Synthesis and evaluation of a new bifunctional chelating agent for 99mTc labeling proteins: p-carboxyethylphenylglyoxal-di(N-methylthiosemicarbazone)

A new bifunctional chelating agent, p-carboxyethylphenylglyoxal-di(N-methylthiosemicarbazone) (CE-DTS), containing a di(N-methylthiosemicarbazone) as the technetium coordinating site and an aralkyl carboxylate site for the protein conjugation was synthesized. Coupling to human serum albumin (HSA), selected as a model protein was carried out by the phosphorylazide method using diphenylphosphoryl azide (DPPA). The conjugation level of CE-DTS to HSA played a critical role in its biological evaluation. A ^99mTc-CE-DTS-HSA with high in vivo stability was obtained when CE-DTS was coupled to HSA at 1:1 molar ratio. This compound showed similar in vivo stability to ¹³¹I labeled HSA in mice and rabbits.