A new cyclic tetrapeptide composed of alternating l-proline and 3-aminobenzoic acid subunits

A cyclic tetrapeptide composed of alternating l-proline and 3-aminobenzoic acid subunits has been synthesized and its structure determined in solution and in the solid state. The cyclopeptide possesses a significantly smaller cation affinity than the corresponding hexapeptide. Derivatives with suitable substituents on the aromatic subunits can be used as tweezer-type receptors.