Conformation of Mononucleotides and Dinucleoside Monophosphates

The phosphorus-proton nuclear Overhauser effect (NOE) was used to investigate the quantitative distribution of rotamers about the C3'-03' bond (&') of 3'-AMP and 2',3'-cyclic-CMP and the C4'-C5', C5' 05' bonds (41, 0) 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' 5')-adenosine (ApA). The major 41 rotamer in 5'-AMP is the 60° (gg) form, while the major X rotamer is the 180° (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 k' distribution of 3'-AMP is dominated (77%) by the 1800 grotamer. The 3AMP 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.