Synthesis and properties of a new class of nucleosides with spin source.

Novel spin-labeled ribonucleosides 1-5 were synthesized to investigate stability and behavior of N-tert-butyl aminoxyl radical on nucleobase. Site selective lithiation of tri-O-protected ribonucleosides followed by the reaction with 2-methyl-2-nitrosopropane (MNP) resulted in introduction of N-tert-butylhydroxylamino group into various positions of purine or pyrimidine nucleus. Oxidation of the obtained hydroxylamines with Ag2O led to formation of 1-5. EPR study showed that the unpaired electron of the aminoxyl radical was delocalized into the nucleobase and hyperfine structures were dependent on the position of the radical.