The stepwise mammalian oxidation of the hydantoin 1-methylimidazolidine-2,4-dione into methylimidazolidinetrione via 5-hydroxy-1- methylimidazolidine-2,4-dione
1-methylhydantoin (2) is described. The major and general metabolic route in mammals, represented by formulae (2)→(7), includes two consecutive stepwiseoxidations giving 5-hydroxy-1-methylhydantoin (3) and thence 1-methylparabanic acid (4). Since the first oxidation proved to be stereoselective, the step was thought to be enzymatic. Although enantiomeric products (3a) and (3b)(ca. 3 : 1) could not be separated