SYNTHESIS AND 2-DIMENSIONAL NUCLEAR-MAGNETIC-RESONANCE ANALYSIS OF A TETRA-SACCHARIDE AND A HEXASACCHARIDE FRAGMENT OF THE O-SPECIFIC POLYSACCHARIDE OF SHIGELLA-DYSENTERIAE TYPE-1

The synthesis of the tetra- and hexa-saccharide methyl glycosides alpha-D-Gal p-(1 --> 3)-alpha-D-Glc p NAc-(1 --> 3)-alpha-L-Rha p-(1 --> 3)-alpha-L-Rha p-OMe (1), and alpha-L-Rha p-(1 --> 3)-alpha-L-Rha p-(1 --> 2)-alpha-D-Gal p-(1 --> 3)-alpha-D-Glc p NAc-(1 --> 3)-alpha-L-Rha p-(1 --> 3)-alpha-L-Rha p-OMe (3) is described, which represent various epitopes of the O-specific polysaccharide of Shigella dysenteriae type 1. The following monosaccharide intermediates were used: 1,3-di-O-acetyl-2- O-benzoyl-4-O-benzyl-alpha-L-rhamnopyranose (6 alpha), methyl 2,4-di-O-benzyl-alpha-L-rhamnopyranoside (7), methyl 2,4-di-O-benzoyl-1-thio-alpha-L-rhamnopyranoside (8), 2,3,4-tri-O-benzoyl-alpha-L-rhamnopyranosyl bromide (9), methyl 3,4,6-tri-O-benzyl-2-O-(4-methoxybenzyl)-1-thio-beta-D-galactopyranoside (13), methyl 2,3,4,6-tetra-O-benzyl-1-thio-beta-D-galactopyranoside (16), and 2-azido-4,6-O-benzylidene-3-O-bromoacetyl-2-deoxy-beta-D-glucopyranosyl chloride (19). A detailed analysis of the H-1 and C-13 NMR spectra of oligosaccharides I and 3 confirmed that the hexasaccharide 3 better approaches the conformation of the native polysaccharide, than either 1 or the homologous pentasaccharide 41.