Macrocyclic diamide ligand systems: potential chelators for 64Cu- and 68Ga-based positron emission tomography imaging agents.

The N(4)-macrocyclic ligand 2,10-dioxo-1,4,8,11-tetraazabicyclo[11.4.0]1,12-heptadeca-1(12),14,16-triene H(2)L has been synthesized by the [1 + 1] condensation reaction between N,N'-bis(chloroacetyl)-1,2-phenylenediamine and 1,3-propylenediamine. The coordination chemistry of this ligand has been investigated with the metal ions Cu(II), Ni(II), Zn(II), and Ga(III) (complexes 1, 2, 3 and 4, respectively). H(2)L and its metal complexes have been fully characterized by the use of NMR, UV/vis, electron paramagnetic resonance, and elemental analysis where appropriate. The four metal complexes 1-4 have been structurally characterized by X-ray crystallography which confirmed that in all cases the amide nitrogen atoms are deprotonated and coordinated to the metal center. Complexes 3 and 4 are five-coordinate with a water molecule and chloride ion occupying the apical site, respectively. Cyclic voltammetric measurements on complex 1 show that this complex is oxidized reversibly with a half-wave potential, E(1/2) = 0.47 V, and reduced irreversibly at E(P) = -1.84 V. Density functional theory calculations reproduce the geometries of the four complexes. The one-electron reduction and oxidation potentials for 1 were calculated by using two solvent models, DMF and H(2)O. The calculations indicated that the one electron oxidation of 1 may involve removal of an electron from the ligand as opposed to the metal center, producing a diradical. The diamide macrocyle is of interest for the development of new positron emission tomography (PET) and single photon emission computed tomography (SPECT) imaging agents, and a radiolabeled complex has been synthesized with the positron emitting isotope (64)Cu. In vivo biodistribution studies for the (64)Cu labeled complex, (64)Cu-1, in male Lewis rats, showed that the activity is cleared rapidly from the blood within 1-2 h post-administration.

In vitro and in vivo evaluations of a hydrophilic 64Cu-bis(thiosemicarbazonato)-glucose conjugate for hypoxia imaging.

UNLABELLED: A water-soluble glucose conjugate of the hypoxia tracer 64Cu-diacetyl-bis(N4-methylthiosemicarbazone) (64Cu-ATSM) was synthesized and radiolabeled (64Cu-ATSE/A-G). Here we report our initial biological experiments with 64Cu-ATSE/A-G and compare the results with those obtained for 64Cu-ATSM and 18F-FDG. METHODS: The uptake of 64Cu-ATSE/A-G and 64Cu-ATSM into HeLa cells in vitro was investigated at a range of dissolved oxygen concentrations representing normoxia, hypoxia, and anoxia. Small-animal PET with 64Cu-ATSE/A-G was performed in male BDIX rats implanted with P22 syngeneic carcinosarcomas. Images of 64Cu-ATSM and 18F-FDG were obtained in the same model for comparison. RESULTS: 64CuATSE/A-G showed oxygen concentration-dependent uptake in vitro and, under anoxic conditions, showed slightly lower levels of cellular uptake than 64Cu-ATSM; uptake levels under hypoxic conditions were also lower. Whereas the normoxic uptake of 64Cu-ATSM increased linearly over time, 64Cu-ATSE/A-G uptake remained at low levels over the entire time course. In the PET study, 64CuATSE/A-G showed good tumor uptake and a biodistribution pattern substantially different from that of each of the controls. In marked contrast to the findings for 64Cu-ATSM, renal clearance and accumulation in the bladder were observed. 64Cu-ATSE/A-G did not display the characteristic brain and heart uptake of 18F-FDG. CONCLUSION: The in vitro cell uptake studies demonstrated that 64Cu-ATSE/A-G retained hypoxia selectivity and had improved characteristics when compared with 64Cu-ATSM. The in vivo PET results indicated a difference in the excretion pathways, with a shift from primarily hepatointestinal for 64Cu-ATSM to partially renal with 64Cu-ATSE/A-G. This finding is consistent with the hydrophilic nature of the glucose conjugate. A comparison with 18F-FDG PET results revealed that 64Cu-ATSE/A-G was not a surrogate for glucose metabolism. We have demonstrated that our method for the modification of Cu-bis(thiosemicarbazonato) complexes allows their biodistribution to be modified without negating their hypoxia selectivity or tumor uptake properties.

