Synthesis of small cyclic peptides constrained with 3-(3-aminomethylphenyl)propionic acid linkers using free radical-mediated macrocyclization

In this letter, we report that small peptides (di- and tri-) having a 3-bromobenzyl group at the C-termini and an acryloyl group at the N-termini undergo an efficient Bu3SnH–AIBN mediated intramolecular free radical cyclization to afford cyclic peptides in good yields. We also propose that these cyclizations are occurring via a pre-organized acyclic structure dictated by a reverse turn (γ/β-turn).