| Abstract
| - Ab initio molecular orbital (MO) and density functional theory (DFT) calculations using a polarizedsplit-valence basis set have been performed on 2-deoxy-β-d-ribofuranosylamine (2-deoxy-β-d-erythro-pentofuranosylamine) in its unprotonated (3) and protonated (4) forms. Structural data confirm three previouslyreported factors influencing bond lengths in aldofuranosyl rings, and suggest the existence of a new 1,4-lonepair effect. Conformational energy profiles for 3 and 4 were compared to that described recently for 2-deoxy-β-d-ribofuranose (2-deoxy-β-d-erythro-pentofuranose) 5. Results show that preferred conformation and energybarriers to pseudorotation are affected significantly by changes in C1 substitution. N-Protonation of 3 reducespseudorotational barriers, suggesting a more flexible ring relative to the unprotonated molecule. NMR spin−spin coupling constants involving C1 and H1 were calculated in 3 and 4 using DFT methods described previously(Cloran et al.J. Phys. Chem.1999, 103, 3783−3795). Trends in computed couplings as a function of ringconformation and C1 substitution confirm prior predictions based on experimental observations in aminosugarsand nucleosides. In general, one- and two-bond JCH and JCC values appear more influenced by O → N substitutionand by N-protonation than vicinal 3JCH and 3JCC. These results will be useful in studies of related NMR scalarcoupling constants in biologically relevant aminosugars and nucleosides, either free in solution or as componentsof oligosaccharides and oligonucleotides.
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