8-AZAADENOSINE AND ITS 2'-DEOXYRIBONUCLEOSIDE - SYNTHESIS AND OLIGONUCLEOTIDE BASE-PAIR STABILITY

The synthesis of 8-azaadenosine (1a; z(8)A) has been performed by SnCl 4-catalyzed glycosylation of 8-azaadenine (4) with 1,2,3,5-tetra-O-ace tyl-beta-D-ribofuranose (5), followed by the separation of the regiois omers 6 and 7 and subsequent deacetylation. The ribonucleoside 1a as w ell as its 2'-deoxy derivative 1b (z(8)A(d)) were converted into oligo nucleotide building blocks - the phosphonate 2 as well as the phosphor amidites 3 and 19. They were used to prepare the oligoribonucleotide ( z(8)A-U)(6) and oligodeoxyribonucleotides. The T-m values and the ther modynamic data of duplex formation of the modified duplexes showed no significant changes compared to those containing A(d) or A residues. T his indicates that the stereoelectronic effect of the 8-azaadenine bas e which was found for the monomeric nucleoside has only a minor influe nce on the duplex stability.