A new compound, (2-chloroethoxy-4’-dimethylaminophenyl)phosphorylacetic acid N -acetohydrazide (II) has been synthesized. Compound II is proposed to be a metabolite of 2-(chloroethoxy-4’-dimethylaminophenyl)phosphoryl acetohydrazide (CAPAH, I) – a phosphorylacetic acid derivative possessing nootropic activity. Psychotropic and antiarrhythmic properties of II were studied in comparison to those of I. It is established that II does not possess nootropic and antidepressant activities, but its antiarrhythmic properties are more pronounced. It is suggested that C(O)CH 3 fragment, being a substitute of hydrazide in the structure of II, decreases penetration of this compound through blood-brain barrier, which can explain the absence of psychotropic activity.