A heterocyclic compound that is involved in pyrimidine synthesis. It is synthesized from carbamoyl phosphate and aspartate by the enzyme dihydroorotate dehydrogenase. It is combined with phosphoribosyl pyrophosphate and uracil by the enzyme UMP synthase to form uridine monophosphate. Deficiency of UMP synthase (orotic aciduria) or certain enzymes involved in the urea cycle (e.g., ornithine transcarbamylase) can result in orotic acid accumulation.