C([O:4][CH2:5][CH2:6][C:7]1[CH:12]=[CH:11][C:10]([NH:13][C:14](=[O:16])[CH3:15])=[CH:9][CH:8]=1)(=O)C.[OH-].[Na+]>CO>[OH:4][CH2:5][CH2:6][C:7]1[CH:12]=[CH:11][C:10]([NH:13][C:14](=[O:16])[CH3:15])=[CH:9][CH:8]=1A solution of the product from step (b) (55.3 g) in methanol (250 ml) and 1N aqu. NaOH (500 ml) was stirred at room temperature for 1 hour. The methanol was evaporated in vacuo and the remaining aqueous solution adjusted to pH 4 (2N aqu. HCl), saturated with NaCl, and extracted with ethyl acetate (×3). The combined extracts were washed with water and brine, dried over MgSO4 and evaporated in vacuo to give a brown oil which was flash chromatographed through a silica column using ethyl acetate and then crystallised from ethyl acetate to give the desired product (51.7 g).
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