To a solution of 5-({[t-butyl(dimethyl)silyl]oxy}methyl)-3-ethyl-N′-hydroxythiophene-2-carboximidamide (0.16 g, 0.50 mmol) that was obtained in Example 10 (10d) and 4-(2-fluorophenoxy)benzoic acid (0.13 g, 0.55 mmol) that was obtained in Example 10 (10e) in dichloromethane (1.5 ml) was added N,N′-dicyclohexylcarbodiimide (0.11 g, 0.55 mmol) with stirring, and the resulting mixture was stirred at room temperature for 30 minutes. After stirring, hexane (2 ml) was added to the reaction mixture, and insoluble materials were removed by filtration, and the filtrate obtained was evaporated in vacuo. Subsequently, to a solution of the residue obtained in tetrahydrofuran (1 ml) was added a 1.0 M solution of tetrabutylammonium fluoride in tetrahydrofuran (0.75 ml, 0.75 mmol) with stirring, and the resulting mixture was stirred at 60° C. for 1 hour. After cooling to room temperature, the reaction mixture was poured into water (10 ml) and extracted with ether. The extract was washed with a saturated aqueous solution of sodium chloride and dried over magnesium sulfate. After filtration, the filtrate was evaporated in vacuo, and the crude product of the title compound thus obtained was purified by chromatography on a silica gel column using a mixed solvent of ethyl acetate and hexane (3:7 to 5:5) as the eluent to afford the title compound (0.18 g) in a yield of 89% as a white crystalline solid.
