Cyclic peptides are more stable cyclic peptides with various physiological functions and medicinal values than linear peptides. Since the discovery of the first antibacterial cyclic peptide GramicidinS in the 1940s, people have continuously isolated cyclic peptides with special structures from plants, fungi, bacteria and marine organisms. Natural cyclic peptides often contain uncommon amino acids, such as D-amino acid, p-amino acid and a, p-didehydroamino acid, etc., which are mainly divided into two categories: homocyclic peptides (Homodetic cyclopeptides) and heterocyclic peptides (Heterodetic cyclopeptides). Homocyclic peptides that are all composed of amino acids and are strictly cyclic by peptide bonds; the main chain is composed of peptide bonds, and other functional groups such as disulfide bonds, ester bonds, ether bonds, thioether bonds, etc. The composed pseudopeptides (Depsipeptides or peptolides) are called heterocyclic peptides.

Bioactive cyclic peptides can form a restricted conformation, and have better resistance to enzymatic hydrolysis and chemical degradation in vivo compared with the corresponding linear peptides. As well as toxins and other aspects show a rich variety of biological activities. The elucidation and successful synthesis of physiologically active cyclic peptides such as insulin, oxytocin, antibodies, and mycotoxins have made the medicinal chemistry of cyclic peptides develop rapidly, and have considerable development prospects in many aspects such as biomedicine. Receptor antagonists and many other aspects also have broad application potential.

Melanotan 2 is a peptide containing a cyclic peptide structure, which can be mass-produced by solid-phase peptide synthesis technology.