Alternating d(G-C)3 and d(C-G)3 hexanucleotides containing 7-deaza-2'-deoxyguanosine or 8-aza-7-deaza-2'-deoxyguanosine in place of dG

摘要

The synthesis of alternating hexamers (8–13) derived from d(C-G)₃ or d(G-C)₃ but containing c7z8G_d (2) or c7G_d [3) instead of dG is described employing phosphoramidite-chemistry. Apart from the isobutyryl group the dimethyiaminomethylene residue was used for the nucleobase-protection of 3. The methyl- and the cyanoethyl-phosphoramidites of 3 (5a-c) were synthesized. They were employed together with those of c7G or c7z8G_d [12] in automated oligonucleotide synthesis. Tm-values as well as thermodynamic data of the oligomers 9, I0, 12, and 13 indicated that duplexes were destabilized if c7G_d replaced dG, whereas c7z8G_d stabilized the duplex structure. In contrast to d(C-G)₃ which underwent salt-dependent B-Z transition, CD-spectra of oligomers containing c7G_d or c7z8G_d in place of dG showed retained B-conformation.