[BH4-].[Na+].B(F)(F)F.CCOCC.[CH2:12]([O:19][C:20]([N:22]1[CH2:26][C@H:25]([O:27][S:28]([CH3:31])(=[O:30])=[O:29])[CH2:24][C@H:23]1[CH2:32][O:33][CH2:34][C:35](=O)[NH2:36])=[O:21])[C:13]1[CH:18]=[CH:17][CH:16]=[CH:15][CH:14]=1.Cl>O1CCCC1.CO.C(O)C>[NH2:36][CH2:35][CH2:34][O:33][CH2:32][C@@H:23]1[CH2:24][C@@H:25]([O:27][S:28]([CH3:31])(=[O:29])=[O:30])[CH2:26][N:22]1[C:20]([O:19][CH2:12][C:13]1[CH:14]=[CH:15][CH:16]=[CH:17][CH:18]=1)=[O:21]To a suspension of sodium borohydride (3.05 g) in tetrahydrofuran (155 ml) was added boron trifluoride etherate (35.6 ml) in a nitrogen stream with stirring at 0°-5° C. for 30 minutes. The mixture was stirred at the same condition for 30 minutes. To the mixture was added a solution of (2S,4R)-1-benzyloxycarbonyl-2-(carbamoylmethyloxymethyl)-4-methanesulfonyloxypyrrolidine (15.5 g) in tetrahydrofuran (45 ml) at 0°-5° C. for 30 minutes. The reaction mixture was stirred at 0°-5° C. for 30 minutes and at ambient temperature overnight. Ethanol (46.5 ml) was added to the mixture below 10° C. After 2 hours, insoluble material was filtered off and the filtrate was concentrated under reduced pressure to give a residue. A solution of the residue in a mixture of concentrated hydrochloric acid (15.5 ml) and methanol (155 ml) was stirred at ambient temperature overnight. The mixture was concentrated under reduced pressure to give (2S,4R)-2-[(2-aminoethyl)oxymethyl]-1-benzyloxycarbonyl-4-methanesulfonyloxypyrrolidine. To a solution of the compound obtained above in a mixture of water (46.5 ml) and tetrahydrofuran (77.5 ml) was added a solution of potassium cyanate (16.3 g) in water (50 ml) at 40°-50° C., keeping the pH between 4-5 with concentrated hydrochloric acid. The mixture was extracted with ethyl acetate. The organic layer was washed with brine, dried over magnesium sulfate and concentrated under reduced pressure to give (2S,4R)-1-benzyloxycarbonyl-4-methanesulfonyloxy-2-[(2-ureidoethyl)oxymethyl]pyrrolidine (13.28 g).
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