Dithiocarbamate complexes as radiopharmaceuticals for medical imaging

Ts2O mediated deoxygenative C2-dithiocarbamation of quinoline N-oxides with CS2 and amines

A general, efficient and practical protocol for Ts2O promoted deoxygenative dithiocarbamation of quinoline N-oxides with in situ generated dithiocarbamic acids from CS2 and amines is reported. The reaction proceeded well under transition-metal free conditions to obtain a variety of novel quinoline-dithiocarbamate compounds with wide functional group tolerance and good to high yields.

Synthesis, characterization and in vitro cytotoxicity of gallium(III)-dithiocarbamate complexes

A library of homoleptic mononuclear Ga(III) complexes of the general formula [Ga(DTC)3], where DTC is an alicyclic or a linear dithiocarbamate chelator, is reported. The complexes were prepared in high yields starting from Ga(NO3)3·6H2O and fully characterized by elemental analysis and IR and NMR spectroscopy. Crystals of five of these complexes were obtained. The antitumor activity of the newly synthesized compounds against a panel of human cancer cell lines was evaluated. The chemical nature of the DTC does not have a marked impact on the structural features of the final compound. X-ray crystal structure analyses revealed that all these complexes have a trigonal prismatic geometry with three identical chelating DTCs coordinating the Ga(III) ion. It is noteworthy that in complex 22, [Ga(NHEt)3] (NHEt = N-ethyldithiocarbamate), the asymmetric unit is formed by two independent and structurally different molecules. Cellular studies showed that all the synthesized Ga-DTC complexes exhibit marked cytotoxic activity, even against human colon cancer cells that are less sensitive to cisplatin. Among the tested compounds, 6 ([Ga(CEPipDTC)3], CEPipDTC = (ethoxycarbonyl)-piperidinedithiocarbamate) and 21 ([Ga(Pr-13)3], PR13 = 4 and N-(2-ethoxy-2-oxoethyl)-N-methyldithiocarbamate) are very promising derivatives, but they have no selectivity towards cancer cells. Nevertheless, the obtained data provide a foundation for developing gallium-dithiocarbamate complexes as anticancer agents.

Synthesis of carbon-11 radiolabelled transition metal complexes using 11C-dithiocarbamates

A novel radiolabelling method exploiting ¹¹C-dithiocarbamate ligands has been used to generate ¹¹C-labelled Au(I), Au(III), Pd(II) and Pt(II) complexes in high radiochemical yields (71-99%). Labelled complexes were prepared in a rapid one-pot procedure via the substitution reaction of ¹¹C-dithiocarbamate ligands with appropriate transition metal chloride precursors.

The Versatility in the Applications of Dithiocarbamates

Dithiocarbamate ligands have the ability to form stable complexes with transition metals, and this chelating ability has been utilized in numerous applications. The complexes have also been used to synthesize other useful compounds. Here, the up-to-date applications of dithiocarbamate ligands and complexes are extensively discussed. Some of these are their use as enzyme inhibitor and treatment of HIV and other diseases. The application as anticancer, antimicrobial, medical imaging and anti-inflammatory agents is examined. Moreover, the application in the industry as vulcanization accelerator, froth flotation collector, antifouling, coatings, lubricant additives and sensors is discussed. The various ways in which they have been employed in synthesis of other compounds are highlighted. Finally, the agricultural uses and remediation of heavy metals via dithiocarbamate compounds are comprehensively discussed.

Synthesis and evaluation of new mixed "2 + 1" Re, 99mTc and 186Re tricarbonyl dithiocarbamate complexes with different monodentate ligands

