A 50-mL, one-neck, round bottomed flask equipped with a magnetic stirrer and a digital thermometer was charged with tert-butyl [3-(N-hydroxycarbamimidoyl)phenyl]carbamate (5.56 g, 22.1 mmol), diisopropylethylamine (4.29 g, 33.2 mmol) and THF (25 mL). The reaction mixture was then cooled to 0° C. in an ice/salt bath. 3-Carbomethoxypropionyl chloride (3.99 g, 26.6 mmol) was then added dropwise to the reaction mixture. Once the addition was complete, the cooling bath was removed and the mixture stirred at room temperature for an additional 3 h. The reaction was then concentrated under reduced pressure, the residue dissolved in ethyl acetate (60 mL), and the resulting solution washed with 2 M aqueous potassium carbonate solution (2×60 mL). Drying over sodium sulfate, filtration and concentration under reduced pressure afforded a quantitative yield of 3-tert-butyloxycarbonylamino-N-(3-carbomethoxypropionyloxy)benzamidine as a white solid that was used directly. 1H NMR (CDCl3) δ (ppm) 7.71 (s, 1H), 7.50 (m, 2H,), 7.33 (m, 2H), 6.58 (bs, 1H), 5.19 (bs, 2H), 3.71 (s, 3H), 2.83 (m, 2H), 2.75 (m, 2H), 1.52 (s, 9H).
