Oligoalanine helical callipers for cell penetrationElectronic supplementary information (ESI) available. See DOI: 10.1039/c8cc02304b

Even for short peptides that are enriched in basic amino acids, the large chemical space that can be spanned by combinations of natural amino acids hinders the rational design of cell penetrating peptides. We here report on short oligoalanine scaffolds for the fine-tuning of peptide helicity in different media and the study of cell penetrating properties. This strategy allowed the extraction of the structure/activity features required for maximal membrane interaction and cellular penetration at minimal toxicity. These results confirmed oligoalanine helical callipers as optimal scaffolds for the rational design and the identification of cell penetrating peptides. Even for short peptides that are enriched in basic amino acids, the large chemical space that can be spanned by combinations of natural amino acids hinders the rational design of cell penetrating peptides.