A series of "2 + 1" mixed ligand tricarbonyl complexes of the general formula fac-[Re/^99mTc/¹⁸⁶Re(CO)₃(DDTC)(L)] containing diethyldithiocarbamate (DDTC) as a monoanionic bidentate ligand and a series of monodentate ligands L was synthesized, characterized and evaluated. The impact of ligand L on the radiochemical yield (RCY) and biodistribution of the final compounds was also investigated. DDTC and the appropriate L ligand [cyclohexyl isocyanide (cisc), tert-butyl isocyanide (tbi), triphenylphosphine (PPh₃), methyldiphenylphosphine (PPh₂Me), triphenylarsine (AsPh₃), imidazole (im), and 4-aminopyridine (4AP)] readily reacted in equimolar amounts with the [Et₄N]₂[Re(CO)₃Br₃] precursor to afford fac-[Re(CO)₃(DDTC)(cisc)], Re1, fac-[Re(CO)₃(DDTC)(tbi)], Re2, fac-[Re(CO)₃(DDTC)(PPh₃)], Re3, fac-[Re(CO)₃(DDTC)(PPh₂Me)], Re4, fac-[Re(CO)₃(DDTC)(AsPh₃)], Re5, fac-[Re(CO)₃(DDTC)(im)], Re6 and fac-[Re(CO)₃(DDTC)(4AP)], Re7, complexes in high yields (>80%). All Re complexes were fully characterized by IR, NMR, and in addition Re4, Re5, and Re7 with X-ray crystallography. Analogous reactions as performed with Re were subsequently explored on the ^99mTc and ¹⁸⁶Re-tracer levels using the corresponding fac-[^99mTc/¹⁸⁶Re(CO)₃(H₂O)₃]⁺ precursor. Complexes ^99mTc1 - ^99mTc5, ¹⁸⁶Re1 and ¹⁸⁶Re3 were obtained in high radiochemical yield (>91%), while the complexes ^99mTc6, ^99mTc7 and ¹⁸⁶Re7 formed with radiochemical yields of 55%, 28%, and 75%, respectively. The ^99mTc and ¹⁸⁶Re-complexes were characterized by comparative HPLC analysis using the analogous Re complexes. During histidine and cysteine challenge experiments at 37 °C through 6 h, complexes ^99mTc1 - ^99mTc5 remained > 92% stable, while complexes ^99mTc6 and ^99mTc7 remained only 8% stable through 3 h. Similar studies for ¹⁸⁶Re-complexes showed that ¹⁸⁶Re1 and ¹⁸⁶Re3 remained > 95% stable for up to 48 h, while ¹⁸⁶Re7 had decreased to 7% after 3 h. LogD_7.4 data of ^99mTc1 - ^99mTc5, ¹⁸⁶Re1, and ¹⁸⁶Re3 complexes, which ranged from 2.59 to 3.39, suggested high lipophilicity. Biodistribution studies in healthy Swiss albino mice showed hepatobiliary excretion for ^99mTc1, ^99mTc2, and ^99mTc4, fast blood clearance for ^99mTc4, while high liver uptake and retention for ^99mTc3 and ^99mTc5 were measured. Moreover, ^99mTc2 showed high accumulation in the lungs with sustained retention (52.80% ID/g at 4 h p.i.) and significant brain uptake at 2 min p.i. (1.89% ID/g). The study showed the great influence of monodentate ligand in the synthesis and biodistribution of the mixed ligand complexes.

Production of copper-64 using a hospital cyclotron: targetry, purification and quality analysis

OBJECTIVES

To construct and evaluate a 64Cu production system that minimises the amount of costly 64Ni, radionuclidic impurities and nonradioactive metal contamination and maximises radiochemical and radionuclidic purity and molar activity; and to report analytical and quality control methods that can be used within typical PET radiochemistry production facilities to measure metal ion concentrations and radiometal molar activities.

METHODS

Low volume was ensured by dissolving the irradiated nickel in a low volume of hydrochloric acid (<1 mL) using the concave gold target backing as a reaction vessel in a custom-built target holder. Removal of contaminating 55Co and nonradioactive trace metals was ensured by adding an intermediate hydrochloric acid concentration step during the conventional ion-exchange elution process. The radionuclidic purity of the product was determined by half-life measurements, gamma spectroscopy and ion radiochromatography. Trace metal contamination and molar activity were determined by ion chromatography.

RESULTS AND CONCLUSIONS

On a small scale, suitable for preclinical research, the process produced typically 3.2 GBq 64Cu in 2 mL solution from 9.4 ± 2.1 mg nickel-64 electroplated onto a gold target backing. The product had high molar activity (121.5 GBq/µmol), was free of trace metal contamination detectable by ion chromatography and has been used for many preclinical and clinical PET imaging applications.

Regioselective C-H dithiocarbamation of indolizines with tetraalkylthiuram disulfide under metal-free conditions

An efficient and straightforward metal-free regioselective C-H dithiocarbamation of indolizines with tetraalkylthiuram disulfide has been described. A series of indolizine-dithiocarbamate derivatives were easily accessed in moderate to good yields with a broad scope. In addition, imidazo[1,2-a]pyridines were also well tolerated to afford diverse imidazoheterocycle-dithiocarbamate products, which are expected to be utilized for drug discovery. Of note, the reaction could be readily scaled up, and shows its practical value in organic synthesis.

Selective C-H dithiocarbamation of arenes and antifungal activity evaluation

This paper discloses a transition metal-free selective C-H dithiocarbamation of drug skeletons using disulfiram (DSF) in the presence of KI/K2S2O8 in DMF/H2O. Drug skeletons, including 5-aminopyrazoles, indoles, pyrroloquinoline, and Julolidine, underwent C-H dithiocarbamation smoothly to afford a variety of drug-like molecules in moderate to good yields. It was found that the in situ formed 5-aminopyrazole iodide is the key intermediate for the dithiocarbamation. Bioassay results show that some of these N-heterocyclic dithiocarbamate derivatives exhibit good antifungal activity against Colletotrichum gloeosprioides and Fusarium oxysporum, F. proliferatum, Fusarium solani, Geotrichum candidum, Penicillium digitatum, Penicillium italicum, Phyricularia grisea.

