Triphenylphosphine → (2R)-2-[3-cyclopentyl-2-(3,4-dichloro-phenyl)-propionylamino]-thiazole-4-carboxylic acid methyl ester

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A solution triphenylphosphine (164 mg, 0.63 mmol) in methylene chloride (3 mL) was cooled to 0° C. and then treated with N-bromosuccinimide (112 mg, 0.63 mmol) in small portions. The resulting orange reaction mixture was stirred at 0° C. for 20 min and then treated with (2R)-3-cyclopentyl-2-(3,4-dichloro-phenyl)-propionic acid (prepared in Example 54, 150 mg, 0.52 mmol). The reaction mixture was stirred at 0° C. for an additional 15 min and then allowed to warm to 25° C. The reaction mixture was then treated with 2-aminothiazole-4-carboxylic acid methyl ester (181 mg, 1.15 mmol). The resulting reaction mixture was stirred at 25° C. for 15 h. The crude reaction mixture was directly purified by flash chromatography (Merck Silica gel 60, 230-400 mesh, 3/1 hexanes/ethyl acetate) to afford impure (2R)-2-[3-cyclopentyl-2-(3,4-dichloro-phenyl)-propionylamino]-thiazole-4-carboxylic acid methyl ester. The impure product was diluted with ethyl acetate and then washed with a saturated aqueous sodium bicarbonate solution. The organic layer was dried over magnesium sulfate, filtered, and concentrated in vacuo to provide pure (2R)-2-[3-cyclopentyl-2-(3,4-dichloro-phenyl)-propionylamino]-thiazole-4-carboxylic acid methyl ester (92 mg, 41%) as a white solid: mp 143-144° C.; [α]23589=−10.2° (c=0.98, chloroform); EI-HRMS m/e calcd for C19H20Cl2N2O3S (M+) 426.0572, found 426.0562.

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