Structural studies of racecadotril and its process impurities by NMR and mass spectroscopy

Three unknown impurities in racecadotril bulk drug at levels below 0.5% were detected by simple reverse phase isocratic high performance liquid chromatography (HPLC). Structures for these impurities were proposed by molecular ion information and their fragmentation pattern obtained by LC-MS and these impurities were confirmed by NMR spectroscopy. The impurities I, II and III were characterized as benzyl 2-methyl carboximido acetate, benzyl 2-phenyl ethyl carboximido acetate, and benzyl 2-(1-benzyl vinyl carboximido) acetate. These structures were further confirmed by co-injecting of synthetic standards of impurities with racecadotril. The mechanism of the formation of these process related impurities is discussed.