Large-scale synthesis of the bifunctional chelating agent 2-(p-nitrobenzyl)-1,4,7,10-tetraazacyclododecane-N,N',N'',N'''-tetr aacetic acid, and the determination of its enantiomeric purity by chiral chromatography.

The attachment of radiometals to monoclonal antibodies for medical applications requires extreme stability under physiological conditions, with no significant release of metal. Chelators that can hold radiometals like 111In, 67Ga, and 90Y with high stability under these conditions are essential for radiotherapy or immunoscintigraphy. 2-(p-Nitrobenzyl)-1,4,7,10-tetraazacyclododecane- N,N',N'',N'''-tetraacetic acid (nitrobenzyl-DOTA) is one of the most promising bifunctional chelating agents. A large-scale synthesis of nitrobenzyl-DOTA is described. The overall yield for the nine-step synthesis sequence starting from nitrophenylalanine is 5.6%. Synthesis of nitrobenzyl-DOTA according to the new procedure yields up to approximately 10 g without special apparatus. Both enantiomers of the chiral chelate nitrobenzyl-DOTA have been prepared, and their enantiomeric purity has been checked by chiral chromatography.