Metal complexes as artificial proteases: toward catalytic drugs

New Insights on the Chemical Origin of Life: The Role of Aqueous Polymerization of N-carboxyanhydrides (NCA)

At the origin, the emergence of proteins was based on crucial prebiotic stages in which simple amino acids-based building blocks spontaneously evolved from the prebiotic soup into random proto-polymers called protoproteins. Despite advances in modern peptide synthesis, these prebiotic chemical routes to protoproteins remain puzzling. We discuss in this perspective how polymer science and systems chemistry are reaching a point of convergence in which simple monomers called N-carboxyanhydrides would be able to form such protoproteins via the emergence of a protometabolic cycle involving aqueous polymerization and featuring macromolecular Darwinism behavior.

Reactivity of metal-oxo clusters towards biomolecules: from discrete polyoxometalates to metal-organic frameworks

Metal-oxo clusters hold great potential in several fields such as catalysis, materials science, energy storage, medicine, and biotechnology. These nanoclusters of transition metals with oxygen-based ligands have also shown promising reactivity towards several classes of biomolecules, including proteins, nucleic acids, nucleotides, sugars, and lipids. This reactivity can be leveraged to address some of the most pressing challenges we face today, from fighting various diseases, such as cancer and viral infections, to the development of sustainable and environmentally friendly energy sources. For instance, metal-oxo clusters and related materials have been shown to be effective catalysts for biomass conversion into renewable fuels and platform chemicals. Furthermore, their reactivity towards biomolecules has also attracted interest in the development of inorganic drugs and bioanalytical tools. Additionally, the structural versatility of metal-oxo clusters allows for the efficiency and selectivity of the biomolecular reactions they promote to be readily tuned, thereby providing a pathway towards reaction optimization. The properties of the catalyst can also be improved through incorporation into solid supports or by linking metal-oxo clusters together to form Metal-Organic Frameworks (MOFs), which have been demonstrated to be powerful heterogeneous catalysts. Therefore, this review aims to provide a comprehensive and critical analysis of the state of the art on biomolecular transformations promoted by metal-oxo clusters and their applications, with a particular focus on structure-activity relationships.

Cascade autohydrolysis of Alzheimer's Aβ peptides

Protein/peptide self-assembly into amyloid structures associates with major neurodegenerative disorders such as Alzheimer's disease (AD). Soluble assemblies (oligomers) of the Aβ peptide and their aggregates are perceived as neurotoxic species in AD. While screening for synthetic cleavage agents that could break down such aberrant assemblies through hydrolysis, we observed that the assemblies of Aβ oligopeptides, containing the nucleation sequence Aβ14-24 (H14QKLVFFAEDV24), could act as cleavage agents by themselves. Autohydrolysis showed a common fragment fingerprint among various mutated Aβ14-24 oligopeptides, Aβ12-25-Gly and Aβ1-28, and full-length Aβ1-40/42, under physiologically relevant conditions. Primary endoproteolytic autocleavage at the Gln15-Lys16, Lys16-Leu17 and Phe19-Phe20 positions was followed by subsequent exopeptidase self-processing of the fragments. Control experiments with homologous d-amino acid enantiomers Aβ12-25-Gly and Aβ16-25-Gly showed the same autocleavage pattern under similar reaction conditions. The autohydrolytic cascade reaction (ACR) was resilient to a broad range of conditions (20-37 °C, 10-150 μM peptide concentration at pH 7.0-7.8). Evidently, assemblies of the primary autocleavage fragments acted as structural/compositional templates (autocatalysts) for self-propagating autohydrolytic processing at the Aβ16-21 nucleation site, showing the potential for cross-catalytic seeding of the ACR in larger Aβ isoforms (Aβ1-28 and Aβ1-40/42). This result may shed new light on Aβ behaviour in solution and might be useful in the development of intervention strategies to decompose or inhibit neurotoxic Aβ assemblies in AD.

