[C:1]([O:5][C:6]([NH:8][C@@H:9]([CH2:13][CH:14]([CH3:16])[CH3:15])[C:10](O)=[O:11])=[O:7])([CH3:4])([CH3:3])[CH3:2].C(OC(OC(C)(C)C)=O)(OC(C)(C)C)=O.[N:32]1C=CC=CC=1.[OH-].[NH4+]>CC#N>[NH2:32][C:10](=[O:11])[C@@H:9]([NH:8][C:6](=[O:7])[O:5][C:1]([CH3:4])([CH3:3])[CH3:2])[CH2:13][CH:14]([CH3:16])[CH3:15]A mixture of (S)-2-(tert-butoxycarbonylamino)-4-methylpentanoic acid (1.8 g), di-tert-butyl dicarbonate (CAN:24424-99-5, 12 mmol) and pyridine (3 mL) in CH3CN (50 mL) was stirred at room temperature for 20 min. Ammonium hydroxide solution (25%-28% NH3, 15 mL) was added dropwise during 30 min. The resulting reaction mixture was stirred overnight. During the removal of solvents, the product precipitated, was collected by filtration and dried to give the target compound as a white solid (1.55 g, 86%). MS (D): m/e=253.2 [M+Na]+.
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