[C:1]([O:5][C:6]([NH:8][CH2:9][C@@H:10]1[CH2:14][N:13]([C:15]([O:17][C:18]([CH3:21])([CH3:20])[CH3:19])=[O:16])[C@@H:12]([C:22](O)=[O:23])[CH2:11]1)=[O:7])([CH3:4])([CH3:3])[CH3:2].B>C1COCC1>[C:1]([O:5][C:6]([NH:8][CH2:9][C@@H:10]1[CH2:14][N:13]([C:15]([O:17][C:18]([CH3:21])([CH3:20])[CH3:19])=[O:16])[C@@H:12]([CH2:22][OH:23])[CH2:11]1)=[O:7])([CH3:2])([CH3:4])[CH3:3]A solution of trans-4-(N-tert-butoxycarbonylaminomethyl)-N-tert-butoxycarbonyl-D-proline (1.0 g, 2.9 mmol) in anhydrous THF (24 mL) was cooled to -10° C. and borane in THF (1M, 26 mL) was added at that temperature. The reaction was left to stir for 5 hours at 0° C. The reaction was quenched with methanol (100 mL) at 0° C. and left for 1.5 hours to stir at 20° C. The solvents were removed in vacuo , and EtOAc (100 mL) was then added to the reaction mixture and the organic phase washed with 1M NaOH (2×50 mL), brine (2×50 mL), dried over Na2SO4 and concentrated in vacuo. The residue was purified by silica gel chromatography (50% EtOAc:Hexanes) to give the title compound (433mg, 45%). Rf(60% EtOAc-Hexanes; ninhydrin)=0.29. 1H NMR (CDCl3, 300 MHz) δ 1.45 (s, 9 H), 1.47 (s, 9 H), 1.69 (m, 1 H), 2.01 (m, 1 H), 2.47 (m, 1 H), 3.16 (m, 3 H), 3.55-3.77 (m, 2 H), 3.60 (m, 1 H), 3.85 (br m, 1 H). MS: 353.2 (M+Na).
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