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Background  Despite significant progresses in antimicrobial therapy, infectious diseases caused by bacteria and fungi remain a major worldwide health problem because of the rapid development of resistance to existing antimicrobial drugs. Therefore, there is a constant need for new antimicrobial agents. There are a large number of heterocyclic derivatives containing nitrogen atoms that possess a broad spectrum of biological activities including pyridine and pyridazine, which are two of the most important heterocycles in medicinal chemistry.    Results  The reaction of 3-oxo-2-arylhydrazonopropanals  2  with ethyl cyanoacetate and malononitrile  3a,b  has led to the formation of 2-amino-5-arylazo-6-aryl substituted nicotinates  8a-k  as sole isolable products when the aryl group in the arylazo moiety was substituted with an electron-withdrawing group like Cl, Br, NO 2 . The pyridazinones  10  were formed from the same reaction when the arylazo moiety was phenyl or phenyl substituted with an electron-donating group. The 2-aminoazonicotinates  8  were condensed with DMF-DMA to afford the amidines  13a,b , which then were cyclized to afford the targeted pyrido[2,3- d ]pyrimidine derivatives  15a,b,  respectively. The structures of all new substances prepared in this investigation were determined by using X-ray crystallographic analysis and spectroscopic methods. Most of the synthesized compounds were tested and evaluated as antimicrobial agents and the results indicated that many of the obtained compounds exhibited high antimicrobial activity comparable to ampicillin, which was used as the reference compound.    Conclusion  A general rule for the synthesis of 2-amino-5-arylazo-6-aryl substituted nicotinic acid and pyridazinone was established using 3-oxo-2-arylhydrazonopropanal as a precursor. Moreover, a novel route to pyrido[2,3- d ]pyrimidine was achieved. Most of the synthesized compounds were found to exhibit strong inhibitory effects on the growth of Gram-positive bacteria especially  Bacillus subtilis . Compounds  1a, 8a-h ,  10a-c ,  15b  and  16  showed a broad spectrum of antimicrobial activity against  B. subtilis .

chemistry central journal

Approaches towards the synthesis of a novel class of 2-amino-5-arylazonicotinate, pyridazinone and pyrido[2,3-d]pyrimidine derivatives as potent antimicrobial agents