Hydrochloric Acid → 3-({[4-({Cyclohexyl[2-ethyl-5-(2-methylpropanoyl)thiophen-3-yl]methyl}amino)phenyl]carbonyl}amino)propanoic acid

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To a mixture of 4-({cyclohexyl[2-ethyl-5-(2-methylpropanoyl)thiophen-3-yl]methyl}amino)benzoic acid (140 mg) synthesized above, ethyl β-alaninate hydrochloride (62.5 mg), 1-hydroxybenzotriazole monohydrate (62.3 mg) and triethylamine (57 μL) in N,N-dimethylformamide (10 mL) was added 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (78.0 mg), and the mixture was stirred at room temperature for 2.5 days. 1N Hydrochloric acid was added to quench the reaction, and the mixture was extracted with ethyl acetate. The extract was washed with saturated brine, dried over magnesium sulfate, and concentrated under reduced pressure. The residue was purified by silica gel column chromatography (40% ethyl acetate/hexane), and then purified by NH-silica gel column chromatography (ethyl acetate) to give a colorless oil. To a mixture of the obtained oil, tetrahydrofuran (5 mL) and ethanol (5 mL) was added 1N aqueous sodium hydroxide solution (1 mL), and the mixture was stirred at room temperature for 1 hr, and concentrated under reduced pressure. The residue was dissolved in water (10 mL), and 1N hydrochloric acid (1 mL) was added at 0° C. The resulting precipitate was collected by filtration to give the title compound (116 mg, 70%) as a white solid.

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