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 rise 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 incorporation of both 5'R and 5'S diastereoisomers of 5',8-cyclopurine 2'-deoxyribonucleosides into oligodeoxynucleotides to facilitate the assessment of the biochemical and biophysical features of such lesions. We report the preparation 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'-deoxyguanosine (4). Fully protected compounds 10, 18, and 25 were then inserted into several oligonucleotides by automated procedures. Analysis of modified DNA oligomers 26-31 by electrospray mass spectrometry and enzymatic digestions with exo- and endonucleases confirmed the base compositions and the integrity of free radical-induced tandem lesions 2-4 that were chemically inserted.