Formation of Cyclopyrimidines Via the Direct Effects of Gamma Radiation of Pyrimidine Nucleosides

Summary

Continuing our study of the direct effects of gamma radiation on DNA and its model compounds, we have isolated and characterized quantitatively an important lesion formed by irradiating pyrimidine 2′-deoxyribonucleosides in frozen aqueous solution. We report here the formation of 5′,6-cyclo-5,6-dihydropyrimidine nucleosides via hydrogen abstraction at C5′ of the osidic moiety with subsequent intramolecular attack at C6 of the base. We have so far managed to isolate six of the possible eight diastereomers of 5′,6-cyclo-5,6-dihydrothymidine, and all four possible 5′,6-cyclo-5,6-dihydro-2′-deoxyuridines formed by irradiation of 2′-deoxycytidine. Also presented is a detailed discussion of the configurational analysis of each isomer based on ¹H NMR data.