Z-Glu-Obzl 3 (1.0 g, 2.7 mmol) was dissolved in dry THF (10 mL) at rt. Carbonyl diimidazole (0.48 g, 2.96 mmol) was added slowly and the mixture was then stirred for another 2 h. After the solution was cooled to 0° C., ethyl magnesium malonate solution 2 (4.7 mL, 1.2 mmol) was added, and the mixture was then stirred at rt overnight. The product was extracted with ester, and washed with 10% NaHCO3, water, and brine. After the solvent was evaporated, the residue was purified by flash chromatography on silica gel (Hexanes:EtOAc=1:1) and afford a white solid (0.9 g, 2.03 mmol, 75.2%). 1H NMR (400 MHz, CDCl3, 25° C.) δ 1.23 (t, 3H), 1.90-2.00 (m, 1H), 2.10-2.30 (m, 1H), 2.50-2.70 (m, 2H), 3.36 (s, 2H), 4.16 (q, 2H), 4.30-4.50 (m, 1H), 5.10 (s, 2H), 5.12 (s, 2H) 5.36 (m, 1H), 7.25-7.40 (m, 10H).
