C(Cl)(=O)C(Cl)=O.CS(C)=O.C(N(CC)CC)C.[C:18]([O:22][C:23]([N:25]1[CH2:30][CH2:29][N:28]([CH2:31][C:32]2[CH:37]=[CH:36][CH:35]=[CH:34][CH:33]=2)[CH2:27][C@@H:26]1[CH2:38][CH2:39][OH:40])=[O:24])([CH3:21])([CH3:20])[CH3:19]>ClCCl>[C:18]([O:22][C:23]([N:25]1[CH2:30][CH2:29][N:28]([CH2:31][C:32]2[CH:33]=[CH:34][CH:35]=[CH:36][CH:37]=2)[CH2:27][C@@H:26]1[CH2:38][CH:39]=[O:40])=[O:24])([CH3:21])([CH3:20])[CH3:19]Add dichloromethane (3 mL) to a 50 mL dry schlenk flask, followed by oxalyl chloride (0.178 g, 1.4 mmol) and cool the solution to −78° C. and treat with dimethyl sulfoxide (0.171 g, 2.2 mmol) and triethylamine (0.505 g, 5.0 mmol). After 10 min, add a solution of (S)-4-benzyl-2-(2-hydroxy-ethyl)-piperazine-1-carboxylic acid tert-butyl ester (0.320 g, 1.0 mmol) in dichloromethane (5 mL) and stir the resulting mixture at −78° C. for 1 hour. Quench the reaction mixture by adding sat. NaHCO3, extract the aqueous solution with CH2Cl2, wash the organic solvent with brine, and dry over Na2SO4. Purification by silica gel chromatography of the crude product using MeOH/CH2Cl2 (5% to 10%) as eluent to give the title compound (160 g, 50%) as a light yellow oil: mass spectrum (Electrospray): m/z=319.2 (M+1); 1H NMR (400 MHz, CDCl3): δ9.74 (t, 1H, J=2.0 Hz), 7.33–7.21 (m, 5H), 4.57 (br, 1H), 3.88 (m, 2H), 33.52–3.40 (m, 21H), 3.15–3.05 (m, 1H), 2.83–2.66 (m, 4H), 2.22–2.18 (m, 1H), 2.03 (dt, 1H, J=3.4, 11.8 Hz), 1.44 (s, 9H).
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