To a solution of 2-tert-butoxycarbonylamino-propionic acid chloromethyl ester (4) (0.6207 g, 2.61 mmol) and 3-(3-ethyl-5-isopropyl-2,6-dioxo-1,2,3,6-tetrahydro-pyrimidine-4-carbonyl)-5-methyl-benzonitrile (0.780 g, 2.40 mmol) in DMF (10 mL) was added K2CO3 and tetrabutylammonium iodide (0.193 g, 0.522 mmol), and the reaction mixture stirred for 48 h. The reaction mixture was concentrated, diluted with ethyl acetate and washed with H2O (2×), brine, dried (MgSO4) and concentrated. The residue was purified by flash column chromatography (silica gel, 0 to 50% ethyl acetate/hexane) to give a yellow foam (5) (0.9028 g, 71%). 1H NMR (300 MHz, CDCl3): 8.01 (s, 1H), 7.94 (s, 1H), 7.77 (s, 1H), 6.1-5.9 (m, 2H), 5.05 (br s, 1H), 4.32 (br s, 1H), 3.9-3.8 (m, 1H), 3.2-3.1 (m, 1H), 2.49 (s, 3H), 2.2-2.1 (m, 1H), 1.39 (s, 9H), 1.37 (s, 3H), 1.2-1.1 (m, 9H). Mass spectrum: 549.1 (M+Na).
