N,N-diisopropylethylamine (41 mL), N,O-dimethylhydroxyamine hydrochloride (17.4 g), EDCI (34.3 g), HOBt (24.1 g) were added in sequence to a DMF (400 mL) solution of ((2R,3R)-3-benzyloxy-2-t-butoxycarbonylaminobutoxy)acetic acid (42.1 g), and stirring was continued for 16 hours at room temperature. The solvent was removed under a vacuum, and ethyl acetate and water were added, and the organic layer was partitioned. The organic layer was washed with brine and dried over anhydrous magnesium sulfate, and the solvent was removed under a vacuum. After passing the residue through a silica pad (silica gel 500 cc), the solvent was removed under a vacuum, and the title compound (46.0 g) was obtained. The physical property values are as follows.
