Pteridines

Pteridines are a class of nitrogen-containing heterocyclic compounds characterized by a bicyclic ring system formed by the fusion of a pyrazine and a pyrimidine ring, providing a rigid pteridine core. This fused structure serves as a versatile scaffold for various substituents and oxidation states.

In biology, pteridines occur as pterins, which are oxidized or reduced derivatives of the core structure. They are prominent as components of larger molecules such as tetrahydrobiopterin (BH4) and as parts of folate derivatives. Related compounds include neopterin and sepiapterin. The pteridine/pterin moiety is found across plants, animals, and microorganisms, contributing to metabolism and coloration.

Biosynthesis typically begins with GTP, which is converted by GTP cyclohydrolase I to dihydroneopterin triphosphate. Through subsequent transformations and reductions, neopterin and other pterins are formed, while further reduction yields tetrahydropterins. Pteridines can also be prepared synthetically in the laboratory.

Functions and applications of pteridines are diverse. As cofactors, tetrahydropterins like BH4 participate in essential redox reactions, serving as cofactors for hydroxylases and nitric oxide synthase. Pteridines also function as pigments in some organisms, contributing yellow to orange coloration in certain insects such as butterflies. In medicine, neopterin is used as a biomarker of immune activation, reflecting cellular immune response.

Overall, pteridines are a structurally and functionally important family of heterocycles with roles in metabolism, physiology, and biology, as well as ongoing interest in synthetic chemistry and materials science.