Cucurbit[7]uril: A high-affinity host for encapsulation of amino saccharides and supramolecular stabilization of their α-anomers in water

Abstract

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=103 to 104 M-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 α-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 (Ka=1.6×104 M -1). Such a strong affinity for any saccharide in water using a synthetic receptor is unprecedented, as is the supramolecular stabilization of an α-anomer by the host. Sweet pockets: Cucurbit[7]uril binds protonated amino saccharides with excellent affinity in water. It stabilizes the α-anomers of the bound saccharides, thereby preventing any mutarotation in water, which is otherwise impossible. N blue, O red, H white. Copyright © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.