Prospects of metal complexes peripherally substituted with sugars in biomedicinal applications

Carbohydrate effect of novel arene Ru(II) phenanthroline-glycoconjugates on metastatic biological processes

Novel water-soluble half-sandwich ruthenium(II) polypyridyl-glycoconjugates [Ru(p-cymene)Cl{N-(1,10-phenanthroline-5-yl)-β-glycopyranosylamine}][Cl] (glycopyranosyl = d-glucopyranosyl (1), D-mannopyranosyl (2), L-rhamnopyranosyl (3) and l-xylopyranosyl (4)) have been synthesized and fully characterized. Their behaviour in water under physiological conditions has been studied by nuclear magnetic resonance spectroscopy, revealing their hydrolytic stability. Interactions of the novel compounds with duplex-deoxiribonucleic acid (dsDNA) were investigated by different techniques and the results indicate that, under physiological pH and saline conditions, the metal glycoconjugates bind DNA in the minor groove and/or through external, electrostatic interactions, and by a non-classical, partial intercalation mechanism in non-saline phosphate buffered solution. Effects of compounds 1-4 on cell viability have been assessed in vitro against two human cell lines (androgen-independent prostate cancer PC-3 and non-tumorigenic prostate RWPE-1), showing moderate cytotoxicities, with IC50 values higher than those found for free ligands [N-(1,10-phenanthroline-5-yl)-β-glycopyranosylamine] (glycopyranosyl = d-glucopyranosyl (a), D-mannopyranosyl (b), L-rhamnopyranosyl (c) and l-xylopyranosyl (d)) or corresponding metal-aglycone. Cell viability was assayed in the presence and absence of the glucose transporters (GLUTs) inhibitor [N4-{1-(4-cyanobenzyl)-5-methyl-3-(trifluoromethyl)-1H-pyrazol-4-yl}-7-fluoroquinoline-2,4-dicarboxamide] (BAY-876), and the results point to a negligible impact of the inhibition of GLUTs on the cytotoxicity caused by Ru(II) compounds 1-4. Remarkably, glycoconjugates 1-4 potently affect the migration pattern of PC-3 cells, and the wound healing assay evidence that the presence of the carbohydrate and the Ru(II) center is a requisite for the anti-migratory activity observed in these novel derivatives. In addition, derivatives 1-4 strongly affect the matrix metalloproteinase MMP-9 activities of PC-3 cells, while proMMP-2 and especially proMMP-9 were influenced to a much lesser extent.

In Vitro Effects of Aminopyridyl Ligands Complexed to Copper(II) on the Physiology and Interaction Process of Trypanosoma cruzi

Chagas disease is derived from the infection by the protozoan Trypanosoma cruzi. In many countries, benznidazole is the only drug approved for clinical use despite several side effects and the emergence of resistant parasite strains. In this context, our group has previously pointed out that two novel aminopyridine derivatives complexed with Cu²⁺, namely, cis-aquadichloro(N-[4-(hydroxyphenyl)methyl]-2-pyridinemethamino)copper (3a) and its glycosylated ligand cis-dichloro (N-{[4-(2,3,4,6-tetra-O-acetyl-β-D-glucopyranosyloxy)pheny]lmethyl}-2-pyridinemethamino)copper (3b), are effective against T. cruzi trypomastigote forms. With this result in mind, the present work aimed to investigate the effects of both compounds on trypomastigotes physiology and on the interaction process with host cells. Apart from loss of plasma membrane integrity, an increased generation of reactive oxygen species (ROS) and decreased mitochondrial metabolism were observed. Pretreatment of trypomastigotes with these metallodrugs inhibited the association index with LLC-MK₂ cells in a typical dose-dependent manner. Both compounds showed low toxicity on mammalian cells (CC₅₀ > 100 µM), and the IC₅₀ values calculated for intracellular amastigotes were determined as 14.4 µM for 3a and 27.1 µM for 3b. This set of results demonstrates the potential of these aminopyridines complexed with Cu²⁺ as promising candidates for further antitrypanosomal drug development.

MRI Contrast Agents in Glycobiology

Molecular recognition involving glycoprotein-mediated interactions is ubiquitous in both normal and pathological natural processes. Therefore, visualization of these interactions and the extent of expression of the sugars is a challenge in medical diagnosis, monitoring of therapy, and drug design. Here, we review the literature on the development and validation of probes for magnetic resonance imaging using carbohydrates either as targeting vectors or as a target. Lectins are important targeting vectors for carbohydrate end groups, whereas selectins, the asialoglycoprotein receptor, sialic acid end groups, hyaluronic acid, and glycated serum and hemoglobin are interesting carbohydrate targets.

