In a 10 mL round bottomed flask, 9-Methyl-6-[4-(2-oxo-2,3-dihydro-1H-benzimidazol-1-yl)piperidin-1-yl]-9H-purine-8-carboxylic acid (250 mg, 0.68 mmol, 1 equiv) and HATU (390 mg, 1.03 mmol, 1.5 equiv) were suspended anhydrous dimethylformamide (3 mL). Diisopropylethylamine (235 μL, 1.35 mmol, 2 equiv) followed by hydrazine monohydrate (330 μL, 6.81 mmol, 10 equiv) were added and the reaction stirred for one hour. The reaction mixture was diluted with ethyl acetate (20 mL), and the extracted with water (10 mL). The combined aqueous layer was then acidified with 1N aqueous hydrochloric acid to precipitate the desired product. This precipitate was filtered off, washed with water (2 mL) and acetonitrile (1 mL) and air dried yielding 115 mg of 9-methyl-6-(4-(2-oxo-2,3-dihydro-1H-benzo[d]imidazol-1-yl)piperidin-1-yl)-9H-purine-8-carbohydrazide, which was used directly in the next step.
