A solution of 6-amino-4-(2-furyl)-1H-pyrazolo[3,4-d]pyrimidin-1-ylacetic acid (200 mg, 0.77 mmol) in DMF (3 mL) was treated with carbonyl diimidazole (125 mg, 0.77 mmol), stirred at room temperature for 2 h, treated with 2-aminopyridine (72 mg, 0.77 mmol), heated to 50° C. for 3 h, cooled and diluted with water. The resulting white solid was filtered, suspended in MeOH, treated with HCl in dioxan (4-M, 1 mL) diluted with diethyl ether and filtered to give the title compound (187 mg, 59%) as a yellow solid.
