[C:1](Cl)(=[O:3])[CH3:2].[NH2:5][CH:6]([C:11]1[CH:16]=[C:15]([F:17])[CH:14]=[CH:13][C:12]=1[F:18])[CH2:7][C:8](O)=[O:9].Cl>C(O)C>[CH2:1]([O:3][C:8](=[O:9])[CH2:7][CH:6]([NH2:5])[C:11]1[CH:16]=[C:15]([F:17])[CH:14]=[CH:13][C:12]=1[F:18])[CH3:2]Acetyl chloride (4 ml) was added dropwise at room temperature to a round-bottom flask containing ethanol (50 ml). 3-Amino-3-(2,5-difluorophenyl)propionic acid (2.94 g) was added to the ethanolic hydrochloric acid solution thus prepared, and the mixture was stirred at 50° C. for three hours. Subsequently, the mixture was concentrated under reduced pressure, and the residue was admixed with 1N sodium hydroxide solution (100 ml) and extracted immediately with dichloromethane (3×50 ml). The combined organic phases were dried (Na2SO4), filtered and concentrated. The product (3.2 g) was used without further purification.
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