Conformational analysis of carbohydrates inferred from NMR spectroscopy and molecular modeling. Applications to the behavior of oligo-galactomannan chains.

In both the biological functions and industrial applications of carbohydrates, their conformational behavior along with the dynamic fluctuations that their structures experience are of great significance. The elucidation of the three-dimensional characteristics of carbohydrates and carbohydrate-containing molecules is in general performed by a combination of high-resolution nuclear magnetic resonance (NMR) spectroscopy and molecular modeling. Heteronuclear couplings and nuclear Overhauser effect (NOE) data are major tools for structural determination. The angular dependence of carbon-proton coupling constants has been shown to depend also on the pathways involved. Concerning molecular modeling, the goal is to generate the ensemble of structures that are consistent with the experimental data. This approach is illustrated in the galactomannan chain. It consists of the conformational study of two model disaccharides (mannobiose and epimelibiose) of galactomannans through carbon-proton coupling constants and NOE measurements. Experimental data are then compared to results of conformational analysis that predicted the stable conformers in solution. From these results helical conformations of oligomers are generated and are discussed in terms of the influence of the position and number of galactose units on the conformation of the mannan backbone.