NORMAL GENOMIC

• Pietzsch HJ et al.
• Chemical and biological characterization of technetium(I) and Rhenium(I)tricarbonyl complexes with dithioether ligands serving as linkers forcoupling the Tc(CO)(3) and Re(CO)(3) moieties to biologically activemolecules.
• Bioconjug Chem. 2000; 11: 414-24
• Display abstract

• The organometallic precursor (NEt(4))(2)[ReBr(3)(CO)(3)] was reacted withbidendate dithioethers (L) of the general formula H(3)C-S-CH(2)CH(2)-S-R(R = -CH(2)CH(2)COOH, CH(2)-C&tbd1;CH) and R'-S-CH(2)CH(2)-S-R' (R' =CH(3)CH(2)-, CH(3)CH(2)-OH, and CH(2)COOH) in methanol to form stablerhenium(I) tricarbonyl complexes of the general composition[ReBr(CO)(3)L]. Under these conditions, the functional groups do notparticipate in the coordination. As a prototypic representative of thistype of Re compounds, the propargylic group bearing complex[ReBr(CO(3))(H(3)C-S-CH(2)CH(2)-S-CH(2)C&tbd1;CH)] Re2 was studied byX-ray diffraction analysis. Its molecular structure exhibits a slightlydistorted octahedron with facial coordination of the carbonyl ligands. Thepotentially tetradentate ligand HO-CH(2)CH(2)-S-CH(2)CH(2)-S-CH(2)CH(2)-OHwas reacted with the trinitrato precursor [Re(NO(3))(3)(CO)(3)](2-) toyield a cationic complex[Re(CO)(3)(HO-CH(2)CH(2)-S-CH(2)CH(2)-S-CH(2)CH(2)-OH)]NO(3) Re8 whichshows the coordination of one hydroxy group. Re8 has been characterized bycorrect elemental analysis, infrared spectroscopy, capillaryelectrophoresis, and X-ray diffraction analysis. Ligand exchange reactionof the carboxylic group bearing ligandsH(3)C-S-CH(2)CH(2)-S-CH(2)CH(2)-COOH andHOOC-CH(2)-S-CH(2)CH(2)-S-CH(2)-COOH with (NEt(4))(2)[ReBr(3)(CO)(3)] inwater and with equimolar amounts of NaOH led to complexes in which thebromide is replaced by the carboxylic group. The X-ray structure analysisof the complex [Re(CO)(3)(OOC-CH(2)-S-CH(2)CH(2)-S-CH(2)-COOH)] Re6 showsthe second carboxylic group noncoordinated offering an ideal site forfunctionalization or coupling a biomolecule. The no-carrier-addedpreparation of the analogous (99m)Tc(I) carbonyl thioether complexes couldbe performed using the precursor fac-[(99m)Tc(H(2)O)(3)(CO)(3)](+), withyields up to 90%. The behavior of the chlorine containing (99m)Tc complex[(99m)TcCl(CO)(3)(CH(3)CH(2)-S-CH(2)CH(2)-S-CH(2)CH(3))] Tc1 in aqueoussolution at physiological pH value was investigated. In saline, thechromatographically separated compound was stable for at least 120 min.However, in chloride-free aqueous solution, a water-coordinated cationicspecies Tc1a of the proposed composition[(99m)Tc(H(2)O)(CO)(3)(CH(3)CH(2)-S-CH(2)CH(2)-S-CH(2)CH(3))](+) occurred.The cationic charge of the conversion product was confirmed by capillaryelectrophoresis. By the introduction of a carboxylic group into thethioether ligand as a third donor group, the conversion could besuppressed and thus the neutrality of the complex preserved.Biodistribution studies in the rat demonstrated for the neutral complexes[(99m)TcCl(CO)(3)(CH(3)CH(2)-S-CH(2)CH(2)-S-CH(2)CH(3))] Tc1 and[(99m)TcCl(CO)(3)(CH(2)-S-CH(2)CH(2)-S-CH(2)-C&tbd1;CH)] Tc2 a significantinitial brain uptake (1.03 +/- 0.25% and 0.78 +/- 0.08% ID/organ at 5 min.p.i.). Challenge experiments with glutathione clearly indicated that notranschelation reaction occurs in vivo.