A Genetically Encoded, Phage-Displayed Cyclic-Peptide Library.

Superior to linear peptides in biological activities, cyclic peptides are considered to have great potential as therapeutic agents. To identify cyclic-peptide ligands for therapeutic targets, phage-displayed peptide libraries in which cyclization is achieved by the covalent conjugation of cysteines have been widely used. To resolve drawbacks related to cysteine conjugation, we have invented a phage-display technique in which its displayed peptides are cyclized through a proximity-driven Michael addition reaction between a cysteine and an amber-codon-encoded N -acryloyl-lysine (AcrK).

The nitrilimine-alkene cycloaddition is an ultra rapid click reaction.

The transient formation of nitrilimine in aqueous conditions is greatly influenced by pH and chloride. In basic conditions (pH 10) with no chloride, a diarylnitrilimine precursor readily ionizes to form diarylnitrilimine that reacts almost instantly with an acrylamide-containing protein and fluorescently labels it.