Acetylation of ursolic acid (5.00 g, 10.96 mmol) with acetic anhydride (2.60 mL, 26.00 mmol) in pyridine (80 mL) was carried out by adding triethylamine (3.00 mL, 21.68 mmol) and a catalytic amount of DMAP for a 12 h reaction at 25°C. The reaction was carried out by aqueous post-treatment. Upon completion of the reaction, an aqueous post-treatment and purification by silica gel column chromatography (SiO2, eluent: hexane/ethyl acetate, 8:2) afforded the target compound 14 (5.30 g, 97% yield) as a colorless solid. Thin layer chromatography (TLC) showed Rf = 0.71 (SiO2, eluent: hexane/ethyl acetate, 7:3). The melting point of the compound is 235-238°C (literature value:[8] 242-244°C). Specific optical rotation [α]D = +64.89° (c = 0.86, CHCl3) (literature value:[8] [α]D = +71.2° (c = 1.0, CHCl3)). Mass spectra (ESI, MeOH) showed m/z = 499.1 (15%, [M + H]+), 521.3 (30%, [M + Na]+), 1019.3 (100%, [2M + Na]+).
