740 mg (3.5 mmol) of EDC and 1.2 g (9.6 mmol) of 4-dimethylaminopyridine are added to a solution of 1 g (3.2 mmol) of 2-tert-butoxycarbonylamino-3-hydroxy-3-(4-methoxyphenyl)propanoic acid, 1.1 g (3.5 mmol) of 3-butoxy-3-o-tolylazetidine trifluoroacetate and 480 mg (3.5 mmol) of HOAT in 10 ml of dichloromethane cooled to 0° C. After stirring for 24 hours at ambient temperature, the reaction medium is treated with a 1N aqueous solution of sodium hydroxide and then extracted with ethyl acetate. The organic phase is washed successively with a 1N aqueous solution of hydrochloric acid and water, and then dried over magnesium sulphate, filtered and concentrated. The residue obtained is purified by silica gel chromatography (eluent: 60/40 heptane/ethyl acetate). 1.4 g of tert-butyl[1-(3-butoxy-3-o-tolylazetidine-1-carbonyl)-2-hydroxy-2-(4-methoxyphenyl)ethyl]carbamate are obtained in the form of a colourless oil with a yield of 87%.
