A beta peptide is a type of macromolecule with important biochemical properties that is made up of of beta amino acids. Beta peptides are a type of peptidomimetic, molecules known as alpha peptides or simply peptides with chemical structures similar to a group of molecules and essential to life due to their role in protein synthesis, metabolism, and other biological processes. Unlike regular peptides, however, most forms of beta peptides are not commonly found in nature. Beta peptides are used in medicine, as their chemical structure allows them to mimic or improve upon the effects of some medications based on alpha peptides.
Amino acids are composed of amines, a class of nitrogen compounds similar to ammonia, carboxylic acids, and a third component called a side chain that can vary greatly from one amino acid to another. In alpha amino acids, the amine and carboxylic acid are both bonded to the same carbon atom, called the alpha carbon. In the beta amino acids that make up a beta peptide, however, the carboxylic acid group bonds to the alpha carbon while the peptide bonds to the next carbon atom down, called the beta carbon.
All peptides are polymers, large molecules made from a chain of chemically bonded repeating smaller units. The constituent amino acids of peptides are held together by a series of covalent bonds in which each unit's amine group bonds to the carboxylic acid group of the next unit in the chain. The chemical structure of peptides is the same as that of proteins, but proteins are longer. The dividing line between peptides and proteins is not sharply defined, though one common definition applies the term peptide to polymer chains of 50 amino acids or less and the term protein to molecules larger than that.
Several types of beta peptide are used as medical treatments. Alpha peptides are useful in antibiotic drugs but are often vulnerable to being broken down or degraded by enzymes in the patient's body, a process called proteolysis. Some types of beta peptide are able to produce the same medicinal effects as their alpha peptide counterparts but are chemically different enough to resist proteolysis.
Beta alanine is the only beta amino acid common in nature, so beta peptides such as those used in beta peptide-based antibiotics are synthesized artificially. The most common method is called the Arndt–Eistert reaction, or Arndt–Eistert synthesis, named after the chemists Bernd Eistert and Fritz Arndt. This method turns alpha amino acids into beta amino acids through a sequence of chmeical reactions using light, heat, or silver oxide as a catalyst.