Cucurbit[7]uril: A High-Affinity Host for Encapsulation of Amino Saccharides and Supramolecular Stabilization of Their α-Anomers in Water

摘要

Cucurbit[7]uril (CB[7]), an uncharged and water-soluble macrocyclic host, binds protonated amino saccharides (D-glucosamine, D-galactosamine, D-mannosamine and 6-amino-6-deoxy-D-glucose) with excellent affinity (K_a = 10~3 to 10~4M~(-1)). The host-guest complexation was confirmed by NMR spectroscopy, isothermal titration calorimetry (ITC), and MALDI-TOF mass spectral analyses. NMR analyses revealed that the amino saccharides, except D-mannosamine, are bound as a-anomers within the CB[7] cavity. ITC analyses reveal that CB[7] has excellent affinity for binding amino saccharides in water. The maximum affinity was observed for D-galactosamine hydrochloride (K_a = 1.6 × 10~4 M~(-1)). Such a strong affinity for any saccharide in water using a synthetic receptor is unprecedented, as is the supramolecular stabilization of an a-anomer by the host.