To enable the optical resolution of subject compound so as to provide the S-isomer having an optical purity sufficient for application to practical use as a synthetic intermediate for a therapeutic agent for diabetes in high yield by using a specific amine compound as an optical resolving agent.
A base, as necessary, is added to a solution containing a mixture of the R-isomer of a compound represented by formula I (R1, R2 and R3 are each H, a halogen, a lower alkyl or an alkoxy) with the S-isomer thereof (e.g. the solution prepared by dissolving a racemic modification of the compound represented by formula I in water, alcohols, a mixed solvent of the water with the alcohols or a mixed solvent of carboxylic acid esters with water) and a compound which is the S-isomer or the R-isomer having a structural formula represented by formula II (R4 is H or Cl; * is asymmetric carbon) is then added thereto. Thereby, (A) a diastereomeric salt is formed and separated from the solution. The R-isomer or S-isomer of the compound represented by formula I is then liberated from the resultant diastereomeric salt A.
TOYODA KAZUTOSHI
YOSHIDA KAZUTO
