Structural characterization of a bridged 99Tc-Sn-dimethylglyoxime complex: implications for the chemistry of 99mTc-radiopharmaceuticals prepared by the Sn (II) reduction of pertechnetate.

Abstract

Reduction of pertechnetate by tin(I) in the presence of dimethylglyoxime is shown, by single crystal x-ray analysis, to yield a technetium-tin-dimethylglyoxime complex in which tin and technetium are intimately connected by a triple bridging arrangement. One bridge consists of a single oxygen atom and it is hypothesized that this bridge arises from the inner sphere reduction of technetium by tin(II), the electrons being transferred through a technetium "yl" oxygen which eventually becomes the bridging atom. Two additional bridges arise from two dimethylglyoxime ligands that function as bidentate nitrogen donors towards Tc and monodentate oxygen donors towards Sn. The tin atom can thus be viewed as providing a three-pronged "cap" on one end of the Tc-dimethylglyoxime complex. The additional coordination sites around Tc are occupied by the two nitrogens of a third dimethylglyoxime ligand, making the Tc seven-coordinate. The additional coordination sites around Sn are occupied by three chloride anions, giving the Sn a fac octahedral coordination environment. From indirect evidence the oxidation states of tin and technetium are tentatively assigned to be IV and V, respectively. Since most 99mTc-radiopharmaceuticals are synthesized by the tin(I) reduction of pertechnetate, it is likely that the Sn-O-Tc linkage described in this work is an important feature of the chemistry of these species. This linkage also provides a ready rationale for the close association of tin and technetium observed in many 99mTc-radiopharmaceuticals. The practice of diagnostic nuclear medicine involves the use of noninvasive procedures in order to image various organs of the body (1-3). These procedures are based on the tendency of the body to concentrate some chemical form of a particular gamma-ray-emitting isotope in the organ of interest; subsequent scanning of the organ with a gamma-ray camera provides an image from which diagnostic information can be obtained (4-8). It is clear that the radioisotope with optimum nuclear properties for clinical gamma-ray scanning is 99mTc (1, 9, 10) and many imaging procedures based on this isotope are currently in use (3).All 99mTc-radiopharmaceuticals, except pertechnetate itself, are prepared via the reduction of 99mTc04- (pertechnetate) in the presence of a potential ligand, the reductant most commonly employed being an aqueous HCl solution of stannous chloride. We have recently reviewed the synthesis of 99mTc-radiopharmaceuticals by the reduction of pertechnetate (11) and it is clear that the chemistry of reduced technetium radiopharmaceuticals is only poorly understood. Several recent papers have indicated that the tin used to reduce pertechnetate not only can function as an electron donor but also may often be intimately associated with the product 99mTc-radiopharmaceutical. In three specific cases, i.e., 99mTc(Sn)-tetracycline (12), 99MTc(Sn)-ethane-l-hydroxy-1,1-diphosphonate (13), and 99mTc(Sn)-polyphosphate (14), double labeling with radioactive tin and technetium has established tha...

Structural characterization of a technetium-99-diphosphonate complex. Implications for the chemistry of technetium-99m skeletal imaging agents

“…The catalysts were prepared by reduction of Co2+ ions exchanged into Aand Y-type zeolites. 9 CoA zeolite has been reported to be a propylene hydroformylation catalyst,10 but its lack of shape selectivity, indicated by the n-to isobutyraldehyde product distribution, suggests that destruction of the alumino-silicate structure occurred, which, we infer, might have resulted from hightemperature reduction of Co2+ ions by reactant H2 inside the zeolite pores during catalysis.11 Therefore, to prevent "decationization"5 followed by destruction of the zeolite, we used metal vapors instead of hydrogen as the reducing agent. 12 The products of Cd-vapor reduction of CoA (designated Co°-CdA) and of CoY (designated Co°-CdY) were shown by X-ray diffraction to have maintained their zeolitic framework structures.…”

Technetium-99m Pharmaceuticals

“…Interest in the question, whether stannous or stannic tin could be involved in the radiopharmaceutical was further stimulated by the formation of a tincapped 99 Tc-dimethylglyoxime complex, 99 Tc(oxime) 3 (l-OH)SnCl 3 (Deutsch et al 1976). As outlined above, there is a high excess of tin ± as Sn(II) and Sn(IV) ± over technetium and this fact leads to the idea that mixed-metal complexes may be formed in radiopharmaceutical preparations.…”

Oxidative addition from a six-coordinate to an eight-coordinate complex. Single-crystal structures of dichlorobis[o-phenylenebis(dimethylarsine)]technetium perchlorate and tetrachlorobis[o-phenylenebis(dimethylarsine)]technetium hexafluorophosphate

“…Single crystals of orange [Tc(diars)2Cl2]C104 were grown from ethanol containing 10-4 M HCIO4 by slow cooling of a warm, saturated solution. These crystals belong to the monoclinic space group C2, Z = 2, with a = 13.001 (10), b = 10.409 (3), c= 11.796 (8) A; j8 = 114.49 (15)°; ¿ca|cd = 1.93, ¿obsd = 1.92 (2) g cm-3. The structure was solved by standard Patterson and Fourier methods using 1474 independent reflections [/ > 2 ( ), 2 < 54°, Mo Ka radiation] .…”