8-Hydroxyquinoline as a building block for artificial receptors: binding preferences in the recognition of glycopyranosides

8-Hydroxyquinoline-based receptors 1-3, containing a trisubstituted triethylbenzene core, were prepared and their binding properties towards glycosides were evaluated. H-1 NMR and fluorescence titrations as well as binding studies in two-phase systems, such as dissolution of solid carbohydrates in apolar media and phase transfer of sugars from aqueous into organic solvents, revealed beta-vs. alpha-anomer binding preferences in the recognition of glycosides. Compared to the previously described three-armed aminopyridine-based receptor, compounds 1 and 2 showed significantly increased affinity to beta-galactoside. Receptor 2, incorporating two 8-hydroxyquinoline units, was shown to be the most effective receptor for beta-galactoside. Compound 3, bearing one 8-hydroxyquinoline group, was found to be a highly effective receptor for beta-glucoside and shown to be a more powerful receptor than the quinoline-based compound 4, indicating an important role of the quinoline hydroxy group in the complex formation.