A solution of 6-(3-cyclopentyl-2-{4-[(pyridine-3-carbonyl)-amino]-phenyl}-propionylamino)-nicotinic acid methyl ester (prepared in Example 16, 87.2 mg, 0.18 mmol) in tetrahydrofuran (8 mL) and water (2 mL) was treated with lithium hydroxide (17.0 mg, 0.41 mmol). The reaction was stirred at 25° C. for 20 h. At this time, the reaction was concentrated in vacuo. The residue was diluted with water (25 mL) and extracted with diethyl ether (1×20 mL). The aqueous layer was acidified to pH=1 with a 3N aqueous hydrochloric acid solution and was extracted with methylene chloride (3×50 mL). The combined organic extracts were washed with water (1×50 mL) and a saturated aqueous sodium chloride solution (2×50 mL), dried over magnesium sulfate, filtered, and concentrated in vacuo. High pressure liquid chromatography (Chromegasphere SI-60, 10 μM, 60 Å, 25 cm×23 cm ID, 100% ethyl acetate with acetic acid) afforded 6-[3-cyclopentyl-2-(4-nitro-phenyl)-propionylamino]-nicotinic acid (6.4 mg, 7.5%) as a pale yellow oil: EI-HRMS m/e calcd for C16H26N4O4 (M+) 458.1954, found 458.1967.
