Abstract: Provided is a separating method for an optical isomer mixture comprising the steps of mixing an amino acid derivative such as N-(tert-butoxycarbonyl)-DL-alanine in which optical isomers of a D type and an L type are present in a mixture with a hydrophilic compound such as ?-cyclodextrin having a different affinity to two kinds of the optical isomers described above and then bringing the resulting aqueous solution or aqueous suspension into contact with a hydrophobic substance such as a solid matter subjected on a surface thereof to hydrophobic treatment on the condition that the pH is 3.5 or lower or under the coexistence of ions including an atomic group having hydrophobicity which can be a counter ion for the amino acid derivative described above such as a triethylammonium ion to thereby separate the D type amino acid derivative from the L type amino acid derivative present in the above aqueous solution or aqueous suspension.

Abstract: Provided is a separating method for an optical isomer mixture comprising the steps of mixing an amino acid derivative such as N-(tert-butoxycarbonyl)-DL-alanine in which optical isomers of a D type and an L type are present in a mixture with a hydrophilic compound such as &bgr;-cyclodextrin having a different affinity to two kinds of the optical isomers described above and then bringing the resulting aqueous solution or aqueous suspension into contact with a hydrophobic substance such as a solid matter subjected on a surface thereof to hydrophobic treatment on the condition that the pH is 3.5 or lower or under the coexistence of ions including an atomic group having hydrophobicity which can be a counter ion for the amino acid derivative described above such as a triethylammonium ion to thereby separate the D type amino acid derivative from the L type amino acid derivative present in the above aqueous solution or aqueous suspension.