0.025 g of 1-hydroxybenzotriazole, 0.38 g of (S)-2-(2-methoxyphenyl)propionic acid and 0.32 cm3 of diisopropylethylamine are added to a suspension of 0.8 g of (3aS,4S,7aS)-7,7-diphenyl-4-(2-methoxyphenyl)perhydroisoindol-4-ol hydrochloride in 60 cm3 of dry dichloromethane, this solution is then cooled to +5° C. and a suspension of 0.43 g of 1-[3-(dimethylamino)propyl]-3-ethylcarbodiimide in 10 cm3 of dry dichloromethane is rapidly added. The reaction mixture is stirred for 2 hours at +5° C. and for 2 hours at room temperature, washed with 20 cm3 of water, then washed with 20 cm3 of a saturated aqueous sodium chloride solution (twice), dried over magnesium sulphate and concentrated to dryness under reduced pressure (2.7 kPa). The residue is chromatographed on a column of Merck silica gel (particle size 0.04-0.06 mm, diameter 2.8 cm, height 20 cm), eluting under a pressure of 0.5 bar of nitrogen with a mixture of cyclohexane and ethyl acetate (80/20 by volume) and collecting 25 cm3 fractions. Fractions 9 to 15 are combined and then concentrated to dryness under reduced pressure (2.7 kPa). The residue is crystallized from a mixture of acetonitrile and diisopropyl ether. There is obtained 0.17 g of (3aS,4S,7aS)-7,7-diphenyl-4-(2-methoxyphenyl)-2-[(S)-2-(2-methoxyphenyl)propionyl]perhydroisoindol-4-ol in the form of white crystals melting at 244° C.