Interaction of organoruthenium(II)-polypyridyl complexes with DNA and BSA

The interaction of four arene ruthenium complexes [(η⁶-p-cymene)Ru(Me₂dppz)Cl]PF₆ (1) with Me₂dppz = 11,12-dimethyldipyrido[3,2-a:2',3'-c]phenazine, [(η⁶-p-cymene)Ru(aip)Cl]PF₆ (2) with aip = 2-(9-anthryl)-1H-imidazo[4,5-f][1,10] phenanthroline), ([(ƞ⁶-toluene)Ru(ppf)Cl]PF₆) (3) and ([(ƞ⁶-p-cymene)Ru(ppf)Cl]PF₆) (4) with ppf = pyrido[2',3':5,6] pyrazino[2,3-f][1,10]phenanthroline with calf thymus DNA were investigated. All of four complexes exhibit DNA-binding activity. UV-Vis spectroscopic studies revealed the intrinsic binding constants of the order 10⁴ M^-1 of magnitude, indicating non-intercalative mode. Fluorescence quenching analysis showed that all complexes interfere with intercalator ethidium bromide and minor groove binder Hoechst 33258 by a singular non-intercalative mode with extent that differs by two orders of magnitude. Gel electrophoresis results on DNA cleavage assay demonstrated that all complexes produced conformational changes of supercoiled circular plasmid pUC19 in concentration dependent way. The results of fluorescence titration bovine serum albumin by 1, 2, 3 and 4 showed that all complexes significantly quench tryptophan residues fluorescence through a static quenching mechanism. The antimicrobial activity against both Gram-positive and Gram-negative bacteria analyzed. Complex 1 was most active, even on Escherichia coli was more active than positive control compound.

A novel binuclear Pd(ii) complex displaying synergic peptide cleavage behaviour

Mononuclear Pd(ii) complexes with two leaving groups are able to promote His-, Cys- and Met-orientated peptide hydrolysis, and exploring the peptide cleavage behavior of a novel Pd(ii) complex may provide "Omics" studies a promising artificial protease. In this study, a novel binuclear Pd(ii) complex [Pd₂(μ-O-L-H)(μ-Cl)](ClO₄)₂ (L = 2,6-bis(N-2'-aminoethylaminomethyl)-p-cresol) was constructed to promote peptide hydrolysis. Although each Pd(ii) center has only one leaving group (Cl) in this complex, electrophoresis and LC-MS-MS determination discloses that this complex enables myoglobin cleavage on the second upstream peptide bond from His and Met. A study on peptide cleavage also confirms the His- and Met-orientated peptide hydrolysis, yet no Cys-orientated hydrolysis was observed, although the cysteine-induced peptide/complex binding is distinct. Cysteine in the peptide even prevents the complex from promoting His-orientated hydrolysis, whereas the oxidized cysteine residue recovers the His-orientated hydrolysis. This peptide cleavage behavior is quite different from the simultaneous His-, Cys-, and Met-orientated hydrolysis promoted by the mononuclear Pd(ii) complexes. A theoretical study suggests that the two Pd(ii) centers of this complex might promote His- and Met-orientated hydrolysis in a synergic manner: one Pd(ii) center binds selectively on peptides or proteins and the other coordinates with the amide bond and water favoring nucleophilic attack on the peptide bond. The thiol group of cysteine is inclined to bridge the two Pd(ii) centers to form a "closed" sulphur-bridged structure, disfavoring the Cys-orientated hydrolysis. This study not only demonstrates the peptide cleavage behavior of this binuclear Pd(ii) complex, but also provides a polynuclear strategy to regulate the peptide cleavage behavior of Pd(ii) complexes.

An easy-to-implement combinatorial approach involving an activity-based assay for the discovery of a peptidyl copper complex mimicking superoxide dismutase

A strategy combining combinatorial chemistry and an activity-based screening leads to the development of a peptidyl catalytic drug that reduces the oxidative stress in cellular models.

Catalysis Concepts in Medicinal Inorganic Chemistry

Catalysis has strongly emerged in the field of medicinal inorganic chemistry as a suitable tool to deliver new drug candidates and to overcome drawbacks associated to metallodrugs. In this Concept article, we discuss representative examples of how catalysis has been applied in combination with metal complexes to deliver new therapy approaches. In particular, we explain key achievements in the design of catalytic metallodrugs that damage biomolecular targets and in the development of metal catalysis schemes for the activation of exogenous organic prodrugs. Moreover, we discuss our recent discoveries on the flavin-mediated bioorthogonal catalytic activation of metal-based prodrugs; a new catalysis strategy in which metal complexes are unconventionally employed as substrates rather than catalysts.

