C(=O)(O)[O-].[Na+].[NH:6]([C:16]([O:18][C:19]([CH3:22])([CH3:21])[CH3:20])=[O:17])[C@H:7]([C:13]([OH:15])=[O:14])[CH2:8][CH2:9][CH2:10][CH2:11][NH2:12].Cl.N1(S([N:32]=[N+:33]=[N-])(=O)=O)C=CN=C1.S(=O)(=O)(O)[O-].[K+]>CO.O.O.O.O.O.S([O-])([O-])(=O)=O.[Cu+2].O>[N:12]([CH2:11][CH2:10][CH2:9][CH2:8][C@H:7]([NH:6][C:16]([O:18][C:19]([CH3:22])([CH3:21])[CH3:20])=[O:17])[C:13]([OH:15])=[O:14])=[N+:32]=[N-:33]
Sodium bicarbonate (0.65 g, 7.74 mmol) was added to a mixture of Boc-Lys-OH (Compound tk39) (1.0 g, 4.06 mmol) and copper sulfate pentahydrate (20 mg, 0.081 mmol) in methanol (15 mL)-water (3 mL) at room temperature, followed by addition of 1H-imidazole-1-sulfonyl azide hydrochloride synthesized by the method described in the literature (Org. Lett., 2007, 9, 3797) (1.02 g, 4.87 mmol). Sodium bicarbonate (0.65 g, 7.74 mmol) was added to the reaction mixture, followed by stirring at room temperature for 23 hours. The reaction mixture was cooled in an ice bath, followed by addition of a saturated aqueous potassium bisulfate solution (10 mL). The resulting mixture was filtered through celite and washed with ethyl acetate, and the filtrate was then concentrated under reduced pressure. The resulting residue was purified by reverse-phase silica gel column chromatography (0.05% aqueous trifluoroacetic acid solution/0.05% trifluoroacetic acid-acetonitrile solution) to afford (S)-6-azido-2-((tert-butoxycarbonyl)amino)hexanoic acid (Compound tk48) (948.7 mg, 86%).
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