Anion templated surface assembly of a redox-active sensory rotaxane.

Anion templation is used to assemble novel redox-active bis-ferrocene functionalised rotaxane self-assembled monolayers (SAMs) on to gold electrode surfaces; after template removal, the unique SAM rotaxane binding domain is capable of selectively sensing chloride ions electrochemically.

Synthesis of sulfonamide conjugates of Cu(II), Ga(III), In(III), Re(V) and Zn(II) complexes: carbonic anhydrase inhibition studies and cellular imaging investigations.

Carbonic anhydrase IX (CA IX) is currently generating great interest as a marker of tumour hypoxia and a potential chemotherapeutic target. In order to test the principle that a CA IX inhibitor could be used for targeting PET or SPECT metallic radioisotopes to tumours we have prepared a number of conjugates involving aryl-sulfonamides or an acetazolamide derivative linked to a range of copper, indium, rhenium, 99m-technetium and zinc complexes. Radiolabelled (64)Cu and (99m)Tc analogues of the 'cold' Cu and some of the Re complexes were prepared in good radiochemical incorporation. Inhibition of various human carbonic anhydrase isoforms (I, II, IX and XII) was tested with the 'cold', non-radiolabelled complexes, and compared with an acetazolamide standard (AZA). The molecular structure of a new, tri-sulfonated porphyrin-labeled sulfonamide was determined using synchrotron X-ray crystallography.

Nitroimidazole conjugates of bis(thiosemicarbazonato)64Cu(II) - Potential combination agents for the PET imaging of hypoxia.

Combination agents comprising two different pharmacophores with the same biological target have the potential to show additive or synergistic activity. Bis(thiosemicarbazonato)copper(II) complexes (e.g. (64)Cu-ATSM) and nitroimidazoles (e.g. (18)F-MISO) are classes of tracer used for the delineation of tumor hypoxia by positron emission tomography (PET). Three nitroimidazole-bis(thiosemicarbazonato)copper(II) conjugates were produced in order to investigate their potential as combination hypoxia imaging agents. Two were derived from the known bifunctional bis(thiosemicarbazone) H(2)ATSM/A and the third from the new precursor diacetyl-2-(4-N-methyl-3-thiosemicarbazone)-3-(4-N-ethylamino-3-thiosemicarbazone) - H(2)ATSM/en. Oxygen-dependent uptake studies were performed using the (64)Cu radiolabelled complexes in EMT6 carcinoma cells. All the complexes displayed appreciable hypoxia selectivity, with the nitroimidazole conjugates displaying greater selectivity than a simple propyl derivative used as a control. Participation of the nitroimidazole group in the trapping mechanism is indicated by the increased hypoxic uptake of the 2- vs. the 4-substituted (64)Cu-ATSM/A derivatives. The 2-nitroimidazole derivative of (64)Cu-ATSM/en demonstrated superior hypoxia selectivity to (64)Cu-ATSM over the range of oxygen concentrations tested. Biodistribution of the radiolabelled 2-nitroimidazole conjugates was carried out in EMT6 tumor-bearing mice. The complexes showed significantly different uptake trends in comparison to each other and previously studied Cu-ATSM derivatives. Uptake of the Cu-ATSM/en conjugate in non-target organs was considerably lower than for derivatives based on Cu-ATSM/A.

Towards nanomedicines: design protocols to assemble, visualize and test carbon nanotube probes for multi-modality biomedical imaging.

Nanomedicine is an interdisciplinary field, still in its infancy, where an accurate scientific assessment of potential risks and benefits is urgently needed, as is the engagement of end users and the public in this facet of the nanotechnology debate. There is increasing interest in improving our understanding of the interactions between nanomaterials and living systems, with regard to both the underlying chemistry and the physics of effects on the nanoscale. Ultimately, such knowledge promises new vistas for designing the 'smart' medicines of the future, of which targeted personalized drugs are the holy grail. Imaging and therapeutic components, including metallic radioisotopes, semiconductor quantum dots and magnetic materials, may be used to construct 'nanocarriers' (by encapsulation or conjugation) by rapid and simple (covalent and supramolecular) chemistry. The biomedical functions of the resulting materials are as yet largely unexplored. Encapsulation in nanocarriers could achieve delivery of the reagents (imaging and therapeutic drugs) to the sites of action in the body, while minimizing systemic toxicity and enzymatic degradation. These functional systems have the potential to become a general solution in drug delivery. Here we review recent developments concerning the applications of nanoparticles, including carbon nanotubes, as synthetic scaffolds for designing nanomedicines. This article will also focus on how understanding and design at the molecular level could help interdisciplinary teams develop research towards new diagnostics and therapeutics both in the short and the long term.