Crystal structure of bis-{μ2-2,2'-[(4,10-dimethyl-1,4,7,10-tetra-aza-cyclo-dodecane-1,7-di-yl)bis(meth-yl-ene)]bis-(4-oxo-4H-pyran-3-olato)}dicobalt-calcium bis-(perchlorate) 1.36-hydrate

The title compound, [CaCo2(C22H30N4O6)2](ClO4)2·1.36H2O or {Ca[Co(H-2L1)]2}·2ClO4·1.36H2O {where L1 is 4,10-bis-[(3-hy-droxy-4-pyron-2-yl)meth-yl]-1,7-dimethyl-1,4,7,10-tetra-aza-cyclo-dodecane}, is a trinuclear complex whose asymmetric unit comprises a quarter of the {Ca[Co(H-2L1)]2}2+ trinuclear complex, half of a perchlorate ion and 0.34-water mol-ecules. In the neutral [Co(H-2L1)] moiety, the cobalt ion is hexa-coordinated in a trigonal-prismatic fashion by the surrounding N4O2 donor set. A Ca2+ cation holds together two neutral [Co(H-2L1)] moieties and is octa-coordinated in a distorted trigonal-dodeca-hedral fashion by the surrounding O atoms belonging to the deprotonated oxide and carbonyl groups of two [Co(H-2L1)] units. The coordination of the CoII cation preorganizes L1 and an electron-rich area forms, which is able to host hard metal ions. The comparison between the present structure and the previously published ones suggests a high versatility of this ligand; indeed, hard metal ions with different nature and dimensions lead to complexes having different stoichiometry (mono- and dinuclear monomers and trinuclear dimers) or even a polymeric structure. The heterotrinuclear CoII-CaII-CoII complexes are connected in three dimensions via weak C-H⋯O hydrogen bonds, which are also responsible for the inter-actions with the perchlorate anions and the lattice water mol-ecules. The perchlorate anion is disordered about a twofold rotation axis and was refined giving the two positions a fixed occupancy factor of 0.5. The crystal studied was refined as a two-component inversion twin [BASF parameter = 0.14 (4)].

Designing metallodrugs with nuclease and protease activity

The accidental discovery of cisplatin some 50 years ago generated renewed interest in metallopharmaceuticals. Beyond cisplatin, many useful metallodrugs have been synthesized for the diagnosis and treatment of various diseases, but toxicity concerns, and the propensity to induce chemoresistance and secondary cancers make it imperative to search for novel metallodrugs that address these limitations. The Amino Terminal Cu(ii) and Ni(ii) (ATCUN) binding motif has emerged as a suitable template to design catalytic metallodrugs with nuclease and protease activities. Unlike their classical counterparts, ATCUN-based metallodrugs exhibit low toxicity, employ novel mechanisms to irreversibly inactivate disease-associated genes or proteins providing in principle, a channel to circumvent the rapid emergence of chemoresistance. The ATCUN motif thus presents novel strategies for the treatment of many diseases including cancers, HIV and infections caused by drug-resistant bacteria at the genetic level. This review discusses their design, mechanisms of action and potential for further development to expand their scope of application.

Sonochemical synthesis, characterization, antimicrobial activity and textile dyeing behavior of nano-sized cobalt(III) complexes

Using ultrasonic irradiations, nano-sized cobalt(III) coordination complexes, [Co(NH₃)₆]Cl₃·2H₂O (A), [Co(en)₃]Cl₃·3H₂O (B) (en-ethylenediamine) and [Co(dien)₂]Cl₃·3.5H₂O (C) (dien-diethylenetriamine) were synthesized. These complexes were characterized by spectroscopic studies like IR, UV/Visible and NMR. Morphology of these complexes was determined by SEM and particle size with the help of TEM & Zeta-sizer. The comparative thermal stability along with phase difference between nano structures and their respective bulk complexes has been studied by thermal gravimetric analysis (TGA) and X-ray powder diffraction (XRD) study respectively. The dyeing behavior of nano-sized Co(III) complexes and their respective bulks has also been studied (using both exhaust and pad dyeing methods) on cotton and wool fabrics and results shown rationalized dyeing behavior. All these complexes were further tested for antimicrobial activity (against B. subtilis, E. coli, K. pneumoniae, F. oxysporum and A. alternate) and it was observed that nano sized complexes enhanced the activity further.

