A novel class of macrobicyclic receptors for carbohydrate recognition based on upper rim, peptide-bridged calixarenes has been designed and synthesized. Receptor 12, in which a charged phosphate group cooperates with peptide hydrogen-bonding donor and acceptor groups in the binding process, is the most efficient and selective in the complexation of simple carbohydrate derivatives. The selectivity observed is toward beta-glucoside 13a, which is better bound (DeltaGdegrees = 19.6 kJ mol(-1)) compared to the corresponding alpha anomer 13b (DeltaGdegrees = 17.0 kJ mol-1) and to the beta-galactoside 13c (DeltaGdegrees = 17.7 kJ mol(-1)) in CDCl3. A substantial drop in the stability constant is observed by esterification of the phosphate group in the host 12 or by alkylation of the OH groups in the 2 and 3 positions in the beta-glucoside and beta-galactoside derivatives. On the basis of a careful analysis of the H-1 NMR data available, a binding mode of the beta-octylglucoside 13a to receptor 12 is proposed.
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