Genetically Encoding Propiolamide Warhead for the Construction of Phage Displayed Cyclic Peptide Library.

Phage display is foundational to cyclic peptide-based ligand discovery, and recently genetically encoded electrophilic noncanonical amino acids (ncAAs) have proven useful in constructing phage-displayed cyclic peptide libraries via proximity-induced crosslinking. However, electrophilic ncAAs exploited for this purpose remain quite rare, thus impeding the broad application of this emerging technology. Herein, we design and genetically encode propiolamide-bearing ncAAs into proteins and demonstrate the capability of propiolamide warhead in conjugating to proximal Cys via a stable and rigid vinyl sulfide connectivity. Importantly, the encoded propiolamide warhead could be facilely displayed on phage surface and support large recombinant library construction. Via biopanning, cyclic peptide-based inhibitor targeting SARS-CoV-2 main protease was discovered.