Technetium-99m (99mTc; t1/2 = 6.01 h, γ= 140 keV) is one of the most widely used imaging radionuclides due to the wide availability of 99Mo/99mTc generators. Two rhenium radioisotopes, 186Re (t1/2= 88.8 h, β- = 1.070 MeV) and 188Re (t1/2= 17.0 h, β- = 2.120 MeV) have nuclear properties suitable for radiotherapeutic applications. 186Re can be produced in high specific activity in cyclotrons or in low specific activity in nuclear reactors. 188Re is available from 188W/188Re generators. Due to rhenium’s chemical similarity to technetium, they have been proposed as theranostic radioisotope pairs with 99mTc. The tricarbonyl core of rhenium(I) and technetium(I) is compact and highly stable, making it of high interest for use in potential radiopharmaceuticals. The low-spin d6 configuration of Tc(I)/Re(I) makes their complexes kinetically inert to substitution when paired with tridentate chelators. Because of this, many complexes of the form fac-[M(CO)3L] (M=Re, Tc) are known. An advantage of the M(I) tricarbonyl core is that the triaqua complexes, fac-[M(CO)3(OH2)3]+ (M=Re, Tc), can be quickly and easily synthesized by the facile substitution for the three waters. Trithiol chelating ligands are being investigated as the basis of potential bifunctional chelating agents for the tricarbonyl core with rhenium at the macroscopic scale and 99mTc at the radiotracer level. A model trithiol chelator, namely 2,2-bis(mercaptomethyl)-propane-1-thiol, was used to investigate this. Trinuclear complexes were observed at the macroscopic level with Re and potentially at the radiotracer level with 99mTc. Formation of multinuclear complexes at the radiotracer scale is assumed to be kinetically unfavorable due to the very low concentrations involved, however Alberto recently reported on multinuclear 99mTc complexes with monothiols. This suggests that the trithiol ligand reported here may have formed a trinuclear complex analogous to the fully characterized Re complex. The higher number of radiometals per molecule may make the analogous 186,188Re complexes suited for use for therapy because they could deliver a higher dose of radiation per molecule than mononuclear complexes.

Multinuclear Re and 99mTc tricarbonyl trithiol complexes

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.