B3LYP/6-311++G∗∗ study of structure and spin–spin coupling constant in methyl 2-O-sulfo-α-l-iduronate

Structures of three most stable conformers (1C4, 4C1, 2S0) of methyl 2-O-sulfo-α-l-iduronate monosodium salt have been analyzed by DFT using the B3LYP/6-311++G∗∗ method. The optimized geometries confirmed the influence of both 2-O-sulfate and carboxylate groups upon the pyranose ring geometry. The computed energies showed that the chair 1C4 form is the most stable one. Time-averaged DFT-calculated proton–proton and proton–carbon spin–spin coupling constants agree with the experimental data and indicate that only two chair forms contribute to the conformational equilibrium of methyl 2-O-sulfo-α-l-iduronate monosodium salt. The influence of the charged groups upon the magnitudes of spin–spin coupling constants is also discussed.

Graphical abstractStructures and spin–spin coupling constants of three most stable conformations (1C4, 4C1, 2S0) of methyl 2-O-sulfo-α-l-iduronate monosodium salt have been analyzed by DFT at the B3LYP/6-311++G∗∗ level of theory.