C[O:2][C:3]1[C:8]([N:9]2[C:13](=[O:14])[C:12]3=[CH:15][CH:16]=[CH:17][CH:18]=[C:11]3[C:10]2=[O:19])=[CH:7][CH:6]=[C:5]([O:20]C)[N:4]=1.[BrH:22].CCOCC>C(O)(=O)C>[BrH:22].[O:19]=[C:10]1[C:11]2[C:12](=[CH:15][CH:16]=[CH:17][CH:18]=2)[C:13](=[O:14])[N:9]1[C:8]1[C:3]([OH:2])=[N:4][C:5]([OH:20])=[CH:6][CH:7]=11,3-Dioxo-2-(2,6-dihydroxypyridin-3-yl)-isoindoline hydrobromide (7) was prepared and isolated as follows. To a flask were added 2,6-dimethoxy-3-phthalimidopyridine (150 mg, 0.528 mmol) and hydrogen bromide solution in acetic acid (30%, 6 ml). The mixture was stirred at an 70° C. oil bath under N2 for 54 h. The mixture was cooled to room temperature, dry ether was added, and the supernatant liquid was decanted. Then ethyl acetate was added, solid precipitated, filtered and washed with ethyl acetate to afford 7 (126 mg, 71%) as a white solid: 1H NMR (CD3OD) δ 7.83-7.77 (m, 4H), 6.37 (d, J=8.1 Hz, 1H), 6.37 (d, J=8.1 Hz, 1H); MS (CI/CH4) 256 [M]+; HRMS (DEI) m/z calcd for C13H8N2O4 256.0484. found 256.0483.
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