Synthesis and characterization of oligonucleotides containing 5 ',8-cyclopurine 2 '-deoxyribonucleosides: (5 ' R)-5 ',8-cyclo-2 '-deoxyadenosine, (5 ' S)-5 ',8-cyclo-2 '-deoxyguanosine, and (5 ' R)-5 ',8-cyclo-2 '-deoxyguanosine

Radiation-induced degradation bf purine and-pyrimidine nucleosides gave ris e to carbon-bridged cyclocompounds. Such cyclonucleosides represent a class of tandem lesions in which modification of both the base and 8-deoxyribose has occurred. A solid-phase synthetic method was designed for the incorpor ation of both 5'R and 5'S diastereoisomers of 5',8-cyclopurine 2'-deoxyribo nucleosides into oligodeoxynucleotides to facilitate the assessment of the biochemical and biophysical features of such lesions. We report the prepara tion of the phosphoramidite synthons of (5'R)-5',8-cyclo-2'-deoxyadenosine (2), (5'S)-5',8-cyclo-2'-deoxyguanosine (3), and (5'R)-5',8-cyclo-2'-deoxyg uanosine (4). Fully protected compounds 10, 18, and 25 were then inserted i nto several oligonucleotides by automated procedures. Analysis of modified DNA oligomers 26-31 by electrospray mass spectrometry and enzymatic digesti ons with exo- and endonucleases confirmed the base compositions and the int egrity of free radical-induced tandem lesions 2-4 that were chemically inse rted.