A solution of tert-butyl 4-(2-amino-5-bromo-3-nitropyridin-4-yl)piperazine-1-carboxylate (250 mg, 0.62 mmol) in CH2Cl2 (2.5 mL) at 0° C. was treated with TFA (2.5 mL) and stirred at 0° C. for 1.5 h. After this time, the solvents were evaporated in vacuo and the excess TFA removed by azeotroping with toluene (3×10 ml). The residue was suspended in CHCl3 (2.5 mL) and treated with DIPEA (5 eq, 3.11 mmol, 0.54 mL) and phenyl isocyanate (1.05 eq, 0.65 mmol, 0.07 mL). The reaction was warmed to room temperature and stirred for 12 h. The formed precipitate was filtered off and dried to give the product as a yellow solid (221 mg, 84% for two steps); 1H-NMR (500 MHz, DMSO-d6) 3.07 (br s, 4H, piperazine N(CH2)2), 3.58 (br s, 4H, piperazine N(CH2)2), 6.94 (tt, J=7.4, 1.1 Hz, 1H, phenyl H-4), 7.03 (br s, 2H, NH2), 7.24 (dd, J=8.5, 7.5 Hz, 2H, phenyl H-3 & H-5), 7.45 (dd, J=8.5, 1.1 Hz, 2H, phenyl H-2 & H-6), 8.21 (s, 1H, pyridine H-6), 8.59 (br s, 1H, NH);
