Novel multi-dimensional heteronuclear NMR techniques for the study of 13C-O-acetylated oligosaccharides: expanding the dimensions for carbohydrate structures.

Complex carbohydrates have critical roles in a wide variety of biological processes. An understanding of the molecular mechanisms that underlie these processes is essential in the development of novel oligosaccharide-based therapeutic strategies. Unfortunately, obtaining detailed structural information for larger oligosaccharides (> 10 residues) can be exceedingly difficult, especially where the amount of sample available is limited. Here we demonstrate the application of 13C O-acetylation in combination with novel NMR experiments to obtain much of the information required to characterize the primary structure of oligosaccharides. (H)CMe COH-HEHAHA and H(CMe)COH-HEHAHA experiments are presented that use heteronuclear Hartmann-Hahn transfer to correlate the acetyl groups with sugar ring protons in peracetylated oligosaccharides. The in-phase, pure absorption nature of the correlation peaks in these experiments allows measurement of both chemical shifts and, importantly, 1H-1H coupling constants that are used to define the stereochemistry of the sugar ring. The (HCMe)COH and (HCMe)COH-RELAY experiments provide additional methods for obtaining chemical shift assignments for larger oligosaccharides to define the sites of glycosidic linkages from the patterns of acetylation.