[CH2:1]([N:3]([CH2:17][CH3:18])[CH2:4][CH2:5][S:6][C:7]1[C:11]([N:12]2[CH:16]=[CH:15][N:14]=[CH:13]2)=[N:10][S:9][N:8]=1)[CH3:2].S(=O)(=O)(O)[OH:20].B1([O-])OO1.O.O.O.O.[Na+]>CO>[CH2:17]([N:3]([CH2:1][CH3:2])[CH2:4][CH2:5][S:6]([C:7]1[C:11]([N:12]2[CH:16]=[CH:15][N:14]=[CH:13]2)=[N:10][S:9][N:8]=1)=[O:20])[CH3:18]A cold (0° C.) solution of the compound of Example 10 in methanol istreated slowly with excess 30% sulfuric acid an then sodium perborate tetrahydrate (10 equivalents) is added. The mixture is stirred at 0° C. for 2 hrs and then at ambient temperature for 2 hrs. The methanol is removed in vacuo and the residue basified with 50% sodium hydroxide and filtered. The filter cake is washed with methylene chloride and the aqueous filtrate extracted with the methylene chloride washings. The combined extract is washed with water, dried, and concentrated to obtain the title compound.
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