[C:1]1(=[O:17])[N:5]([C:6]2[CH:11]=[CH:10][C:9]([CH2:12][C:13](O)=[O:14])=[CH:8][CH:7]=2)[C:4](=[O:16])[CH:3]=[CH:2]1.C(Cl)(=O)C([Cl:21])=O>ClCCl>[C:1]1(=[O:17])[N:5]([C:6]2[CH:11]=[CH:10][C:9]([CH2:12][C:13]([Cl:21])=[O:14])=[CH:8][CH:7]=2)[C:4](=[O:16])[CH:3]=[CH:2]11.0 g (4.33 mmol) of p-maleinimidophenylacetic acid were suspended in 25 ml of dichloromethane and diluted with a 2.5-fold excess of oxalic acid dichloride (1.37 g, 945 μl; 10.82 mmol). The reaction mixture was heated to 30-40° C. with the exclusion of moisture and stirred for 15 h. Then the solvent was removed under a vacuum and dried under a high vacuum. Crystallization from toluene yielded a yellow powder (yield: 59%); melting point: 154° C.; Rf-value: 0.29 (acetic ester/hexane 4/1); Elementary analysis: calculated: C: 58.91% H: 3.30% N: 5.75%, Cl: 14.49%; (C12H8NO3Cl) found: C: 60.61% H: 3.64% N: 5.13% Cl: 13.80%.
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