives with amido, substituted hydrazone, and heterocyclic functionality at the para position of the phenyl substituent. Guanylhydrazones and N-substituted guanylhydrazones of the 4''-formyl-substituted compounds are very active against the blood state Tryopanosoma rhodesiense in mice by subcutaneous or oral administraton. The most potent compounds attain 100% survival for 30 days at doses of 5.0 mg/kg (po). Weaker activity is noted for certain other 4''-substituents such as carboxamidines and carboxamide oximes. Considerable variation in structure, including replacing of the imidazo[1,2-a]pyridinium ring by other cationic heterocyclic rings and insertion of linking groups between the heterocyclic ring and phenyl group, can be done, and a high level of activity is maintained. Relationships between these structural changes and biological activity are discussed.
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