Mass spectrometry of oligopeptides in the presence of large amounts of alkali halides using desorption/ionization induced by neutral cluster impact

Oligopeptides in the presence of large amounts of salt were desorbed and ionized using desorption/ionization induced by neutral clusters (DINeC) for further analysis by means of mass spectrometry (MS). Using oligopeptides in alkali halide solutions as a model system, DINeC was shown to yield clear and fragmentation free mass spectra of the biomolecules even from environments with a large excess of salt. The results were traced back to a phase separation between salt and biomolecules during sample preparation. The ratio between alkali metal complexes [M+A](+) and bare biomolecules [M+H](+) was controlled using different preparation schemes. DINeC was applied to the products of a tryptic digest of bovine serum albumin in the presence of sodium chloride; the results of a mass fingerprint analysis did not show a major difference for the spectra with and without salt in the original solution. The metal-ion/peptide interaction was further investigated by means of tandem-MS.

Catalytic metallodrugs based on the LaR2C peptide target HCV SLIV IRES RNA

Prior work has demonstrated the potential effectiveness of a new class of metallopeptides as catalytic metallodrugs that target HCV IRES SLIIb RNA (Cu-GGHYrFK, 1). Herein new catalytic metallodrugs (GGHKYKETDLLILFKDDYFAKKNEERK, 2; and GGHKYKETDL, 3) are described based on the LaR2C peptide that has been shown to bind to the SLIV HCV IRES domain. In vitro fluorescence assays yielded KD values ∼10 μM for both peptides and reaction of the copper derivatives with SLIV RNA demonstrated initial rates comparable across different assays as well as displaying pseudo-Michaelis-Menten behavior. The sites of reaction and cleavage mechanisms were determined by MALDI-TOF mass spectrometry. The primary site of copper-promoted SLIV cleavage is shown to occur in the vicinity of the 5'-G17C18A19C20-3' sequence that corresponds to a known binding site of the RM2 motif of the human La protein and has previously been reported to be important for viral translation. This domain also flanks the internal start codon (AUG). Both copper complexes also showed efficacy in an HCV replicon assay (IC50 = 0.75 μM for 2-Cu, and 2.17 μM for 3-Cu) and show potential for treatment of hepatitis C, complementing other marketed drugs by acting on a distinct therapeutic target by a novel mechanism of action.

Metal complexes and metalloproteases: targeting conformational diseases

In recent years many metalloproteases (MPs) have been shown to play important roles in the development of various pathological conditions. Although most of the literature is focused on matrix MPs (MMPs), many other MPs have been demonstrated to be involved in the degradation of peptides or proteins whose accumulation and dyshomeostasis are considered as being responsible for the development of conformational diseases, i.e., diseases where non-native protein conformations lead to protein aggregation. It seems clear that, at least in principle, it must be possible to control the levels of many aggregation-prone proteins not only by reducing their production, but also by enhancing their catabolism. Metal complexes that can perform this function were designed and tested according to at least two different strategies: (i) intervening on the endogenous MPs by directly or indirectly modulating their activity; (ii) acting as artificial MPs, replacing or synergistically functioning with endogenous MPs. These two different bioinorganic approaches are widely represented in the current literature and the aim of this review is to rationally organize and discuss both of them so as to give a critical insight into these approaches and highlighting their limitations and future perspectives.

Approaches to the design of catalytic metallodrugs

Metal ions are known to act as catalytic centres in metallo-enzymes. On the other hand, low-molecular-weight metal complexes are widely used as catalysts in chemical systems. However, small catalysts do not have a large protein ligand to provide substrate selectivity and minimize catalyst poisoning. Despite the challenges that the lack of a protein ligand might pose, some success in the use of metal catalysts for biochemical transformations has been reported. Here, we present a brief overview of such reports, especially involving catalytic reactions in cells. Examples include C-C bond formation, deprotection and functional group modification, degradation of biomolecules, and redox modulation. We discuss four classes of catalytic redox modulators: photosensitizers, superoxide dismutase mimics, thiol oxidants, and transfer hydrogenation catalysts. Catalytic metallodrugs offer the prospect of low-dose therapy and a challenging new design strategy for future exploration.

Synthesis of a chitosan-based functional biopolymer with both catalytic and binding groups for protein and DNA hydrolysis

Protein and DNA hydrolysis by chitosan-based biopolymer with catalytic and binding groups.

