To a mixture of 5-bromo-4-(4-(4-fluorobenzyl)piperazin-1-yl)-3-nitropyridin-2-amine (0.12 g, 0.30 mmol) and EtOH (5 mL), 4-(morpholinomethyl)benzaldehyde (0.068, 0.33 mmol) in EtOH (1.8 mL) was added followed by a freshly prepared aqueous solution of Na2S2O4 (1M; 0.9 mL, 0.9 mmol). The reaction mixture was heated at 85° C. for 24 h, then allowed to cool to room temperature and the solvents were removed in vacuo. The residue was absorbed on silica gel and purified by column chromatography on a Biotage SP1 system eluting with methanol (2-10%) in dichloromethane. The title compound was isolated as a pale yellow solid after trituration with diethyl ether (0.013 g, 7.6%); 1H-NMR (500 Mz, DMSO-d6): δ 2.38 (m, 4H), 2.60 (m, 4H), 3.54 (s, 2H, NCH2), 3.56 (s, 2H, NCH2), 3.59 (t, J=4.5 Hz, 4H), 3.66 (m, 4H), 7.17 (d, J=8.5 Hz, 2H, ArH, C6H4—F), 7.40 (br dd, J=8.5, 6.0 Hz, 2H, ArH, C6H4—F), 7.47 (d, J=8.0 Hz, 2H, ArH), 8.14 (d, J=8.0 Hz, 2H, ArH), 8.23 (s, 1H, imidazo[4,5-b]pyridine 5-H), 13.47 (br s, 1H, imidazo[4,5-b]pyridine N—H); LC (Method B)-MS (ESI, m/z) 2.33 min—565/567 [(M+H)+, Br isotopic pattern]. ESI-HRMS: Found: 565.1725, calculated for C28H31BrFN6O (M+H)+: 565.1727.
