To a stirring solution of 6-oxospiro[3.3]heptane-2-carboxylic acid (50 mg, 0.32 mmol) in anhydrous NMP (1 mL) was added 1,1′-carbonyldiimidazole (CDI) (52.3 mg, 0.32 mmol). The reaction was stirred for 3 minutes. N-(5-(N′-hydroxycarbamimidoyl)-2-methylphenyl)imidazo[1,2-a]pyridine-3-carboxamide (9) (100 mg, 0.32 mmol) was added and the reaction was stirred for 25 minutes. Then, the reaction was heated at 120° C. for 15 minutes. The crude reaction was purified by reverse phase preparative HPLC to give N-(2-methyl-5-(5-(6-oxospiro[3.3]heptan-2-yl)-1,2,4-oxadiazol-3-yl)phenyl)imidazo[1,2-a]pyridine-3-carboxamide (F75). MS m/z 428.2 (M+1)+.
