[F:1][CH:2]([F:12])[C:3]([NH2:11])([CH2:7][CH2:8][CH2:9][NH2:10])[C:4]([OH:6])=[O:5].Cl.O.FC(F)C(N)(CCCN)C(O)=O.[CH2:27]([O:34][C:35](Cl)=[O:36])[C:28]1[CH:33]=[CH:32][CH:31]=[CH:30][CH:29]=1.S>O.[Cu].C(=O)([O-])[O-].[Cu+2]>[NH2:11][C:3]([CH:2]([F:12])[F:1])([CH2:7][CH2:8][CH2:9][NH:10][C:35]([O:34][CH2:27][C:28]1[CH:33]=[CH:32][CH:31]=[CH:30][CH:29]=1)=[O:36])[C:4]([OH:6])=[O:5]To a solution of the copper salt of 2-difluoromethyl-2,5-diaminopentanoic acid in water, prepared by reacting 2-difluoromethyl-2,5-diaminopentanoic acid monohydrate hydrochloride (2.4 g) with copper carbonate (6 g), is added slowly at 0° C. with stirring 1.1 g of benzylchloroformate. The reaction mixture is stirred for an additional 3 hours at room temperature after which hydrogen sulfide is passed through the solution until it becomes colorless. The precipitate is filtered off, and the pH of the aqueous solution is adjusted to 6 by the addition of hydrochloric acid. Upon concentration 2-amino-5-benzyloxycarbonylamino-2-difluoromethylpentanoic acid is obtained.
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