Neutral Re(I) Complex Platform for Live Intracellular Imaging

Luminescent metal complexes are a valuable platform for the generation of cell imaging agents. However, many metal complexes are cationic, a factor that can dominate the intracellular accumulation to specific organelles. Neutral Re(I) complexes offer a more attractive platform for the development of bioconjugated imaging agents, where charge cannot influence their intracellular distribution. Herein, we report the synthesis of a neutral complex (ReAlkyne), which was used as a platform for the generation of four carbohydrate-conjugated imaging agents via Cu(I)-catalyzed azide-alkyne cycloaddition. A comprehensive evaluation of the physical and optical properties of each complex is provided, together with a determination of their utility as live cell imaging agents in H9c2 cardiomyoblasts. Unlike their cationic counterparts, many of which localize within mitochondria, these neutral complexes have localized within the endosomal/lysosomal network, a result consistent with examples of dinuclear carbohydrate-appended neutral Re(I) complexes that have been reported. This further demonstrates the utility of these neutral Re(I) complex imaging platforms as viable imaging platforms for the development of bioconjugated cell imaging agents.

New derivatives of 4'-phenyl-2,2':6',2″-terpyridine as promising anticancer agents

Terpyridine derivatives are known from their broad application including anticancer properties. In this work we present the newly synthesized 4'-phenyl-2,2':6',2″-terpyridine group with high antiproliferative activity. We suggest that these compounds influence cellular redox homeostasis. Cancer cells are particularly susceptible to any changes in the redox balance because of their handicapped and inefficient antioxidant cellular systems. The antiproliferative activity of the studied compounds was tested on five different cell lines that represent several types of tumours; glioblastoma, leukemia, breast, pancreatic and colon. Additionally, we also tested their selectivity towards normal cells. We performed molecular biology studies in order to detect the response of a cell to its treatment with the compounds that were tested. We looked at the in-depth changes in the proteins and cellular pathways that lead to cell cycle inhibition (G0/G1 and S), and consequently, death on the apoptosis and autophagy pathways. We proved that the studied compounds targeted DNA as well. Special attention was paid to the targets connected with ROS generation.

Cyclometalated iridium(iii) complex nanoparticles for mitochondria-targeted photodynamic therapy

Cyclometalated Ir(iii) complexes, with a long triplet state lifetime and good photophysical properties, are good candidates for simultaneous imaging and photodynamic therapy (PDT). Herein, we synthesize a cyclometalated Ir(iii) complex, Ir(tiq)₂ppy, whose triplet excited state lifetime is 2.9 μs and singlet oxygen generation quantum yield is approximately 100% (compared to tetraphenylporphyrin). Ir(tiq)₂ppy nanoparticles (Ir(tiq)₂ppy NPs) are prepared to achieve water solubility and mitochondria-targeting ability by co-precipitating with polystyrene grafted with carboxyl-terminated poly(ethylene glycol) (PS-PEG). Ir(tiq)₂ppy NPs have higher PDT efficiency than Ir(tiq)₂ppy at concentrations as low as 1.6 μg mL^-1 for MCF-7 breast cancer cells under white light irradiation at quite low light intensity (5 mW cm^-2). Besides, it is worth noting that the emission quenching of Ir(tiq)₂ppy in aqueous solution has been conquered by using Ir(tiq)₂ppy NPs, thus the distribution of the therapeutic agents in mitochondria can be tracked by confocal laser scanning microscopy (CLSM). The mechanism of killing cancer cells under irradiation is investigated, and the results indicate that cell death is caused by mitochondria-mediated apoptosis, which is induced by the ROS generated under light irradiation.

Metal complexes of 4,6-O-ethylidene-β-d-glucopyranosylamine derivatives and their application in organic synthesis

