Diverse backbone-cyclized peptides via codon reprogramming.

We report a methodology for the ribosomal synthesis of backbone-cyclized peptides involving genetic code reprogramming to introduce one or more nonproteinogenic amino acids. Expression of linear peptides bearing a cysteine-proline dipeptide sequence followed by glycolic acid results in self-rearrangement to a C-terminal diketopiperadine-thioester, which non-enzymatically generates a cyclized peptide. We demonstrate the ribosomal synthesis of several naturally occurring backbone-cyclized peptides and a library based on a bicyclic scaffold, and we identify bioactive sequences by screening and deconvolution.