A convenient synthesis of bifunctional chelating agents based on diethylenetriaminepentaacetic acid and their coordination chemistry with yttrium(III)

The bifunctional chelating agents N,N,N',N',N'-pentakis(carboxymethyl)-1- (4-aminophenyl)methyl]-diethylenetriamine and N,N,N',N',N'-pentakis(carboxymethyl)-1-(4-aminophenyl)methyl]-4- methyldiethylenetriamine were prepared in six-step syntheses in overall yields of 38% and 31%, respectively. The use of bromoacetate esters in the synthesis allowed large-scale flash chromatographic purification of reaction products. The synthesis of N,N,N',N',N'-pentakis(carboxymethyl)-1- (4-aminophenyl)-methyl]-4-methyldiethylenetriamine resulted in a mixture of two diastereomers. Chelation of yttrium-(III) with these bifunctional chelating agents resulted in 1:1 chelates. In the case of N,N,N',N',N'-pentakis(carboxymethyl)-1-4- aminophenyl)methyl]diethylenetriamine, two diastereomers were observed upon chelation, as expected. In the case of N,N,N',N',N'- pentakis(carboxymethyl)-1-(4-aminophenyl)-methyl]-4- methyldiethylenetriamine, only three of the four anticipated diastereomers were observed.