An unconventional method for purifying the N-carboxyanhydride derivatives of gamma-alkyl-L-glutamates

Common impurities in the phosgenation of alpha-amino acids to produce their N-carboxyanhydride (NCA) derivatives include hydrogen chloride and the hyd rochloride salt of the starting amino acid. These impurities can be effecti vely removed by washing the reaction mixture with water and aqueous bicarbo nate at 0 degrees C prior to isolation of the NCA., despite the well known sensitivity of the NCA to water. The method should be particularly useful f or NCA derivatives which are isolated as oils since purifying them by recry stallization or solvent washes is not feasible. This study involved specifi cally the purification of NCA derivatives from a variety of gamma-alkyl-L-g lutamates and gamma-benzyl-L-glutamate.