Measurement of long-range2 super(13)C- super(1)H coupling constants of 95% uniformly super(13)C-labeled polysaccharide from Streptococcus mitis J22

The coaggregation of Streptococcus mitis strain J22 in the early stages of dental plaque formation has been shown to result from interaction of cell wall polysaccharides with lectins on the surface of other oral bacterial species. This bacterium was grown in a medium containing super(13)C as the sole carbon source. We have isolated the lectin receptor polysaccharide from this strain with full enrichment in super(13)C and have determined a number of two-bond and three-bond super(13)C- super(1)H coupling constants from measurements of the offsets in two-dimensional homonuclear nmr spectra [exclusive correlated spectroscopy (E-COSY) method]. A scheme for reliable extraction of these coupling constants from homonuclear Hartman n-Hahn and nuclear Overhauser effect spectroscopy spectra is tested in model compounds. We interpret the three-bond coupling across the glycosidic linkage in terms of dihedral angles in order to provide conformational information to supplement molecular modeling and nuclear Overhauser effect data. We show that the E-COSY method works well even for coupling constants smaller than the nmr line width and that a number of the super(3)J sub(CH) across the glycosidic linkage are in the range of 1-2 Hz, which is much smaller than many previously reported values.