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

Abstract

The disaccharides α-l-Rhap-(1 → 3)-β-d-GlcpA and β-·-GlcpA-(1 → 3)-α-l-Rhap 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.