Isoalloxazine is the structural foundation of flavins such as riboflavin (vitamin B2) and is a heterocyclic compound.

[2] It has a tricyclic structure which means it has three interconnected rings of atoms and is a tautomer of alloxazine.

[1] The structure is formed by primary-secondary aromatic o-diamines and they are a high-melting crystalline substance.

[1] The R-group is used to attach various flavin groups It has a similar structure to pteridines which has two interconnected rings.

Isoalloxazine rings can exist in different redox and ionization states depending on the chemistry of FMN and FAD associated with it.