Abstract
AbstractThe mechanism of the isotopic exchange reaction of the 5‐H hydrogen of uracil and its methyl derivatives in water and organic solvents has been studied. The key intermediate of the reaction is a C‐5 tautomer of uracil in which the carbon atom at the 5‐position has two hydrogen atoms, its hybridization is changed from sp2 to sp3, and the aromaticity of the pyrimidine ring is lost. We have used 1H NMR spectroscopy to follow the kinetics of the hydrogen/deuterium exchange reaction. In aqueous media a general base catalysis was observed and for exchange in organic solvents we have proposed a reaction mechanism that involves the participation of solvent molecules. The reaction rates determined by NMR can be rationalized by density functional computations. We have shown that the hydrogen‐to‐deuterium exchange reaction is much faster in some suitable nucleophilic solvents than in water. These findings could be used for the tritium labeling of pyrimidine nucleic acid bases.
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