Design, synthesis and biophysical evaluation of sialyl triazoles as glycomimetic ligands for Siglec-8. Sulfonate is a viable replacement for sulfate.

Ligand design and synthesis for Siglec-8 is important due to its roles in immune responses to allergens, chronic inflammatory disorders and malignancies. Here the synthesis, from readily accessible intermediates, of glycomimetics of Neu5Acα2-3 (6-O-sulfo-Gal), the minimal glycan ligand for Siglec-8, is reported. The mimetics retain Neu5Ac, while replacing the 6-O-sulfo-Gal component by a triazole containing linker presenting either carboxylate or sulfonate groups. Isothermal calorimetry (ITC) measurements showed that the sialyl triazole derivatives were ligands for Siglec-8, with a Kd of 45.5 μM established for the best ligand from the series. The ITC measurements showed that sulfonate was better than carboxylate as a replacement for sulfate, while the incorporation of the naphthylsulfonate group at the Neu5Ac C-9 of the ligands gave affinity improvement, consistent with earlier research. An NMR based binding study supports the conformational change to Siglec-8 to accommodate the 9-naphthylsulfonate group and indicates a similar mode of binding for the highest affinity triazole derivative to previously reported cyclohexane based glycomimetics. The perturbation of NMR signals, docking and binding pose metadynamics support binding of the ligand to the carbohydrate recognition domain. The research provides new Siglec-8 ligands from readily accessible intermediates as a basis for further development.