[CH3:1][C:2]1([CH3:28])[CH2:11][CH2:10][C:9]([CH3:13])([CH3:12])[C:8]2[CH:7]=[C:6]([C:14]([C:18]3[CH:27]=[CH:26][C:21]([C:22]([O:24]C)=[O:23])=[CH:20][CH:19]=3)=[C:15]([CH3:17])[CH3:16])[CH:5]=[CH:4][C:3]1=2.[OH-].[K+].Cl>CO>[CH3:1][C:2]1([CH3:28])[CH2:11][CH2:10][C:9]([CH3:12])([CH3:13])[C:8]2[CH:7]=[C:6]([C:14]([C:18]3[CH:27]=[CH:26][C:21]([C:22]([OH:24])=[O:23])=[CH:20][CH:19]=3)=[C:15]([CH3:16])[CH3:17])[CH:5]=[CH:4][C:3]1=2To a suspension of the ester 19 (0.115 g, 0.304 mmol) in 75% aqueous methanol (3 mL) was added one pellet of potassium hydroxide (0.12 g), The mixture was stirred at 75° C. for 1 h during which time the material dissolved. The solution was cooled to room temperature, acidified with 1N aqueous hydrochloric acid, and then extracted with 80% ethyl acetate/hexane. The combined organic layers were dried over anhydrous MgSo4, filtered, and concentrated to afford the desired acid 20 as a white powder (0.11 g, 99%): m.p. 204°-206° C. The structure of the product was also confirmed using IR, 1H NMR and mass spectroscopy.
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