C([O:3][C:4](=[O:36])[C:5]1[CH:10]=[C:9]([C:11]2[CH:12]=[C:13]3[C:19]([C:20]4[CH:25]=[CH:24][CH:23]=[CH:22][C:21]=4[O:26][CH3:27])=[N:18][N:17](COCC[Si](C)(C)C)[C:14]3=[N:15][CH:16]=2)[CH:8]=[N:7][CH:6]=1)C.[F-].C([N+](CCCC)(CCCC)CCCC)CCC>C1COCC1>[CH3:27][O:26][C:21]1[CH:22]=[CH:23][CH:24]=[CH:25][C:20]=1[C:19]1[C:13]2[C:14](=[N:15][CH:16]=[C:11]([C:9]3[CH:8]=[N:7][CH:6]=[C:5]([CH:10]=3)[C:4]([OH:36])=[O:3])[CH:12]=2)[NH:17][N:18]=1To a solution of 5-[3-(2-methoxy-phenyl)-1-(2-trimethylsilanyl-ethoxymethyl)-1H-pyrazolo[3,4-b]pyridin-5-yl]-nicotinic acid ethyl ester (494 mg, 0.98 mmol) in THF (20 mL) was added tetra-n-butylammonium fluoride in THF (1M, 10 ml, 10 mmol) and activated 4 Å molecular sieves. The resulting mixture was stirred at 70° C. for 7 h. The sieves were filtered off, washing with ethyl acetate and the resulting filtrate concentrated. The residue was distributed between dichloromethane and water. The aqueous phase was extracted three times with dichloromethane and the organic phases combined, dried over sodium sulfate, filtered and concentrated to afford of 5-[3-(2-methoxy-phenyl)-1H-pyrazolo[3,4-b]pyridin-5-yl]-nicotinic acid (654 mg, 62% purity, 405 mg, 119% yield) as a brown solid. 1H-NMR (500 MHz, d6-DMSO) δ 13.98 (s, 1H), 8.99 (d, 1H), 8.95 (s, 1H), 8.88 (d, 1H), 8.43 (t, 1H), 8.40 (d, 1H), 7.67 (dd, 1H), 7.47 (ddd, 1H), 7.23 (d, 1H), 7.10 (dt, 1H), 3.86 (s, 3H). MS: m/z 345 (96%) [M−H−].
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