Labeling of proteins using [105Rh]Rh-4-(p-aminobenzyl)-diethylenetriamine

A bifunctional ligand 4-(p-aminobenzyl)-diethylenetriamine has been synthesized. 105Rh complexes with this ligand were prepared with an overall yield of 79% at pH 9.0 in bicarbonate buffer. The preformed complex was converted to the isothiocyanate derivative using thiophosgene. Conjugation yields of 75% with IgG and 85% with HSA could be obtained for a 4 h conjugation reaction. Affinity chromatography of human-IgG coupled to the rhodium complex in an anti-human IgG agarose gel indicated no denaturation of the labeled protein. The procedure reported here can be adapted for the preparation of 105Rh-labeled antibodies for therapeutic applications.