[C:1]([O:5][C:6]([NH:8][C@H:9]([C:12]([OH:14])=[O:13])[CH2:10][SH:11])=[O:7])([CH3:4])([CH3:3])[CH3:2].Br[CH2:16][C:17]([O:19][CH2:20][C:21]1[CH:26]=[CH:25][CH:24]=[CH:23][CH:22]=1)=[O:18].C(N(CC)CC)C>C1COCC1.C(OCC)(=O)C>[CH2:20]([O:19][C:17]([CH2:16][S:11][CH2:10][C@@H:9]([C:12]([OH:14])=[O:13])[NH:8][C:6]([O:5][C:1]([CH3:4])([CH3:2])[CH3:3])=[O:7])=[O:18])[C:21]1[CH:26]=[CH:25][CH:24]=[CH:23][CH:22]=1N-(tert-Butyloxycarbonyl)-L-cysteine (3.5 g, 15.8 mmol), benzyl 2-bromoacetate (3.7 g, 16.1 mmol) and triethylamine (1.8 g, 18.0 mmol) were dissolved in THF (100 ml). The mixture was stirred for 18 hours at room temperature then diluted with ethyl acetate (100 ml), washed with 0.3M KHSO4, sat NaHCO3, water and brine, dried (Na2SO4) and evaporated in vacuo. The residue was purified by flash chromatography on silica gel (eluant: 95% chloroform, 4% methanol, 1% acetic acid) to give a colourless oil identified as S-(benzyloxyrarbonylmethyl)-N-(tert-butyloxycarbonyl)-L-cysteine (5.2 g, 14.1 mmol, 89%).
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