[C:1]([O:5][C:6]([NH:8][C@H:9]1[CH2:14][CH2:13][C@H:12]([C:15](OC)=[O:16])[CH2:11][CH2:10]1)=[O:7])([CH3:4])([CH3:3])[CH3:2].C1COCC1.[Cl-].[Ca+2].[Cl-].[BH4-].[Na+]>C(O)C>[OH:16][CH2:15][C@H:12]1[CH2:11][CH2:10][C@H:9]([NH:8][C:6](=[O:7])[O:5][C:1]([CH3:3])([CH3:2])[CH3:4])[CH2:14][CH2:13]1Methyl trans-4-(tert-butoxycarbonylamino)cyclohexanecarboxylate (55.5 g, 216 mmol) was suspended in ethanol (900 ml) and THF (100 ml) and the mixture was cooled to 5° C. Granular calcium chloride (47.9 g, 431 mmol) was added portionwise to give a milky suspension. Sodium borohydride (32.6 g, 863 mmol) was added portionwise over 25 mins at 5° C. The reaction mixture (white emulsion) was stirred at 5° C. for 1 hour, the water bath was removed and then the reaction mixture was allowed to warm to room temperature and stirred at room temperature overnight. The reaction mixture was cooled to 10° C. and 5% potassium carbonate (200 ml) was added dropwise until the pH of the solution was pH11. A colourless precipitate formed which was filtered off. The solid was stirred with ethyl acetate (2000 ml) and water (500 ml). The organic layer was separated and washed with 0.5M HCl (200 ml), then washed with water (2×200 ml) and saturated brine (100 ml). The organic solution was dried over anhydrous MgSO4, filtered and evaporated to give a white solid. The solid was dried under high vacuum overnight to constant weight; [M+H]+230.
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