59 g (127.8 mmol) of methyl 5-[(N-methyl-N-butylamino)carbonyl]-2,4-bisbenzyloxybenzoate are dissolved in 200 ml of THF and added to a solution of 100 g (4.2 mol) of lithium hydroxide in 300 ml of water and 150 ml of methanol. The mixture is stirred for 12 h at 22° C., diluted with 250 ml of diethyl ether and acidified using 1N hydrochloric acid. The organic phase is separated off and washed a further three times with 100 ml of N hydrochloric acid each time, dried over sodium sulfate and evaporated. The crude product obtained in this way (80 g) is crystallised from ethyl acetate: 33 g (57.7%) of 5-[(N-methyl-N-butylamino)carbonyl]-2,4-bisbenzyloxybenzoic acid (white crystals); MW 447.5;
