S(Cl)([Cl:3])=O.[CH2:5]([O:12][C:13]([NH:15][C@@H:16]([C:19]([OH:21])=[O:20])[CH2:17][NH2:18])=[O:14])[C:6]1[CH:11]=[CH:10][CH:9]=[CH:8][CH:7]=1.[CH3:22]O>>[ClH:3].[CH3:22][O:20][C:19](=[O:21])[C@H:16]([NH:15][C:13]([O:12][CH2:5][C:6]1[CH:7]=[CH:8][CH:9]=[CH:10][CH:11]=1)=[O:14])[CH2:17][NH2:18]Thionyl chloride (3.22 ml) was added dropwise to methanol (25 ml) at 4° C. under a nitrogen atmosphere. After stirred for 30 minutes, to the reaction mixture was added 2(R)-benzyloxycarbonylamino-β-alanine (3 g), followed by warming to the ambient temperature and stirring overnight. The insoluble material was collected by filtration, washed with diisopropyl ether, and dried under a reduced pressure to give 2(R) -benzyloxycarbonylamino-β-alanine methyl ester hydrochloride (3.15 g) as a white solid.
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