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Synthesis and radiolabeling of technetium radiopharmaceuticals based on N‐substituted iminodiacetic acid: Effect of radio‐labeling conditions on radiochemical purity
Author(s) -
Fields Anna T.,
Porter David W.,
Callery Patrick S.,
Harvey Elizabeth B.,
Loberg Michael D.
Publication year - 1978
Publication title -
journal of labelled compounds and radiopharmaceuticals
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.432
H-Index - 47
eISSN - 1099-1344
pISSN - 0362-4803
DOI - 10.1002/jlcr.2580150145
Subject(s) - chemistry , iminodiacetic acid , radiochemistry , technetium , technetium 99m , tritium , nuclear chemistry , nuclear medicine , chelation , organic chemistry , scintigraphy , medicine , physics , nuclear physics
Prerequisite to the development of technetium‐99m containing drug and biochemical analogs is the ability to synthesize radiochemically pure technetium chelates from mixtures of an appropriate chelating agent, pertechnetate, and various reducing agents. This paper reports the synthesis of a series of N‐substituted iminodiacetates (IDA) in which the pKa of the imino nitrogen was varied from 5.0 to 8.7. The chelating agents were labeled with Tc‐99m using the stannous reduction method at aqueous pH's of 4.0, 5.5 and 8.0 and in absolute methanol. The radiochemical purity of each chelate was examined by high pressure liquid chromatography, paper electrophoresis, paper chroma‐tography, and tissue distribution studies. Aqueous radiolabeling conditions resulted in pure technetium chelates only when the pKa of the imino nitrogen was approximately 6. Methanolic labeling conditions resulted in pure radiochemicals for all N‐substituted imino‐diacetic acids provided the imino nitrogen had a pKa of greater than 6. Under non‐aqueous conditions, however, the radiochemical purity deteriorated with time for all compounds in which the pKa of the imino nitrogen was greater than 7. These results indicate that only those IDA derivatives in which the in vivo nitrogen has a pKa of approximately 6 show a high degree of radiochemical purity when radiolabeled using stannous ion as the reducing agent.