320 mg (0.661 mmol) of methyl 2-{4-[(4-{[(5-chloro-2-thienyl)carbonyl]amino}-1,3-dioxo-1,3-dihydro-2H-isoindol-2-yl)methyl]phenyl}ethaneimidothioate are suspended in 40 ml of methanol, and 153 mg (1.98 mmol) of ammonium acetate and 106 mg (1.98 mmol) of ammonium chloride are added. The mixture is stirred at room temperature overnight, diluted with methanol and methylene chloride until a clear solution is formed and adsorbed on silica gel. Chromatography on silica gel (CH2Cl2/EtOH=10/1 to 3/1) gives the desired compound. The product is dissolved in methanol and methylene chloride, and trifluoroacetic acid is added. Removal of the solvent under reduced pressure gives 298 mg (80% of theory) of the desired product as trifluoroacetic acid salt.
