Pyridine → N3-(2,6-Dioxomorpholinoethyl)-N6-(ethoxycarbonylmethyl)-3,6-diazaoctanedioic Acid

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Reaction Steps

A suspension of 21.1 g (50 mmol) of N3,N6-bis-(carboxymethyl)-N9-(ethoxy-carbonylmethyl)-3,6,9-triazaundecanedioic acid in 250 ml of acetic anhydride is allowed to stir for three days at room temperature after the addition of 42.2 ml of pyridine. Then, the precipitate is suctioned off, washed three times with 50 ml of acetic anhydride each and then stirred for several hours with absolute diethyl ether. After suctioning off, washing with absolute diethyl ether and drying in a vacuum at 40° C., 18.0 g (=89% of theory) of a white powder with a melting point of 195-196° C. is obtained.

Provenance & Evidence