[C:1]([C:4]1[CH:9]=[CH:8][C:7]([S:10]([NH2:13])(=[O:12])=[O:11])=[C:6]([Cl:14])[CH:5]=1)(=[O:3])[CH3:2].[C:15](OC(=O)C)(=[O:17])[CH3:16].S(=O)(=O)(O)O>C(#N)C.O>[C:1]([C:4]1[CH:9]=[CH:8][C:7]([S:10]([NH:13][C:15](=[O:17])[CH3:16])(=[O:12])=[O:11])=[C:6]([Cl:14])[CH:5]=1)(=[O:3])[CH3:2]To a solution of the product obtained in step 2 (0.40 mg, 1.71 mmol) in ACN (3 ml) was added acetic anhydride. Concentrated sulphuric acid (2.8 μl, 5 mg, 51 μM) was added at 60° C. and the reaction mixture was stirred for 40 min at that temperature. The cooled reaction mixture was diluted with water, extracted with dichloromethane, dried over sodium sulfate, filtered and the solvent was removed under reduced pressure. The desired product was obtained (yield: 460 mg, 97%) and used in the following step without further purification.
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