Proton nuclear magnetic resonance measurement of the amide hydrogen exchange rates of group A streptococcal polysaccharide in H2O

The solvent exchange rates of the acetamido hydrogen of the 2-acetamido-2-deoxy-beta-D-glucopyranosyl unit of group A streptococcal polysaccharide dissolved in H2O have been measured and compared with the corresponding exchange rates in the solvated model compound 1-O-methyl-2-acetamido-2-deoxy-beta-D-glucopyranoside. Amide hydrogen exchange rates were measured at 25 degrees C over a wide pH range by a combination of two separate NMR techniques: the transfer of solvent saturation and the amide hydrogen saturation recovery NMR experiments. The data indicate that the acetamido hydrogen essentially exists in a solvated environment and that its contribution to the conformational stability of this polysaccharide through intramolecular hydrogen bonding is negligible.