8‐Aza‐7‐deazaadenine N8‐ and N8‐(β‐ D ‐2′‐Deoxyribofuranosides): Building blocks for automated DNA synthesis and properties of oligodeoxyribonucleotides

Oligonucleotides with alternating 8‐aza‐7‐deaza‐2′‐deoxyadenosine (= c7z8Ad2) and dT residues (see 11, 14 and 16) or 4‐aminopyrazolo [3,4‐d] pyrimidine N2‐(β‐D‐2′‐deoxyribofuranoside) (= c7z8A′d1); (3) and dT residues (see 12) have been prepared by solid‐phase synthesis using P(III) chemistry, Additionally, palindromic oligomers derived from d(C‐T‐G‐G‐A‐T‐C‐C‐A‐G) but containing 2 or 3 instead of dA (see 18–22) have been synthesized. Benzoylation of 2 or 3, followed by 4,4′‐dimethoxytritylation and subsequent phosphitylation yielded the methyl or the cyanoethyl phosphoramidites 8a,b and 9. They were employed in automated. DNA synthesis. Alternating oligomers containing 2 or 3 showed increase dTm values compared to those with dA, in particular 12 with an unusual N2‐glycosylic bond. The palindromic oligomers 18‐22 containing 2 or 3 instead of dA outside of the enzymic recognition side reduced the hydrolysis rate, replacement within d(G‐A‐T‐C) abolished phosphodiester hydrolysis.