A 13C-n.m.r. study of some Shigella flexneri O-polysaccharides.

13C-N.m.r. data for some Shigella flexneri O-polysaccharides are reported. It is concluded that the chemical shifts observed for the linear Shigella flexneri type Y O-polysaccharide are similar to those calculated by adding substituent shifts, obtained from disaccharides with similar stereochemistry around the glycosidic linkage, to the chemical shifts for the monomers. The influence of substitution with alpha-D-glucopyranosyl and/or O-acetyl groups in different positions of this polysaccharide on the chemical shifts has been investigated. Possible interactions between sugar residues involved in the branching have been investigated by energy minimisations (GESA) of disaccharide and of trisaccharide elements.