Glycosylamine derivatives of 4,6-O-ethylidene-d-glucose have been used for complexing the alkali, alkaline earth and transition metal ions. Three different series of ligands have been reported where N-(o-carboxyphenyl)-4,6-O-ethylidene-β-d-glucopyranosylamine has been used for complexing the diamagnetic (Li⁺, Na⁺, K⁺, Mg²⁺, Ca²⁺, Ba²⁺, Zn²⁺, Cd²⁺, Hg²⁺) metal ions. N-(2-Hydroxybenzoyl)-L-alanyl-4,6-O-ethylidene-β-d-glucopyranosylamine selectively interacts with molecular cupric acetate and the adduct acts as a catalyst in selective oxidation of primary and secondary alcohols into their corresponding carbonyl compounds. Salicylidene derivatives of 4,6-O-ethylidene-β-d-glucopyranosylamine have been used in complexing Ni²⁺, Cu²⁺, Zn²⁺, VO²⁺, MoO₂²⁺ and UO₂²⁺ metal ions, where Cu(II) and Mo(VI) complexes have been further used in the organic synthesis. Dinuclear copper complex exhibited catecholase like activity and also catalyzed the oxidation of primary and secondary alcohols selectively into their corresponding carbonyl compounds. Trinuclear copper complex has been reported to activate the C-Cl bond of solvent chloroform in the presence of mild organic bases below room temperature. Mo(VI) complex has been used as a catalyst for epoxidation, organic sulfide oxidation and synthesis of bis(indolyl)methanes.

A highly efficient and selective antitumor agent based on a glucoconjugated carbene platinum(ii) complex

A Pt(ii) complex with a glucosylated carbene shows very high in vitro cytotoxicity and selectivity toward malignant cells.

C-Glycosylation in platinum-based agents: a viable strategy to improve cytotoxicity and selectivity

The glycosylation of five-coordinate Pt(ii) compounds through a Pt–C linkage can be a very effective strategy for attacking cancer cells, while preserving the survival of the healthy ones.

Glycosylated metal chelators as anti-parasitic agents with tunable selectivity

Metal complexation imparts selective anti-parasitic activity to aminopyridyl ligands: Zn(ii) and Cu(ii) complexes show potent activity and remarkable selectivity indexes.

Toward biocompatible dinitrosyl iron complexes: sugar-appended thiolates

Herein, we report the synthesis, characterization, and NO transfer/release studies of the first ‘sugar appended’ DNICs, which harness the hydrophilicity and cell targeting potential of the thiosugar, in addition to showing increased stability in air.

Synthesis and characterization of metallo-supramolecular polymers

The incorporation of metal centers into the backbone of polymers has led to the development of a broad range of organometallic and coordination compounds featuring properties that are relevant for potential applications in diverse areas of research, ranging from energy storage/conversion to bioactive or self-healing materials. In this review, the basic concepts and synthetic strategies leading to these types of materials as well as the scope of available characterization techniques will be summarized and discussed.

Synthesis and Applications of (ONO Pincer)Ruthenium-Complex-Bound Norvalines

Two (ONO pincer)ruthenium-complex-bound norvalines, Boc-[Ru(pydc)(terpy)]Nva-OMe (1; Boc=tert-butyloxycarbonyl, terpy=terpyridyl, Nva=norvaline) and Boc-[Ru(pydc)(tBu-terpy)]Nva-OMe (5), were successfully synthesized and their molecular structures and absolute configurations were unequivocally determined by single-crystal X-ray diffraction. The robustness of the pincer Ru complexes and norvaline scaffolds against acidic/basic, oxidizing, and high-temperature conditions enabled us to perform selective transformations of the N-Boc and C-OMe termini into various functional groups, such as alkyl amide, alkyl urea, and polyether groups, without the loss of the Ru center or enantiomeric purity. The resulting dialkylated Ru-bound norvaline, n-C11 H23 CO-l-[Ru(pydc)(terpy)]Nva-NH-n-C11 H23 (l-4) was found to have excellent self-assembly properties in organic solvents, thereby affording the corresponding supramolecular gels. Ru-bound norvaline l-1 exhibited a higher catalytic activity for the oxidation of alcohols by H2 O2 than parent complex [Ru(pydc)(terpy)] (11 a).

Antibacterial effect of silver (I) carbohydrate complexes on oral pathogenic key species in vitro

Background

It was the aim of this study to evaluate the antibacterial impact of two silver(I) carbohydrate complexes with tripodal thioglycosides, namely tris[2-(β-D-thio-glucopyranosyl)ethyl]-amine-silver(I)-nitrate (3) and tris[2-(α-D-thio-manno-pyranosyl)ethyl]-amine-silver(I)-nitrate (4), on five oral pathogenic bacterial strains. Furthermore, cytocompatibility was tested using human gingival fibroblasts (HGF).

Methods

Minimum inhibitory concentrations (MIC) were determined on five oral pathogenic bacterial strains by using the broth microdilution method: Fusobacterium nucleatum (ATCC 10953), Aggregatibacter actinomycetemcomitans (ATCC 33384), Porphyromonas gingivalis (ATCC 33277), Streptococcus mutans (ATCC 25175) and Enterococcus faecalis (DSMZ 20376). Furthermore, antimicrobial efficiency was tested using agar diffusion assays. To evaluate cytocompatibility, human gingival fibroblasts (HGFs) were exposed to AgNO₃ and complex 3 followed by a live/dead staining.

