Beta-peptide

β-peptides are peptides derived from β-amino acids. The parent β-amino acids is H2NCH2CH2CO2H but most examples feature substituents in place of one or more C-H bonds. The only common naturally occurring β amino acid is β-alanine. β-peptides in general do not appear in nature. β-peptide-based antibiotics are being explored as ways of evading antibiotic resistance. Early studies in this field were published in 1996 by the group of Dieter Seebach and that of Samuel Gellman.
Synthesis.
Two main types of β-peptides exist: those with the organic residue (R) next to the amine are called β3-peptides and those with position next to the carbonyl group are called β2-peptides.
β-Amino acids have been prepared by many routes. notably those based on the Arndt-Eistert synthesis.
Secondary structure.
Because their backbones are longer than those of normal peptides, β-peptides form disparate secondary structures. The alkyl substituents at both the α and β positions in a β amino acid favor a gauche conformation about the bond between the α-carbon and β-carbon. This also affects the thermodynamic stability of the structure.
Many types of helix structures consisting of β-peptides have been reported. These conformation types are distinguished by the number of atoms in the hydrogen-bonded ring that is formed in solution; 8-helix, 10-helix, 12-helix, 14-helix, and 10/12-helix have been reported. Generally speaking, β-peptides form a more stable helix than α-peptides.
Clinical potential.
β-peptides are stable against proteolytic degradation in vitro and in vivo, an potential advantage over natural peptides. β-Peptides have been used to mimic natural peptide-based antibiotics such as magainins, which are highly potent but difficult to use as drugs because they are degraded by proteolytic enzymes.
List.
8 beta forms exist: alanine, leucine, lysine, arginine, glutamate, glutamine, phenylalanine, tyrosine forms. Aspartic acid is regarded as both beta and alpha forms, although the beta form is found in microcystins.