A solution of 3-cyclopentyl-2-(4-methanesulfonyl-3-nitrophenyl)-propionic acid (prepared as in Example 14, 150 mg, 0.439 mmol) in methylene chloride (2 mL) was treated with N,N-dimethylformamide (2 drops) and then cooled to 0° C. The reaction mixture was then treated with oxalyl chloride (0.042 mL, 0.483 mmol). The resulting reaction mixture was allowed to warm to 25° C. where it was stirred for 30 min. The reaction mixture was then treated with a mixture of cytosine (102 mg, 0.922 mmol) and N,N-diisopropylethylamine (0.191 mL, 1.098 mmol) in N,N-dimethylformamide (2 mL). The resulting reaction mixture was allowed to stir at 25° C. overnight. The reaction mixture was then diluted with water (30 mL), a 1N aqueous hydrochloric acid solution (5 mL), and ethyl acetate (30 mL). The layers were separated, and the organic layer was dried over magnesium sulfate, filtered, and concentrated in vacuo. Biotage chromatography (FLASH 40S, Silica, 20/1 methylene chloride/methanol) afforded impure 3-cyclopentyl-2-(4-methanesulfonyl-3-nitro-phenyl)-N-(2-oxo-1,2-dihydro-pyrimidin-4-yl)-propionamide (25 mg) as a pale yellow solid. Re-purification by recrystallization from chloroform afforded 3-cyclopentyl-2-(4-methanesulfonyl-3-nitro-phenyl)-N-(2-oxo-1,2-dihydro-pyrimidin-4-yl)-propionamide (12 mg, 6.5%) as a white solid: mp 256–258° C. (dec); FAB-HRMS m/e calcd for C19H22N4O6S (M+H)+ 435.1338, found 435.1334.
