4-hydroxy-2-(pyridazin-3-yl)pyrimidine-5-carboxylic acid, 13-b, (350 mg, 1.6 mmol, which was prepared from compound 1-e via sodium hydroxide hydrolysis in a similar manner as the conversion of 3-b to 3-c) in thionyl chloride (10 ml) was heated at reflux for 4 h. The mixture was concentrated under vacuum and the residue was co-evaporated with dichloromethane twice. The remaining oil was dissolved in dichloromethane (10 ml). p-toluenesulfonamide (329 mg, 1.93 mmol), triethylamine (486 mg, 4.82 mmol) and DMAP (390 mg, 3.2 mmol) were added to the solution at room temperature. The mixture was subsequently stirred at room temperature overnight. The mixture was then concentrated under vacuum and the residue was diluted with water (10 ml). The solid crashed out and then filtered out of the solution. The solids were then recrystallization in methanol/ethyl acetate to afford compound 13-1 (300 mg, 50%). 1H NMR (DMSO-d6, 300 MHz): δ 12.92 (br, 1H), 9.51 (s, 1H), 8.53 (s, 2H), 8.00 (m, 3H), 7.46 (s, 2H), 2.41 (s, 3H). (M+H)+=372.1.
