To a DMF (4 ml) solution of 9-bromo-N-[2,4-bis(methylthio)-6-methyl-3-pyridyl]nonanamide (90 mg, 0.22 mmol) and 7-methoxycarbonyl-2-mercaptobenzoxazole (45 mg, 0.22 mmol) were added 18-crown-6 (6 mg, 0.02 mmol) and potassium carbonate (36 mg, 0.26 mmol), and the mixture was stirred at 80° C. for 4 hours. The reaction mixture was diluted with water, and then extracted with ethyl acetate. The organic layer was washed with water and then with a saturated aqueous solution of sodium chloride, and dried over magnesium sulfate. Subsequently, the solvent was distilled off, and the resulting crude product was recrystallized from a mixture of ethyl acetate and hexane to obtain 84 mg (yield 72%) of the desired compound as a colorless powdery crystal.
