To a suspension of 4,5-bis(phenylmethoxy)-2-pyridinecarboxylic acid (7.1 g, 21.17 mmol), hydroxybenzotriazole (0.29 g, 2.12 mmol) and N-aminopiperazine-2,3-dione (2.73 g, 21.17 mmol) in 140 ml of dry dimethylformamide was added, after 15 minutes of stirring, 4.80 g (23.3 mmol) of dicyclohexylcarbodiimide. After stirring for 21 hours at room temperature, dicyclohexylurea was filtered off (4.0 g ) and the solvent was evaporated in vacuo. The solid residue was triturated for 40 minutes with 240 ml of tetrahydrofuran, filtered, washed with tetrahyrofuran and dried in vacuo to yield 7.76 g of the title compound, melting point 231.1° C.
