[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 sodium hydroxide and benzyl chloroformate (5.5 mL, 38.7 mmol) was added dropwise and the pH maintained at 9.5 with 2N sodium hydroxide. The reaction was stirred for an additional 1 hour at room temperature. The organic solvent was evaporated in vacuo, diethyl ether (100 mL) and water (50 mL) was added to the residue. The aqueous layer separated, the pH of the solution was adjusted to 2.8 with 3N hydrochloric acid and ethyl acetate (150 mL) was added. The organic layer was separated and dried (MgSO4); the filtrate was concentrated in vacuo to give 9.6 g (95%) of a clear oil.
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