Measurement of inter-glycosidic 13C-1H coupling constants in a cyclic beta(1-->2)-glucan by 13C-filtered 2D (1H,1H)ROESY.

A method for measuring three-bond 13C-1H 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 3JC1H2' and 3JC2'H1 in a natural-abundance 13C-omega 1-half-filtered (1H,1H)ROESY experiment.