An octa-urea [Pd2L4]4+ cage that selectively binds to n-octyl-α-D-mannoside.

Designing compounds for the selective molecular recognition of carbohydrates is a challenging task for supramolecular chemists. Macrocyclic compounds that incorporate isophtalamide or bisurea spacers linking two aromatic moieties have proven effective for the elective recognition of all-equatorial carbohydrates. Here, we explore the molecular recognition properties of an octa-urea [Pd2L4]2+ cage complex (4). It was found that small anions like NO3- and BF4- bind inside 4 and inhibit binding of n-octyl glycosides. When the large non-coordinating anion 'BArF' was used, 4 showed excellent selectivity towards n-octyl-α-D-Mannoside with binding in the order of  Ka ≈ 16 M-1 versus non-measurable affinities for other glycosides including n-octyl-β-D-Glucoside (in CH3CN/H2O 91:9).