Synthesis of oligonucleotides containing 7-(2-deoxy-β-d-erythro-pentofuranosyl)guanine and 8-amino-2′-deoxyguanosine

The synthesis of oligonucleotides containing 7-(2-deoxy-β-D-erythro-pentofuranosyl)guanine and 8-amino-2′-deoxyguanosine was accomplished. The viable intermediate N2-isobutyryl-7-(2-deoxy-β-D-erythro-pentofuranosyl)guanine (6) was prepared via a four step deoxygenation procedure from 7-β-D-ribofuranosylguanine (1). The 5′-hydroxyl group of 6 was protected as 4,4′-dimethoxytrityl ether and then converted to the target phosphoramidite (8) via conventional phosphitylation procedure. The amino groups of 8-amino-2′-deoxyguanosine (9) were protected in the form of N-(dimethylainino)methylene functions to give the protected nucleoside 10, which was subsequently converted to the target phosphoramidite 12 via dimethoxytritylation followed by phosphitylation. The phosphoramidites 8 and 12 were incorporated into a 26-mer and a 31-mer G-rich oligonucleotide using solid-support, phosphoramidite methodology. Analysis of antiparallel triplex formation by the oligonucleotides containing 7-(2-deoxy-β-D-erythro-pentofura-nosyl)guanine in place of 2′-deoxyguanosine showed no enhancement in triple helix formation.