Cl.[CH:2]1([CH2:8][C@@H:9]([C:11]([OH:13])=[O:12])[NH2:10])[CH2:7][CH2:6][CH2:5][CH2:4][CH2:3]1.[CH2:14]([O:21][C:22](Cl)=[O:23])[C:15]1[CH:20]=[CH:19][CH:18]=[CH:17][CH:16]=1>[OH-].[Na+].O1CCCC1>[CH2:14]([O:21][C:22]([NH:10][C@H:9]([C:11]([OH:13])=[O:12])[CH2:8][CH:2]1[CH2:7][CH2:6][CH2:5][CH2:4][CH2:3]1)=[O:23])[C:15]1[CH:20]=[CH:19][CH:18]=[CH:17][CH:16]=1To a solution of 3-cyclohexylalanine, hydrochloride (4.75 , 22.8 mmol) in 2N sodium hydroxide (11.4 mL) were added at 0° C., simultaneously, a solution of benzylchloroformate (3.2 mL, 36 mmol) in tetrahydrofuran (10 mL) and 2N sodium hydroxide (11.4 mL). (The pH of the mixture was maintained around 9-10 by addition of 2N sodium hydroxide.) The mixture was stirred for 1.5 hours. The solution was washed with diethyl ether (3×20 mL). The aqueous phase was acidified to pH 2 with 3N aqueous hydrochloric acid and extracted with ethyl acetate (3×50 mL). The combined organic layers were dried over anhydrous magnesium sulphate. Filtration and removal of the solvent in vacuo left 4.80 g of the expected product (yellow oil, 69% yield).
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