To a suspension of 9-methyl-6-oxo-6,7,8,9-tetrahydropyrido[3′,2′:4,5]pyrrolo[1,2-a]pyrazine-2-carboxylic acid (Intermediate J, 47 mg, 0.19 mmol) and HOBt (31 mg, 0.23 mmol) in DMF (0.5 mL) is added 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (44 mg, 0.23 mmol), followed by 3-aminopyridine (22 mg, 0.23 mmol) and DMAP (2.8 mg, 0.023 mmol). The mixture is stirred at 60° C. under a continuous stream of nitrogen, which slowly concentrates the solution. After being stirred for 5 h, the mixture was warmed to 80° C. and stirred overnight. The reaction mixture is diluted with methanol (0.5 mL) and ether (1 mL). The resultant precipitate is collected by filtration to afford the title compound as a dark yellow solid (21 mg, 34%).
