MEASUREMENT OF LONG-RANGE 2 C-13-H-1 COUPLING-CONSTANTS OF 95-PERCENTUNIFORMLY C-13-LABELED POLYSACCHARIDE FROM STREPTOCOCCUS-MITIS-J22

The coaggregation of Streptococcus mitis strain J22 in the early stage s of dental plaque formation has been shown to result from interaction of cell wall polysaccharides with lectins on the surface of other ora l bacterial species. This bacterium was grown in a medium containing C -13 as the sole carbon source. We have isolated the lectin receptor po lysaccharide from this strain with full enrichment in C-13 and have de termined a number of two-bond and three-bond C-13-H-1 coupling constan ts 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 Hartmann-Hahn and nuclear Overhauser effect spectroscopy spectra is te sted in model compounds. We interpret the three-bond coupling across t he glycosidic linkage in terms of dihedral angles in order to provide conformational information to supplement molecular modeling and nuclea r Overhauser effect data. We show that the E-COSY method works well ev en for coupling constants smaller than the nmr line width and that a n umber of the (3)J(CH) across the glycosidic linkage are in the range o f 1-2 Hz, which is much smaller than many previously reported values. (C) 1994 John Wiley and Sons, Inc.