Biomimetic macrocyclic receptors for carboxylate anion recognition based on C -linked peptidocalix[4]arenes

Abstract

Two neutral macrobicyclic anion receptors 4 and 6, containing a calix[4]arene in the cone conformation, two L-alanine units, and a 2,6-diacylpyridine or a phthaloyl bridge, are described. The x-ray crystal structure of the acetone complexes of the pyridine containing macrocycle 6 shows the four amide NH groups to be in close proximity to the chiral pocket delimited by the pyridine and one aromatic nucleus of the calix[4]arene. This conformation is also the most stable in acetone-d6 solution, as proven by one-and twodimensional NMR spectral measurements. Electrospray ionization-MS and 1 H NMR experiments reveal that the two ligands strongly bind carboxylate anions in acetone solution. H-bonding interactions between the carboxylate anions and the amide NH groups, together with ͞ stacking, are invoked to explain the efficiency and the selectivity of these anion receptors.

Novel cinchona carbamate selectors with complementary enantioseparation characteristics for N-acylated amino acids

“…Most importantly, basketshaped cyclophanes have been demonstrated to exhibit selective recognition properties for a broad range of molecular entities, including many biologically relevant substrates, such as sugars and amino acids. 15 In general, the molecular recognition potential of calixarenes may be readily tailored by the introduction of dedicated functionalities at the "upper" as well as the "lower" rim of the macrocycles. Depending on the chemical nature and position(s) of these appendices, calixarenes are capable of binding both neutral molecules as well as charged species, such as metal ions and anions.…”

Calix[4]arene Anion Receptors Bearing 2,2,2-trifluoroethanol Groups at TheUpperRim

“…However, a comparison with receptors which contain simple alcoholic functions, which show no binding ability towards acetate anion [31], points out the importance of the electrowithdrawing groups CF3 in enhancing the H bonding ability of the OH groups. The modest binding constants and the "normal" acetate > benzoate selectivity observed for ligand 3a suggests that the apolar cavity of the calix [4]arene does not play an important role in anion binding in contrast to that observed with other receptors [16,55,57,58].…”

Anion Receptors Based on Calixarenes

“…Upper rim bridged macrocyclic receptors 61a,b possessing two L-alanine units show [79] very strong binding of various carboxylates in acetone-d 6 with pronounced selectivity towards benzoate (K 60a =4.4·10 4 M -1 , K 60b =4.0·10 4 M -1 ) while simple inorganic anions are bound only weakly (Cl -, K 60b =2.8·10 3 M -1 , NO 3 -, K 60b =200 M -1 ). The enhanced binding of benzoate can be explained by the additional p-p interactions of anion with aromatic bridging unit (benzene or ditopic receptors [85] that simultaneously bind both cationic and anionic guest molecules.…”