3-Deazaguanine N7- and N9-(2′-Deoxy-β-D-ribofuranosides): Building Blocks for Solid-Phase Synthesis and Incorporation into Oligodeoxyribonucleotides

Oligonucleotides continuing 3-deaza-2′-deoxyguanosine ( I ) or its N⁷-regioisomer 2 were prepared by solid-phase synthesis using P¹¹¹ chemistry. Protection of ¹ or ² with N,N V-dimethylformamide diethyl acetal followed by 4,4′-dimethoxytritylation afforded imidazo4,5-c]pyridines 10b and 11b , respectively. The latter were converted into the 3′-phosphonates 10c or lie, respectively; the cyanoethyl N,N-diisopropylphosphoramidite 10d was also prepared. The oligonucleotide building blocks were employed in automated solid-phase synthesis. 1 he self-complementary oligomers 13 , 15 , and 17 were prepared and characterized by enzymatic hydrolysis with snake-venom phosphodiesterase followed by alkaline phosphatase. There CD spectra exhibited the general structure of a B-DNA.