To a solution of tert-butyl (1-(4-(9H-benzo[f]pyrido[2,3-b][1,2,4]triazolo[4,3-d][1,4]diazepin-3-yl)benzoyl)piperidin-4-yl)carbamate (0.25 g, 0.47 mmol) in dichloromethane (10 mL) was added 4N HCl in dioxane (0.5 mL). The reaction mixture was stirred at room temperature for 20 hours. The solids were filtered off, washed with ether and dried under vacuum, yielding (4-(9H-benzo[f]pyrido[2,3-b][1,2,4]triazolo[4,3-d][1,4]diazepin-3-yl)phenyl)(4-aminopiperidin-1-yl)methanone hydrochloride as a yellow solid (0.21 g, 88%). M.p.=258-263° C.; 400 MHz 1H NMR (DMSO-d6) δ: 8.83 (br.s, 1H), 8.25-8.18 (m, 3H), 7.97 (dd, J=7.6, 1.2 Hz, 1H), 7.51 (d, J=8.0 Hz, 2H), 7.48-7.42 (m, 3H), 7.36 (d, J=8.4 Hz, 1H), 7.20 (dd, J=8.0, 1.2 Hz, 1H), 7.15 (t, J=7.2 Hz, 1H), 6.94 (dd, J=8.0, 4.4 Hz, 1H), 4.55-4.4 (m, 1H), 3.7-3.65 (m, 1H), 3.35-3.25 (m, 1H), 3.22-3.05 (m, 1H), 3.0-2.8 (m, 1H), 2.2-1.85 (m, 2H), 1.6-1.4 (m, 2H); LCMS [M+H]: 438.
