N7-DNA: Synthesis and base pairing of oligonucleotides containing 7-(2-deoxy-β-D-erythro-pentofuranosyl)adenine (N7A(d))

Article abstract of DOI:10.1002/hlca.19940770302

The synthesis of oligonucleotides containing 7-(2-deoxy-β-D-erythro-pentofuranosyl)adenine (N⁷A(d); 1) is described. Compound 1 was obtained from the precursor 4-amino-1H-imidazole-5-carbonitrile 2-deoxyribonucleoside 6 and was found to be much more labile than A(d). The N⁶-benzoyl protecting group (see 8) destabilized the N-glycosylic bond further and was difficult to remove by NH₃-catalyzed hydrolysis. Therefore, a (dimethylamino)methylidene residue was introduced (→9). Amidine 9 was blocked at OH-C(5') with the dimethoxytrityl residue ((MeO)₂Tr), and phosphonate 4 as well as phosphoramidite 5 were prepared under standard conditions. Phosphonate 4 was employed in solid-phase oligonucleotide synthesis. Homooligonucleotides as well as self-complementary oligonucleotides were prepared. The oligomer d[(N⁷A)₁₁-A] (11) formed a duplex with d(T₁₂) (13). Antiparallel chain polarity and reverse Watson-Crick base pairing was deduced from duplex formation of the self-complementary d[(N⁷A)₈-T₈] (14).