[CH2:1]([O:8][C:9](=[O:17])[NH:10][C:11]1([C:14](=[O:16])[NH2:15])[CH2:13][CH2:12]1)[C:2]1[CH:7]=[CH:6][CH:5]=[CH:4][CH:3]=1.C([O-])(O)=O.[Na+].[CH2:23]([O:25][C:26](=[O:31])[C:27](=O)[CH2:28]Br)[CH3:24]>C1COCC1>[CH2:23]([O:25][C:26]([C:27]1[N:15]=[C:14]([C:11]2([NH:10][C:9]([O:8][CH2:1][C:2]3[CH:3]=[CH:4][CH:5]=[CH:6][CH:7]=3)=[O:17])[CH2:12][CH2:13]2)[O:16][CH:28]=1)=[O:31])[CH3:24]To a solution of (1-carbamoyl-cyclopropyl)-carbamic acid benzyl ester (3.0 g, 8.1 mmol) in THF (100 mL) was added NaHCO3 (9.7 g, 120 mmol) and 3-bromo-2-oxo-propionic acid ethyl ester (8.1 mL, 64.0 mmol). The reaction was heated at 70° C. for 15 h. The resulting orange suspension was filtered through celite and concentrated under reduced pressure. The resulting orange oil was dissolved in THF (10 mL) and to this was added trifluoroacetic anhydride (1 mL). The mixture was stirred at room temperature for 24 h. The reaction was quenched with satd NaHCO3 and extracted with EtOAc (3×50 mL). The combined extracts were washed with water, brine and dried with MgSO4. The mixture was filtered, concentrated and purified by reverse phase HPLC. The combined HPLC fractions were extracted with EtOAc (3×100 mL). The extracts were washed with water, brine and dried with MgSO4. The mixture was filtered and concentrated to give 2-(1-benzyloxycarbonylamino-cyclopropyl)-oxazole-4-carboxylic acid ethyl ester (1.3 g, 3.9 mmol) as a white solid.
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