[CH3:1][O:2][C:3](=[O:17])[C:4]1[CH:9]=[C:8]([N:10]2[CH2:14][CH2:13][CH2:12][C:11]2=[O:15])[CH:7]=[C:6]([NH2:16])[CH:5]=1.CCN(CC)CC.[C:25](OC(=O)C)(=[O:27])[CH3:26]>C(Cl)Cl.CCOC(C)=O>[CH3:1][O:2][C:3](=[O:17])[C:4]1[CH:9]=[C:8]([N:10]2[CH2:14][CH2:13][CH2:12][C:11]2=[O:15])[CH:7]=[C:6]([NH:16][C:25](=[O:27])[CH3:26])[CH:5]=1To a solution of 3-amino-5-(2-oxo-pyrrolidin-1-yl)-benzoic acid methyl ester (D4a) (80 mg, 0.34 mmol, 1 equiv) in CH2Cl2 (10 ml) was added NEt3 (0.142 ml, 1.02 mmol, 2 equiv) and acetic anhydride (0.078 ml, 0.82 mmol, 2.4 equiv). The resulting mixture was stirred at room temperature for 16 h. The reaction was then diluted with AcOEt (20 ml), washed with 2N aqueous HCl solution (20 ml), dried over MgSO4, and concentrated in vacuo to give 3-acetylamino-5-(2-oxo-pyrrolidin-1-yl)-benzoic acid methyl ester (B50) (67 mg, 71%) as a pale yellow foam.
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