Molecular structure of the nucleoside analogue inosine using DFT methods: Conformational analysis, crystal simulations and possible behaviour

Five tautomers of the nucleoside inosine were determined and optimized at the MP2 and B3LYP levels of theory. Several correlations were identified. A comprehensive conformational analysis was carried out on the most stable tautomer N1, and the whole conformational parameters (χ, β, γ, δ, ε, ε′, P, νmax) were studied as well as the NBO Natural atomic charges. The calculations were carried out with full relaxation of all geometrical parameters. The search located at least 69 stable structures, 3 of which are within a 1 kcal/mol electronic energy range of the global minimum, and 4 conformers are within a 1 kcal/mol Gibbs energy range. A lower reactivity in inosine than in the natural nucleoside guanosine appears in the N1 and N3 nitrogen atoms. The solid state was simulated through a pentamer form and the structural parameters were compared with the X-ray crystal data available. Several general conclusions were emphasized.