Accessing diverse bicyclic peptide conformations using 1,2,3-TBMB as a linker

Bicyclic peptides are a powerful modality for the engagement of challenging drug targets such as protein-protein interactions. The most common crosslinkers used to generate bicyclic peptides are C3-symmetrical, with evenly positioned peptide loops facing radially outwards from a linker core to favour globular conformations. In contrast, linkers with alternative symmetries can potentially provide access to a more diverse conformational landscape of bicyclic peptides. Here, we use 1,2,3-tris(bromomethyl) benzene (1,2,3-TBMB) to access bicyclic peptides with multiple isomeric configurations, leading to conformations that differ substantially from both the parent linear peptides and the conventional bicyclization products formed with 1,3,5-TBMB, as observed in 2D NMR and CD experiments. Bicyclization at cysteine residues proceeds efficiently under standard aqueous buffer conditions, with broad substrate scope, compatibility with high-throughput screening, and clean conversion (>90%) of linear precursors to bicyclic products for 88 of the 106 diverse peptide sequences tested. We envisage that the 1,2,3-TBMB linker will be applicable to a variety of peptide screening techniques, thereby enabling the discovery of unconventional bicyclic peptides that can engage a broad range of novel drug targets.