Results

MIC of the silver(I) complexes ranged between 0.625 and 5.0 mmol/L. The silver complexes 3 and 4 showed higher antibacterial efficiency against all tested species than AgNO₃. Antibacterial efficiency of complexes 3 and 4 on F. nucleatum (≥18 mm) and A. actinomycetemcomitans (≥23 mm) was more pronounced than against P. gingivalis (≥15 mm). Complex 3 (20 mM) induced the largest inhibition zones (30 to 31 mm) on Gram-negative strains. For Gram-positive strains, the largest inhibition zones were achieved by complex 3 (20 mM/S. mutans: 28 mm, E. faecalis: 18 mm). Complex 3 had a lower cytotoxic impact on HGFs compared to AgNO₃ by the power of ten.

Conclusions

The findings suggest that silver(I) carbohydrate complexes 3 and 4 might function as novel antimicrobial agents for the treatment of periodontal, carious or endodontic diseases.

ONO-pincer ruthenium complex-bound norvaline for efficient catalytic oxidation of methoxybenzenes with hydrogen peroxide

A Ru-bound norvaline shows enhanced catalytic activity for the oxidation of methoxybenzenes with unique chemoselectivity.

Influence of the π-coordinated arene on the anticancer activity of ruthenium(II) carbohydrate organometallic complexes

The synthesis and in vitro cytotoxicity of a series of Ru^II(arene) complexes with carbohydrate-derived phosphite ligands and various arene co-ligands is described. The arene ligand has a strong influence on the in vitro anticancer activity of this series of compounds, which correlates fairly well with cellular accumulation. The most lipophilic compound bearing a biphenyl moiety and a cyclohexylidene-protected carbohydrate is the most cytotoxic with unprecedented IC₅₀ values for the compound class in three human cancer cell lines. This compound shows reactivity to the DNA model nucleobase 9-ethylguanine, but does not alter the secondary structure of plasmid DNA, indicating that other biological targets are responsible for its cytotoxic effect.

New cyclodextrin-bearing 8-hydroxyquinoline ligands as multifunctional molecules

Recent investigations have rekindled interest in 8-hydroxyquinolines as therapeutic agents for cancer, Alzheimer's disease, and other neurodegenerative disorders. Three new β-cyclodextrin conjugates of 8-hydroxyquinolines and their copper(II) and zinc(II) complexes have been synthesized and characterized spectroscopically. In addition to improving aqueous solubility, due to the presence of the cyclodextrin moiety, the hybrid systems have interesting characteristics including antioxidant activity, and their copper(II) complexes are efficient superoxide dismutase (SOD) mimics. The ligands and their copper(II) complexes show low cytotoxicity, attributed to the presence of the cyclodextrin moiety. These compounds have potential as therapeutic agents in diseases related both to metal dyshomeostasis and oxidative stress.

[(2R,3S)-Butane-1,2,3,4-tetraol-κ3O1,O2,O3](ethanol-κO)tris(nitrato-κ2O,O′)samarium(III)

The title Sm^III–erythritol complex, [Sm(NO₃)₃(C₂H₆O)(C₄H₁₀O₄)], is isotypic with its Nd, Eu, Y, Gd, Tb and Ho analogues. The Sm^III cation exhibits a coordination number of ten and is chelated by a tridentate erythritol ligand and three bidentate nitrate anions. It is additionally coordinated by an O atom of an ethanol mol­ecule, completing an irregular coordination sphere. The Sm—O bond lengths range from 2.416 (2) to 2.611 (2) Å. In the crystal, extensive O—H⋯O hydrogen bonding involving all hy­droxy groups and some of the nitrate O atoms links the mol­ecules into a three-dimensional network.

Synthesis and photodynamic properties of maltohexaose-conjugated porphyrins

A series of porphyrin derivatives with one to four maltohexaose moieties in their meso positions have been synthesized. Zinc or free-base m-THPP (5,10,15,20-tetrakis(m-hydroxyphenyl)-porphyrin) was used as the porphyrin platform. The reaction of m-THPP with 3-iodopropyl nonadecaacetylmaltohexaoside afforded a mixture of all possible combinations of glycoconjugated porphyrins having one to four maltohexaose moieties; monoglycosylated (Ac-1), bisglycosylated (Ac-cis-2 and Ac-trans-2), triglycosylated (Ac-3), and tetraglycosylated (Ac-4) porphyrins were obtained in 11–26% yield. Removal of acetyl groups at maltohexaose moiety afforded highly water-soluble glycoconjugated porphyrins 1–4. Zinc derivatives were synthesized in a similar manner. These maltohexaose-linked porphyrins exhibit remarkable water-solublity (530 mg/mL for 4). The singlet oxygen production ability upon visible light irradiation is not affected by the maltohexaose substitution. Photo- and dark cytotoxicities of the maltohexaose-conjugated porphyrins 1–4 and Zn-1–4 were examined against a HeLa cell line, which showed that the mono-maltohexaosylated derivative (1 and Zn-1) was the most effective photosensitizer for PDT.

