Chemical Synthesis and Application of Biotinylated Oligo-α-(1 → 3)- d -Glucosides To Study the Antibody and Cytokine Response against the Cell Wall α-(1 → 3)- d -Glucan of Aspergillus fumigatus
Résumé
Biotinylated hepta-, nona- and undeca-α-(1 → 3)-d-glucosides representing long oligosaccharides of α-(1 → 3)-d-glucan, one of the major components of the cell walls of the fungal pathogen Aspergillus fumigatus, were synthesized for the first time via a blockwise strategy. Convergent assembly of the α-(1 → 3)-d-glucan chains was achieved by glycosylation with oligoglucoside derivatives bearing 6- O-benzoyl groups. Those groups are capable of remote α-stereocontrolling participation, making them efficient α-directing tools even in the case of large glycosyl donors. Synthetic biotinylated oligoglucosides (and biotinylated derivatives of previously synthesized tri- and penta-α-(1 → 3)-d-glucosides) loaded on streptavidin microtiter plates were shown to be better recognized by anti-α-(1 → 3)-glucan human polyclonal antibodies and to induce higher cytokine responses upon stimulation of human peripheral blood mononuclear cells than their natural counterpart, α-(1 → 3)-d-glucan, immobilized on a conventional microtiter plate. Attachment of the synthetic oligosaccharides equipped with a hydrophilic spacer via the streptavidin-biotin pair allows better spatial presentation and control of the loading compared to the random sorption of natural α-(1 → 3)-glucan. Increase of oligoglucoside length results in their better recognition and enhancement of cytokine production. Thus, using synthetic α-(1 → 3)-glucan oligosaccharides, we developed an assay for the host immune response that is more sensitive than the assay based on native α-(1 → 3)-glucan.