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A solution of N-(2,2-difluoroethyl)-2-(4-(2,4-difluorophenoxyl)piperidin-1-yl)-5,6,7,8-tetrahydropyrido[3,4-b]pyrazin-3-amine TFA salt (15 mg, 0.028 mmol), DIPEA (10.8 mg, 0.083 mmol), and 2,2-difluoroacetic anhydride (7.3 mg, 0.042 mmol) in DCM (278 μL) was stirred at room temperature for 2 h. The crude reaction mixture was diluted in DMF, filtered through a hydrophilic PTFE 0.45 μm filter (Millipore® Millex-LCR), and purified via HPLC Method A to give the title compound as a TFA salt (3 mg) as a clear oil. 1H NMR (400 MHz, methanol-d4, mixture of rotamers) δ ppm 1.92-2.02 (m, 2H), 2.09-2.17 (m, 2H), 2.80 (t, J=5.9 Hz, 0.8H), 2.86 (t, J=5.4 Hz, 1.2H), 2.96-3.04 (m, 2H), 3.34-3.43 (m, 2H), 3.77 (td, J=14.3, 4.0 Hz, 2H), 3.90 (t, J=5.8 Hz, 1.2H), 3.93 (t, J=6.1 Hz, 0.8H), 4.46 (tt, J=7.6, 3.7 Hz, 1H), 4.61 (s, 0.8H), 4.63 (s, 1.2H), 5.89-6.21 (m, 1H), 6.42-6.71 (m, 1H), 6.84-6.91 (m, 1H), 6.98 (ddd, J=11.2, 8.5, 3.0 Hz, 1H), 7.17 (td, J=9.2, 5.6 Hz, 1H); ESI-MS m/z [M+H]+ 504.4.
