B3LYP/6-311++G** study of structure and spin-spin coupling constant in methyl 2-O-sulfo-alpha-L-iduronate.

Structures of three most stable conformers ((1)C4, (4)C1, (2)S0) of methyl 2-O-sulfo-alpha-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 (1)C4 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-alpha-L-iduronate monosodium salt. The influence of the charged groups upon the magnitudes of spin-spin coupling constants is also discussed.