Abstract: The present invention relates to a method of forming a macrocyclic peptide bearing a pharmacophore and said produced macrocyclic peptide, wherein the method comprises the steps of: reacting a peptide with two thiol groups of cysteine side chains with the reactive compound 1,5-dichloropentanedion-2,4. The reaction between the reactive compound and the peptide produces an 1,3-diketone-containing macrocyclic polypeptide. The macrocycle with a 1,3-diketone group is then modified by reaction of said macrocycle with an alkyl or aryl hydrazine group bearing a pharmacophore in benign aqueous conditions. The macrocycles may be displayed in a library, such as a phage display library, and used to biopan for affinity against a selected target.

Abstract: The invention relates to a bicyclic peptide complex comprising a peptide construct, said construct comprising (i) a polypeptide with free terminus (N or C); (ii) optionally, a nucleic acid encoding the polypeptide; (iii) a twofold-symmetric linker (TSL) compound attached to said polypeptide where the linker is attached to the terminus of polypeptide via a covalent bond and to at least two discrete side chains of the peptide. The invention also relates to libraries, and to methods for making complexes and to methods of screening using the same.