Reaction Steps
Under argon, 2,5-dichloro-3-nitropyridine (666 mg, 3.18 mmol) was dissolved in toluene (45 ml), and aqueous potassium carbonate solution (2M, 3.47 ml) was added. After 5 minutes of stirring at room temperature, 2-diisopropylaminocarbonylphenylboronic acid (1000 mg, 3.81 mmol) and tetrakis(triphenylphosphine)palladium(0) (110 mg, 0.09 mmol) were added. The resulting reaction mixture was stirred at 80° C. for 13 h and, after cooling to room temperature, concentrated under reduced pressure. After addition of water and ethyl acetate, the aqueous phase was extracted repeatedly with ethyl acetate. The combined organic phases were dried over magnesium sulphate, filtered off and concentrated under reduced pressure. Purification by column chromatography (gradient ethyl acetate/n-heptane) of the residue that remained gave the first synthesis intermediate 2-[6-chloro-3-nitropyridin-2-yl]-N,N-diisopropylbenzamide (560 mg, 49% of theory) in the form of a colourless solid. 2-[6-Chloro-3-nitropyridin-2-yl]-N,N-diisopropylbenzamide (270 mg, 0.75 mmol) was then dissolved in abs. tetrahydrofuran, and 1-methylpiperazine (0.17 ml, 1.49 mmol) and N,N-diisopropylethylamine (0.14 ml, 0.82 mmol) were added. The resulting reaction solution was stirred at 65° C. for 5 h, ethyl acetate and water were added after cooling to room temperature and the aqueous phase was re-extracted repeatedly with ethyl acetate. The combined organic phases were dried over magnesium sulphate, filtered and concentrated under reduced pressure. Without further purification, the resulting 2-[3-(nitro)-6-(4-methylpiperazin-1-yl)pyridin-2-yl]-N,N-diisopropylbenzamide (300 mg, 94% of theory) was dissolved under argon in a high pressure reaction vessel in methanol, and palladium on carbon (Pd content 10%, water-moist, 40 mg) was added. Hydrogen was then introduced, and the mixture was stirred at room temperature and a pressure of 2 bar for two hours. The reaction mixture was then filtered off through Celite, the filter cake was washed with methanol and the filtrate was concentrated under reduced pressure. Without further purification, the resulting 2-[3-amino-6-(4-methylpiperazin-1-yl)pyridin-2-yl]-N,N-diisopropylbenzamide (220 mg, 79% of theory) was dissolved in abs. tetrahydrofuran and, after 5 min of stirring at room temperature, cooled to −65° C. Lithium diisopropylamide (179 mg, 1.67 mmol) was then slowly added a little at a time, and the resulting reaction mixture was stirred at −65° C. for 10 min and then warmed to room temperature over a period of 1 h. After careful addition of water, the aqueous phase was repeatedly extracted thoroughly with ethyl acetate. The combined organic phases were dried over magnesium sulphate, filtered off and concentrated under reduced pressure. Purification of the residue that remained by column chromatography (gradient ethyl acetate/n-heptane) gave 2-(4-methylpiperazin-1-yl)benzo[c]-1,5-naphthyridin-6(5H)-one (90 mg, 52% of theory) in the form of a colourless solid. 1H-NMR (400 MHz, CD3OD δ, ppm) 8.78 (d, 1H), 8.39 (s, 1H), 7.89 (dd, 1H), 7.71 (dd, 1H), 7.60 (d, 1H), 7.10 (d, 1H), 3.72 (m, 4H), 3.32 (s, 3H), 2.65 (m, 4H); 13C-NMR (100 MHz, CD3OD δ, ppm) 163.3, 156.9, 137.2, 134.9, 133.9, 129.9, 128.3, 128.0, 127.4, 125.9, 124.9, 111.5, 55.8, 46.4, 46.2.
