[C:1]1(=O)[CH2:5][CH2:4][CH2:3][CH2:2]1.[CH2:7]([O:9][C:10]([C@H:12]1[C@@H:17]([NH2:18])[C@H:16]2[CH2:19][C@@H:13]1[CH2:14][CH2:15]2)=[O:11])[CH3:8].C([BH3-])#N.[Na+].C(=O)(O)[O-].[Na+]>CO.C(O)(=O)C>[CH2:7]([O:9][C:10]([C@H:12]1[C@@H:17]([NH:18][CH:1]2[CH2:5][CH2:4][CH2:3][CH2:2]2)[C@H:16]2[CH2:19][C@@H:13]1[CH2:14][CH2:15]2)=[O:11])[CH3:8]
Cyclopentanone (0.12 mL, 1.38 mmol) was added to a solution of (1S,2R,3S,4R)-3-amino-bicyclo[2.2.1]heptane-2-carboxylic acid ethyl ester (prepared as described in Example 6k, 230 mg, 1.26 mmol) in anhydrous methanol (10 mL) at 25° C. under a nitrogen atmosphere. After stirring for 10 min, glacial acetic acid (0.5 mL) and sodium cyanoborohydride (260 mg, 3.15 mmol) were added sequentially, and the resulting mixture was stirred at 50° C. for 30 min. The reaction mixture was poured into saturated aqueous sodium bicarbonate solution and extracted with ethyl acetate. The combined organic layers were washed with saturated aqueous brine solution, dried over sodium sulfate and filtered. The filtrate was concentrated in vacuo to afford the desired product, (1S,2R,3S,4R)-3-cyclopentylamino-bicyclo[2.2.1]heptane-2-carboxylic acid ethyl ester (237 mg, 0.94 mmol, 75%), as a yellow oil. LC-MS (ESI) calcd for C15H25NO2 251.19, found 252.0 [M+H+].
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