C(Cl)(=O)C(Cl)=O.[CH3:7][C:8]1[C:12]([CH2:13][CH2:14][C:15]([OH:17])=O)=[C:11]([CH3:18])[O:10][N:9]=1.[C:19]([O:23][C:24]([CH3:27])([CH3:26])[CH3:25])(=[O:22])[NH:20][NH2:21]>ClCCl.CN(C)C=O>[NH3:9].[CH3:7][C:8]1[C:12]([CH2:13][CH2:14][C:15]([NH:21][NH:20][C:19]([O:23][C:24]([CH3:27])([CH3:26])[CH3:25])=[O:22])=[O:17])=[C:11]([CH3:18])[O:10][N:9]=1Oxalyl chloride (5.16 mL, 59.2 mmol) was added to a solution of β-(3,5-dimethyl-4-isoxazolyl)propionic acid (J. Org. Chem. 59(10); 1994; 2882) (2.5 g, 14.8 mmol) in dichloromethane (50 mL) and N,N-dimethylformamide (1 drop), and the solution was stirred at room temperature for 30 minutes. The mixture was concentrated under reduced pressure and the residue was azeotroped with dichloromethane (5×) to provide a brown liquid. This was dissolved in dichloromethane (25 mL), and tert-butyl carbazate (2.93 g, 22.2 mmol) was added portionwise. The mixture was diluted with further dichloromethane (23 mL) and the reaction was stirred for 18 hours at room temperature. The mixture was concentrated under reduced pressure, the residue was suspended in dichloromethane, the resulting precipitate was filtered off and the filtrate was evaporated under reduced pressure. The residue was purified by column chromatography on silica gel using an elution gradient of dichloromethane:methanol:0.88 ammonia (95:5:0.5 to 90:10:1) to provide the title compound as an oil, 3.08 g.
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