New n.m.r.-spectroscopic approaches for structural studies of polysaccharides: application to the Haemophilus influenzae type a capsular polysaccharide

The extension of several modern nuclear magnetic resonance (n.m.r.) spectroscopic techniques to polysaccharides is discussed and illustrated, using the native Haemophilus influenzae type a capsular polysaccharide. These techniques provide for the unambiguous assignment of all n.m.r. resonances (1H, 13C, and 31P) via high-sensitivity homonuclear and 1H-detected heteronuclear correlations, and they are capable of locating the intersaccharide linkages (both O-linked and phosphoric diester-linked) and appended groups (e.g. O-acetyl groups). To illustrate the power and sensitivity of these methods, a 10-mg sample of the H. Influenzae type a polysaccharide (repeat unit mol. wt. = 376) was studied. The combined acquisition time for the two-dimensional 1H-13C correlation data (one-bond and multiple-bond), the 1H-31P correlation data, and the 1H-1H (homonuclear Hartmann-Hahn) data was approximately 18 h.