The design and synthesis of antibody binding site probes: three pentasaccharide analogues of the Brucella A antigen prepared by activation in situ of thioglycosides with bromine.

Three pentasaccharide analogues of the Brucella A antigen [----2)-alpha-D-Rhap4NFo-(1----], each with one formamido group replaced by a hydroxyl group, have been prepared as their methyl glycosides. Mono- and di-saccharide thioglycosides of D-rhamnose and 4-azido-4,6-dideoxy-D-mannose were used as glycosyl donors for the preparation of protected pentasaccharide derivatives with trisaccharides as intermediates. Glycosylations were performed by activation in situ of the thioglycosides with bromine 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 pentasaccharides.