The binding motifs found in the crystal structures of complexes formed between artificial receptors and monosaccharides, reported previously by our group, have inspired us to design new macrocyclic and acyclic receptors, which were expected to form strong 1:1 complexes with monosaccharides, in particular with β-glucosides, through participation in the formation of CH-π interactions and hydrogen bonds with the sugar substrate. As first representatives of these compounds we have prepared the macrocycles 8-12 and the acyclic molecules 13-16, incorporating two central triethylbenzene units. The new compounds had been designed to bind monosaccharides via interactions of both central benzene rings with the sugar CH groups. Initial binding studies have confirmed the expected favorable binding capabilities of the macrocyclic compounds and indicated interesting binding properties of the acyclic analogues.

Carbohydrate receptors combining a macrocyclic building block and two flexible side arms were designed on the base of the analysis of the binding motifs found in the crystal structures of the complexes formed between artificial receptors and monosaccharides, reported previously by our group. Binding studies in two-phase systems, such as extractions of sugars from water into organic phase, as well as in homogeneous organic media, using (1)H NMR and fluorescence spectroscopic titrations, confirmed the suitability of the designed compounds to act as highly effective and selective carbohydrate receptors. Depending on the nature of the bridges and side arms used as the building blocks, various receptors with different binding properties could be developed. The obtained results confirmed the validity of the receptor design and revealed that crystalline receptor-sugar complexes are particularly a valuable basis for the design of new effective receptor systems.

New representatives of compounds combining both a macrocyclic building block and two flexible side arms as recognition units were prepared and their binding properties toward selected carbohydrates were evaluated. The aim of this study was to examine the effects of the replacement of the heterocycle-bearing side arms by smaller units, such as hydroxy groups, on the binding capability. The design of this type of receptor was inspired by the participation of the side chain hydroxy group of serine and threonine in the biorecognition of carbohydrates. Such structural modifications enable the recognition of structure-activity relationships, which are of high importance in the development of carbohydrate receptors with predictable binding strength and selectivity.

Due to the problems with the exact prediction of the binding properties of an artificial carbohydrate receptor, the identification of characteristic structural features, having the ability to influence the binding properties in a predictable way, is of high importance. The purpose of our investigation was to examine whether the previously observed higher affinity of 2-aminopyrimidine-bearing carbohydrate receptors in comparison with aminopyridine substituted analogues represents a general tendency of aminopyrimidine-bearing compounds. Systematic binding studies on new compounds consisting of 2-aminopyrimidine groups confirmed such a tendency and allowed the identification of interesting structure-activity relationships. Receptors having different symmetries showed systematic preferences for specific glycosides, which are remarkable for such simple receptor systems. Particularly suitable receptor architectures for the recognition of selected glycosides were identified and represent a valuable base for further developments in this field.

No abstract