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 selective recognition of all-equatorial carbohydrates. Here, we explore the molecular recognition properties of an octa-urea [Pd₂L₄]⁴⁺ 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 'BAr^F' 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).