C[O:2][C:3](=[O:24])[CH:4]([C:11]1[CH:16]=[CH:15][C:14]([S:17]([CH3:20])(=[O:19])=[O:18])=[C:13]([N+:21]([O-:23])=[O:22])[CH:12]=1)[CH2:5][CH:6]1[CH2:10][CH2:9][CH2:8][CH2:7]1.[OH-].[Li+].Cl.C(OCC)(=O)C>O1CCCC1.O>[CH:6]1([CH2:5][CH:4]([C:11]2[CH:16]=[CH:15][C:14]([S:17]([CH3:20])(=[O:19])=[O:18])=[C:13]([N+:21]([O-:23])=[O:22])[CH:12]=2)[C:3]([OH:24])=[O:2])[CH2:10][CH2:9][CH2:8][CH2:7]1
A solution of 3-cyclopentyl-2-(4-methanesulfonyl-3-nitrophenyl)-propionic acid methyl ester (1.17 g, 3.29 mmol) in tetrahydrofuran (6 mL) was treated with a 0.8M aqueous lithium hydroxide solution (6.17 mL, 4.94 mmol). The reaction mixture was stirred at 25° C. for 3 h. The reaction mixture was then diluted with water (50 mL), a 1N aqueous hydrochloric acid solution (10 mL), and ethyl acetate (50 mL). The layers were separated, and the aqueous layer was back-extracted with ethyl acetate (2×50 mL). The combined organic layers were dried over magnesium sulfate, filtered, and concentrated in vacuo. Flash chromatography (Merck Silica gel 60, 230-400 mesh, 1/1 hexanes/ethyl acetate) afforded 3-cyclopentyl-2-(4-methanesulfonyl-3-nitrophenyl)-propionic acid (993 mg, 88%) as a yellow foam which contained a small impurity. A small amount of the yellow foam (50 mg) was re-purified using Biotage chromatography (FLASH 40S, Silica, 3/1 then 1/1 hexanes/ethyl acetate) to afford 3-cyclopentyl-2-(4-methanesulfonyl-3-nitrophenyl)-propionic acid as a white foam: mp 114-118° C. (foam to gel); FAB-HRMS m/e calcd for C15H19NO6S (M+H)+ 342.1011, found 342.1014.
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