Bernhard Spingler

Click-to-Chelate : Design and Incorporation of Triazole-Containing Metal-Chelating Systems into Biomolecules of Diagnostic and Therapeutic Interest

The site-specific conjugation of metal chelating systems to biologically relevant molecules is an important contemporary topic in bioinorganic and bioorganometallic chemistry. In this work, we have used the CuI-catalyzed cycloaddition of azides and terminal alkynes to synthesise novel ligand systems, in which the 1,2,3-triazole is an integral part of the metal chelating system. A diverse set of bidentate alkyne building blocks with different aliphatic and aromatic backbones and various donor groups were prepared. The bidentate alkynes were reacted with benzyl azide in the presence of a catalytic amount of CuI to form tridentate model ligands. The chelators were reacted with [ReBr3(CO)3]2- to form well-defined and stable complexes with different overall charges, structures and hydrophilicities. In all cases tridentate coordination of the ligands, including through N3 of the 1,2,3-triazole ring, was observed. The ligand systems could also be quantitatively radiolabelled with the precursor [99 mTc (H2O)3(CO)3]+ at low ligand concentrations. Similarly the alkynes were reacted with an azido thymidine derivative to form a series of compounds, which could be radiolabelled in situ to form single products. Subsequent incubation of the neutral and cationic organometallic 99 mTc thymidine derivatives with human cytosolic thymidine kinase, a key enzyme in tumour proliferation, revealed that only the neutral compounds maintained substrate activity towards the enzyme. Bioconjugation, radiolabelling and enzymatic reactions were successfully performed in a matter of hours. Thus, click chemistry provides an elegant method for rapidly functionalising a biologically relevant molecule with a variety of efficient metal chelators suitable for (radio)labelling with the M(CO)3 core (M=99 mTc, Re), to offer new potential for technetium-99 m in clinical and preclinical tracer development.

Visible-Light-Induced Annihilation of Tumor Cells with Platinum–Porphyrin Conjugates†

Despite the extensive use of porphyrins in photodynamic therapy (PDT), tetraplatinated porphyrins have so far not been studied for their anticancer properties. Herein, we report the synthesis of such novel platinum-porphyrin conjugates as well as their photophysical characterization and in vitro light-induced anticancer properties. These conjugates showed only minor cytotoxicity in the dark, but IC50 values down to 19 nM upon irradiation with light at 420 nm.These values correspond to an excellent phototoxic index (PI=IC50 in the dark/IC50 in light), which reached 5000 in a cisplatin-resistant cell line. After incubation with HeLa cells, nuclear Pt concentrations were 30 times higher than with cisplatin. All of these favorable characteristics imply that tetraplatinated porphyrin complexes are worthy of exploration as novel PDT anticancer agents in vivo.

[(Cp-R)M(CO)3] (M=Re or 99mTc) Arylsulfonamide, Arylsulfamide, and Arylsulfamate Conjugates for Selective Targeting of Human Carbonic Anhydrase IX†

Enhanced receptor selectivity: carbonic anhydrase inhibitors are relevant for both cancer diagnosis and therapy. Combining non-radioactive Re compounds with their radioactive (99m)Tc homologs enables the use of identical molecules for therapy and imaging (theragnostic). The syntheses and in vitro evaluation of [(Cp-R)M(CO)(3)] (Cp=cyclopentadienyl, M=Re, (99m)Tc) with R being a highly potent carbonic-anhydrase-targeting vector is reported.

DMSO‐Mediated Ligand Dissociation: Renaissance for Biological Activity of N‐Heterocyclic‐[Ru(η6‐arene)Cl2] Drug Candidates

Slipped under the radar? (1) H NMR spectroscopic examination revealed that [Ru(η(6) -arene)Cl2 (L)] (L=N-heterocyclic ligands) complexes readily undergo ligand exchange reaction in DMSO, a popular medium for preparing stock solutions for biological screening. It is therefore highly important for researchers to study stability in DMSO before reporting on the biological activity of such type of complexes.

Syntheses, structural characterization and CO releasing properties of boranocarbonate H3BCO2H](-) derivatives

CO plays an important role in biological processes and molecules which release CO in a controllable way could therefore be used for medicinal purposes. Beside organometallic carbonyl complexes, boranocarbonate [H(3)BCO(2)H](-) is one of the most promising candidates but releases CO too rapidly. In order to delay the CO release, we have prepared boranocarbamates [H(3)BCONH-R](-) from [H(3)BCO(2)H](-) which comprise histamine, morpholine, aniline and ethylene-diamine bound via amides to the {H(3)BCO} moiety. The syntheses of the new derivatives is described together with their structural characterization. These compounds release CO at a much slower rate than the parent compound and are therefore potential CO releasing molecules for biological and medicinal application.

Induction of DNA-double-strand breaks by auger electrons from 99mTc complexes with DNA-binding ligands.

The potential of certain Auger electron emitting nuclides for systemic radiotherapeutic applications has recently gained much attention. In particular, the ability of several nuclides, including 111In, 125I, and 123I, to induce DNA double‐strand breaks (dsb), a good indicator of cytotoxicity, has been extensively studied. However, this ability has never previously been shown experimentally for 99mTc, which, besides the well‐known γ radiation that is used for diagnostic applications, also emits an average of 1.1 conversion electrons and 4 Auger or Coster–Kronig electrons per decay. Owing to the short range of Auger electrons, the radionuclide needs to be located very close to the DNA for dsb to occur. We synthesized two cationic 99mTcI–tricarbonyl complexes with pendant DNA binders, pyrene and anthraquinone. The X‐ray crystal structures of the two complexes could be elucidated. Linear dichroism and UV/Vis spectroscopy revealed that the complex with pyrene intercalates DNA with a stability constant, K, of 1.1×106 M−1, while the analogous complex with anthraquinone interacts with DNA in a groove‐binding mode and has an affinity value of K=8.9×104 M−1. We showed with ϕX174 double‐stranded DNA that the corresponding 99mTc complexes induce a significant amount of dsb, whereas non‐DNA‐binding [TcO4]− and nonradioactive Re compounds did not. These results indicate that the Auger electron emitter 99mTc can induce dsb in DNA when decaying in its direct vicinity and this implies potential for systemic radiotherapy with 99mTc complexes.

