To a solution of thiosalicylic acid (500 mg) in ethanol (15 ml) and 2N sodium hydroxide aqueous solution (3.2 ml) was added 3-(9-fluorenylmethoxycarbonylamino)-propyl bromide at ambient temperature and the suspension was stirred for 2 hours. The resulting clear solution was diluted with water (20 ml) and acidified with 1N hydrochloric acid (6.5 ml). White crystals were collected by filtration and the solid was washed with ethanol-water (1:3, 15 ml) and then with n-hexane - diethyl and either (2:1, 15 ml) to give 2-[3-(9-fluorenylmethoxycarbonylamino)-propylthio]benzoic acid (1.07 g).
