[C:1]([N:8]1[CH2:13][CH2:12][CH:11]([CH:14]=O)[CH2:10][CH2:9]1)([O:3][C:4]([CH3:7])([CH3:6])[CH3:5])=[O:2].[NH:16]1[CH2:21][CH2:20][NH:19][CH2:18][CH2:17]1.C(O[BH-](OC(=O)C)OC(=O)C)(=O)C.[Na+]>C1COCC1.C(#N)C>[C:1]([N:8]1[CH2:13][CH2:12][CH:11]([CH2:14][N:16]2[CH2:21][CH2:20][NH:19][CH2:18][CH2:17]2)[CH2:10][CH2:9]1)([O:3][C:4]([CH3:7])([CH3:6])[CH3:5])=[O:2]To a stirring solution of 1-Boc-piperidine-4-carboxaldehyde (2.4 g, 11.3 mmol) in THF (60 mL) and acetonitrile (15 mL) was added piperazine (4.85 g, 56.3 mmol). After stirring for 5 h, sodium triacetoxyborohydride (2.87 g, 13.5 mmol) was added and the reaction was allowed to stir overnight. The next morning, the solvents were removed by rotary evaporation and the residue was dissolved in ethyl acetate, washed twice with satd aq. NaHCO3, followed by water, then dried over MgSO4, filtered and concentrated in vacuo. The residue was then chromatographed over silica gel, eluting with a step gradient of 2% through 15% (2 N ammonia/methanol) in dichloromethane. The product containing fractions were combined and concentrated in vacuo to give 4.03 g (48%) of the title compound.
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