Artificial carbohydrate antigens: synthesis of rhamnose trisaccharide and disaccharide haptens common to Shigella flexneri O-antigens

Publisher Website
Google Scholar
Abstract
The rhamnose di- and tri-saccharide glycosides, α-L-Rham(p)-(1 → 3)-α-L-Rham(p) and α-L-Rham(p)-(1 → 2)-α-L-Rham(p)-(1 → 3)-α-L-Rham(p), representing portions of the Shigella flexneri serogroup Y lipopolysaccharide repeating unit, have been synthesised in high yield by a series of Königs–Knorr reactions. The synthetic methods used are designed to provide di- and tri-saccharide artificial antigens, after complete deblocking and covalent attachment to protein. 8-Methoxycarbonyloctyl α-L-rhamnopyranoside was converted into the corresponding 2,4-di-O-benzoate via a 2,3-orthobenzoate. Königs–Knorr reaction between this partially blocked rhamnoside and either 2,3,4-tri-O-acetyl-α-L-rhamnopyranosyl bromide or 2-O-acetyl-3,4-di-O-benzyl-α-L-rhamnopyranosyl chloride gave respectively the fully blocked disaccharide and the disaccharide precursor of the trisaccharide. Selective transesterification of the 2′-O-acetate group in the presence of 2,4-di-O-benzoates provides the disaccharide selectively deblocked at the C-2′ position. Reaction with 2,3,4-tri-O-acetyl-α-L-rhamnopyranosyl bromide gave the fully blocked trisaccharide. Removal of the blocking groups yielded the trisaccharide hapten. The 13C and 1H n.m.r. spectra together with the T1 parameters for the haptens are consistent with a conformation about the aglyconic-oxygen-to-aglyconic-carbon bond (torsional angle ψ) that approaches the eclipsed rather than the staggered arrangement.

This publication has 0 references indexed in Scilit: