[C:1]([O:5][C:6]([N:8]1[CH2:12][C@@H:11]([NH:13][C@@H:14]([C:16]2[CH:21]=[CH:20][CH:19]=[CH:18][CH:17]=2)[CH3:15])[C@H:10]([C:22]([N:24]2[CH2:29][CH2:28][CH2:27][C@@H:26]([CH2:30][C:31]3[CH:36]=[CH:35][C:34]([F:37])=[CH:33][CH:32]=3)[CH2:25]2)=O)[CH2:9]1)=[O:7])([CH3:4])([CH3:3])[CH3:2].O1CCCC1.C(O)(=O)C>CO>[C:1]([O:5][C:6]([N:8]1[CH2:12][C@@H:11]([NH:13][C@@H:14]([C:16]2[CH:21]=[CH:20][CH:19]=[CH:18][CH:17]=2)[CH3:15])[C@@H:10]([CH2:22][N:24]2[CH2:29][CH2:28][CH2:27][C@@H:26]([CH2:30][C:31]3[CH:32]=[CH:33][C:34]([F:37])=[CH:35][CH:36]=3)[CH2:25]2)[CH2:9]1)=[O:7])([CH3:2])([CH3:3])[CH3:4](3R,4S)-3-[(S)-3-(4-fluorobenzyl)-piperidine-1-carbonyl]-4-[(R)-1-phenyl-ethylamino]-pyrrolidine-1-carboxylic acid tert-butyl ester (150 mg, 294 μmol)) was treated with borane-tetrahydrofuran complex in tetrahydrofuran (1.0 M; 11.64 mL, 11.64 mmol) and stirred for 20 h. The mixture was treated slowly with 20% acetic acid in methanol (20 mL), and the resulting mixture was stirred at room temperature for 36 h. The solvents were removed, and the residue was dissolved in water, made basic (pH 11) with 50% sodium hydroxide, and extracted with dichloromethane. The combined organic phases were dried (Na2SO4) and concentrated. The residue was purified by flash column chromatography (60% ethyl acetate/hexane) to provide the product (100 mg, 68%).
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