Peptido- and glycocalixarenes: playing with hydrogen bonds around hydrophobic cavities

This Account reviews the synthesis, conformations, and supramolecular properties of calixarenes endowed with alpha-amino acids or peptides (Peptidocalixarenes) and carbohydrate units (Glycocalixarenes), with a major emphasis on calix[4]arenes functionalized on the aromatic nuclei (upper or wide rim). Most properties of N-linked peptidocalix[4]arenes are found to be quite different from those of the corresponding C-linked derivatives. An interesting example is the tendency of C-linked peptidocalix[4]arenes to form self-assembled nanotubes in the solid state. In several cases the hydrogen bonding donor and acceptor groups of the amino acid residues and the cavity of cone calix[4]arenes act cooperatively in guest binding in nonpolar solvents but not in water, where hydrophobic interactions dominate. Upper-rim bridged peptidocalix[4]arenes act as vancomycin mimics being able to bind d-alanyl-d-alanine (d-Ala-d-Ala) residues. Glycocalix[4]arenes show the phenomenon of multivalency in their binding to specific lectins, and those bearing thiourea spacers between the calix[4]arene scaffold and the sugar units are able to bind aromatic carboxylates and phosphates, making them attractive as novel site specific drug delivery systems.