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.

Cone calix[4]arenes, functionalized with two or four l-alanine or l-phenylalanine units at the upper rim, have been synthesized. These compounds, in which the amino acids are attached to the calix[4]arene macrocycle through their carboxy groups, have been named C-linked peptidocalix[4]arenes. The solubility, conformational, and recognition properties of this novel class of chiral receptors are quite different from those previously reported for N-linked peptidocalix[4]arenes. The tetrafunctionalized phthaloyl derivatives 2 are soluble in low polarity media, whereas the corresponding acetyl and benzoyl derivatives 4 and 5 are completely insoluble in CDCl 3 , suggesting a high degree of aggregation of the latter [a]

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