A reverse approach to 1H-n.m.r. assignments of bacterial polysaccharides.

A new approach is reported for obtaining the assignment of the 1H-n.m.r. spectra of bacterial polysaccharides which are not amenable to analysis using conventional strategies. An unambiguous assignment of the 13C-n.m.r. spectrum is made by 13C-COSY of the polysaccharide labelled to a high level with 13C. Assignment of the 1H-n.m.r. spectrum is then made by proton-detected CH-correlation spectroscopy of material that is labelled at a low level. Using this approach, virtually complete assignments have been made for the Klebsiella K3 serotype polysaccharide under physiological conditions of temperature and pH.