Methyl 3-[[4-Chloro-2-(phenylamino)phenyl]methylamino]-3-oxopropanoate-d3 is labelled Methyl 3-[[4-Chloro-2-(phenylamino)phenyl]methylamino]-3-oxopropanoate (M295145), an impurity of Clobazam (C582500) which is a benzodiazepine psychotherapeutic agent.