(3aS,7aS)-4′-(Benzo[d]isothiazol-3-yl)octahydrospiro[isoindole-2,1′-piperazin]-2-ium Methanesulfonate is an intermediate in the synthesis of ent-Lurasidone Hydrochloride (L474940), an impurity of the drug Lurasidone (L474920), an antipsychotic used for treatment of schizophrenia.