2.77 g (11 mMol) of 3-ethoxy-4-ethoxycarbonyl-phenylacetic acid are added at ambient temperature to a solution of 2.71 g (11 mMol) of anhydrous (S)-3-methyl-1-(2-piperidino-phenyl)-1-butylamine (ee=98.5%) in 30 ml of absolute toluene and the mixture is stirred until dissolved. Then 2.38 g (11.55 mMol) of N,N'-dicyclohexyl-carbodiimide are added and the mixture is stirred at ambient temperature. After 24 hours a further 0.54 g (2.14 mMol) of 3-ethoxy-4-ethoxycarbonyl-phenylacetic acid and 0.48 g (2.33 mMol) of N,N'-dicyclohexylcarbodiimide are added and the mixture is stirred overnight. It is then cooled to an internal temperature of +5° C. and suction filtered to separate the precipitate, which is washed once with 5 ml of toluene. The combined toluene filtrates are evaporated down in vacuo to a volume of about 10 ml. The resulting solution is heated over the steam bath and petroleum ether is added in batches thereto (total of 55 ml) until the turbidity remains. It is cooled in ice, whereupon crystallisation takes place. It is suction filtered and dried at 75° C./4 torr. The product obtained (4.57 g; melting point 111-112° C.; ee=98.9%) is suspended in 50 ml of petroleum ether. The mixture is heated over the steam bath and sufficient toluene is added in batches (8 ml in total) until a solution is obtained. This is then cooled in ice and suction filtered to separate the crystals, which are dried at 75° C./4 torr.
