102 mg (0.22 mmol) of ethyl ({4-[3-(4-fluorobenzyl)-4-methoxybenzyl]-3,5-dimethylphenyl}amino)(oxo)acetate (Example 3) in 5 ml of dichloromethane at −78° C. under argon are treated slowly with 65 mg (0.25 mmol) of BBr3. The reaction mixture is stirred overnight while reaching room temperature. It is again cooled to −78° C. and a further 65 mg (0.25 mmol) of BBr3 is added. The mixture is stirred at room temperature for 2 hours. Pouring into ice-water, stirring for 2 hours, extraction with dichloromethane and ethyl acetate and drying over sodium sulphate are followed by concentration in a rotary evaporator. The residue is stirred with ether and the solid is filtered off with suction. 51 mg (48%) of ({4-[3-(4-fluorobenzyl)-4-hydroxy-benzyl]-3,5-dimethylphenyl}amino)(oxo)acetic acid are obtained.
