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 p rocesses. An understanding of the molecular mechanisms that underlie these processes is essential in the development of novel oligosaccharide-based th erapeutic strategies. Unfortunately, obtaining detailed structural informat ion for larger oligosaccharides (> 10 residues) can be exceedingly difficul t, especially where the amount of sample available is limited. Here we demo nstrate the application of C-13 O-acetylation in combination with novel NMR experiments to obtain much of the information required to characterize the primary structure of oligosaccharides. (H)CMeCOH-HEHAHA and H(C-Me)COH-HEH AHA experiments are presented that use heteronuclear Hartmann-Hahn transfer to correlate the acetyl groups with sugar ring protons in peracetylated ol igosaccharides. The in-phase, pure absorption nature of the correlation pea ks in these experiments allows measurement of both chemical shifts and, imp ortantly, H-1-H-1 coupling constants that are used to define the stereochem istry of the sugar ring. The (HCMe)COH and (HCMe)COH-RELAY experiments prov ide additional methods for obtaining chemical shift assignments for larger oligosaccharides to define the sites of glycosidic linkages from the patter ns of acetylation.