[Cl:1][C:2]1[C:3]([CH:9]=O)=[N:4][CH:5]=[C:6]([Cl:8])[N:7]=1.[CH2:11]([NH:18][CH2:19][C@@H:20]([OH:22])[CH3:21])[C:12]1[CH:17]=[CH:16][CH:15]=[CH:14][CH:13]=1.C(O[BH-](OC(=O)C)OC(=O)C)(=O)C.[Na+].C(=O)([O-])O.[Na+]>C1COCC1.C(OCC)(=O)C.C(O)(=O)C>[CH2:11]([N:18]([CH2:9][C:3]1[C:2]([Cl:1])=[N:7][C:6]([Cl:8])=[CH:5][N:4]=1)[CH2:19][C@@H:20]([OH:22])[CH3:21])[C:12]1[CH:17]=[CH:16][CH:15]=[CH:14][CH:13]=1
To a solution of 3,5-dichloropyrazine-2-carbaldehyde (3.0 g), (2S)-1-(benzylamino)propan-2-ol (3.36 g) and acetic acid (4.9 mL) in THF (50 mL) was added sodium triacetoxyborohydride (7.18 g), and the mixture was stirred at room temperature overnight. The reaction solution was diluted with ethyl acetate, and basified with saturated aqueous sodium hydrogen carbonate. The organic layer was separated, washed with water and saturated brine, dried over anhydrous magnesium sulfate, and concentrated under reduced pressure. The obtained residue was purified by basic silica gel column chromatography (solvent gradient: 5→25% ethyl acetate/hexane) to give the title compound (3.48 g, 63%) as a pale-yellow oil.
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