[CH3:1][O:2][CH2:3][N:4]1[C:9]2[CH:10]=[C:11]([CH2:14]O)[CH:12]=[CH:13][C:8]=2[S:7][C:6]2[N:16]=[CH:17][CH:18]=[N:19][C:5]1=2.N1C=CC=CC=1.CS([Cl:30])(=O)=O.C(Cl)Cl.C(=O)([O-])O.[Na+]>CN(C)C=O>[Cl:30][CH2:14][C:11]1[CH:12]=[CH:13][C:8]2[S:7][C:6]3[N:16]=[CH:17][CH:18]=[N:19][C:5]=3[N:4]([CH2:3][O:2][CH3:1])[C:9]=2[CH:10]=1
Into a solution of 19 g of 10-methoxymethyl-10H-pyrazino[2,3-b][1,4]benzothiazine-8-methanol and 13.9 ml of pyridine in N,N-dimethylformamide (150 ml) was added dropwise under a nitrogen atmosphere 13.3 ml of methanesulfonyl chloride at 0° C. Then the reaction mixture was stirred at room temperature for 1 hour and then poured into a pre-cooled aqueous solution of methylene chloride/sodium hydrogen carbonate. Then it was extracted with ethyl acetate, washed with water and dried over anhydrous sodium sulfate. After distilling off the solvent under reduced pressure, the residue was purified by silica gel column chromatography (eluted with methylene chloride) to thereby give 13.6 g of the title compound as pale yellow crystals.
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