Analytical Tools for Dynamic Combinatorial Libraries of Cyclic Peptides.

Target-directed dynamic combinatorial chemistry is a very attractive strategy for the discovery of bioactive peptides. However, its application has not yet been demonstrated, presumably due to analytical challenges that arise from the diversity of a peptide library with combinatorial side-chains. We previously reported an efficient method to generate, under biocompatible conditions, large dynamic libraries of cyclic peptides grafted with amino acid's side-chains, by thiol-to-thioester exchanges. In this work, we present analytical tools to easily characterize such libraries by HPLC and mass spectrometry, and in particular to simplify the isomers' distinction requiring sequencing by MS/MS fragmentations. After structural optimization, the cyclic scaffold exhibits a UV-tag, absorbing at 415 nm, and an ornithine residue which favors the regioselective ring-opening and simultaneous MS/MS fragmentation, in the gas-phase.

Dynamic Amino Acid Side-Chains Grafting on Folded Peptide Backbone.

An efficient strategy for the synthesis of large libraries of conformationally defined peptides is reported, using dynamic combinatorial chemistry as a tool to graft amino acid side chains on a well-ordered 3D (3-dimension) peptide backbone. Combining rationally designed scaffolds with combinatorial side chains selection represents an alternative method to access peptide libraries for structures that are not genetically encodable. This method would allow a breakthrough for the discovery of protein mimetic for unconventional targets for which little is known.