Chemical Synthesis of the Galacturonic Acid Containing Pentasaccharide Antigen of the O-Specific Polysaccharide of Vibrio cholerae O139 and Its Five Fragments

Three pentasaccharides, two tetrasaccharides, and a trisaccharide fragment of the O-specific antigen of Vibrio cholerae O139 were synthesized by applying 1 + 1, 2 + 1, 3 + 1, and 4 + 1 coupling strategies. The most challenging tasks involved were the synthesis of the 1,2-cis-glycosidic linkage between galactose and the linker (spacer) molecule and final purification of the target multicharged substances. Difficulties with final deprotection by hydrogenation/hydrogenolysis caused by the presence of galacturonic acid were overcome by protecting the acid with a group inert to the treatment with hydrogen. Some intermediates described previously as incompletely characterized amorphous materials were obtained in the crystalline condition and were fully characterized for the first time.