From Traditional Drug Design to Catalytic Metallodrugs: A Brief History of the Use of Metals in Medicine

Traditional drug design has been effective in the development of therapies for a variety of disease states but there is a need for new approaches that will tackle new challenges and complement current paradigms. The use of metals in medicine has resulted in several successes and allows for the introduction of properties that cannot be achieved by use of organic compounds alone, but also introduces new challenges that can be addressed by a careful understanding of the principles of inorganic chemistry. Toward this end, the unique structural and coordination chemistry, as well as the reactivity of metals, has been used to design novel classes of therapeutic and diagnostic agents. This review briefly summarizes progress in the field of therapeutics, from the earliest use of metals to more recent efforts to design catalytic metallodrugs that promote the irreversible inactivation of therapeutically relevant targets.

Use of a molybdenum(VI) complex as artificial protease in protein photocleavage

In this study, a molybdenum(VI) peroxo α-amino acid complex, MoO(O2)2(α-leucine) (H2O), was prepared and used as an artificial protease for site-specific cleavage of porcine pepsin, a model protein. Cleavage of pepsin by MoO(O2)2(α-leucine) (H2O) was achieved under photochemical conditions at room temperature and pH 7.0. The reaction was activated by irradiation of the MoO(O2)2(α-leucine) (H2O)-protein mixture by UV light (320 and 340nm) for up to 30min. No cleavage was observed in the absence of MoO(O2)2(α-leucine) (H2O) or the light. The photocleavage yield increased with irradiation time. The cleaved fragments were sequencable, and the cleavage site was assigned to Leu(112)-Tyr(113). The cleavage reaction was quenched by ethanol. Therefore, hydroxyl radicals may be involved in the reaction and responsible for the cleavage of the protein. This is the first demonstration of the successful photocleavage of proteins by a molybdenum complex. This observation can provide a new approach for the photochemical footprinting of metal binding sites on proteins.

Deoxynucleoside triphosphates bearing histamine, carboxylic acid, and hydroxyl residues--synthesis and biochemical characterization

Modified nucleoside triphosphates (dA(Hs)TP, dU(POH)TP, and dC(Val)TP) bearing imidazole, hydroxyl, and carboxylic acid residues connected to the purine and pyrimidine bases through alkyne linkers were prepared. These modified dN*TPs were excellent substrates for various DNA polymerases in primer extension reactions. Moreover, the combined use of terminal deoxynucleotidyl transferase (TdT) and the modified dNTPs led to efficient tailing reactions that rival those of natural counterparts. Finally, the triphosphates were tolerated by polymerases under PCR conditions, and the ensuing modified oligonucleotides served as templates for the regeneration of unmodified DNA. Thus, these modified dN*TPs are fully compatible with in vitro selection methods and can be used to develop artificial peptidases based on DNA.

Target-directed catalytic metallodrugs

Most drugs function by binding reversibly to specific biological targets, and therapeutic effects generally require saturation of these targets. One means of decreasing required drug concentrations is incorporation of reactive metal centers that elicit irreversible modification of targets. A common approach has been the design of artificial proteases/nucleases containing metal centers capable of hydrolyzing targeted proteins or nucleic acids. However, these hydrolytic catalysts typically provide relatively low rate constants for target inactivation. Recently, various catalysts were synthesized that use oxidative mechanisms to selectively cleave/inactivate therapeutic targets, including HIV RRE RNA or angiotensin converting enzyme (ACE). These oxidative mechanisms, which typically involve reactive oxygen species (ROS), provide access to comparatively high rate constants for target inactivation. Target-binding affinity, co-reactant selectivity, reduction potential, coordination unsaturation, ROS products (metal-associated vs metal-dissociated; hydroxyl vs superoxide), and multiple-turnover redox chemistry were studied for each catalyst, and these parameters were related to the efficiency, selectivity, and mechanism(s) of inactivation/cleavage of the corresponding target for each catalyst. Important factors for future oxidative catalyst development are 1) positioning of catalyst reduction potential and redox reactivity to match the physiological environment of use, 2) maintenance of catalyst stability by use of chelates with either high denticity or other means of stabilization, such as the square planar geometric stabilization of Ni- and Cu-ATCUN complexes, 3) optimal rate of inactivation of targets relative to the rate of generation of diffusible ROS, 4) targeting and linker domains that afford better control of catalyst orientation, and 5) general bio-availability and drug delivery requirements.

