8-Azaadenosine and its 2'-deoxyribonucleoside: Synthesis and oligonucleotide base-pair stability

Article abstract of DOI:10.1002/hlca.19980810527

The synthesis of 8-azaadenosine (1a; z⁸A) has been performed by SnCl₄- catalyzed glycosylation of 8-azaadenine (4) with 1,2,3,5-tetra-O-acetyl-β- D-ribofuranose (5), followed by the separation of the regioisomers 6 an d7 and subsequent deacetylation. The ribonucleoside 1a as well as its 2'-deoxy derivative 1b (z⁸A(d)) were converted into oligonucleotide building blocks- the phosphonate 2 as well as the phosphoramidites 3 and 19. They were used to prepare the oligoribonucleotide (z⁸A-U)₆ and oligodeoxyribonucleotides. The T(m) values and the thermodynamic data of duplex formation of the modified duplexes showed no significant changes compared to those containing A(d) or A residues. This indicates that the stereoelectronic effect of the 8-azaadenine base which was found for the monomeric nucleoside has only a minor influence on the duplex stability.