What’s a Beta Peptide?

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A beta peptide is a type of macromolecule with important biochemical properties which is made up of beta amino acids. Beta peptides are a type of peptidomimetic, molecules known as alpha peptides or simply peptides with similar chemical structures to a group of molecules and essential for 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 enhance the effects of some alpha peptide drugs.

Amino acids are composed of amines, a class of ammonia-like nitrogenous compounds, 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 the 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, called the beta carbon.

All peptides are polymers, large molecules made up of 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 the amino group of each unit 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 line between peptides and proteins is not sharply defined, although a common definition applies the term peptide to polymer chains of 50 amino acids or less and the term protein to molecules larger than that.

Different types of beta peptides are used as medical treatments. Alpha peptides are useful in antibiotic drugs, but are often vulnerable to breakdown or degradation by enzymes in the patient’s body, a process called proteolysis. Some types of beta peptides are capable of producing 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 that is common in nature, so beta peptides such as those used in beta peptide antibiotics are synthesized artificially. The most common method is called the Arndt-Eistert reaction, or Arndt-Eistert synthesis, named after chemists Bernd Eistert and Fritz Arndt. This method transforms alpha amino acids into beta amino acids through a sequence of chemical reactions that use light, heat or silver oxide as a catalyst.

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