Site-specific Bioorthogonal Chemistry on Phage for the Display of Secondary Amine Cyclised Peptides

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The discovery of selective ligands against disease targets remains a formidable challenge. The success of screening campaigns, for example in macrocycle screening, depends on the ability to build large and structurally diverse collections of compounds. Among current strategies, phage-based selection of ligands based on cyclic peptides attached covalently to an organic core shows great promise. However, the use of organic cores for cyclisation can reduce significantly the infectivity, limits loop size and diversity and finally adds constraint into the final molecule. Here we will explore an alternative strategy that does not use an organic core to form the cyclic structure. Instead, we will design peptide repertoires cyclised through a stable secondary amine bond between an encoded lysine and a dehydroalanine residue, converted from a cysteine residue using a bis-alkylation/elimination procedure. Iterative affinity selections against different disease targets and selections will be then performed to validate the approach. Hits obtained from the selection, will then be prepared and characterised in various binding and physicochemical assays as well as relevant cell based potency assays. We believe that further development of the proposed strategy, which thus circumvents the constraints of peptide cyclisation using an organic scaffold, will provide chemical access to a theoretically vast molecular space largely inaccessible by other current approaches, allowing the precision of synthetic chemistry to be brought to expand chemical diversity on phage.