Fluorescent copper(II) bis(thiosemicarbazonates): synthesis, structures, electron paramagnetic resonance, radiolabeling, in vitro cytotoxicity and confocal fluorescence microscopy studies.

Copper bis(4-ethyl-3-thiosemicarbazonato) acenaphthenequinone (1) and copper bis(4-methyl-3-thiosemicarbazonato) acenaphthenequinone (2) are synthesized and characterized in solution, in the solid state, and radiolabeled. Serum-protein binding radioassays show good stability in solution and about 25 % binding to protein over 1 h, which is comparable with the hypoxia selective tracer [(64)Cu(ATSM)]. Cyclic voltammetry shows fast and reversible reduction at redox potentials similar to the values known for hypoxia-selective copper compounds. However, despite this, complex 1 does not show any hypoxic-selective uptake in HeLa cells over 1-h standard assays. Possible reasons for this are studied by using the intrinsic fluorescence of the Cu(II) complexes to determine the cellular distributions and uptake mechanism by confocal microscopy. The complexes are found to bind to the external cell membrane and disperse evenly in the cytoplasm only after a very slow cell internalization (>1 h). No significant changes in distribution are observed by fluorescence imaging under hypoxic conditions. The rate of localization in the cytoplasm contrasts with their Zn(II) analogues, which are known to have fast cell uptake (up to 20 min) and a clear localization in lysosomes and mitochondria. The cytotoxicity mechanism of 1 over 24 h against a number of adherent cell lines is seen to be by membrane disruption and is of a comparable magnitude to that of [Cu(ATSM)], as demonstrated by methyl tetrazolium (MTT) and lactate dehydrogenase (LDH) assays.

Molecular architectures for trimetallic d/f/d complexes: magnetic studies of a LnCu2 core.

Five new trinuclear Cu-Ln-Cu cluster complexes have been prepared by a one-pot reaction using H3bcn (tris- N,N',N''-(2-hydroxybenzyl)-1,4,7-triazacyclononane) and Ln = La(III), Nd(III), Gd(III), Dy(III), and Yb(III) where the d- and f-block metal ions are in close proximity desirable for magnetic studies. The [LnCu2(bcn)2]ClO4.nH2O complexes possess the same stoichiometry as the previously reported [LnNi2(bcn)2]ClO4.nH2O and [LnZn2(bcn)2]ClO4.nH2O systems. Additionally, the solid state structures of the LnCu2 complexes appear to be isostructural to the LnNi2 and LnZn2 species as determined by their nearly superimposable IR spectra. The similarities in the structures of the [LnTM2(bcn)2]ClO4.nH2O series, where TM = Zn(II), Ni(II), and Cu(II), allow for direct comparison of their magnetic exchange. An empirical approach, removing first-order anisotropic contributions determined from the analogous [LnZn2(bcn)2]ClO4.nH2O was used to study the d/f/d spin interactions in the [LnCu2(bcn)2]ClO4.nH2O complexes. A ferromagnetic exchange was determined where Ln = Gd(III), Dy(III), or Yb(III) and an antiferromagnetic exchange for Ln = Nd(III), identical to the magnetic exchange observed for the [LnNi2(bcn)2]ClO4.nH2O complexes. An exchange integral of 3.67 cm(-1) for the trimetallic [GdCu2(bcn)2]ClO4.3H2O species was determined using a modified spin Hamiltonian. The [Cu(Hbcn)] and the [Cu3(Hbcn)2](ClO4)2 building blocks of the larger coaggregated d/f/d species were also synthesized, and their structures are reported.

Molecular architectures for trimetallic d/f/d complexes: structural and magnetic properties of a LnNi2 core.

