Synthetic studies towards the O-specific polysaccharide of Shigella sonnei

Synthetic routes are described to zwitter-ionic disaccharides that are diastereoisomerically related to frame-shifted repeating units of the title polysaccharide that contains 2-acetamido-4-amino-2,4,6-trideoxy-D-galactose and 2-acetamido-2-deoxy-L-altruronic acid. The intermediates corresponding to the trideoxygalactose residue feature acylamino functions at C-2 and an azido group at C-4. Best results were obtained with N-phthaloyl- and N-trichloroacetyl-protected derivatives. The intermediates corresponding to the uronic acid residue were either a D-altruronic acid-derived acceptor or a D-altrose-derived donor in which C-6 was oxidized after disaccharide formation.