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|1. (WO2018051972) NAHLSGEN OPTICAL RESOLUTION METHOD|
|Title:||NAHLSGEN OPTICAL RESOLUTION METHOD|
Provided is a method for separating the four optical isomers of Nahlsgen. According to the present invention, a method for producing a mixture of D-2-amino-4-[(Rp)-(3-carboxymethylphenoxy)(methoxy)phosphoryl]butanoic acid hydrate and L-2-amino-4-[(Sp)-(3-carboxymethylphenoxy)(methoxy)phosphoryl]butanoic acid hydrate is characterized by comprising a step of: subjecting a mixture of the four optical isomers represented by the following formula (1') to fractional crystallization using water or a mixed solvent of water and a water-soluble organic solvent, and causing a mixture of a compound represented by the following formula (1-1'-1) and a compound represented by the following formula (1-4'-1) to deposit.