Preparation and characterization of two complexes of technetium with 2-mercaptocarboxylic acids

We have synthesized the tetraphenylarsonium salts of oxotechnetium(V)bis-(2-mercaptopropionate) and oxotechnetium(V)bis-(2-mercaptohexadecanoate) containing macromolar quantities of the long-lived isotope technetium-99. The compounds were investigated by elemental analysis, paper electrophoresis, and infrared and ultraviolet-visual spectroscopy, proton nuclear magnetic resonance, and field-desorption mass spectrometry. The findings suggest that the technetium atom is coordinated by two sulfur and three oxygen atoms in a square pyramid, the two sulfur atoms and two of the oxygen atoms forming the base and the third oxygen atom the apex. The carboxyl oxygen coordinated to technetium will not be available for binding in vivo. This factor should be considered in the design of technetium 99m-labeled radiopharmaceuticals containing a mercapto group alpha to a carboxyl group.