Effects of 8-methyl-2′-deoxyadenosine incorporation into quadruplex forming oligodeoxyribonucleotides Original Research Article

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 molecular modelling and shown to form fourfolds symmetric G-quadruplex structures, with all strands parallel and equivalent to each other. The complexes are characterized by thermal stabilities comparable to that of their natural counterparts. NOE patterns involving 8-methyl group in A8Me residues allowed us to define the main structural features at the 5′-end of the complexes. Particularly, inter- and intrastrand NOEs show a syn-orientation and a symmetrical arrangement of A8Me bases stacking on the adjacent G-tetrad.