Biotinylated Oligo-α-(1 → 4)-d-galactosamines and Their N-Acetylated Derivatives: α-Stereoselective Synthesis and Immunology Application.

ABSTRACT

Using 3-O-benzoyl-4,6-O-di-tert-butylsilylidene-2-azido-2-deoxy-selenogalactoside, biotinylated oligo-α-(1 → 4)-d-galactosamines comprising from two to six GalN units were prepared for the first time together with their N-acetylated derivatives. The combination of blocking groups used herein provided stereocontrol for the α-stereospecific glycosylation, to show also high efficiency of phenyl 2-azido-2-deoxy-selenogalactosides as glycosyl donors. The obtained glycoconjugates are related to fragments of exopolysaccharide galactosaminogalactan (GG) found in Aspergillus fumigatus, which is the most important airborne human fungal pathogen in industrialized countries. The synthesized glycoconjugates were arrayed on streptavidin-coated plates and used to investigate the GG epitopes recognized by mouse monoclonal antibodies against GG and by human antibodies in the sera of patients with aspergillosis. The obtained data showed that the oligo-α-(1 → 4)-d-galactosamines and their N-acetylated derivatives allowed the first precise analysis of the specificity of the antibody responses to this extremely complex fungal polysaccharide.