[NH2:1][C:2]1[C:3]([N:8]2[CH2:13][CH2:12][NH:11][CH2:10][CH:9]2[C:14]([O:16][C:17]([CH3:20])([CH3:19])[CH3:18])=[O:15])=[N:4][CH:5]=[CH:6][CH:7]=1.[CH3:21][C:22]([CH3:24])=O.CC(O)=O.[BH-](OC(C)=O)(OC(C)=O)OC(C)=O.[Na+].C([O-])(O)=O.[Na+]>ClC(Cl)C>[C:14]([CH:9]1[CH2:10][NH:11][CH2:12][CH2:13][N:8]1[C:3]1[C:2]([NH:1][CH:22]([CH3:24])[CH3:21])=[CH:7][CH:6]=[CH:5][N:4]=1)([O:16][C:17]([CH3:20])([CH3:19])[CH3:18])=[O:15]
3-amino-2-(Boc-piperazine)pyridine 7 (3.813 g, about 11.16 mmol, crude) was dissolved in dichloroethane (75 mL). Acetone (1.7 mL, 23.12 mmol) was added, followed by an addition of HOAc (1.0 mL, 17.45 mmol) at room temperature. After about 10 min, NaBH(OAc)3 (7.46 g, 33.44 mmol) was added. An additional amount of dichloroethane (25 mL) was added. The resulting mixture was stirred at room temperature for 64 h. 5% aqueous NaHCO3 was added to quench the reaction. The organic phase was separated and the aqueous phase was extracted with dichloromethane (2×50 mL). The combined organic solution was washed with brine, dried over anhydrous Na2SO4, concentrated. The residue was purified via flash column chromatography over silica gel with 5-35% ethyl acetate in hexane to afford the product as solid in quantitative yield. 1H-NMR (CDCl3): 7.673 (dd, J=5.0 Hz and 1.5 Hz, 1 H, Ar—H), 6.904 (dd, J=8.0 Hz and 5.0 Hz, 1 H, Ar—H), 6.812 (dd, J=8.0 Hz and 1.5 Hz, 1 H, Ar—H), 4.150 (d, J=7.5 Hz, 1 H, NH), 3.569-3.517 (m, 5 H, 2CH2 and CH), 2.997 (t, J=5.0 Hz, 4 H, 2 CH2), 1.477 (s, 9 H, 3 CH3), 1.23 (d, J=6.0 Hz, 6 H, 2 CH3). (ref. Romero D. L. et al. J. Med. Chem. 37, 999-1014, 1994.)
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