A solution of 2-(5-methyl-2-thienyl)-3H-imidazo[4,5-b]pyridine-3-acetic acid (5.0 g, 0.0183 mole) and 1,1'-carbonyldiimidazole (2.97 g, 0.0183 mole) in tetrahydrofuran (100 ml) was stirred at room temperature for 3 hours with a stream of nitrogen bubbling through it. A solution of dipropylamine (5.56 g, 0.055 mole) in tetrahydrofuran (7 ml) was added and the reaction mixture was stirred overnight at room temperature. The solvents were evaporated and the residue was partitioned between water and ethyl acetate. The layers were separated and the aqueous layer was extracted again with ethyl acetate. The combined organic layer was washed twice with water, twice with a 5% potassium hydroxide solution, and twice again with water. The organic layer was dried over magnesium sulfate, treated with charcoal, filtered, and evaporated to give a solid which was dissolved in hot isopropyl alcohol and filtered while hot. Addition of water and cooling caused a solid to precipitate. The solid was dissolved again in hot isopropyl alcohol with charcoal, filtered while hot and brought to the cloud point by addition of water. Upon cooling, solid precipitated which was collected by filtration, rinsed with water, and dried under high vacuum at 50° C. overnight to give 2.28 g (35%) of title compound, mp 125°-127° C.
