STUDIES ON THE BASE-PAIRING PROPERTIES OF N-7-(2-DEOXY-BETA-D-ERYTHRO-PENTOFURANOSYL)GUANINE (N(7)G(D))

The base-pairing properties of N-7-(2-deoxy-beta-D-erythro-pentofurano syl) (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 3,5-di-O-(4-toluoyl)alpha-D-erythro- pentofuranosyl chloride (8) was studied. The N-9/N-7-glycosylation rat io was found to be 1:1 when 6-isopropoxypurin-2-amine (3d) was used, w hereas 6-(2-methoxyethoxy)purin-2-amine (3i) gave mainly the N-9-nucle oside (2:1). Oligonucleotides containing compound 1 were prepared by s olid-phase synthesis and hybridized with complementary strands having the four conventional nucleosides located opposite to N(7)G(d). Accord ing to T-m values and enthalpy data of duplex formation, a base pair b etween N(7)G(d) and dG is suggested. From the possible N(7)G(d).dG bas e pair motives, Hoogsteen pairing can be excluded as 7-deaza-2'-deoxyg uanosine forms the same stable base pair with N(7)G(d) as dG.