Ribosomal Synthesis of Macrocyclic Peptides with Linear γ⁴- and β-Hydroxy-γ⁴-amino Acids

Herein, we report the ribosomal elongation of linear γ⁴- and β-hydroxy-γ⁴-amino acids (statines) to expand the nonproteinogenic amino acid repertoire of natural product-like combinatorial peptide libraries. First, we demonstrated the successful ribosomal incorporation of four linear γ⁴-amino acids (γ⁴Gly, (S)-γ⁴Ala, (S)-γ⁴Nva, and (R)-γ⁴Leu) into a 10-mer macrocyclic peptide scaffold. Given the promising effects reported for statines on the cell permeability of macrocyclic peptides, we also designed and tested the ribosomal incorporation of six statines derived from Ala and d-val. Four Ala-derived statines were successfully incorporated into peptides, and γ^4SAla^3R-OH (GP2) showed a similar efficiency of incorporation to that of (S)-β²hAla and l-Ala. These new building blocks might confer the important pharmacological properties of protease resistance and membrane permeability to macrocyclic peptides and expand the diversity of future combinatorial peptide libraries that can be translated by the ribosome.