Ammonium Acetate → 4-Piperidinamine, 1-(5-isoquinolinylsulfonyl)-

To 50 ml of methanol were added 2.9 g of the thus obtained 1-(5-isoquinolinesulfonyl)-4-piperidone, 2.31 g of ammonium acetate and 0.63 g of sodium cyanoborohydride, followed by stirring at 20° C. for 24 hours. The methanol was removed under reduced pressure, and 100 ml of chloroform was added to the resultant product. Then, the mixture was washed twice with 50 ml each of water, washed once with 50 ml of a 50% aqueous sodium hydrogencarbonate solution, and dried with anhydrous sodium sulfate. The solvent was removed under reduced pressure to obtain a residue. The residue thus obtained was subjected to purification by silica gel column chromatography (Wacogel C-200, 150 g; solvent: chloroform) to obtain 2.39 g of 1-(5-isoquinolinesulfonyl)-4-aminopiperidine [Compound (51)]. Compound (51) was analyzed to give the following data.