A series of cationic, trimetallic d/f/d complexes have been prepared which use a multidentate, macrocyclic amine phenol ligand to coordinate divalent first row d-block transition metal ions (TM) and lanthanides (Ln) ions in close proximity, desirable for magnetic studies. Isolable complexes of the d/f/d cluster compounds with the formula [Ln(TM)2(bcn)2]ClO4.nH2O, where H3bcn is tris-N, N', N''-(2-hydroxybenzyl)-1,4,7-triazacyclononane, TM = Zn(II) and Ni(II) and Ln = La(III), Nd(III), Gd(III), Dy(III), and Yb(III), were synthesized by a one-pot sequential reaction of stoichiometric amounts of H 3bcn with the TM(II) and Ln(III) metal ions. The spontaneously formed cationic complexes were characterized by a variety of analytical techniques including IR, NMR, +ESI-MS, and EA. The [TM(Hbcn)].nH2O and [TM3(bcn)2].nH2O complexes were also synthesized to probe the building blocks of the d/f/d coaggregated species. The solid-state X-ray crystal structures of [GdNi2(bcn)2(CH3CN)2]ClO4.CH3CN and [GdZn2(bcn)2(CH3CN)2]ClO4.CH3CN were determined to be nearly identical with each TM(II) encapsulated in an octahedral geometry by the N3O3 binding pocket of the bcn (3-) ligand. The eight coordinate Gd(III) was bicapped by two [TM(bcn)](-) moieties and coordinated by two solvent molecules. Because of the isostructurality of the [LnZn2(bcn)2]ClO4.nH2O and [LnNi2(bcn)2]ClO4.nH2O complexes, an empirical approach using the LnZn2 magnetic data was utilized to remove first-order anisotropic contributions from the LnNi2 species. Ferromagnetic spin interactions were determined for the [LnNi2(bcn)2]ClO4.nH2O complexes, where Ln = Gd(III), Dy(III), and Yb(III), while an antiferromagnetic exchange was observed for Ln = Nd(III).

Ruthenium complexes with tridentate PNX (X = O, S) donor ligands.

The ligands, PhPNXMe (1), PhPNXPh (2), and PhPNSMe (3), (PhPNX = 2-Ph2P-C6H4CH[double bond, length as m-dash]NC6H4X-2; X = O, S) have been prepared. A range of new ruthenium complexes were synthesised using these and related ligands, namely: [{RuCl(PhPNO)}2Cl] (4), [Ru(PhPNO)2] (5), [RuCl(PhPNXR)(PPh3)]BPh4 [X = O, R = Me (6); X = O, R = Ph (7); X = S, R = Me (8)], [{RuCl(PhPNX'R)}2Cl]X [X' = O, R = Me, X = Cl(-) (9); X' = S, R = Me, X = BPh4(-) or PF6(-) (10)], and [RuCl(PhPNO-eta 6C6H5)]BPh4 (11). The catalytic activity of these complexes with respect to the hydrosilyation of acetophenone and the hydrogenation of styrene has been investigated, giving an insight into the requirements for an active complex in these reactions.

Anion-templated calix[4]arene-based pseudorotaxanes and catenanes.

We present the rational design and anion-binding properties of the first anion-templated pseudorotaxanes and catenanes in which the "wheel" component is provided by a calix[4]arene macrobicyclic unit. The designs and syntheses of two new calix[4]arene macrobicycles, 2 and 3, are presented, and the abilities of these new species both to bind anions and to undergo anion-dependent pseudorotaxane formation are demonstrated. Furthermore, it is shown that performing ring-closing metathesis reactions on some of these pseudorotaxane assemblies gives novel catenane species 14 and 15, in which the yield of interlocked molecule obtained is critically dependent on the presence of a suitable anion template, namely, chloride. Exchange of the chloride anion in catenane 14 a for hexafluorophosphate gives catenane 14 d, which contains a unique anion-binding domain defined by the permanently interlocked hydrogen-bond-donating calix[4]arene macrobicycle and pyridinium macrocycle fragments. The anion-binding properties of this domain are presented, and shown to differ from non-interlocked components.

Glucosamine conjugates of tricarbonylcyclopentadienyl rhenium(I) and technetium(I) cores.

