Simple structural requirements for sequence-selective peptide receptors? Tripeptide binding by a podand ionophore

A simple, dye(R)-labeled and conformationally restricted ionophore 2 was prepared and screened for peptide binding using solid-supported combinatorial libraries of 24 389 protected and unprotected tripeptides. The ionophore was found generally to bind unhindered cationic peptides having arginines or N-terminal glycines. The podand was particularly selective in the case of unprotected tripeptides and was able to selectively bind a single tripeptide (L-Arg-L-Phe-D-AsP) from the unprotected similar to 24000-member tripeptide library. These results indicate that relatively simple organic molecules can make highly sequence-selective receptors for tripeptides. Structural features of such receptors are discussed.