205 mg (1.1 mmol) of EDC and then 145 mg (1.1 mmol) of HOBt are added to a solution of 250 mg (0.9 mmol) of (R)-2-tert-butoxycarbonylamino-3-(4-hydroxyphenyl)-propanoic acid in 5 ml of dimethylformamide. After stirring for 15 minutes at ambient temperature, 300 mg (1.1 mmol) of 3-butoxy-3-o-tolylazetidine trifluoro-acetate (described in Example 15.5) and 0.5 ml (3.6 mmol) of triethylamine are added. The reaction medium is stirred for 2 h at ambient temperature and then a 1N aqueous solution of hydrochloric acid is added and the mixture is extracted with ethyl acetate. The organic phase is washed with water, and then dried over magnesium sulphate, filtered and evaporated. The residue is purified by silica gel chromatography, elution being carried out with a 60/40 heptane/ethyl acetate mixture. 410 mg of [2-(3-butoxy-3-o-tolyl-azetidin-1-yl)-1-(4-hydroxybenzyl)-2-oxoethyl]-3-(3H-imidazol-4-yl)propionamide are obtained with a yield of 90%.
