A solution of 2-[3-cyclopentyl-2-(4-phenoxy-phenyl)-propionylamino]-thiazole-4-carboxylic acid ethyl ester (prepared in Example 13, 300 mg, 0.65 mmol) in ethanol (20 mL) at 25° C. was treated with a solution of potassium hydroxide (109 mg, 1.94 mmol) in water (6 mL). This light yellow solution was stirred at 25° C. for 2 h and then concentrated in vacuo to remove ethanol. The resulting aqueous solution was acidified to pH=2 with a 1N aqueous hydrochloric acid solution and then extracted with methylene chloride (3×10 mL). The combined organic extracts were dried over sodium sulfate, filtered, and concentrated in vacuo. Flash chromatography (Merck Silica gel 60, 230-400 mesh, 20/80 hexanes/ethyl acetate plus 1% acetic acid) afforded 2-[3-cyclopentyl-2-(4-phenoxy-phenyl)-propionylamino]-thiazole-4-carboxylic acid (226 mg, 80%) as a white solid: mp >200° C.; FAB-HRMS m/e calcd for C24H24N2O4S (M+H)+ 437.1535, found 437.1534.
