[C:1]([O:5][C:6](=[O:20])[CH2:7][C@H:8]([NH:12][C:13]([O:15][C:16]([CH3:19])([CH3:18])[CH3:17])=[O:14])[C:9](O)=[O:10])([CH3:4])([CH3:3])[CH3:2].CN1CCOCC1.C(OC(Cl)=O)C(C)C.[Cl-].[NH4+].S([O-])([O-])(=O)=O.[Mg+2]>O.C(OCC)(=O)C.O1CCCC1>[C:16]([O:15][C:13]([NH:12][C@H:8]([CH2:9][OH:10])[CH2:7][C:6]([O:5][C:1]([CH3:4])([CH3:3])[CH3:2])=[O:20])=[O:14])([CH3:18])([CH3:17])[CH3:19]2.0 g of (S)-4-t-butoxy-2-(t-butoxycarbonylamino)-4-oxobutanoic acid and 14 mL of tetrahydrofuran were added to 50 mL flask and then the resulting reaction solution was cooled to 0° C. While the reaction solution was stirred, 1.0 mL of 4-methylmorpholine was dropped, and after 10 minutes, 1.2 mL of isobutylchloroformate was dropped, and then stirred for 1 hour. The produced solid was filtered with diatomite, was washed with 14 mL of tetrahydrofuran, and then the filtrate was cooled to 0° C. 523 mg of sodium borohydride was added to the cooled filtrate, and stirred for 4 hours while the reaction temperature was naturally increased to room temperature. After completing the reaction, the reaction solution was cooled to 0° C. and then 10 mL of ammonium chloride aqueous solution was dropped. 20 mL of ethyl acetate and 10 mL of water were added and then stirred for 10 minutes. An organic layer was isolated, dehydrated with magnesium sulfate and then concentrated under reduced pressure. A concentrated residue was isolated with column chromatography (n-hexane:ethyl acetate=2:1) and then concentrated under reduced pressure to obtain 1.86 g of a title compound.
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