Radiochemical Characterization of Ga Labeled DOTA Derivatives

C-aryl derivatives of DOTA (N,N’,N”,N”’-tetrakis(carboxymethyl)1,4,7,10-tetraazacyclododecane) including phenyl-DOTA and 3-NO2Ph-DOTA were synthesized by a template reductive reaction. GaCl3 or GaCl3 was taken and transformed into Ga-acetylacetone (Ga(acac)3) before labeling to the DOTA derivatives. The Ga or Ga labeled complexes were generated by ligand-ligand exchange of acetylacetonate with the DOTA derivatives. The labeling efficiency of PhDOTA with Ga could be higher than 95% under the reaction being facilitated via sonication, at ambient temperature for 20 min. By a similar reaction, the labeling efficiency of 3-NO2-Ph-DOTA with Ga was found to be lower (~ 40%). The stability of Ga-Ph-DOTA was high, maintaining at ≥ 98% yield even at 24 h post-preparation. The Ga labeled Ph-DOTA complex was radiochemically characterized to be anionic and hydrophilic. It is anticipated from the result that Ga in the form of Ga(III) may be six coordinated with Ph-DOTA by 4N from the ring and 2O from two of four pendent acetic groups, leaving other two acetic groups uncoordinated.