[OH-].[Na+].C[O:4][C:5](=[O:25])[CH:6]([CH2:16][NH:17][C:18]([O:20][C:21]([CH3:24])([CH3:23])[CH3:22])=[O:19])[CH2:7][NH:8][C:9]([O:11][C:12]([CH3:15])([CH3:14])[CH3:13])=[O:10].O.C(O)(=O)CC(CC(O)=O)(C(O)=O)O>C1COCC1>[C:21]([O:20][C:18]([NH:17][CH2:16][CH:6]([CH2:7][NH:8][C:9]([O:11][C:12]([CH3:15])([CH3:14])[CH3:13])=[O:10])[C:5]([OH:25])=[O:4])=[O:19])([CH3:23])([CH3:24])[CH3:22]Aqueous 2N sodium hydroxide (2.48 mL, 4.96 mmol) was added to a stirring solution of the methyl ester 13 (0.41 g, 1.24 mmol) in THF (7.5 mL) and the mixture was stirred at rt. for 24 h. Water (15 mL) was added and the solution was acidified with 5% aqueous citric acid. The mixture was extracted with CHCl3 (3×25 mL) and the combined organic extracts were washed with brine (30 mL), dried (Na2SO4), and evaporated in vacuo to leave the acid 14 as a viscous, colourless oil (280 mg).
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