S(Cl)([Cl:3])=O.Cl.[NH2:6][CH2:7][C@H:8]([NH:12][C:13]([O:15][CH2:16][C:17]1[CH:22]=[CH:21][CH:20]=[CH:19][CH:18]=1)=[O:14])[C:9]([OH:11])=[O:10].[CH:23](OC(C)C)(C)C>CO>[ClH:3].[NH2:6][CH2:7][C@H:8]([NH:12][C:13]([O:15][CH2:16][C:17]1[CH:22]=[CH:21][CH:20]=[CH:19][CH:18]=1)=[O:14])[C:9]([O:11][CH3:23])=[O:10]7.4 ml (100.8 mmol) of thionyl chloride are added dropwise, at −15° C., to 50 ml of absolute methanol. 12 g (50.4 mmol) of 3-amino-(2S)-benzyloxycarbonylamino propionic acid hydrochloride are added, followed by 40 ml of absolute methanol. After stirring at −15° C. for 45 min and at room temperature for 20 h, the reaction mixture is poured into diisopropyl ether and the precipitate is filtered off with suction and dried under high vacuum. 14.18 g (98%) of (3.7) are obtained as a colorless solid.
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