5-(carbamoylamino)-4-hydroxy-2-oxo-3H-imidazole-4-carboxylate 4-hydroxy-2-oxo-5-ureido-3H-imidazole-4-carboxylate 4-hydroxy-2-keto-5-ureido-3H-imidazole-4-carboxylate 5-(aminocarbonylamino)-4-hydroxy-2-oxo-3H-imidazole-4-carboxylate