To obtain a 99mTc glucose conjugate for imaging, double-ligand transfer (DLT) and related reactions were examined for the preparation of CpM(CO)3 (Cp = cyclopentadienyl; M = Re, Tc) complexes with pendant carbohydrates at Cp. Tricarbonyl{N-(1,3,4,6-tetra-O-acetyl-2-amino-2-deoxy-beta-D-glucopyranose)cyclopentadienyl carboxamide}rhenium(I) (1a) and tricarbonyl{N-(2-amino-2-deoxy-beta-D-glucopyranose)cyclopentadienyl carboxamide}rhenium(I) (2a) were prepared. The compounds were fully characterized by mass spectrometry, elemental analysis, IR, and NMR spectroscopy. Full assignment of the NMR spectra verified the pendant nature of the glucosamine moieties in the solution state and that 2a exists as both anomers. The solid-state structure of 2a was determined by X-ray crystallography, again confirming the pendant nature of the glucosamine, but differing from the solution state in that the beta anomer crystallized preferentially (93%). Compound 2a was determined to be a high-affinity competitive inhibitor (Ki = 330 +/- 70 microM) of the glucose metabolism enzyme hexokinase, demonstrating that it retains certain biological activity. The 99mTc analogues 1b and 2b were prepared in moderate radiochemical yields by means of the single-ligand transfer (SLT) route, which is more pertinent to radiopharmaceutical synthesis.

Carbohydrate-appended 3-hydroxy-4-pyridinone complexes of the [M(CO)3]+ core (M = Re, 99mTc, 186Re).

This work describes the use of 3-hydroxy-4-pyridinone ligands for binding the [M(CO)(3)](+) core (M = Re, Tc) in the context of preparing novel Tc(I) and Re(I) glucose conjugates. Five pyridinone ligands bearing pendent carbohydrate moieties, HL(1-5), were coordinated to the [M(CO)(3)](+) core on the macroscopic scale (M = Re) and on the tracer scale (M = (99m)Tc, (186)Re). On the macroscopic scale the complexes, ReL(1-5)(CO)(3)(H(2)O), were thoroughly characterized by mass spectrometry, IR spectroscopy, UV-visible spectroscopy, elemental analysis, and 1D/2D NMR spectroscopy. Characterization confirmed the bidentate coordination of the pyridinone and the pendent nature of the carbohydrate and suggests the presence of a water molecule in the sixth coordination site. In preliminary biological evaluation, both the ligands and complexes were assessed as potential substrates or inhibitors of hexokinase, but showed no activity. Labeling via the [(99m)Tc(CO)(3)(H(2)O)(3)](+) precursor gave the tracer species (99m)TcL(1-5)(CO)(3)(H(2)O) in high radiochemical yields. Similar high radiochemical yields when labeling with (186)Re were facilitated by in situ preparation of the [(186)Re(CO)(3)(H(2)O)(3)](+) species in the presence of HL(1-5) to give (186)ReL(1-5)(CO)(3)(H(2)O). Stability challenges, incubating (99m)TcL(1-5)(CO)(3)(H(2)O) in the presence of excess cysteine and histidine, confirmed complex stability up to 24 h.

Carbohydrate conjugates for molecular imaging and radiotherapy: 99mTc(I) and 186Re(I) tricarbonyl complexes of N-(2'-Hydroxybenzyl)-2-amino-2-deoxy-D-glucose.

An approach to a new class of potential radiopharmaceuticals is demonstrated by the labeling of a glucosamine derivative with the tricarbonyls of 99mTc and 186Re. The proligand HL2 (N-(2'-hydroxybenzyl)-2-amino-2-deoxy-D-glucose) was produced by hydrogenation of the corresponding Schiff base and reacted with [NEt4]2[Re(CO)3Br3] to form the neutral complex [(L2)Re(CO)3] in 40% yield. 1H and 13C NMR spectra indicate that the [Re(CO)3] core is bound in a tridentate fashion via the amino N, phenolato O, and C-3 hydroxyl O atoms of the ligand. At the tracer-level, labeling of HL2 with [99mTc(CO)3(H2O)3]+ and [186Re(CO)3(H2O)3]+ was achieved in aqueous conditions in 95 +/- 2% and 94 +/- 3% average radiochemical yields, respectively.

Dlf complexes with uniform coordination geometry: structural and magnetic properties of an LnNi2 core supported by a heptadentate amine phenol ligand.

