The compound (46 mg) prepared in step (d) of Example 133 was dissolved in dichloromethane (1 ml). m-Chloroperbenzoic acid (19 mg) was added to the solution at 0° C., and the mixture was stirred at 0° C. for one hr. Water was added to the reaction solution, and the mixture was extracted with chloroform. The extract was dried over anhydrous MgSO41 and the solvent was then removed by distillation under the reduced pressure. The residue was purified by preparative TLC (n-hexane:ethyl acetate=1:4) to give 4-[10-oxo-9-(2,2,2-trifluoroethylcarbamoyl)-9,10-dihydro-10λ4-thioxanthen-9-yl]butyl bromide (38 mg).
