General procedure for the synthesis of 2-(4-methylpiperazinyl)-3-aminopyridine from 1-methyl-4-(3-nitro-2-pyridinyl)piperazine: preparation of 2-(4-methylpiperazin-1-yl)-3-nitropyridine (PP26, 0.50 g, 2.25 mmol), ammonium formate (1.00 g, 15.85 mmol) and 10% Pd/C (0.050 g) ) solution in methanol (20 mL). The reaction mixture was stirred at room temperature for 1 h. The filtrate was subsequently filtered through diatomaceous earth (Celite) and concentrated. The residue was dissolved in ethyl acetate, washed sequentially with aqueous potassium carbonate and brine, dried over anhydrous magnesium sulfate and concentrated to give 0.35 g (81% yield) of 2-(4-methylpiperazinyl)-3-aminopyridine (PP24) as a violet oil, which was used directly in the next reaction without further purification. The product was confirmed by NMR hydrogen spectroscopy (CDCl3): δ 7.77 (dd, J = 4.6, 1.7 Hz, 1H), 6.90 (dd, J = 7.5, 1.7 Hz, 1H), 6.79 (dd, J = 7.9, 5.0 Hz, 1H), 3.71 (br s, 2H), 3.15 (br s, 4H), 2.57 (br s, 4H) , 2.34 (s, 3H).
