[C:1]([O:5][C:6]([N:8]1[CH2:12][CH2:11][CH2:10][C@H:9]1[CH2:13][OH:14])=[O:7])([CH3:4])([CH3:3])[CH3:2].C(N(CC)CC)C.[CH3:22][S:23](Cl)(=[O:25])=[O:24]>ClCCl>[C:1]([O:5][C:6]([N:8]1[CH2:12][CH2:11][CH2:10][C@H:9]1[CH2:13][O:14][S:23]([CH3:22])(=[O:25])=[O:24])=[O:7])([CH3:4])([CH3:3])[CH3:2]A flame dried flask charged with (S)-2-Hydroxymethyl-pyrrolidine-1-carboxylic acid tert-butyl ester (1 g, 5 mmol), dichloromethane (DCM) (20 mL) and triethylamine (0.70 mL, 5.2 mmol) is cooled to 0° C. under N2 is added a solution of methanesulfonylchloride (0.38 mL, 5 mmol) in DCM (5 mL) dropwise over 10 minutes. The reaction is stirred for 1 hour. After addition of DCM (100 mL), the reaction mixture is washed with brine, dried and concentrated in vacuo. The residue is purified by chromatography on SiO2 (5% EtOAc/Hexanes) to give 1.38 g of methanesulfonate ester (P) as a clear colorless oil: LCMS (ES) 280.10 (MH+).
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