Rhenium and technetium-99m complexes with coenzyme M (MESNA)

New rhenium and technetium-99m complexes with the monodentate thiol HSCH2CH2SO3Na (coenzyme M, MESNA) have been prepared for radiopharmaceutical purposes. Using the ʹ3 + 1ʹ approach, the anionic rhenium complex [ReO(SCH2CH2SCH2CH2S) (SCH2CH2SO3)]- was prepared in two different ways: (1) reaction of MESNA with the complex [ReO(SCH2CH2SCH2CH2S)Cl]; and (2) reaction of the tridentate ligand S(CH2CH2SH)2 with the MESNA complex [ReO(SCH2CH2SO3Na)4]-. The structure of this ʹ3 + 1ʹ complex was determined by X-ray crystallographic studies, showing the characteristic {ReOS4} coordination around the metal atom. The sulfonate group of the coordinated MESNA is located far from the rhenium metal and near to the sodium cations. Chromatographic analysis of the reaction products after subsequent addition of MESNA and the tridentate ligand to the 99m-Tc gluconate precursor revealed the formation of a mixture of the ʹ3 + 1ʹ technetium complex [99mTcO(SCH2CH2SCH2CH2S)(SCH2CH2SO3)]- and the complex with the monothiol [99mTcO(SCH2CH2SO3Na)4]-. The limited solubility of the ʹ3 + 1ʹ rhenium complex in water may explain the high yield obtained in the rhenium synthesis compared with the lower yield observed in the same reaction with the homologous technetium99m complexes.