corrin

Corrin is a heterocyclic macrocycle that forms the core of corrinoids, a family of cobalt-containing compounds that includes vitamin B12 (cobalamin). The corrin ring is closely related to porphyrins but differs in having one fewer methine bridge and one saturated carbon in the ring, making it more flexible and less aromatic than porphyrin. This structural distinction underlies the unique chemistry of corrinoids, particularly their ability to form and break carbon–cobalt bonds.

In cobalamin, cobalt sits at the center of the corrin ring and is coordinated by the four inner nitrogens. An upper axial ligand binds trans to a lower axial ligand, which in many B12 derivatives is a 5,6-dimethylbenzimidazole moiety linked to the ring system. The corrin scaffold stabilizes cobalt in multiple oxidation states (commonly Co(I), Co(II), and Co(III)) and accommodates a variety of organometallic groups on cobalt, enabling diverse biochemical transformations.

Biological relevance of corrinoids is broad. Cobalamin acts as a cofactor in essential enzymatic reactions, including methyl transfer in methionine synthesis and rearrangements mediated by methylmalonyl-CoA mutase. Humans rely on dietary B12, as it is produced by certain bacteria and archaea. Deficiency can lead to anemia and neuropathy.

Corrin-based ligands are studied in coordination chemistry and bioinorganic chemistry for their distinctive macrocyclic properties, and the industrial production of B12 relies on microbial synthesis.