A mixture that consists of 54.1 g (100 mmol) of 2,3,4,6-tetra-O-benzyl-mannopyranose, 1.39 g (5 mmol) of tetrabutylammonium chloride in 350 ml of toluene and 150 ml of 50% aqueous potassium hydroxide solution is cooled to 0° C. At 0° C., 30.12 g (200 mmol) of chloroacetic acid-tert-butyl ester is added in drops over 20 minutes while being stirred vigorously. It is stirred for one hour at 10° C. 250 ml of methyl-tert-butyl ether is added, the organic phase is separated, and the aqueous phase is extracted twice with 250 ml of water. The solvent of the combined organic phases is distilled off in a vacuum, and the residue is taken up in 500 ml of ethanol. 40 ml of 50% aqueous sodium hydroxide solution is added, and it is refluxed for 0.5 hour. It is cooled to 0° C., set at pH 8 with 10% aqueous hydrochloric acid, and then the solvent is distilled off (vacuum). The residue is shaken up in 300 ml of water and 500 ml of ethyl acetate, and the pH of the aqueous phase is set at 2 while being stirred (10% aqueous hydrochloric acid). The organic phase is separated, and the aqueous phase is extracted once more with 200 ml of ethyl acetate. The combined organic phases are dried on magnesium sulfate, the solvent is distilled off in a vacuum, and the residue is chromatographed on silica gel (mobile solvent: dichloromethane/n=hexane/ethanol/acetic acid=20:5:3:0.5). The product-containing fractions are concentrated by evaporation, dissolved in 400 ml of ethyl acetate and shaken out three times with 200 ml of water. Then, the organic phase is separated and evaporated to the dry state in a vacuum.
