[Br:1][C:2]1[CH:3]=[CH:4][C:5]([OH:21])=[C:6]([CH:20]=1)[CH2:7][N:8]([C:11]1[N:16]=[N:15][C:14]([C:17]([OH:19])=O)=[CH:13][CH:12]=1)[CH2:9][CH3:10].S(=O)(=O)(O)O.[CH2:27](O)[CH3:28]>>[Br:1][C:2]1[CH:3]=[CH:4][C:5]([OH:21])=[C:6]([CH:20]=1)[CH2:7][N:8]([C:11]1[N:16]=[N:15][C:14]([CH2:17][O:19][CH2:27][CH3:28])=[CH:13][CH:12]=1)[CH2:9][CH3:10]The 6-[N-(5-bromo-2-hydroxybenzyl)-N-ethylamino]pyridazine-3-carboxylic acid (example 8) (6.5 g) was suspended in ethanol (30 ml) and treated cautiously with concentrated sulphuric acid (1.5 ml). The reaction was heated to reflux overnight, then the organic solvent was evaporated. The residue was partitioned between ethyl acetate/water and the organic phase was dried over (MgSO4) and evaporated to give the title compound as a brown solid (5.86 g).
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