[NH2:1][C:2]1[C:7]([S:8]([NH2:11])(=[O:10])=[O:9])=[CH:6][C:5]([Br:12])=[CH:4][N:3]=1.[CH2:13]([O:15][C:16](=[O:21])[CH2:17][C:18](Cl)=[O:19])[CH3:14].C(=O)(O)[O-].[Na+]>O1CCOCC1>[CH2:13]([O:15][C:16](=[O:21])[CH2:17][C:18]([NH:1][C:2]1[C:7]([S:8](=[O:9])(=[O:10])[NH2:11])=[CH:6][C:5]([Br:12])=[CH:4][N:3]=1)=[O:19])[CH3:14]2-Amino-5-bromo-pyridine-3-sulfonic acid amide (2.5 g, 9.9 mmol) was dissolved in 1,4-dioxane (50 mL). Chlorocarbonyl-acetic acid ethyl ester (1.9 mL, 14.85 mmol) was added and the mixture was heated at 90° C. while stirring for 2 h. Upon cooling to 25° C., the mixture was poured into half-saturated aqueous sodium bicarbonate solution (250 mL). A solid precipitated and was collected by vacuum filtration, rinsed with water (50 mL) and dried in vacuo to afford the desired product, N-(5-bromo-3-sulfamoyl-pyridin-2-yl)-malonamic acid ethyl ester (2.5 g, 6.82 mmol, 69%), as a light beige solid. 1H NMR (400 MHz, DMSO-d6) δ: 1.19 (3H, t, J=7.0 Hz), 3.67 (2H, s), 4.10 (2H, q, J=7.3 Hz), 7.78 (2H, bs), 8.33 (1H, d, J=2.3 Hz), 8.70 (1H, d, J=2.4 Hz), 9.85 (1H, bs).
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