Synthesis of 2-(4-aminophenyl)ethyl [formula omitted] acid, a highly branched pentasaccharide corresponding to structures found in lipopolysaccharides from Moraxella catarrhalis

Abstract

Syntheses of the pentasaccharide 2-(4-aminophenyl)ethyl 3- deoxy-5-O-(3,4,6- tri-O-β- d- glucopyranosyl-α- d-glucopyranosyl)-α- d-manno- oct-2- ulopyranosidonic acid and of the tetrasaccharide 3,4,6- tri-O-β- d- glucopyranosyl-α- d- glucopyranoside , both as its methyl and 2-(4-trifluoroacetamidophenyl)ethyl glycoside, are described. These oligosaccharides correspond to structures found in the lipopolysaccharide of Moraxella catarrhalis and were needed for biological experiments aimed at producing antibodies against the bacteria. The best way to introduce the glucopyranosyl groups into the 3-, 4-, and 6-positions of the branched target compounds was found to be a one-step reaction using a 3,4,6-triol as acceptor and 2,3,4,6- tetra-O- benzoyl- d-glucopyranosyl bromide as donor in a silver trifluoromethanesulfonate-promoted coupling. The spacer arm, necessary for the formation of immunoactive glycoconjugates, was introduced into the glucose moiety via a dimethyl(methylthio)sulfonium trifluoromethanesulfonate-promoted reaction using the ethyl thioglucoside as donor, whereas for Kdo, the acetylated glycal derivative, methyl 4,5,7,8- tetra-O- acetyl-2,6- anhydro-3- deoxy- d -manno- oct-2- enonate , was used as donor and phenylselenyl trifluoromethanesulfonate as a stereocontrolling promoter.