Optical Resolution by Replacing Crystallization of Ammonium Salts of N-Acetyl-DL-2-aminobutanoic Acid, N-Acetyl-DL-norvaline, and N-Acetyl-DL-norleucine

Ammonium salts of N-acetyl-DL-2-aminobutanoic acid, N-acetyl-DL-norvaline (DL-AcNva·AM salt), and N-acetyl-DL-norleucine were optically resolved by replacing crystallization in the presence of the ammonium salt of N-acetyl-L-alanine to give their salts with L-configuration. The optical resolution of the DL-AcNva·AM salt, espcially, gave the optically pure L-AcNva4·AM salt by purification in 80% yield based on the half amount of the DL-salt used as the starting material.