(4-dimethylamino-4-phenylcyclohexyl)acetic acid hydrochloride (298 mg, 1.0 mmol) in dry dimethylformamide under argon. The clear solution was cooled in an ice-bath and dicyclohexylcarbodiimide (417 mg, 2.0 mmol) was added. The reaction mixture was stirred at RT for 3 d and worked up by separating off the urea which had precipitated out and introducing the filtrate into a mixture of saturated NaCl solution (40 ml) and saturated NaHCO3 solution (10 ml). The mixture was diluted with water, 5 M sodium hydroxide solution (4 ml, 20 mmol) was added and the mixture was stored at 5° C. for 16 h. The crude product thereby precipitated out as a beige-coloured substance (400 mg). After purification by chromatography on silica gel with methanol, the product was obtained as a beige-coloured solid in a yield of 35% (144 mg) and with an m.p.
