Studies on the base-pairing properties of N-7-(2-deoxy-beta-D-erythro-pentofuranosyl)guanine (N(7)G(d))

Abstract

The base-pairing properties of N-7-(2-deoxy-beta-D-erythro-pentofuranosyl) (N(7)G(d); 1) are investigated. The nucleoside 1 was obtained by nucleobase-anion glycosylation. The glycosylation reaction of various 6-alkoxy-purin-2-amines 3a-i with 2-deoxy-3,5-di-O-(4-toluoyl)alpha-D-erythro-pentofuranosyl chloride (8) was studied. The N-9/N-7-glycosylation ratio was found to be 1:1 when 6-isopropoxypurin-2-amine (3d) was used, whereas 6-(2-methoxyethoxy)purin-2-amine (3i) gave mainly the N-9-nucleoside (2:1). Oligonucleotides containing compound 1 were prepared by solid-phase synthesis and hybridized with complementary strands having the four conventional nucleosides located opposite to N(7)G(d). According to T-m values and enthalpy data of duplex formation, a base pair between N(7)G(d) and dG is suggested. From the possible N(7)G(d).dG base pair motives, Hoogsteen pairing can be excluded as 7-deaza-2'-deoxyguanosine forms the same stable base pair with N(7)G(d) as dG.