No abstract

The synthesis and binding properties of carbohydrate receptor 1d, which contains two boronic acid binding sites facing each other at opposing sides of a cyclotetrapeptide cavity, are presented. According to electrospray mass spectrometry, 1H NMR spectroscopy, and fluorescence spectroscopy, this receptor forms stable 1:1 complexes with D‐glucose (Ka = 24800 ± 1200 M–1) and L‐glucose (Ka = 11900 ± 1600 M–1) in water/methanol (1:1) at pH = 11.7. Complexes with D‐galactose, D‐mannose, and D‐allose are significantly less stable, while D‐fructose, D‐ribose, and D‐xylose cannot be bound by cooperative action of both boronic acid binding sites. Thus, 1d possesses high affinity and selectivity in glucose recognition combined with good enantioselectivity. Moreover, fluorescence of 1d is quenched upon substrate binding, which allows the use of this receptor as an optical sensor for glucose in aqueous solution. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

C3 Symmetric cyclic hexapeptides containing alternating L-proline and 3-aminobenzoic acid derivatives as subunits possess different affinities towards the two enantiomers of the N,N,N-trimethyl-1-phenylethyl ammonium cation.

The binding of a chiral quaternary ammonium ion to a cyclopeptide containing aromatic amino acid subunits is affected not only by the configuration of the cation but also by the configuration of the chiral counterion. Analysis of the binding equilibria shows that complex formation involves interaction of the whole ion pair with the host indicating that steric requirements of the anion influence complex geometry and stability.