β-Peptides: a surprise at every turn

β-Peptides, i.e. oligomers of β-amino acids, containing as few as six residues may form surprisingly stable helices, with half-lives for the H/D exchange of the central NH protons of up to several days. Furthermore, these β-peptides (carrying the side chains of familiar α-amino acids such as Ala, Val, Leu, Phe, Lys in the 2- and/or 3-position of their 3-amino carboxylic moieties) have been shown to be stable to common peptidases for at least two days. In this article, a brief account of the results obtained since we started work in this area in early 1995 is given. The synthesis of enantiopure β-amino acids can be achieved by homologation of α-amino acids. The greater structural variability of β-amino acids leads to an even greater multitude of possible β-peptide primary and secondary structures. Circular dichroism, NMR and X-ray investigations have unveiled helical, pleated-sheet and tubular arrangements of linear and cyclic β-peptides composed of up to twelve β-amino acids. The prospects for the use of β-peptides as drugs, the construction of large, enzymatically-active β-proteins and their interaction with the natural, α-peptidic counterparts are discussed.