Amide, Amino, Hydroxy and Aminopyridine Groups as Building Blocks for Carbohydrate Receptors
Receptors 1–3, incorporating primary amide, hydroxy or amino groups as recognition units used in nature, as well as 2-aminopyridine units as heterocyclic analogues of the asparagine/glutamine primary amide side chains, were prepared and their binding properties towards neutral sugar molecules were studied. The design of these receptors was inspired by the binding motifs observed in the crystal structures of protein–carbohydrate complexes. The binding studies with β-glucopyranoside 5 indicated the formation of complexes with 1:1 and 2:1 receptor–monosaccharide binding stoichiometries, with an overall β21 binding constant of 107–108M–2. Both hydrogen bonding and interactions of the sugar CH groups with the central phenyl rings of the receptors contribute to the stabilisation of the receptor–sugar complexes. The syntheses, molecular modeling studies and binding properties of the receptors 1–3 are described, as well as comparative binding studies with receptor 4, lacking the third recognition site. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)