Comparative NMR analysis of the decadeoxynucleotide d-(GCATTAATGC)2 and an analogue containing 2-aminoadenine.

The dodecadeoxynucleotide duplex d-(GCATTAATGC)2 has been prepared with all adenine bases replaced by 2-NH2-adenine. This modified duplex has been characterized by nuclear magnetic resonance (NMR) spectroscopy. Complete sequence-specific 1H resonance assignments have been obtained by using a variety of 2D NMR methods. Multiple quantum-filtered and multiple quantum experiments have been used to completely assign all sugar ring protons, including 5'H and 5'H resonances. The assignments form the basis for a detailed comparative analysis of the 1H NMR parameters of the modified and parent duplex. The structural features of both decamer duplexes in solution are characteristic of the B-DNA family. The spin-spin coupling constants in the sugar rings and the relative spatial proximities of protons in the bases and sugars (as determined from the comparison of corresponding nuclear Overhauser effects) are virtually identical in the parent and modified duplexes. Thus, substitution by this adenine analogue in oligonucleotides appears not to disturb the global or local conformation of the DNA duplex.