Iminodiacetic Acid

Several investigators have synthesized bifunctional radiopharmaceuticals that contain both a drug or biochemical portion as well as a chelating group capable of strongly binding radioactive metals. This paper reports the development and testing of a new chelating group, iminodiacetic acid, for incorpora tion into drug and biochemical analogs. Sundberg et al (1) coupled the chelating group ethylenediamine tetraacetic acid (EDTA) to proteins and labeled these bifunctional macromolecules with “In.More recently this type of analog formation has been ex tended to smaller-molecule drugs and biochemicals with the reported synthesis, radiolabeling, and tissue distribution studies of bifunctional analogs of pal mitic acid (2) and tolbutamide (3). The analogs contained either DTPA, EDTA, or diethylene tn amine (DTA) , chelating agents known to bind 99mTc strongly but not particularly suited for incorpora tion into small molecules. We chose to evaluate the chelating agent iminodiacetic acid (IDA) because of its known chelating strength with transition metals (4,5) , its relatively small size, and the ease with which it can be synthetically incorporated into bi functional analogs. Its utility was tested using two new radiopharma ceuticals, DDmTc_methyliminodiacetic acid (99mTc