[CH3:1][O:2][C:3]1[CH:22]=[CH:21][C:6]([C:7]([C:9]2[CH:20]=[CH:19][C:12]([O:13][CH2:14][C:15]([O:17]C)=[O:16])=[CH:11][CH:10]=2)=[O:8])=[CH:5][CH:4]=1.[OH-].[Na+].Cl>COCCOC.O>[CH3:1][O:2][C:3]1[CH:4]=[CH:5][C:6]([C:7]([C:9]2[CH:20]=[CH:19][C:12]([O:13][CH2:14][C:15]([OH:17])=[O:16])=[CH:11][CH:10]=2)=[O:8])=[CH:21][CH:22]=19.0 g of the methyl ester (Example 1) are dissolved in 120 ml of 1,2-dimethoxyethane/water (4:1, v:v), and 15 ml of 2N NaOH are added. The mixture is stirred for three hours, and the pH is adjusted to 3 with 3N HCl. The organic solvent is evaporated off in vacuo, and the precipitated product is filtered off, washed with water and dried under high vacuum.
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