N.m.r. spectroscopy is one of the,most important techniques in structural analysis of oligo-and poly-saccharides. The Jc_,,H_, coupling constants are often used to obtain information about the anomexic configuration of the pyranosyl residues as there is a lo-Hz difference between the values for tl anomers (-170 Hz) and those for /I anomers (-160 Hz)'. The use of these coupling constants is especially valuable for determination of the anomeric configuration of sugar residues with the manno configuration, for which the JHVI ,H-2 values are approximately the same for the c1 and p configurations, and no significant difference in the chemical shifts of the anomeric carbon signals from Q and j? residues is observed. In one-dimensional n.m.r. spectra, the Jc_,,"_, coupling constants can be measured from 13C-n.m.r. spectra recorded without proton decoupling or from, the '3C-satellites observed in 'H-n.m.r. spectra2. Both of these techniques have disadvantages, as low sensitivity of the experiments and often overlap of signals occur. Another problem is the heterogeneity of, or impurities in, the sample, giving rise to signals that interfere with the small satellite signals in the 'H-n.m.r. spectrum.
By use of two-dimensional n.m.r. experiments, the coupling constants can be observed despite the problems discussed above. The heteronuclear J-resolved experi-ment3 resolves the overlap bf signals caused by the coupling, but is rather timeconsuming. A more sensitive two-dimensional technique is proton-detected heteronuclear multiple-quantum coherence (HMQC)'6, where the peak positions are dependent on both the 'H-and the 13C-n.m.r. chemical shifts, which also has the advantage of resolving complex spectra.
In this study, we have compared some different one-and two-dii/ensional experiments with respect to the possibility of obtaining the .&_, coupling constants for the anomeric signals from the Escherichia coli serotype 01 A, O-polysaccharide, for which structure 1 was recently elucidated7. In that study, the anomeric proton and carbon signals were assigned w-D-ManpNAc-(1 +, 6 5.05/100.63; -*2,3