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)-α- l -Alt p NAcA-(1→3)-β- d -Fuc p 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-β- d -glucosamine. The challenging introduction of the 4 B -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 NaN 3 ). A post-glycosylation oxidation strategy was employed to access the altruronate moiety.