The structure of a molecule repeatedly detected in MDMA synthesized through the reductive amination of 3,4-MDP-2-P, using methylamine and sodium cyanoborohydride was determined as N-cyanomethyl-N-methyl-1-(3’,4’-methylenedioxyphenyl)-2-polyamine. Apparently this compound is formed as a manufacturing byproduct only when cyanoborohydride is used as the hydrogen source. Reductive amination of 3,4- DP-2-P using other common hydrogen sources failed to produce this compound as a byproduct. Similarly, reductive amination of P-2-P using methylamine and sodium cyanoborohydride produced the analogous byproduct N-cyanomethyl-N-methyl-1-phenyl-2-polyamine. The presence of these compounds in organic impurity profiles of MDMA or methylamphetamine is a likely indicator that cyanoborohydride was used as the hydrogen source in a reductive amination of 3,4-MDP-2-P or P-2-P with methylamine. Profiling MDMA can provide useful information to law enforcement agencies regarding synthetic route, precursor chemicals, and reagents used. This is useful for the comparative analyses of different drug seizures. The compound was isolated from MDMA by column chromatography, proton and carbon nuclear magnetic resonance spectroscopy, LC/mass spectrometry, and total synthesis.4 tables, 13 figures, and 12 references