The synthesis and physical characterization of a series of lanthanide (Ln(III)) and nickel (Ni(II)) mixed trimetallic complexes with the heptadentate (N(4)O(3)) amine phenol ligand H(3)trn [tris(2'-hydroxybenzylaminoethyl)amine] has been accomplished in order to extend our understanding of how amine phenol ligands can be used to coaggregate d- and f-block metal ions and to investigate further the magnetic interaction between these ions. The one-pot reaction in methanol of stoichiometric amounts of H(3)trn with NiX(2).6H(2)O (X = ClO(4), NO(3)) followed by addition of the corresponding LnX(3).6H(2)O salt, and then base, produces complexes of the general formula [LnNi(2)(trn)(2)]X.nH(2)O. The complexes were characterized by a variety of analytical techniques. Crystals of five of the complexes were grown from methanol solutions and their structures were determined by X-ray analysis: [PrNi(2)(trn)(2)(CH(3)OH)]ClO(4).4CH(3)OH.H(2)O, [SmNi(2)(trn)(2)(CH(3)OH)]NO(3).4CH(3)OH.2H(2)O, [TbNi(2)(trn)(2)(CH(3)OH)]NO(3).4CH(3)OH.3H(2)O, [ErNi(2)(trn)(2)(CH(3)OH)]NO(3).6CH(3)OH, and [LuNi(2)(trn)(2)(CH(3)OH)]NO(3).4.5CH(3)OH.1.5H(2)O. The [LnNi(2)(trn)(2)(CH(3)OH)](+) complex cation consists of two octahedral Ni(II) ions, each of which is encapsulated by the ligand trn(3)(-) in an N(4)O(2) coordination sphere with one phenolate O atom not bound to Ni(II). Each [Ni(trn)](-) unit acts as a tridentate ligand toward the Ln(III) ion via two bridging and one nonbridging phenolate donors. Remarkably, in all of the structurally characterized complexes, Ln(III) is seven-coordinate and has a flattened pentagonal bipyramidal geometry. Such uniform coordination behavior along the whole lanthanide series is rare and can perhaps be attributed to a mismatch between the geometric requirements of the bridging and nonbridging phenolate donors. Magnetic studies indicate that ferromagnetic exchange occurs in the Ni(II)/Ln(II) complexes where Ln = Gd, Tb, Dy, Ho, or Er.

Novel carbohydrate-appended metal complexes for potential use in molecular imaging.

Seven discrete sugar-pendant diamines were complexed to the {M(CO)(3)}(+) ((99m)Tc/Re) core: 1,3-diamino-2-propyl beta-D-glucopyranoside (L(1)), 1,3-diamino-2-propyl beta-D-xylopyranoside (L(2)), 1,3-diamino-2-propyl alpha-D-mannopyranoside (L(3)), 1,3-diamino-2-propyl alpha-D-galactopyranoside (L(4)), 1,3-diamino-2-propyl beta-D-galactopyranoside (L(5)), 1,3-diamino-2-propyl beta-(alpha-D-glucopyranosyl-(1,4)-D-glucopyranoside) (L(6)), and bis(aminomethyl)bis[(beta-D-glucopyranosyloxy)methyl]methane (L(7)). The Re complexes [Re(L(1)-L(7))(Br)(CO)(3)] were characterized by (1)H and (13)C 1D/2D NMR spectroscopy which confirmed the pendant nature of the carbohydrate moieties in solution. Additional characterization was provided by IR spectroscopy, elemental analysis, and mass spectrometry. Two analogues, [Re(L(2))(CO)(3)Br] and [Re(L(3))(CO)(3)Br], were characterized in the solid state by X-ray crystallography and represent the first reported structures of Re organometallic carbohydrate compounds. Conductivity measurements in H(2)O established that the complexes exist as [Re(L(1)-L(7))(H(2)O)(CO)(3)]Br in aqueous conditions. Radiolabelling of L(1)-L(7) with [(99m)Tc(H(2)O)(3)(CO)(3)](+) afforded in high yield compounds of identical character to the Re analogues. The radiolabelled compounds were determined to exhibit high in vitro stability towards ligand exchange in the presence of an excess of either cysteine or histidine over a 24 h period.