Conformation of mononucleotides and dinucleoside monophosphates. P[H] and H[H] nuclear Overhauser effects

The phosphorus-proton nuclear Overhauser effect (NOE) was used to investigate the quantitative distribution of rotamers about the C3'--O3' bond (phi') of 3'-AMP and 2',3'-cyclic-CMP and the C4'--C5', C5'--O5' bonds (psi, phi) of 5'-AMP. Phosphorus-proton and proton-proton NOE's were used to provide a qualitative insight into the backbone conformation and the glycosyl angle torsions of adenosylyl-(3' leads to 5')-adenosine (ApA). The major psi rotamer in 5'-AMP is the 60 degree (gg) form, while the major phi rotamer is the 180 degrees (g'g') form. The constrained model, 2',3'-cyclic-CMP, manifests the C3'endo furanose pucker predominantly. The results from these two models are consistent with nuclear magnetic resonance (NMR) J coupling analyses. The phi; distribution of 3'-AMP is dominated (77%) by the 180 degrees g- rotamer. The 3'-AMP results are consistent with phosphorus-hydrogen coupling constant analyses, but do not accord with phosphorus-carbon coupling constant results. The phosphorus-proton NOE reveals that the phosphorus of ApA occupies a region of conformation space not seen in 5'-AMP. The proton-proton NOE on APA shows a significant portion of syn rotamer in both X distributions and detects a cross-purine ring interaction consistent with base stacking known to exist in this system.