Zwitterionic Polysaccharides of Shigella sonnei: Synthetic Study toward a Ready-for-Oligomerization Building Block Made of Two Rare Amino Sugars.

Shigellosis is an endemic diarrheal disease caused by Gram negative bacteria named Shigella. The most exposed polysaccharides of Shigella sonnei display a zwitterionic disaccharide repeating unit (AB) made of two rare amino sugars: [4)-a-L-AltpNAcA-(1→3)-ß-D-Fucp-NAc4N-(1→]. An original synthesis of a ready-for-oligomerization AB disaccharide is reported. The targeted orthogonally protected disaccharide was synthesized from L-glucose and tetra-O-acetyl-ß-Dglucosamine. The challenging introduction of the 4B-azido group masking the amino moiety of the AAT residue was performed at the disaccharide stage by a two-step procedure (triflation followed by nucleophilic displacement with NaN3). A post-glycosylation oxidation strategy was employed to access the altruronate moiety. [ABSTRACT FROM AUTHOR]