Cyclic, Cell-Penetrating Peptides Tailor-Made for the Creation of Peptide Libraries with Intrinsic Cell Permeability

The discovery of high-affinity peptides to many intracellular targets has become feasible through the development of diverse macrocyclic peptide libraries. But lack of cell permeability is a key feature hampering the use of these peptides as therapeutics. Here, we develop a set of small, cyclic peptide carriers that efficiently carry cargoes into the cytosol. These peptides are cyclized via side-chain alkylation, which makes them ideal for the creation of diverse mRNA or phage-displayed libraries with intrinsic cell permeability.