A solution of 5-(4-(bis(4-methoxybenzyl)amino)-6-methyl-1,3,5-triazin-2-yl)-6-(5-fluoro-6-methoxypyridin-3-ylamino)nicotinaldehyde (380 mg, 0.638 mmol) in DCM (5 mL) was treated with TFA (6.0 mL, 78 mmol) and then TfOH (0.050 mL, 0.563 mmol). The solution was heated at 80° C. under a condenser. After 2.5 h, more TfOH (0.050 mL, 0.563 mmol) was added. After 24 h, the mixture was concentrated. The residue was azeotroped with toluene (10 mL) once. The mixture was suspended in 1:1 DMSO-water (5 mL each) and filtered. The resulting solid was then suspended in saturated NaHCO3 for several hours and filtered. The mother liquor was discarded. The resulting sludge was dissolved in hot DMSO and filtered. The filtrate was diluted with MeOH (2× v/v) and allowed to settle. The resulting suspension was filtered. The resulting solid was again dissolved in hot DMSO and diluted with MeOH. After 3 repetitions, the solid was about 95% pure product (50 mg). LCMS (ES, pos.): calcd for C16H14FN7O2: 355.1. found: 356.2 (M+H)+. 1H NMR (400 MHz, d6-DMSO) δ 12.47 (br. s., 1H); 9.92 (s, 1H); 9.17 (br. s., 1H); 8.81 (br. s., 1H); 8.42 (br. s., 1H); 8.32 (d, J=13.11 Hz, 1H); 8.01 (br. s., 1H); 7.85 (d, J=0.78 Hz, 1H); 3.96 (s, 3H); 2.46 (br. s., 3H). 19F NMR (377 MHz, d6-DMSO) δ −139.31 (d, J=11.44 Hz, 1F).
