Reaction of a nucleobase with nitrosonium ion leads to its diazotization. Due to the instability,the nucleobase-diazonium assumingly falls in dediazotization and successive ring openingreactions. The resulting intermediate of the ring opening reaction is able to covalently cross-linkthe opposite strands of DNA. To examine this assumption for cytosine, some 4-amino-5-cyanopyrimidines were synthesized via [3+3] condensation of amidines with ethoxymethylenemalonitrile and successively converted to the corresponding 4-amino-5carboxyamido derivatives. These compounds were then exposed to nitrosonium ion under different conditions. Results of this study indicate that the diazonium of a 4-aminopyrimidine prefers deamination over the dediazotization. Therefore, the dediazotization and its successive ring-opening reactions of the pyrimidine cation would happen under some exceptionalconditions which deserve to be explored in more detailed studies. In view of the cytosinechemistry and cytotoxicity of NO, the results are presented and discussed. پرونده مقاله