Gold(I) complexes of water-soluble diphos-type ligands: Synthesis, anticancer activity, apoptosis and thioredoxin reductase inhibition

Gold(I) complexes of imidazole and thiazole-based diphos type ligands were prepared and their potential as chemotherapeutics investigated. Depending on the ligands employed and the reaction conditions complexes [L(AuCl)(2)] and [L(2)Au]X (X = Cl, PF(6)) are obtained. The ligands used are diphosphanes with azoyl substituents R(2)P(CH(2))(2)PR(2) {R = 1-methylimidazol-2-yl (1), 1-methylbenzimidazol-2-yl (4), thiazol-2-yl (5) and benzthiazol-2-yl (6)} as well as the novel ligands RPhP(CH(2))(2)PRPh {R = 1-methylimidazol-2-yl (3)} and R(2)P(CH(2))(3)PR(2) {R = 1-methylimidazol-2-yl (2)}. The cytotoxic activity of the complexes was assessed against three human cancer cell lines and a rat hepatoma cell line and correlated to the lipophilicity of the compounds. The tetrahedral gold complexes [(3)(2)Au]PF(6) and [(5)(2)Au]PF(6) with intermediate lipophilicity (logD(7.4) = 0.21 and 0.25) showed significant cytotoxic activity in different cell lines. Both compounds induce apoptosis and inhibit the enzymes thioredoxin reductase and glutathione reductase.

Some thoughts about the single crystal growth of small molecules

This highlight critically compares various techniques to grow single crystals when only a few milligrams are available of the compound of interest. The authors describe vapour diffusion, evaporation, cooling, and layering techniques, as well as crystallisation in gels. A table of successfully applied solvent/antisolvent combinations for initial screening is given. Additionally, a comprehensive table of 107 solvents with their boiling points, densities and dielectric constants helps to optimise the crystal growth.

Lanthanoid-Containing Open Wells–Dawson Silicotungstates: Synthesis, Crystal Structures, and Properties

Five novel lanthanoid-containing silicotungstates with polymeric crystal structures [Ln(2)(H(2)O)(7)Si(2)W(18)O(66)](n)(10n-) [Ln = Gd(III) (Gd-1 and Gd-2), Tb(III), Ho(III)] and [Dy(2)(H(2)O)(6.5)(C(2)H(4)O(2))(0.5)Si(2)W(18)O(66)](n)(10n-) were obtained from the one-step reaction of Na(10)[SiW(9)O(34)]·nH(2)O with Ln(NO(3))(3)·nH(2)O in a sodium acetate buffer. The compounds were characterized by single-crystal X-ray diffraction and a wide range of analytical methods, including FT-IR, UV/vis, and photoluminescence spectroscopy as well as electrochemistry and thermogravimetric analysis. This new polyoxotungstate series is the first example of lanthanoids embedded in the open Wells-Dawson silicotungstate anion [α-Si(2)W(18)O(66)](16-). The lanthanoid-containing Wells-Dawson-type polyoxoanions [Ln(2)(H(2)O)(7)Si(2)W(18)O(66)](10-) [Ln = Gd(III) (Gd-1 and Gd-2), Tb(III), Ho(III)] and [Dy(2)(H(2)O)(6.5)(C(2)H(4)O(2))(0.5)Si(2)W(18)O(66)](10-) are linked by Ln(3+) cations to form 3D architectures for Gd-1 or 2D frameworks for the isostructural compounds Tb-2, Dy-2, Ho-2, and Gd-2. The structure-directing influence of the lanthanoid cation on the local structure of the dimeric building blocks and on the crystal packing motifs is investigated in detail. The photoluminescence properties of Tb-2 and Dy-2 were investigated at room temperature, and Ho-2 exhibits an interesting photochromic behavior. The magnetic susceptibility of Gd-1 and Gd-2 was studied in the temperature range between 2 and 300 K for its effective magnetic moment.

Metal-mediated retro Diels-Alder of dicyclopentadiene derivatives: a convenient synthesis of [(Cp-R)M(CO)3] (M = 99mTc, Re) complexes.

The synthesis of piano-stool type complexes [(Cp-R)99mTc(CO)3] from water and, if possible, directly from [99mTcO4]- is a persisting challenge. Such complexes are very convenient for labeling biomolecules since they are small in size and “innocent” with respect to noncovalent interactions in biological systems. We found that [(Cp-R)99mTc(CO)3] can be prepared directly from the dimerized Diels−Alder precursors and from [99mTcO4]-. Since the concentration of the respective monomers in the reaction solutions was undetectable, the formation of [(Cp-R)99mTc(CO)3] must be based on a metal-mediated retro Diels−Alder reaction with concerted Cp coordination. The authenticity of the formed 99mTc complexes was confirmed by comparing their HPLC retention times with those of the structurally characterized rhenium surrogates. Besides the principle access to piano-stool complexes for radiopharmaceutical studies, a metal-mediated retro Diels−Alder reaction under concomitant formation of the corresponding piano-stool comp...