Pteridine
A pteridine is a bicyclic heterocyclic system with two nitrogen atoms at positions 1 and 4 in ring A, and two nitrogen atoms at positions 1 and 3 in ring B. Pteridines constitute a large group of heterocyclic compounds containing a wide variety of substituents on this parent structure. Pterins and flavins are classes of substituted pteridines that have diverse biological roles.
Image:Pteridinsynth2.svg|thumb|left|322 px|Synthesis of pteridine from 4,5-diaminopyrimidine and glyoxal