[NH:1]1[CH2:9][CH2:8][CH2:7][CH2:6][C@@H:2]1[C:3]([OH:5])=[O:4].[OH-].[Na+].Cl[C:13]([O:15][CH2:16][C:17]1[CH:22]=[CH:21][CH:20]=[CH:19][CH:18]=1)=[O:14]>O1CCCC1.O>[N:1]1([C:13]([O:15][CH2:16][C:17]2[CH:22]=[CH:21][CH:20]=[CH:19][CH:18]=2)=[O:14])[CH2:9][CH2:8][CH2:7][CH2:6][C@@H:2]1[C:3]([OH:5])=[O:4]D-hPro-OH (5.0 g, 38.7 mmol) was dissolved in tetrahydrofuran (100 mL) and water (30 mL). The pH of the solution was adjusted to 9.5 with 2N NaOH and benzyl chloroformate (5.5 mL, 38.7 mmol) was added dropwise and the pH maintained at 9.5 with 2N NaOH. The reaction was stirred for an additional 1 hour at room temperature. The organic solvent was evaporated in vacuo, and diethyl ether (100 mL) and water (50 mL) were added to the residue. The aqueous layer was separated, the pH of the aqueous solution was adjusted to 2.8 with 3N HCl, and ethyl acetate (150 mL) was added. The organic layer was separated and dried (MgSO4) and the filtrate was concentrated in vacuo to give 9.6 g (95%) of a clear oil.
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