To a solution of (2S,3aS,7aS)-1-(tert-butoxycarbonyl) octahydro-1H-indole-2-carboxylic acid (638 mg) and triethylamine (0.392 mL) in tetrahydrofuran (5 mL) was added 2-methylpropyl chlorocarbonate (0.324 mL) at 0° C., and the mixture was stirred at room temperature for 30 min. Thereafter, to the reaction system was added a solution of 3-amino-5-bromothiophene-2-carboxamide (250 mg) produced in Example 1, step D, in tetrahydrofuran (5 mL), and the mixture was stirred at 60° C. for 26 hr. Ethyl acetate (20 mL) and aqueous sodium hydrogen carbonate (10 mL) were added to the reaction mixture, and the separated aqueous layer was extracted with ethyl acetate (5 mL). The combined organic layers were washed with brine (5 mL) and dried over anhydrous sodium sulfate. Insoluble material was filtered off, and the filtrate was concentrated under reduced pressure. The residue was purified by silica gel column chromatography (ethyl acetate/hexane), and the object fraction was concentrated under reduced pressure to give the title compound (345 mg) as a pale-yellow amorphous solid.