DNA duplex-supported artificial esterase mimicking by cooperative grafting functional groups

The molecular structures of enzyme mimics may be modified to optimize their catalytic properties. In this study, to generate artificial enzyme mimics, Watson-Crick base paired DNA duplexes were designed as scaffolds which were assembled by nucleotides modified with specific functional groups. This process allowed various functional groups to be precisely assembled at different sites on the duplexes. By using this strategy, the 5-[2-(1H-imidazolyl-4)-(E)-ethylene]-2'-deoxythymidine (1) analog with the 5-substituted imidazolyl group was incorporated into single strands of DNA. Upon DNA duplex formation, several combinations of the imidazolyl group were formed. Using p-nitrophenyl acetate as the substrate of the catalytic reaction, we evaluated the hydrolysis capabilities of the imidazolyl assemblies. The catalytic ability was closely related to the distribution of imidazolyl groups in the DNA duplex. The most effective catalytic center was that of the duplex O5-O6 construct with three imidazolyl groups. This construct displayed bell-shaped pH-dependent and Mg(2+)-independent kinetic curves, which are typical characteristics of imidazolyl-mediated catalytic reactions.

Selective cleavage of pepsin by molybdenum metallopeptidase

In this study, the cleavage of protein by molybdenum cluster is reported for the first time. The protein target used is porcine pepsin. The data presented in this study show that pepsin is cleaved to at least three fragments with molecular weights of ∼23, ∼19 and ∼16 kDa when the mixture of the protein and ammonium heptamolybdate tetrahydrate ((NH(4))(6)Mo(7)O(24)·4H(2)O) was incubated at 37°C for 24h. No self cleavage of pepsin occurs at 37 °C, 24h indicating that the reaction is mediated by the metal ions. N-terminal sequencing of the peptide fragments indicated three cleavage sites of pepsin between Leu 112-Tyr 113, Leu 166-Leu 167 and Leu 178-Asn 179. The cleavage reaction occurs after incubation of the mixture of pepsin and (NH(4))(6)Mo(7)O(24)·4H(2)O) only for 2h. However, the specificity of the cleavage decreases when incubation time is longer than 48 h. The mechanism for cleavage of pepsin is expected to be hydrolytic chemistry of the amide bonds in the protein backbone.

Targeted catalytic inactivation of angiotensin converting enzyme by lisinopril-coupled transition-metal chelates

A series of compounds that target reactive transition-metal chelates to somatic angiotensin converting enzyme (sACE-1) have been synthesized. Half-maximal inhibitory concentrations (IC(50)) and rate constants for both inactivation and cleavage of full-length sACE-1 have been determined and evaluated in terms of metal chelate size, charge, reduction potential, coordination unsaturation, and coreactant selectivity. Ethylenediaminetetraacetic acid (EDTA), nitrilotriacetic acid (NTA), 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA), and tripeptide GGH were linked to the lysine side chain of lisinopril by 1-ethyl-3-[3-(dimethylamino)propyl]carbodiimide hydrochloride/N-hydroxysuccinimide coupling. The resulting amide-linked chelate-lisinopril (EDTA-lisinopril, NTA-lisinopril, DOTA-lisinopril, and GGH-lisinopril) conjugates were used to form coordination complexes with iron, cobalt, nickel, and copper, such that lisinopril could mediate localization of the reactive metal chelates to sACE-1. ACE activity was assayed by monitoring cleavage of the fluorogenic substrate Mca-RPPGFSAFK(Dnp)-OH, a derivative of bradykinin, following preincubation with metal chelate-lisinopril compounds. Concentration-dependent inhibition of sACE-1 by metal chelate-lisinopril complexes revealed IC(50) values ranging from 44 to 4500 nM for Ni-NTA-lisinopril and Ni-DOTA-lisinopril, respectively, versus 1.9 nM for lisinopril. Stronger inhibition was correlated with smaller size and lower negative charge of the attached metal chelates. Time-dependent inactivation of sACE-1 by metal chelate-lisinopril complexes revealed a remarkable range of catalytic activities, with second-order rate constants as high as 150,000 M(-1) min(-1) (Cu-GGH-lisinopril), while catalyst-mediated cleavage of sACE-1 typically occurred at much lower rates, indicating that inactivation arose primarily from side chain modification. Optimal inactivation of sACE-1 was observed when the reduction potential for the metal center was poised near 1000 mV, reflecting the difficulty of protein oxidation. This class of metal chelate-lisinopril complexes possesses a range of high-affinity binding to ACE, introduces the advantage of irreversible catalytic turnover, and marks an important step toward the development of multiple-turnover drugs for selective inactivation of sACE-1.

