ClC(OCC)=O.[C:7]([O:11][C:12]([N:14]1[CH2:18][C@H:17]([OH:19])[CH2:16][C@H:15]1[C:20]([OH:22])=O)=[O:13])([CH3:10])([CH3:9])[CH3:8].C([N:25](CC)CC)C.N>O1CCCC1>[C:7]([O:11][C:12]([N:14]1[CH2:18][CH:17]([OH:19])[CH2:16][CH:15]1[C:20](=[O:22])[NH2:25])=[O:13])([CH3:10])([CH3:9])[CH3:8]A solution of 4.98 ml of ethyl chloroformate in 50 ml of anhydrous tetrahydrofuran was added, under cooling at -+° C., to a solution of 11.0 g of 1-(t-butoxycarbonyl)-(2S,4R)-4-hydroxy-2-pyrrolidinecarboxylic acid and 7.25 ml of triethylamine in 160 ml of anhydrous tetrahydrofuran, and the mixture was stirred at the same temperature for one hour. 50 ml of concentrated aqueous ammonia were then added, at the same temperature, and the mixture was allowed to stand while its temperature rose to ambient. The reaction mixture was stirred for one hour, and then concentrated by evaporation under reduced pressure. A saturated aqueous solution of sodium chloride was added to the concentrate, which was then extracted three times with ethyl acetate. The extract was dried over anhydrous magnesium sulfate and then concentrated under reduced pressure, to give 7.70 g of (2S,4R)-1-(t-butoxycarbonyl-2-carbamoyl-4-hydroxypyrrolidine.
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