Effects of 8-Methyl-2'-deoxyadenosine incorporation into quadruplex forming oligonucleotides

In this paper we report the synthesis and the structural characterization of two modified oligodeoxyribonucleotides (ODNs), namely d(A8MeGGGT) and d(TA8MeGGGT), where A8Me represents a 8-methyl-2'-deoxyadenosine. Both ODNs have been studied by 1H NMR, CD spectroscopy and mol. modeling and shown to form four-folds sym. G-quadruplex structures, with all strands parallel and equiv. to each other. The complexes are characterized by thermal stabilities comparable to that of their natural counterparts. NOE patterns involving 8-Me group in A8Me residues allowed us to define the main structural features at the 5'-end of the complexes. Particularly, inter- and intra-strand NOEs show a syn-orientation and a sym. arrangement of A8Me bases stacking on the adjacent G-tetrad.