The purpose of present invention is to provide a method to prepare compound that has excellent activity as α2δ ligand.The solution is to provide a method to prepare general formula (I) compound or the salt thereof through optical resolution[wherein, R1: hydrogen atom or C1-C6 alkyl group, R2: hydrogen atom or a protective group for hydroxyl group].本發明課題係提供一種作為α2δ配位體具有優異活性的化合物之製造方法。解決方法係提供經光學解析製造具有通式(I)之化合物或其鹽之方法。[通式中,R1:氫原子或C1-C6烷基,R2:氫原子或羧基之保護基]