Hydrazine hydrate (1:1) → 3-amino-5-sec-butyl-7-(1-methyl-1H-pyrazol-3-yl)-1,5-dihydro-4H-pyrazolo[4,3-c]pyridin-4-one

To a mixture of 1-(sec-butyl)-4-methoxy-5-(1-methyl-1H-pyrazol-3-yl)-2-oxo-1,2-dihydropyridine-3-carbonitrile obtained in Step C (140 mg) and ethanol (5 mL) was added hydrazine monohydrate (122 mg), and the mixture was stirred at 90° C. for 1 hr, cooled to room temperature, and concentrated under reduced pressure. The residue was purified by silica gel column chromatography (basic silica gel, ethyl acetate/hexane), and recrystallized from ethyl acetate/diisopropyl ether to give the title compound (82 mg).