7-DEAZAPURINE OLIGODEOXYRIBONUCLEOTIDES - THE EFFECTS OF 7-DEAZA-8-METHYLGUANINE ON DNA-STRUCTURE AND STABILITY

Oligodeoxyribonucleotides containing 7-deaza-2'droxy-8-methylguanosine (m(8)c(7)G(d); 2b) were prepared. For this purpose, the phosphonate 3 a and the phosphoramidite 3b were synthesized and employed in solid-ph ase oligodeoxyribonucleotide synthesis. The structures and the thermod ynamic data of duplex formation of oligodeoxyribonucleotides containin g 2b were investigated by temperature-dependent CD and UV spectra and compared with those containing 7-deaza-2'-deoxy-7-methylguanosine (m(7 )c(7)G(d)) or 7-deaza-2'-deoxyguanosine (c(7)G(d); 2a). In general, co mpound 2b reduces the duplex stability. In case of the sequence d(m(8) c(7)G-C)(4) (18), the B --> Z transition was Facilitated by the incorp oration of 2b. Moreover, a single 7-deaza-8-methylguanine residue pres ent in an oligodeoxyribonucleotide tract of guanine residues destabili zes the dG quadruplex significantly. This destabilization is more pron ounced than in the case of 7-deazaguanine or 7-deaza-7-methylguanine.