2-({4-[2-(Heptylamino)ethyl]-1,3-thiazol-2-yl}thio)-2-methylpropionic acid tert-butyl ester (3.41 g) synthesized in Example 303-2 was dissolved in N,N-dimethylformamide (43 mL), and diketene (0.75 g) was added dropwise under ice-cooling. After warming to room temperature, the mixture was stirred for one hour. The mixture was diluted with ethyl acetate. The organic layer was washed with saturated brine and dried over anhydrous sodium sulfate. The solvent was evaporated under reduced pressure to give 2-[(4-{2-[acetoacetyl(heptyl)amino]ethyl}-1,3-thiazol-2-yl)thio]-2-methylpropionic acid tert-butyl ester (3.4 g) as a colorless oil. The present compound was used in the next step without particular purification. The present compound (1.0 g) was dissolved in ethanol (10 mL), hydrazine monohydrate (0.103 g) was added thereto at room temperature, and the mixture was stirred overnight. The solvent was evaporated under reduced pressure, the residue was dissolved in tetrahydrofuran (10 mL), diphosphorus pentasulfide (0.459 g) and sodium carbonate (0.437 g) were added thereto, and the mixture was heated under reflux for 2 hr. The solvent was evaporated, and the residue was directly purified by silica gel chromatography (elution solvent; hexane:ethyl acetate=1:1 to 1:2) to give the title compound (0.54 g) as a colorless oil.
