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Synthesis and structure of lower rim C-linked N-tosyl peptidocalix[4]arenes.

Chiral p-tert-butylcalix[4]arenes functionalized at the lower rim with amino acid residues have been prepared. The (1)H and (13)C NMR spectra indicate that the macrocycles preferably adopt a cone conformation. Calix[4]arenes bearing amino acid moieties were prepared as a class of receptors selective for anions that are bound through hydrogen bonding with the NH group. The association constants are dependent on the nature of the substituents at the lower rim. Derivative 9 shows the strongest complexation and the largest selectivity for N-tosyl-(L)-alaninate. Finally, a preliminary X-ray crystal study of the difunctionalized receptor 6f shows the "flattened cone" conformation in the solid state.