Synthesis and spectroscopic studies of homo-binuclear, alkoxo bridged homo- and hetero-tetranuclear metal complexes of a bis-N2O4 Schiff base ligand derived from ethanolamine and macroacyclic tetranaphthaldehyde

Three new homo-binuclear Ni(II), Cu(II), Zn(II) complexes (2-4), homo-tetranuclear Cu(II) complex (5), and hetero-tetranuclear Cu(II)-Ni(II) complex (6) of a macroacyclic potentially bis-hexadentate N2O4 Schiff base have been synthesized. The imino-alcohol ligand, H4L was obtained by the condensation of ethanolamine with 2,2'-[2,3-bis(1-formyl-2-naphthyloxymethyl)-but-2-ene-1,4-diyldioxy]bis(naphthalene-1-carbaldehyde). The structures of both the Schiff base and its complexes have been proposed by elemental analyses, spectroscopic data i.e. IR, 1H and 13C NMR, UV-vis, electrospray ionisation mass spectra, molar conductivities and magnetic susceptibility measurements. The ligand has two similar compartments to bind first primary two metal ions, and acts bi- or tetra-negative, bis-tetradentate forming five membered chelate ring. However, secondary two metal ions (either Cu2+ or Ni2+) are ligated with dianionic oxygen atoms of the alcohol groups and are linked to the 1,10-phenanthroline-nitrogen atoms in the tetranuclear complexes (5 and 6).

Metal-containing peptide nucleic acid conjugates

Peptide Nucleic Acids (PNAs) are non-natural DNA/RNA analogues with favourable physico-chemical properties and promising applications. Discovered nearly 20 years ago, PNAs have recently re-gained quite a lot of attention. In this Perspective article, we discuss the latest advances on the preparation and utilisation of PNA monomers and oligomers containing metal complexes. These metal- conjugates have found applications in various research fields such as in the sequence-specific detection of nucleic acids, in the hydrolysis of nucleic acids and peptides, as radioactive probes or as modulators of PNA·DNA hybrid stability, and last but not least as probes for molecular and cell biology.

Recent Development of Bifunctional Small Molecules to Study Metal-Amyloid-β Species in Alzheimer's Disease

Alzheimer's disease (AD) is a multifactorial neurodegenerative disease related to the deposition of aggregated amyloid-β (Aβ) peptides in the brain. It has been proposed that metal ion dyshomeostasis and miscompartmentalization contribute to AD progression, especially as metal ions (e.g., Cu(II) and Zn(II)) found in Aβ plaques of the diseased brain can bind to Aβ and be linked to aggregation and neurotoxicity. The role of metal ions in AD pathogenesis, however, is uncertain. To accelerate understanding in this area and contribute to therapeutic development, recent efforts to devise suitable chemical reagents that can target metal ions associated with Aβ have been made using rational structure-based design that combines two functions (metal chelation and Aβ interaction) in the same molecule. This paper presents bifunctional compounds developed by two different design strategies (linkage or incorporation) and discusses progress in their applications as chemical tools and/or potential therapeutics.

Discovery of a strongly apoptotic ruthenium complex through combinatorial coordination chemistry

A strategy for combinatorial parallel coordination chemistry is introduced that provides access to libraries of tris-heteroleptic ruthenium complexes in an economical fashion. Using this method, a library of 560 constitutionally unique, monocationic ruthenium complexes was synthesized, followed by a screening for anticancer activity and resulting in the identification of three hits with promising cytotoxic properties in HeLa cancer cells. A subsequent structure-activity relationship led to the discovery of the surprisingly simple anticancer complex [Ru(tBu(2)bpy)(2)(phox)]PF(6) (complex 1), with tBu(2)bpy = 4,4'-di-tert-buty-2,2'-bipyridine and Hphox = 2-(2'-hydroxyphenyl)oxazoline, displaying an LC(50) value in HeLa cells of 1.3 microM and 0.3 microM after incubation for 24 and 72 h, respectively. Complex 1 also shows remarkable antiproliferative and apoptotic properties at submicromolar concentrations in more clinically relevant Burkitt-like lymphoma cells. A reduction of the mitochondrial membrane potential by 1 indicates the involvement of the intrinsic pathway of programmed cell death. Further investigations reveal that 1 requires caspase-3 for the induction of apoptosis but is insensitive to the proapoptotic and antiapoptotic proteins Smac and Bcl-2, respectively.