title: Structurally diverse cyclisation linkers impose different backbone conformations in bicyclic peptides.
abstract: Combinatorial libraries of structurally diverse peptide macrocycles offer a rich source for the development of high-affinity ligands to targets of interest. In this work we have developed linkers for the generation of genetically encoded bicyclic peptides and tested whether the peptides cyclised by them have significant variations in their backbone conformations. Two new cyclisation reagents, each containing three thiol-reactive groups, efficiently and selectively cyclised linear peptides containing three cysteine moieties. When the mesitylene linker of the bicyclic peptide PK15, a potent inhibitor of plasma kallikrein (K(i)=2 nM), was replaced by the new linkers, its inhibitory activity dropped by a factor of more than 1000, suggesting that the linkers impose different conformations on the peptide. Indeed, structural analysis by solution-state NMR revealed different NOE constraints in the three bicyclic peptides, indicating that these relatively small linkers at the centres of bicyclic peptide structures significantly influence the conformations of the peptides. These results demonstrate the prominent structural role of linkers in peptide macrocycles and suggest that application of different cyclisation linkers in a combinatorial fashion could be an attractive means to generate topologically diverse macrocycle libraries.
authors.affiliation: Institute of Chemical Sciences and Engineering, Ecole Polytechnique Fédérale de Lausanne, 1015 Lausanne, Switzerland.
authors.forename: Shiyu
authors.initials: S
authors.lastname: Chen
authors.forename: Julia
authors.initials: J
authors.lastname: Morales-Sanfrutos
authors.forename: Alessandro
authors.initials: A
authors.lastname: Angelini
authors.forename: Brian
authors.initials: B
authors.lastname: Cutting
authors.forename: Christian
authors.initials: C
authors.lastname: Heinis
mesh_terms: D000595:Amino Acid Sequence; D020650:Combinatorial Chemistry Techniques; D003500:Cyclization; D006801:Humans; D008969:Molecular Sequence Data; D015394:Molecular Structure; D019151:Peptide Library; D010455:Peptides / Q000737:chemistry*; D010456:Peptides, Cyclic / Q000138:chemical synthesis / Q000737:chemistry*; D020842:Plasma Kallikrein / Q000037:antagonists & inhibitors / Q000737:chemistry
chemical_list: D019151:Peptide Library; D010455:Peptides; D010456:Peptides, Cyclic; D020842:Plasma Kallikrein