Peptide macrocycles can bind with high affinity and selectivity to protein targets and are an attractive class of molecules for the development of therapeutics. Recently, a phage display-based strategy was developed that allowed to generate potent bicyclic peptide antagonists (Heinis, C., et al., Nat. Chem. Biol., 2009). While bicyclic peptides with nanomolar affinities to a range of protein targe ...