MEASUREMENT OF INTER-GLYCOSIDIC C-13-H-1 COUPLING-CONSTANTS IN A CYCLIC BETA(1-]2)-GLUCAN BY C-13-FILTERED 2D (H-1,H-1) ROESY

A method for measuring three-bond C-13-H-1 scalar coupling constants across glycosidic bonds in a cyclic beta(1-->2)-glucan icosamer is presented. This oligosaccharide molecule, with its high degree of symmetry, represents a particular challenge for NMR spectroscopy to distinguish inter-residue from intra-residue heteronuclear coupling effects. Chemically equivalent H2 protons in adjacent glucosyl residues are distinguished on the basis of their different through-space, dipolar interactions with the anomeric protons (H1). The strong NOE contact between anomeric (H1) and aglyconic (H2') protons permits the selective observation of the inter-residue heteronuclear couplings 3J(C1H2') and 3J(C2'H1) in a natural-abundance C-13-omega1-half-filtered {H-1, H-1} ROESY experiment.