Synthesis of some blocked di-and trisaccharide derivatives related to the repeating unit of the O-antigen from <i>Shigella dysenteriae </i>type 3 in the form of their glycosides

2386-2394Starling from D-galactose and D-galactosaminc hydrochloridc, two new monosaccharide synthons namely 2-(trimethylsilyl)ethyl 4-O-acctyl-2,6-di-O-benzyl-β-D-galactopyranoside 2 and phenyl 3-O-acetyl-4,6-O-benzylidene-2-deoxy-2-phthalimido-1-thio-β-D galactopyranoside 5 have been synthesized which are then allowed to react with the monosaccharide derivatives 3,9, 16, 22 and 24 in the presence of either NIS/TfOH or TESOTf to give two di- and two trisaccharide derivatives related to the repeating unit of Shigella dysenteriae type 3, in the form of their glycosides. These blocked oligosaccharides can be utilized for the synthesis of glycoconjugates as synthetic vaccines