allantoin hydantoin ureas imidazolidinone 1-(5-hydroxy-2-oxo-2,3-dihydroimidazol-4-yl)urea An imidazolidinone that is imidazolin-2-one substituted at positions 4 and 5 by hydroxy and ureido groups respectively. 1-(5-hydroxy-2-oxo-2,3-dihydro-1H-imidazol-4-yl)urea CHEBI:74345 2-oxo-4-hydroxy-5-ureidoimidazoline allantoin, enol-form