1-Benzyloxycarbonyl-4-(3-carboxymethyl-2-oxoperhydropyrimidin-1-yl)piperidine. Potassium tert-butoxide (52 mL, 1 M in tert-butanol) was added to l-benzyloxycarbonyl-4-(2-oxoperhydropyrimidin-1-yl)piperidine (15.0 g), and the solution was stirred for 35 minutes. tert-Butyl bromoacetate (7.65 mL) was then added, and the mixture was stirred overnight. The reaction mixture was diluted with tetrahydrofuran (20 mL) and dichloromethane (10 mL) followed by the addition of tetrabutylammonium iodide (1.74 g), potassium tert-butoxide (52 mL, 1 M in tert-butanol), and tert-butyl bromoacetate (7.65 mL). After being stirred overnight, the reaction mixture was diluted with dichloromethane and washed with water. The separated organic layer was dried, evaporated to an oil, and dissolved in 1 N hydrochloric acid (700 mL), tetrahydrofuran (200 mL), and methanol (200 mL). After being stirred overnight, the reaction mixture was concentrated in vacuo to remove the organic solvents. The resulting aqueous solution was extracted with dichloromethane, acidified with 2 N hydrochloric acid to a pH of 2, and extracted with dichloromethane. The first organic extract was concentrated to give unreacted 1-benzyloxycarbonyl-4-(2-oxoperhydropyrimidin-1-yl)piperidine (7.0 g). The second organic extract was washed with water, dried, and evaporated. The crude product was triturated from ether and filtered to give the title compound as a white solid (8.3 g); MS: m/z=376(M+1); NMR (CDCl3): 7.35 (m,5), 5.12 (s,2), 4.48 (m,1), 4.28 (m,2), 4.02 (s,2), 3.35 (m,2), 3.18 (m,2), 2.87 (m,2), 1.97 (m,2), 1.65 (m,4).
