Synthesis and application of α-d-mannosyl clusters as photoaffinity ligands for mannose-binding proteins: Concanavalin A as a model receptor

Mono-, di-, and tri-antennary α-d-mannopyranosyl derivatives were synthesized as oligosaccharide mimics. The compounds vary in the length of the acyclic aglyconic spacers linking, in the case of the di- and tri-antennary derivatives, the glycosyl endgroups. By haemagglutination assay (Coombs test) the affinity of the α-d-mannopyranosyl ligands against Con A was determined in comparison with methyl α-d-mannopyranoside. Affinity enhancement and strong cross-linking capacity were found with the di- and tri-antennary compounds where α-d-mannopyranosyl endgroups are separated by spacers of 5–37 atoms in length. The optimal ligand had Ki of 5.1 μ M in comparison with 3.12 mM for methyl α-d-mannopyranoside. The monoantennary compound and, to certain extents, one di- and short tri-antennary ligands with short spacer lengths did not differ significantly in affinity from methyl α-d-mannopyranoside. A triantennary, radiolabelled ligand equipped with a photolabile diazirino group was used to covalently modify Con A by photoaffinity labelling. A significant degree of covalent cross-linking of Con A monomers was observed.