New Karplus Equations for Conformational Analysis of Monosaccharides and Acetylated Derivatives

Natural oligosaccharides are composed of multiple monosaccharides that are linked via glycosidic oxygen atom between carbon 1 (anomeric carbon) in one sugar and one of several carbons in the other sugar. A glycosidic linkage between carbon 1 and carbon 6 of two sugars results in greater flexibility because of the “arm-like” structure of the CH2OH group. The chemical linkage between sugars is characterized by dihedral (torsion) angles composed of 4 atoms in each case. Especially the so-called omega-angle, comprising Oglycosidic-C6-C5-C4, allows for greatest flexibility. Because of the complexity of the quantitative description of omega-angles in oligosaccharides, a simplified description of the omega-angle in non-substituted, free CH2OH groups of monosaccharides is required. Evidence for the size of the dihedral angle in solution can be obtained from NMR-experiments and coupling constants (J-values). The experimental coupling values can be described in theory with a so-called Karplus plot that correlates J-values with the dihedral angle between the coupled nuclei. In this study, theoretical NMR calculations were carried out and torsional angles from MD-simulations were measured to construct Karplus plots for a- and ß- anomers of acetylated and unacetylated glucose, galactose, and mannose. Carbohydrates have numerous biochemical functions which include the storage of energy, functioning as structural components, immune responses to infection, “immunization” of babies through human milk, and protein folding. This variation in biochemical function is accredited to carbohydrates’ great structural diversity (constitutions and configurations). Because of the importance of carbohydrates, it is valuable to understand their function and specificity. Theoretical results compared very well to the experimental results obtained in lab. Molecular modeling and dynamic simulation programs such as Spartan ’14, Gaussian ’09, and AMBER 14 (GLYCAM06 force field) were used to help calculate the NMR coupling constants. Preliminary data showed good fit between computed and experimental coupling constants in the monosaccharides studied