Synthesis of carbohydrate-amino acid conjugates related to the capsular antigen K54 from Escherichia coli O6:K54:H10 and artificial antigens therefrom

The disaccharides α- l -Rha p -(1 → 3)-β- d -Glc p A and β-·-Glc p A-(1 → 3)-α- l -Rha p bearing amide- linked l -serine or l -threonine, which represent the repeating unit(s) of the capsular polysaccharide from E. coli O6:K54:H10, have been synthesised. O-tert -Butyl-protected amino acid tert -butyl esters were condensed with the corresponding biouronic acid as the 2-acrylamidoethyl or 2-azidoethyl glycosides. The azido function was replaced by the acrylamido group by catalytic hydrogenation followed by N -acryloylation. The tert -butyl groups were removed by treatment with trifluoroacetic acid to give the target monomers which were copolymerised woth acrylamide to give neococonjugates that are potentially useful for immunochemical studies.