[CH3:1][O:2][C:3](=[O:15])[C@H:4]([CH2:13][SH:14])[NH:5][C:6]([O:8][C:9]([CH3:12])([CH3:11])[CH3:10])=[O:7].C(N(CC)CC)C.[CH2:23](Br)[CH:24]=[CH2:25].CCOC(C)=O>C(Cl)Cl>[CH3:1][O:2][C:3](=[O:15])[C@@H:4]([NH:5][C:6]([O:8][C:9]([CH3:12])([CH3:10])[CH3:11])=[O:7])[CH2:13][S:14][CH2:25][CH:24]=[CH2:23]N—BOC-cysteine methyl ester (obtained from Sigma-Aldrich, Auckland, New Zealand) (5.00 g, 21.2 mmol) was dissolved in anhydrous DCM (30 mL) under an atmosphere of argon. Triethylamine (3.26 mL, 23.3 mmol) and allyl bromide (2.02 mL, 23.3 mmol) were added. The reaction mixture was stirred at rt for eighteen h before being concentrated in vacuo. The residue was partitioned between EtOAc and 1M hydrochloric acid. The organic phase was washed with brine, dried (MgSO4), filtered and concentrated in vacuo. The crude material was purified by flash chromatography on silica using a gradient of EtOAc and (50/70) petroleum ether to yield a white solid, 3.22 g, 55%. Rf=0.19 (1/5 (EtOAc/(50/70) petroleum ether).
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