Carbohydrate−Carbohydrate Interactions in Water with Glycophanes as Model Systems

The synthesis and conformational properties of glycophanes 2 and 3 (cyclodextrin−cyclophane hybrid receptors containing two maltose units linked by (4-hydroxymethyl) benzoic acid spacer) are described. The binding properties in water of these receptors with a series of 4-nitrophenyl glycosides with α- and β-configurations at the anomeric center have been studied using 1 H NMR spectroscopy and molecular mechanics calculations. A comparison of these properties with those of glycophane 1 (an α,α-trehalose containing glycophane) and α-cyclodextrin (αCD) using the same glycosides shows the existence of a stabilizing contribution to the free energy of binding in the case of of glycophanes but not in the case of the αCD system. This contribution is due to carbohydrate−carbohydrate interactions between both host and guest lipophilic sugar surfaces. Glycophanes 1, 2, and 3 show similar α/β selectivity on binding the ligands, despite the great flexibility of 3 related to 1 and 2 . Parallels are drawn between the thermodynamic behavior of these model systems and that proposed for sugar−protein interactions.