1,3,5‐Trisubstituted 2,4,6‐triethylbenzenes consisting of isopropyl groups as recognition units have previously been shown to have interesting binding properties towards selected carbohydrates. The design of such artificial carbohydrate receptors was inspired by the mode of action of carbohydrate‐binding proteins, namely by the participation of the isopropyl side chain of valine in the formation of van der Waals interactions with the carbohydrate substrate. This study aimed to investigate how the replacement of the isopropyl groups by other structural motifs, such as cycloalkyl groups of varying sizes (three to seven‐membered rings), influences the binding properties of the acyclic compounds towards carbohydrates. The cyclopropyl moiety represents a cyclic analog of the isopropyl group, whereas the other cycloalkyl units can be regarded as structural elements, which differ from the structure of the isopropyl group by a –(CH₂)_n‐bridge (n = 1–4) between the two methyl groups. Furthermore, according to the natural interactions, the cyclopentyl group should be able to participate in the formation of van der Waals contacts in a similar way as that observed for the pyrrolidine ring of proline in some protein‐carbohydrate complexes. Such systematic binding studies allow the identification of interesting structure‐activity relationships, which are very useful for the development of artificial carbohydrate receptors with predictable binding properties.

The cyclopentyl group was expected to act as a building block for artificial carbohydrate receptors and to participate in van der Waals contacts with the carbohydrate substrate in a similar way as observed for the pyrrolidine ring of proline in the crystal structures of protein-carbohydrate complexes. Systematic binding studies with a series of 1,3,5-trisubstituted 2,4,6-triethylbenzenes bearing various cycloalkyl groups as recognition units provided indications of the involvement of these groups in the complexation process and showed the influence of the ring size on the receptor efficiency. Representatives of compounds that exhibit a macrocyclic backbone and flexible side arms were now chosen as further model systems to investigate whether the previously observed effects represent a general trend. Binding studies with these macrocycles towards β-D-glucopyranoside, an all-equatorial substituted carbohydrate substrate, included ¹H NMR spectroscopic titrations and microcalorimetric investigations. The performed studies confirmed the previously observed tendency and showed that the compound bearing cyclohexyl groups displays the best binding properties.

In the title monohydrate compound, 1a, and the methanol solvate compound, 1b, the triethylbenzene derivative, C₃₅H₅₁N₅O, has three functionalized side arms and three ethyl groups, the former being located on one side of the central benzene ring, while the latter are directed to the opposite side. Both the crystals are constructed of structurally similar dimers of 1:1 host–guest complexes held together by N—H...O and O—H...N hydrogen bonds, and in 1a additionally by O—H...O hydrogen bonds. The structure of 1b contains additional highly disordered solvent molecules. Thus, the SQUEEZE routine [Spek (2015). Acta Cryst. C71, 9–18] in PLATON was used to generate a modified data set, in which the contribution of the disordered molecules to the structure amplitudes is eliminated. These solvent molecules are not considered in the reported chemical formula.

The synthesis, structural and chemosensing properties of several lower rim-dansylated calix[4]arenes bearing different methylene bridge substituents are described. Compared to bridge-unsubstituted pendants neither the conformational nor the fluorescence characteristics of the calixarene core are perceptibly influenced by the bridge substituent. X-ray structure as well as NMR measurements indicates the lower rim-propoxylated and-dansylated calixarenes to adopt the cone conformation capable of the complexation of Cu²⁺ ions at micromolar level. Fluorescent measurements point to selective 1:2 calixarene: Cu²⁺ complex formation with sensing parameters being of a suitable level to make the use as a potentially immobilisable chemosensor for the detection of Cu²⁺ ions promising.