Ribosomal synthesis and de novo discovery of bioactive foldamer peptides containing cyclic β-amino acids.

Peptides that contain β-amino acids display stable secondary structures, such as helices and sheets, and are often referred to as foldamers. Cyclic β2,3-amino acids (cβAAs), such as 2-aminocyclohexanecarboxylic acid (2-ACHC), are strong helix/turn inducers due to their restricted conformations. Here we report the ribosomal synthesis of foldamer peptides that contain multiple, up to ten, consecutive cβAAs via genetic code reprogramming. We also report the de novo discovery of macrocyclic cβAA-containing peptides capable of binding to a protein target. As a demonstration, potent binders with low-to-subnanomolar KD values were identified for human factor XIIa (hFXIIa) and interferon-gamma receptor 1, from a library of their 1012 members. One of the anti-hFXIIa macrocyclic peptides that exhibited a high inhibitory activity and serum stability was co-crystallized with hFXIIa. The X-ray structure revealed that it adopts an antiparallel β-sheet structure induced by a (1S,2S)-2-ACHC residue via the formation of two γ-turns. This work demonstrates the potential of this platform to explore the previously inaccessible sequence space of cβAA-containing peptides. Cyclic β-amino acids can add useful properties to peptides, such as inducing turn structures or providing resistance to proteases. To harness these properties up to ten consecutive cyclic β-amino acids have now been ribosomally incorporated via genetic code reprogramming into a foldamer peptide library that has been screened for potent binders against a protein target, human factor XIIa.