Under an inert atmosphere, p-aminobenzoic acid (10 g, 73 mmol) was dissolved in anhydrous N-methylpyrrolidone (NMP, 50 mL). Subsequently, a solution of anhydrous NMP (50 mL) of 9-fluorenylmethyl chloroformate (Fmoc-Cl, 18.9 g, 73 mmol) was slowly added dropwise. The reaction mixture was stirred at room temperature for 24 hours. Upon completion of the reaction, the mixture was slowly poured into 400 mL of water to precipitate the product. The colorless precipitate was collected by filtration and washed with plenty of water. Finally, the product was dried under vacuum at 120 °C to afford N-Fmoc-p-aminobenzoic acid (24.8 g, 94% yield). The melting point of the product was 215 °C (decomposition). Nuclear magnetic resonance hydrogen spectrum (1H-NMR, 300 MHz, DMSO-d6): δ 4.33 (t, J = 6.25 Hz, 1H), 4.54 (d, J = 6.25 Hz, 2H), 7.33-7.45 (m, 4H), 7.57 (d, J = 7.35 Hz, 2H), 7.76 (d, J = 7.35 Hz, 2H), and 7.89 (m, 4H), 10.08 (s, 1H), 12.69 (s, 1H). NMR carbon spectrum (13C-NMR and DEPT, 300 MHz, DMSO-d6): δ 46.61 (CH2), 65.83 (CH), 117.5 (CH), 120.22 (CH), 124.48 (C), 125.14 (CH), 127.17 (CH), 127.74 (CH), 130.48 ( CH), 140.86 (C), 143.31 (C), 143.74 (C), 153.31 (C), 167.03 (C). Infrared spectra (IR, ν, cm-1): 3344, 2970, 2887, 2660, 2544, 1709, 1673, 1610, 1592, 1526, 1511, 1411, 1311, 1282, 1221, 1052, 850, 736. reversed-phase high performance liquid chromatography (RP-HPLC) retention time: 26.6 Minutes. Mass spectrometry (FD-MS): m/z (%) = 359.1 (100), 360.1 (17.4); calculated value [C22H17NO4] = 359.1.
