α/β-Peptide foldamers: state of the art

Interplay between proteins, nucleic acids, carbohydrates and/or lipids is involved in almost every process in life on earth. As a consequence, a wide range of diseases results from abnormal interactions of such biomolecules. The main motivation of foldamer science is the development of scaffolds that are capable of adopting defined structures, mimicking parts of biological protagonists in their function. Among the most fundamental interactions in living beings are those between proteins, the so called protein-protein interactions (PPIs). Therefore, peptidic foldamers bear the promise to be an important tool for the inhibition of PPIs, as they are structurally most similar to the original proteins. The great number of possible permutations given by the combination of proteinogenic alpha-amino acid residues along with beta-amino acids opens the door for a larger pool of accessible structures with potential applications. Despite the increasing amount of new secondary structure motifs, only few examples for tertiary and quaternary structure design, as well as inhibition of PPIs, have been realized so far. In this review, we summarize the current knowledge and recent progress made in the field of alpha/beta-peptide foldamers beginning from secondary structure design up to highly sophisticated biological applications, such as protein surface recognition and inhibition of HIV cell entry.