Synthesis, structural characterization and radiochemistry of “2 + 1” fac-[99mTc/Re(CO)3(L)(2-mercaptopyridine)] complexes, where L is phosphine or isocyanide

This work focuses on the development of “2 + 1” technetium and rhenium carbonyl complexes of the formula fac-[99mTc/Re(CO)3(L)(Spy)], where HSpy is 2-mercaptopyridine and acts as (NS) bidentate ligand and L is either triphenylphosphine (PPh3) or benzyl isocyanide (BnNC). Reaction of 2-mercaptopyridine with the precursors fac-(NEt4)2[Re(CO)3Br3] or [Re(CO)5Br] yields the dimeric complex fac-[Re(CO)3(Spy)]2, Re1. Re1 readily reacts with the monodentate ligand to yield the respective “2 + 1” fac-[Re(CO)3(PPh3/BnNC)(Spy)] complexes Re2/Re4. Re2 was also obtained in a single step reaction of the precursor fac-(NEt4)2[Re(CO)3Br3] with the mixture of ligands in equimolar amounts. Furthermore, the rhenium dicarbonyl complex cis, trans-[Re(CO)2(PPh3)2(Spy)] complex Re3 was synthesized by reaction of HSpy with the precursor mer, trans-[Re(CO)3(PPh3)2Cl]. All rhenium complexes were characterized by IR, NMR, elemental analysis and furthermore the structure of Re1, Re2, Re3 was solved by X-ray crystallography. At the 99mTc tracer level, the “2 + 1” complex fac-[99mTc(CO)3(PPh3)(Spy)], 99mTc2, was obtained in high radiochemical yield and low ligand concentrations and the complex was very stable in histidine and cysteine in challenge experiments.

Graphical abstractSynthesis and X-ray study of carbonyl rhenium complexes with 2-mercaptopyridine fac-[Re(CO)3(Spy)]2, fac-[Re(CO)3(PPh3/BnNC)(Spy)] and cis, trans-[Re(CO)2(PPh3)2(Spy)]. Investigation of conditions to prepare “2 + 1” fac-[99mTc(CO)3(PPh3/BnNC)(Spy)] as lead structures for 99mTc radiopharmaceuticals.Figure optionsDownload full-size imageDownload as PowerPoint slide