(4Z)-4-[[4-(Acetyloxy)-3-methoxyphenyl]methylene]-2-methyl-5(4H)-oxazolone is an intermediate in the synthesis of rac 3-O-Methyl DOPA (Levodopa EP Impurity C) (M303805), which is an impurity of Levodopa (D533751). A useful marker that can be used to screen for the absense of Aromatic L-amino acid decarboxylase (AADC).