N-7-DNA - SYNTHESIS AND BASE-PAIRING OF OLIGONUCLEOTIDES CONTAINING N-7-(2-DEOXY-BETA-D-ERYTHRO-PENTOFURANOSYL)GUANINE (N(7)G(D))

The synthesis of oligonucleotides containing N-7-(2-deoxy-beta-D-eryth ro-pentofuranosyl)guanine (N(7)G(d); 1) is described. Compound 1 was p repared by nucleobase-anion glycosylation of 2-amino-6-methoxypurine ( 5) with -3,5-di-O-(toluoyl)-alpha-D-erythro-pentofuranosyl chloride (6 ) followed by detoluoylation and displacement of the MeO group (8-->10 -->1). Upon base protection with the (dimethylamino)methylidene residu e (-->11) the 4,4-dimethoxytrityl group was introduced at OH--C(5')(-- >12). The phosphonate 3 and the phosphoramidite 4 were prepared and us ed in solid-phase oligonucleotide synthesis. The self-complementary do decamer d(N(7)G-C)(6) shows sigmoidal melting. The T-m of the duplex i s 40 degrees. This demonstrates that guanine residues linked via N(7) of purine to the phosphodiester backbone are able to undergo base pair ing with cytosine.