The cyclothiazomycins are a group of natural products, classified as thiopeptides, which are produced by various Streptomyces species of bacteria. These compounds are ribosomally synthesized and post-translationally modified peptides (RiPPs) and can be further classified as thiopeptides. The overall structure of the cyclothiazomycins comprises a macrocyclic bicyclic peptide containing several thiazoles and thiazolines. The cyclothiazomycins are reported to have multiple inhibitory effects ranging from decreasing blood pressure to interfering with RNA transcription; they also exhibit some antibiotic activity. History Cylothiazomycin A was first isolated from Streptomyces sp. NR0516 in 1991. The structure of cyclothiazomycin A was solved via NMR spectroscopy and chemical degradation. Previously, a peptide compound 5102-II had been isolated in 1982 from Streptomyces hygroscopicus 10-22. The discovery of the genes responsible for the biosynthesis of cyclothiazomycin in 2010 showed that 5102-II and cyclothiazomycin A were the same compound. Structural analogues cyclothiazomycin B1 and B2 were isolated from Streptomyces sp. A307 and solved in 2006 with the help of high-resolution mass spectrometry and NMR spectroscopy. A third analogue, cyclothiazomycin C, was discovered in 2014 with the aid of genome mining, nucleophilic 1,4-addition labeling reactions, high resolution mass spectrometry, and NMR spectroscopy. Structure The cyclothiazomycins are thiazole-containing bicyclic and macrocyclic peptides that are structurally similar to thiostrepton and noshiheptide. Formally classified as thiopeptides within the larger family of ribosomally synthesized and post-translationally modified peptides (RiPPs), the cyclothiazomycins are initially biosynthesized as peptides which subsequently undergo chemical modifications, including macrocyclization, aromatization, cyclodehydration, and dehydrogenation. Cyclothiazomycins exist as three analogues that differ at two amino acid residues in the core peptide. The image below denotes in red the differences between the analogues as well as the amino acid sequence that becomes the final compounds. The structure of cyclothiazomycin A was established primarily by two-dimensional nuclear magnetic resonance spectroscopy. Cyclothiazomycin A contains a dehydroalanine and two dehydrohomoalanine residues within a bicyclic, macrocyclic scaffold composed of thiazolines, thiazoles, and a trisubstituted pyridine. Cyclothiazomycin B and C vary from cyclothiazomycin A at the second and third threonine residues in the core sequence of the precursor peptide. In cyclothiazomycin B, the second threonine is an arginine. Cyclothiazomycin B exists as a pair of diastereomers, cyclothiazomycin B1 and cyclothiazomycin B2, that differ at the configuration of one of its dehydrohomoalanine moieties. Cyclothiazomycin B1 and B2 interconvert by isomerization in solution but are stable in the solid state. Cyclothiazomycin C has a lysine in place of the second