CuII and AuIII Complexes with Glycoconjugated Dithiocarbamato Ligands for Potential Applications in Targeted Chemotherapy

This work is focused on the synthesis, characterization, and preliminary biological evaluation of bio-conjugated Au^III and Cu^II complexes with the aim of overcoming the well-known side effects of chemotherapy by improving the selective accumulation of an anticancer metal payload in malignant cells. For this purpose, carbohydrates were chosen as targeting agents, exploiting the Warburg effect that accounts for the overexpression of glucose-transporter proteins (in particular GLUTs) in the phospholipid bilayer of most neoplastic cells. We linked the dithiocarbamato moiety to the C1 position of three different monosaccharides: d-glucose, d-galactose, and d-mannose. Altogether, six complexes with a 1:2 metal-to-ligand stoichiometry were synthesized and in vitro tested as anticancer agents. One of them showed high cytotoxic activity toward the HCT116 colorectal human carcinoma cell line, paving the way to future in vivo studies aimed at evaluating the role of carbohydrates in the selective delivery of whole molecules into cancerous cells.

Technetium-99m labeled Ibuprofen: Development and biological evaluation using sterile inflammation induced animal models

In this study we are presenting the development of technetium-99m (^99mTc) labeled ibuprofen for the imaging of aseptic inflammation. ^99mTc-Ibuprofen complex was developed by optimizing the radiolabeling conditions such as reaction time, ligand and reducing agent concentration, pH, reaction time and temperature. Following the addition of 600 µg of ibuprofen, 4 µg of stannous chloride as reducing agent and 300 MBq ^99mTc radioactivity; the pH of reaction mixture was adjusted to 11 and allowed to react for 15 min at room temperature. Chromatography analysis revealed > 94% ^99mTc-ibuprofen complex formation with promising stability in saline and blood serum up to 6 h. Biodistribution study using normal and sterile inflammation induced mice indicated low accumulation of labeled compound in key body organs; however, kidneys (14.76 ± 0.87% ID/g organ) and bladder (31.6 ± 3.0% ID/g organ) showed comparatively higher radioactivity due to main excretory path. Inflamed to normal tissues ratio (T/NT), at 1 h post-injection, showed promising value (4.57 ± 0.56). The SPECT imaging of artificially inflammation induced rabbit model also verified the biodistribution results. In conclusion, radiochemical purity and biological evaluation of ^99mTc-ibuprofen complex indicates the agent can be utilized for imaging of deep seated aseptic inflammation.

Improved synthesis on solid phase of dithiocarbamic cRGD-derivative and 99m Tc-radiolabelling

In the field of angiogenesis, small cyclic pentapeptides containing the RGD motif are playing a relevant role for their high affinity and specificity for integrin receptors and for the possibility to act at both therapeutic and diagnostic level by inhibiting pathological angiogenesis and by serving as shuttles to deliver imaging-probe including SPECT/PET radionuclides to specific tissues. In the last decade, several new protocols were reported in literature for the direct synthesis of cyclic RDG either in solution or by SPPS. Here, we have elaborated and tested some alternative approaches using different resins and different protective groups. The introduction of the dithiocarbamate function, useful to complex radio-metals suitable for nuclear medicine applications, has also been considered and achieved.

Direct thiocarbamation of imidazoheterocycles via dual C–H sulfurization

Direct thiocarbamation via dual C–H sulfurization.

Crystal structure of bis(μ2-di-n-butyldithiocarbamato-κ3 S,S′:S;κ3 S:S:S′)-hexacarbonyl-di-rhenium(I), C24H36N2O6Re2

C24H36N2O6Re2, triclinic, P1̅ (no. 2), a = 10.3013(2) Å, b = 11.3471(2) Å, c = 14.5967(3) Å, α = 72.540(2)°, β = 73.074(2)°, γ = 85.369(2)°, V = 1557.05(6) Å3, Z = 2, R gt(F) = 0.0214, wR ref(F 2) = 0.0466, T = 100(2) K.

fac-Aceto-nitrile-tricarbon-yl(di-methyl-carbamodi-thio-ato-κ2S,S')rhenium(I): crystal structure and Hirshfeld surface analysis

