[NH2:1][CH2:2][C@@H:3]([OH:20])[C@@H:4]([NH:12][C:13](=[O:19])[O:14][C:15]([CH3:18])([CH3:17])[CH3:16])[CH2:5][C:6]1[CH:11]=[CH:10][CH:9]=[CH:8][CH:7]=1.[F:21][C:22]([C:25]1[CH:26]=[N:27][CH:28]=[C:29]([CH:32]=1)[CH:30]=O)([CH3:24])[CH3:23].[BH-](OC(C)=O)(OC(C)=O)OC(C)=O.[Na+]>C1COCC1.C(O)(=O)C.CCOC(C)=O>[F:21][C:22]([C:25]1[CH:32]=[C:29]([CH2:30][NH:1][CH2:2][C@@H:3]([OH:20])[C@@H:4]([NH:12][C:13](=[O:19])[O:14][C:15]([CH3:17])([CH3:16])[CH3:18])[CH2:5][C:6]2[CH:11]=[CH:10][CH:9]=[CH:8][CH:7]=2)[CH:28]=[N:27][CH:26]=1)([CH3:24])[CH3:23]A solution of tert-butyl (2S,3R)-4-amino-3-hydroxy-1-phenylbutan-2-ylcarbamate (297 mg, 1.06 mmol) in THF was added 5-(2-fluoropropan-2-yl)nicotinaldehyde (180 mg, 1.06 mmol) and stirred for 30 min at room temperature, NaB(OAc)3H (460 mg, 2.12 mmol) was then added portionwise in 30 min., finally 5 drops of acetic acid was added and the resulting mixture was stirred at the same temperature overnight. The reaction mixture was diluted with EtOAc, and washed with saturated aqueous NaHCO3. The organic layer was separated and dried (MgSO4). Concentration in vacuo, followed purification with flash chromatography to give tert-butyl (2S,3R)-4-((5-(2-fluoropropan-2-yl)pyridin-3-yl)methylamino)-3-hydroxy-1-phenylbutan-2-ylcarbamate as a white solid (230 mg, 70% yield). 1H NMR (CDCl3): d: 8.776 (d, J=11.5 Hz, 2H), 7.952 (s, 1H), 7.330-7.205 (m, 5H), 4.823 (d, J=7.7 Hz, 1H), 3.900 (s, 2H), 3.842 (m, 1H), 3.586 (m, 1H), 2.995 (m, 1H), 2.856 (m, 1H), 2.762 (m, 2H), 1.363 (s, 9H).
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