Trithiacyclononane as a ligand for potential technetium and rhenium radiopharmaceuticals: Synthesis of [M(9S3)(SC2H4SC2H4S)][BF4] (M=Tc-99, Re,Re-188) via C-S bond cleavage
Ged. Mullen et al., Trithiacyclononane as a ligand for potential technetium and rhenium radiopharmaceuticals: Synthesis of [M(9S3)(SC2H4SC2H4S)][BF4] (M=Tc-99, Re,Re-188) via C-S bond cleavage, INORG CHEM, 39(18), 2000, pp. 4093-4098
Chemical or electrochemical reduction of the 1,4,7-trithiacyclononane (9S3)
complexes [M-II(9S3)(2)][BF4](2) (M = Re (3a) or Tc (3b)) results in insta
ntaneous C-S bond cleavage to yield ethene and the stable M-III thiolate co
mplexes [M-III(9S3)L][BF4] (hl = Re (4a) or Tc (4b), L = SCH2CH2SCH2CH2S).
Compounds 4 have been characterized by H-1 NMR spectroscopy, and the pseudo
-octahedral geometry of 4b has been confirmed by X-ray crystallography. Upo
n electrochemical reduction 4a loses ethene, while 3b can be reversibly red
uced to [Tc-II(9S3)L], which is then further reduced to Tc(I) with loss of
ethene. Successive ethene loss is observed in the mass spectra of compounds
3 and 4. The radiosynthesis of 4a with Re-188 can be comfortably completed
within 10 min starting with (ReO4-)-Re-188 from a W-188/Re-188 generator,
with a radiochemical yield in excess of 90%. and thus represents a practica
l approach to the preparation of stable Re-188 (and Tc-99m) thioether co le
x derivatives/conjugates for clinical use. Crystal data: 4b, C10H20S6Tc, or
thorhombic Pbca, a = 12.233(2) b = 14.341(2) Angstrom, c = 20.726(3) Angstr
om, Z = 8.