[CH3:1][C:2]([O:5][C:6]([N:8]1[CH2:13][CH2:12][CH2:11][CH2:10][C@H:9]1[CH2:14][C:15]([OH:17])=[O:16])=[O:7])([CH3:4])[CH3:3].[CH3:18]CN(C(C)C)C(C)C.CN(C(ON1N=NC2C=CC=CC1=2)=[N+](C)C)C.[B-](F)(F)(F)F.CO>[Cl-].[Na+].O.CN(C=O)C>[CH3:18][O:16][C:15](=[O:17])[CH2:14][C@@H:9]1[CH2:10][CH2:11][CH2:12][CH2:13][N:8]1[C:6]([O:5][C:2]([CH3:1])([CH3:3])[CH3:4])=[O:7]
Into a 250 ml round bottom flask ((2S)-1-{[(1,1-dimethylethyl)oxy]carbonyl}-2-piperidinyl)acetic acid (1.00 g, 4.11 mmol), DMF (25 ml), DIPEA (2.15 ml, 12.33 mmol) and TBTU (1.98 g, 6.17 mmol) were added. The mixture was stirred at rt for 20 min and a brown colour was formed. After this time MeOH (0.25 ml, 6.17 mmol) was added and the resulting solution stirred at rt for 30 min. Then it was transferred into e separatory funnel containing brine (20 ml) and extracted with EtOAc (20 ml×2), the combined organic layers were washed with water/ice (5×20 ml). The organic layer was dried (Na2SO4), filtered and concentrated. The crude obtained was purified by column chromatography (Biotage SP1, Cy-EtOAc from 100/0 to 85/15). Collected fractions gave the title compound (1.01 g, 3.92 mmol, 95% yield) as a colorless oil. 1H-NMR (500 MHz, CDCl3) δ(ppm): 4.67-4.75 (m, 1H), 3.96-4.05 (m, 1H), 3.67 (s, 3H), 2.79 (t, 1H), 2.61 (dd, 1H), 2.53 (dd, 1H), 1.60-1.70 (m, 6H), 1.46 (s, 9H).
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