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 4and inhibit binding of n-octyl glycosides. When the large non-coordinating anion ‘BAr^F’ was used, 4showed excellent selectivity towards n-octyl-α-D-Mannoside with binding in the order of K_a≈16 M⁻¹versus non-measurable affinities for other glycosides including n-octyl-β-D-Glucoside (in CH₃CN/H₂O 91 : 9).