3-(4-Hydroxyphenyl)propionic acid → 3-(4-Hydroxy-phenyl)-2-[3-(4-hydroxy-phenyl)-propionylamino]-propionic acid methyl ester

A solution of 3(4-hydroxy phenyl) propionic acid (10 grams, 60.17 mmol) and Example 1 (11.7 grams, 60.00 mmol) in anhydrous dichloro methane (100 mL) under a nitrogen atmosphere at 0° C. is added dropwise to a solution of 1,3-dicyclohexyl carbodiimide(31 grams, 150.24 mmol) in dichloro methane (75 mL). The mixture is stirred at room temperature for 6 hours. The resulting solids are filtered off. The organic phase is washed with 5% sodium bicarbonate (2×25 mL) and water (2×25 mL), dried over sodium sulphate, and distilled to give crude 23, which can be purified in appropriate solvent.