[C:1]([O:5][C:6]([N:8]1[C@H:12]([C:13]([OH:15])=O)[CH2:11][S:10][CH2:9]1)=[O:7])([CH3:4])([CH3:3])[CH3:2].O.O[N:18]1C2C=CC=CC=2N=N1.O.N>C(Cl)Cl.CN(C=O)C>[C:1]([O:5][C:6]([N:8]1[C@H:12]([C:13]([NH2:18])=[O:15])[CH2:11][S:10][CH2:9]1)=[O:7])([CH3:4])([CH3:3])[CH3:2](4R)-3-(tert-Butyloxycarbonyl)thiazolidine-4-carboxylic acid (12.5 g, 54.1 mmol) was dissolved in CH2Cl2/DMF (9:1, 150 ml). To this solution at 0° C. was added 1-hydroxybenzotriazole hydrate (14.6 g, 108 mmol) and water-soluble carbodiimide (13.0 g, 65 mmol). After 1 h at 0° C. ammonia (35%, 50 ml) was added. After 18 h at 0° C. to room temperature the solvent was removed in vacuo and the residue was taken up in ethyl acetate (500 ml). This solution was washed with 0.3M KHSO4, sat. NaHCO3, water and brine, dried (Na2SO4) and evaporated in vacuo. The residue was purified by flash chromatography (eluant: 2% methanol, 98% chloroform) to give a colourless oil identified as the title compound (8.9 g, 38.4 mmol, 71%).
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