[C:1]([O:5][C:6](=[O:16])[NH:7][C:8]1[S:9][CH:10]=[C:11]([CH2:13][CH2:14][OH:15])[N:12]=1)([CH3:4])([CH3:3])[CH3:2].C(N(CC)CC)C.[CH3:24][S:25](Cl)(=[O:27])=[O:26]>C(Cl)Cl>[C:1]([O:5][C:6]([NH:7][C:8]1[S:9][CH:10]=[C:11]([CH2:13][CH2:14][O:15][S:25]([CH3:24])(=[O:27])=[O:26])[N:12]=1)=[O:16])([CH3:4])([CH3:2])[CH3:3]To a solution of [4-(2-Hydroxy-ethyl)-thiazol-2-yl]-carbamic acid tert-butyl ester (5 g, 20 mmol) and triethyl amine (5.8 ml, 40 mmol) in DCM (50 ml) was added methanesulfonyl chloride (1.9 ml, 24 mmol) slowly over a period of 10-15 min. The reaction mixture was stirred at r.t. for 4 hr, quenched with brine (10 ml) and extracted in DCM (100 ml), dried over Na2SO4 and passed through a short column of silica gel bed and concentrated to obtain methanesulfonic acid 2-(2-tert-butoxycarbonylamino-thiazol-4-yl)-ethyl ester (6.0 g, 90%) which was used as such for the next step without further purification.
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