1,1'-Carbonyldiimidazole → (5-Benzyloxycarbonylamino-6-hydroxy-hexyl)-carbamic acid tert-butyl ester

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Reaction Steps

To a stirred solution of 2-benzyloxycarbonylamino-6-tert-butoxycarbonylamino-hexanoic acid (Cbz-Lys(Boc)-OH) (Chem-Impex International, 3.8 g, 10 mmol) in THF (25 mL) in a 100 mL round flask was added 1,1′-carbonyldiimidazole (CDI) (1.7 g, 10.5 mmol) at room temperature. After 20 minutes, the THF solution was transferred via a Teflon cannula (+=2 mm) to a stirred solution of sodium borohydride (0.75 g, 20 mmol) in water (10 mL) in a 1 L round flask immersed in a water bath at 5-10° C. The addition caused a strong evolution of hydrogen gas and the mixture was stirred for a couple of hours. The volatiles were then removed on a rotovap, and the residue was dissolved in ethyl acetate (150 mL). The ethyl acetate solution was extracted successively with cold 1 N HCl (2×50 mL), saturated sodium bicarbonate solution (2×50 mL), brine (100 mL), and was dried with anhydrous sodium sulfate. The dried ethyl acetate solution was then pass through a one inch flash pad of silica gel, and concentrated to provide a colorless solid (3.3 g, 91%), TLC Rf=0.24 (95:5:2 EtOAc:MeOH:H2O).

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