The title compound, [Re(C3H6NS2)(C2H3N)(CO)3], features an octa-hedrally coordinated ReI atom within a C3NS2 donor set defined by three carbonyl ligands in a facial arrangement, an aceto-nitrile N atom and two S atoms derived from a symmetrically coordinating di-thio-carbamate ligand. In the crystal, di-thio-carbamate-methyl-H⋯O(carbon-yl) inter-actions lead to supra-molecular chains along [36-1]; both di-thio-carbamate S atoms participate in intra-molecular methyl-H⋯S inter-actions. Further but weaker aceto-nitrile-C-H⋯O(carbonyl) inter-actions assemble mol-ecules in the ab plane. The nature of the supra-molecular assembly was also probed by a Hirshfeld surface analysis. Despite their weak nature, the C-H⋯O contacts are predominant on the Hirshfeld surface and, indeed, on those of related [Re(CO)3(C3H6NS2)L] structures.

Four-Component Reaction for the Synthesis of Dithiocarbamates Starting from Cyclic Imines

An efficient one-pot, four-component reaction for the synthesis of dithiocarbamates using carbon disulfide, cyclic imines, acid chlorides, and commercially available primary or secondary amines has been developed by performing an acid chloride addition to a heterocyclic imine followed by subsequent nucleophilic substitution of in situ generated dithiocarbamic acid. With the aid of the newly developed and powerful multicomponent reaction, a direct route for the synthesis of 24 unknown dithiocarbamates in moderate to good yield under mild conditions is enabled.

Opportunities and challenges for metal chemistry in molecular imaging: from gamma camera imaging to PET and multimodality imaging

The development of medical imaging is a highly multidisciplinary endeavor requiring the close cooperation of clinicians, physicists, engineers, biologists and chemists to identify capabilities, conceive challenges and solutions and apply them in the clinic. The chemistry described in this article illustrates how synergistic advances in these areas drive the technology and its applications forward, with each discipline producing innovations that in turn drive innovations in the others. The main thread running through the article is the shift from single photon radionuclide imaging towards PET, and in turn the emerging shift from PET/CT towards PET/MRI and further, combination of these with optical imaging. Chemistry to support these transitions is exemplified by building on a summary of the status quo, and recent developments, in technetium-99m chemistry for SPECT imaging, followed by a report of recent developments to support clinical application of short lived (Ga-68) and long-lived (Zr-89) positron emitting isotopes, copper isotopes for PET imaging, and combined modality imaging agents based on radiolabelled iron oxide based nanoparticles.

A nuclear chocolate box: the periodic table of nuclear medicine

Radioisotopes of elements from all parts of the periodic table find both clinical and research applications in radionuclide molecular imaging and therapy (nuclear medicine). This article provides an overview of these applications in relation to both the radiological properties of the radionuclides and the chemical properties of the elements, indicating past successes, current applications and future opportunities and challenges for inorganic chemistry.

Technetium-99m and rhenium-188 complexes with one and two pendant bisphosphonate groups for imaging arterial calcification

The first (99m)Tc and (188)Re complexes containing two pendant bisphosphonate groups have been synthesised, based on the mononuclear M(v) nitride core with two dithiocarbamate ligands each with a pendant bisphosphonate. The structural identity of the (99)Tc and stable rhenium analogues as uncharged, mononuclear nitridobis(dithiocarbamate) complexes was determined by electrospray mass spectrometry. The (99m)Tc complex showed greater affinity for synthetic and biological hydroxyapatite, and greater stability in biological media, than the well-known but poorly-characterised and inhomogeneous bone imaging agent (99m)Tc-MDP. It gave excellent SPECT images of both bone calcification (mice and rats) and vascular calcification (rat model), but the improved stability and the availability of two pendant bisphosphonate groups conferred no dramatic advantage in imaging over the conventional (99m)Tc-MDP agent in which the bisphosphonate group is bound directly to Tc. The (188)Re complex also showed preferential uptake in bone. These tracers and the biological model of vascular calcification offer the opportunity to study the biological interpretation and clinical potential of radionuclide imaging of vascular calcification and to deliver radionuclide therapy to bone metastases.

Chelators for copper radionuclides in positron emission tomography radiopharmaceuticals

The development of chelating agents for copper radionuclides in positron emission tomography radiopharmaceuticals has been a highly active and important area of study in recent years. The rapid evolution of chelators has resulted in highly specific copper chelators that can be readily conjugated to biomolecules and efficiently radiolabeled to form stable complexes in vivo. Chelators are not only designed for conjugation to monovalent biomolecules but also for incorporation into multivalent targeting ligands such as theranostic nanoparticles. These advancements have strengthened the role of copper radionuclides in the fields of nuclear medicine and molecular imaging. This review emphasizes developments of new copper chelators that have most greatly advanced the field of copper-based radiopharmaceuticals over the past 5 years.