[C:1]([C:4]1[CH:27]=[CH:26][C:7]([O:8][CH2:9][CH2:10][S:11][C:12]2[NH:13][C:14]3[CH:20]=[C:19]([C:21]([O:23]CC)=[O:22])[CH:18]=[CH:17][C:15]=3[N:16]=2)=[C:6]([CH2:28][CH2:29][CH3:30])[C:5]=1[OH:31])(=[O:3])[CH3:2].Cl>[OH-].[Na+]>[C:1]([C:4]1[CH:27]=[CH:26][C:7]([O:8][CH2:9][CH2:10][S:11][C:12]2[NH:13][C:14]3[CH:20]=[C:19]([C:21]([OH:23])=[O:22])[CH:18]=[CH:17][C:15]=3[N:16]=2)=[C:6]([CH2:28][CH2:29][CH3:30])[C:5]=1[OH:31])(=[O:3])[CH3:2]The above ester (2.20 g) was added to 1 N sodium hydroxide solution (20 ml), and the mixture was refluxed for 30 minutes, then poured into ice-water, made acidic with concentrated hydrochloric acid and extracted with ethyl acetate. The organic layer was washed with water, dried over anhydrous sodium sulfate and evaporated. The resulting residue was purified by silica gel column chromatography, eluting with dichloromethane-methanol (10:1), and recrystallized from n-hexane-ethyl acetate to give the title compound (1.60 g, 77.1 %) as colorless crystals, mp 108-110° C.
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