Sugar-metal ion interactions: the coordination behaviors of lanthanum with erythritol

Three novel lanthanum chloride-erythritol complexes (LaCl(3)·C(4)H(10)O(4)·5H(2)O (LaE(I)), LaCl(3)·C(4)H(10)O(4)·3H(2)O (LaE(II)), and LaCl(3)·1.5C(4)H(10)O(4) (LaE(III)) were synthesized and characterized by single crystal X-ray diffraction, FTIR, far-IR, THz, and Raman spectroscopy. The coordination number of La(3+) is nine. LaE(I) and LaE(II) have similar coordination spheres, but their hydrogen bond networks are different. Erythritol exhibits two coordination modes: two bidentate ligands and tridentate ligands in LaE(III). Chloride ions and water coordinate with La(3+) or participate in the hydrogen-bond networks in the three complexes. Crystal structures, FTIR, FIR, THz, and Raman spectra provide detailed information on the structures and coordination of hydroxyl groups to metal ions in the metal-carbohydrate complexes.

Synthesis of a glycopolymeric Pt(II) carrier and its induction of apoptosis in resistant cancer cells

Post-polymerization modification of a poly(pentafluorostyryl) backbone with β-d-galactose and a terpyridine platinum complex yields a well-defined material that represents the first example of a metal-conjugated glycopolymer. It reveals anti-proliferative activity, no detectable necrotic cytotoxicity, and efficiently induces apoptosis in both wild-type as well as resistant Nalm-6 leukemia cell lines.

A novel carbon monoxide-releasing molecule fully protects mice from severe malaria

Severe forms of malaria infection, such as cerebral malaria (CM) and acute lung injury (ALI), are mainly caused by the apicomplexan parasite Plasmodium falciparum. Primary therapy with quinine or artemisinin derivatives is generally effective in controlling P. falciparum parasitemia, but mortality from CM and other forms of severe malaria remains unacceptably high. Herein, we report the design and synthesis of a novel carbon monoxide-releasing molecule (CO-RM; ALF492) that fully protects mice against experimental CM (ECM) and ALI. ALF492 enables controlled CO delivery in vivo without affecting oxygen transport by hemoglobin, the major limitation in CO inhalation therapy. The protective effect is CO dependent and induces the expression of heme oxygenase-1, which contributes to the observed protection. Importantly, when used in combination with the antimalarial drug artesunate, ALF492 is an effective adjunctive and adjuvant treatment for ECM, conferring protection after the onset of severe disease. This study paves the way for the potential use of CO-RMs, such as ALF492, as adjunctive/adjuvant treatment in severe forms of malaria infection.

Interactions between metal ions and carbohydrates. Spectroscopic characterization and the topology coordination behavior of erythritol with trivalent lanthanide ions

The coordination of carbohydrate to metal ions is important because it may be involved in many biochemical processes. The synthesis and characterization of several novel lanthanide-erythritol complexes (TbCl(3)·1.5C(4)H(10)O(4)·H(2)O (TbE(I)), Pr(NO(3))(3)·C(4)H(10)O(4)·2H(2)O (PrEN), Ce(NO(3))(3)·C(4)H(10)O(4)·2H(2)O (CeEN), Y(NO(3))(3)·C(4)H(10)O(4)·C(2)H(5)OH (YEN), Gd(NO(3))(3)·C(4)H(10)O(4)·C(2)H(5)OH (GdEN)) and Tb(NO(3))(3)·C(4)H(10)O(4)·C(2)H(5)OH (TbEN) are reported. The structures of these complexes in the solid state have been determined by X-ray diffraction. Erythritol is used as two bidentate ligands or as three hydroxyl group donor in these complexes. FTIR spectra indicate that two kinds of structures, with water and without water involved in the coordination sphere, were observed for lanthanide nitrate-erythritol complexes. FIR and THz spectra show the formation of metal ion-erythritol complexes. Luminescence spectra of Tb-erythritol complexes have the characteristics of the Tb ion.