The synthesis of antibody binding-site probes: a hexasaccharide and two pentasaccharides related to the Brucella A antigen and prepared by in situ activation of thioglycosides with bromine.

Two pentasaccharide analogues and a hexasaccharide fragment of the Brucella A antigen [----2)-alpha-D-Rhap4NFo-(1----]n have been prepared as their methyl glycosides. The pentasaccharide analogues each have two formamido groups replaced by hydroxyl groups. Protected derivatives of the three oligosaccharides were prepared by in situ activation with bromine of mono- and di-saccharide thioglycosides of D-rhamnose and 4-azido-4,6-dideoxy-D-mannose in the presence of a glycosyl acceptor and silver triflate as promoter. Reduction of the azido groups with hydrogen sulfide, N-formylation with ethyl formate, and hydrogenolysis then gave the target pentasaccharide glycosides.