To a solution of N-[2-(2-nitro-benzenesulfonylamino)-ethyl]-N-[(thymin-1-yl)-acetyl]-glycine (469 mg, 1.0 mmol) and N-mehtyl morpholine (330 μL, 3 mmol) in THF (10 mL) was added isobutylchloroformatre (205 mg, 1.5 mmol) at −20° C. The reaction mixture was allowed to warm to 0° C. for a period of 1 h. Then water (10 mL) was added to the reaction mixture to precipitate solid. The solid was filtered off, washed with water, dried in vacuo to give the tiltled compound (442 mg, 98%). 1H-NMR (500 MHz; DMSO-d6) δ 11.32 (s, 0.6H), 11.30 (s, 0.4H), 8.35 (m, 1H), 8.12 (dd, 1H), 8.04˜7.96 (m, 2H), 7.35 (s, 0.6H), 7.28 (s, 0.4H), 4.67 (s, 1.2H), 4.59 (s, 0.8H), 4.41 (s, 0.8H), 4.27 (s, 1.2H), 4.04 (m, 1.2H), 3.95 (m, 1.2H), 3.90˜3.85 (m, 1.6H), 1.75 (s, 3H).
