Conformational analysis of alpha-D-Fuc-(1-->4)-beta-D-GlcNAc-OMe. One-dimensional transient NOE experiments and Metropolis Monte Carlo simulations.

One-dimensional transient NOE build-up curves were measured for the synthetic disaccharide alpha-D-Fuc-(1-->4)-beta-D-GlcNAc 1 utilizing Gaussian shaped pulses. Simulated build-up curves from Metropolis Monte Carlo simulations were compared to the experimental data. Disaccharide 1 is structurally related to methyl beta-D-maltoside in that it also contains an alpha-(1-->4) linkage, and it has the same configuration of groups around the glycosidic linkage. Analysis of NOEs in methyl beta-D-maltoside is restricted to those observed upon selective excitation of H1' because of severe spectral overlap. The situation is different in 1 where 1H-NMR signals are well separated. Several interglycosidic NOEs were observed. The corresponding build-up curves allowed an accurate determination of the conformational preferences at the glycosidic linkage in 1. Comparison of experimental and theoretical NOE build-up curves showed clearly that rigid minimum-energy models cannot account for the experimental data. The best fit of experimental NOE build-up curves was obtained with theoretical curves from a 2 x 10(6) step Metropolis Monte Carlo simulation with the temperature parameter set at 1000 K. Finally, it was observed that only the interglycosidic NOE H5'/H6-pro-S significantly depends upon varying conformation distributions at the alpha-(1-->4)-glycosidic linkage, induced by choosing different temperature parameters for the Metropolis Monte Carlo simulations.