INVESTIGATION BY NMR-SPECTROSCOPY AND MOLECULAR MODELING OF THE CONFORMATIONS OF SOME MODIFIED DISACCHARIDE ANTIGENS FOR SHIGELLA-DYSENTERIAE TYPE-1

The O-polysaccharide of Shigella dysenteriae type 1 is made up of mult iple repeats of the linear tetrasaccharide 1-->3)-alpha-D-GlcpNAc-(1-- >3)-alpha-L-Rhap-(1-->, for which the antigenic determinant for a muri ne monoclonal IgM antibody is the disaccharide alpha-L-Rhap-(1-->2)-al pha-D-Galp. This disaccharide and various analogs have been studied by 2D NOESY, POESY, and TOCSY NMR spectroscopy, in conjunction with prot on spin-lattice relaxation rate measurements, restrained molecular mec hanics, and restrained molecular dynamics with simulated annealing. It has been found that replacement of any single hydroxyl group in the d eterminant by a hydrogen atom, or replacement of any single hydroxyl g roup in the Gal residue by a fluorine atom has little if any influence on the conformation of the resulting derivatives.