[N+:1]([C:4]1[CH:24]=[CH:23][C:7]([CH2:8][O:9][C:10]([N:12]2[CH2:16][C@H:15]([OH:17])[CH2:14][C@H:13]2[CH2:18][CH2:19][C:20](O)=[O:21])=[O:11])=[CH:6][CH:5]=1)([O-:3])=[O:2].ClC(OCC)=O.[CH3:31][NH2:32]>O1CCCC1.C(N(CC)CC)C>[N+:1]([C:4]1[CH:24]=[CH:23][C:7]([CH2:8][O:9][C:10]([N:12]2[CH2:16][C@H:15]([OH:17])[CH2:14][C@H:13]2[CH2:18][CH2:19][C:20]([NH:32][CH3:31])=[O:21])=[O:11])=[CH:6][CH:5]=1)([O-:3])=[O:2]To a solution of (2R,4R)-1-p-nitrobenzyloxycarbonyl-2-(2-carboxyethyl)-4-hydroxypyrrolidine (57.73 g) in dry tetrahydrofuran (500 ml), triethylamine (29.27 ml) was added, and ethyl chloroformate (18.74 ml) was further added thereto at -20° to -25° C. under nitrogen stream. The resulting mixture was stirred at the same temperature for 15 minutes and 30% (w/w) ethanolic solution of methylamine (57.5 g) was added thereto, followed by stirring at the same temperature for 1 hour. The solvent was removed, and the residue was combined with water and ether. The precipitated crystals were collected by filtration to give (2R,4R)-1-p-nitrobenzyloxycarbonyl-2-(2-methylaminocarbonylethyl)-4-hydroxypyrrolidine.
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