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

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.