Mechanisms of Bromination of Uracil Derivatives. 6. Cytosine and N-Substituted Derivatives

Article abstract of DOI:10.1021/jo00345a025

The reactions of bromine with cytosine, 1-methylcytosine, cytidine, and 3-methylcytosine in acidic aqueous sloutions have been studied.Initially adducts (5-bromo-5,6-dihydro-6-hydroxycytosines) are produced which are clearly observable by proton NMR, albeit in their protonated forms in the acidic media used.In time the adducts undergo elimination of water to give substitution products, 5-bromocytosines.Kinetic measurements of the initial reaction in the pH range 0-5 are consistent with the adducts resulting from rate-determining attack of bromine in the free base form of the cytosine substrates followed by capture of the cation so produced by water.An alternative mechanism involving first hydration and then bromine attack can be ruled out.