[CH2:1]([O:8][C:9]([NH:11][C@@H:12]([CH2:16][CH2:17][NH:18][CH:19]1[CH2:24][CH2:23][N:22]([C:25]([O:27][C:28]([CH3:31])([CH3:30])[CH3:29])=[O:26])[CH2:21][C:20]1([CH3:33])[CH3:32])[C:13]([OH:15])=O)=[O:10])[C:2]1[CH:7]=[CH:6][CH:5]=[CH:4][CH:3]=1.CCN(C(C)C)C(C)C.CN(C(ON1N=NC2C=CC=CC1=2)=[N+](C)C)C.F[P-](F)(F)(F)(F)F.[OH-].[Na+]>CN(C=O)C.CCOC(C)=O>[CH2:1]([O:8][C:9]([NH:11][C@H:12]1[CH2:16][CH2:17][N:18]([CH:19]2[CH2:24][CH2:23][N:22]([C:25]([O:27][C:28]([CH3:30])([CH3:29])[CH3:31])=[O:26])[CH2:21][C:20]2([CH3:33])[CH3:32])[C:13]1=[O:15])=[O:10])[C:2]1[CH:7]=[CH:6][CH:5]=[CH:4][CH:3]=1To a solution of (25)-2-(benzyloxycarbonylamino)-4-(1-(tert-butoxycarbonyl)-3,3-dimethylpiperidin-4-ylamino)butanoic acid (3.59 g, 7.74 mmol) in DMF (20 mL) was added DIEA (4.1 mL, 23 mmol) and HBTU (3.5 g, 9.3 mmol). The mixture stirred at ambient temperature overnight. The mixture was poured into 1 N NaOH solution and extracted into ethyl acetate. The organic layer was washed with 1 N HCl solution and brine, dried over MgSO4, filtered and concentrated under vacuum. Flash chromatography (7:3 EtOAc:hexanes) gave tert-butyl 4-((S)-3-(benzyloxycarbonylamino)-2-oxopyrrolidin-1-yl)-3,3-dimethylpiperidine-1-carboxylate (0.81 g, 1.8 mmol, 23%) as a white solid.
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