Quinone Ring Research Articles

Bishydroquinone Renieramycin M Induces Apoptosis of Human Lung Cancer Cells Through a Mitochondria-dependent Pathway.

Renieranycin M (RM), a bistetrahydro-isoquinolinequinone isolated from the Thai blue sponge, Xestospongia sp. was reported to be a potent anti-lung cancer agent. Modification at quinone ring enhanced apoptosis over necrosis. Thus, bishydroquinone renieramycin M (HQ-RM) was prepared and evaluated for apoptosis induction in lung cancer cells. HQ-RM was examined for cytotoxicity and apoptosis induction in human lung cancer H292 cells by 3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyltetrazoliumbromide and Hoechst/propidium iodide staining, respectively. The key molecular markers of mitochondrial apoptosis pathway were determined by western blot analysis. HQ-RM exhibited stronger cytotoxicity than RM. HQ-RM reduced vitality of lung cancer cells in a dose-dependent manner. Nuclear staining assay indicated that apoptotic cell death was the main mechanism of toxicity caused by HQ-RM. Protein analysis revealed that HQ-RM-mediated apoptosis involved the increase of pro-apoptotic B-cell lymphoma 2 associated X (BAX) protein, and the decrease of anti-apoptosis myeloid cell leukemia 1 (MCL1) and B-cell lymphoma 2 (BCL2) proteins. Moreover, caspase-9 and -3 and Poly (ADP-ribose) polymerase (PARP) were dramatically cleaved in response to HQ-RM treatment. HQ-RM has highly potent anticancer activity, greater than its parental RM, and induces lung cancer cell apoptosis through a mitochondrial apoptosis caspase-dependent mechanism. This information benefits the development of this compound for cancer therapy.

Synthesis, characterization and serum albumin binding studies of vitamin K3 derivatives

Synthesis, characterization and bovine serum albumin (BSA) binding properties of three derivatives of vitamin K3 have been described. Results of UV–Vis and fluorescence spectra indicate complexation between BSA and the ligands with conformational changes in protein, which is strongly supported by synchronous and three dimensional fluorescence studies. Addition of the ligands quenches the fluorescence of BSA which is accompanied by reduction in quantum yield (Ф) from 0.1010 to 0.0775–0.0986 range. Thermodynamic investigations reveal that hydrophobic interaction is the major binding force in the spontaneous binding of these ligands with BSA. The binding constants obtained depend on the substituent present in the quinone ring, which correlates linearly with the Taft's field substituent constant (σF). The results show that compound with strong electron withdrawing nitro-group forms relatively stronger complex with BSA than amino and thioglycolate substituted ones. Circular dichroism studies show that the α-helical content of the protein, upon complexation with the ligands, decreases in the case of amino and nitro substituted vitamin K3 while increases in thioglycolate substituted compound. Molecular docking studies indicated that the vitamin K3 derivatives are surrounded by hydrophobic residues of the BSA molecule, which is in good agreement with the results of fluorescence spectral and thermodynamic studies.

Crystal structure of 5,7,12,14-tetra-hydro-5,14:7,12-bis-([1,2]benzeno)-penta-cene-6,13-dione.

The lattice of 5,7,12,14-tetra-hydro-5,14:7,12-bis-([1,2]benzeno)-penta-cene-6,13-dione, C34H20O2, at 173 K has triclinic (P-1) symmetry and crystallizes with four independent half-mol-ecules in the asymmetric unit. Each mol-ecule is generated from a C17H10O substructure through an inversion center at the centroid of the central quinone ring, generating a wide H-shaped mol-ecule, with a dihedral angle between the mean planes of the terminal benzene rings in each of the two symmetry-related pairs over the four mol-ecules of 68.6 (1) (A), 65.5 (4) (B), 62.3 (9) (C), and 65.8 (8)° (D), an average of 65.6 (1)°. This compound has applications in gas-separation membranes constructed from polymers of intrinsic microporosity (PIM). The title compound is a product of a double Diels-Alder reaction between anthracene and p-benzo-quinone followed by de-hydrogenation. It has also been characterized by cyclic voltammetry and rotating disc electrode polarography, FT-IR, high resolution mass spectrometry, elemental analysis, and 1H NMR.

Q-Band Electron-Nuclear Double Resonance Reveals Out-of-Plane Hydrogen Bonds Stabilize an Anionic Ubisemiquinone in Cytochrome bo3 from Escherichia coli.

The respiratory cytochrome bo3 ubiquinol oxidase from Escherichia coli has a high-affinity ubiquinone binding site that stabilizes the one-electron reduced ubisemiquinone (SQH), which is a transient intermediate during the electron-mediated reduction of O2 to water. It is known that SQH is stabilized by two strong hydrogen bonds from R71 and D75 to ubiquinone carbonyl oxygen O1 and weak hydrogen bonds from H98 and Q101 to O4. In this work, SQH was investigated with orientation-selective Q-band (∼34 GHz) pulsed 1H electron-nuclear double resonance (ENDOR) spectroscopy on fully deuterated cytochrome (cyt) bo3 in a H2O solvent so that only exchangeable protons contribute to the observed ENDOR spectra. Simulations of the experimental ENDOR spectra provided the principal values and directions of the hyperfine (hfi) tensors for the two strongly coupled H-bond protons (H1 and H2). For H1, the largest principal component of the proton anisotropic hfi tensor Tz' = 11.8 MHz, whereas for H2, Tz' = 8.6 MHz. Remarkably, the data show that the direction of the H1 H-bond is nearly perpendicular to the quinone plane (∼70° out of plane). The orientation of the second strong hydrogen bond, H2, is out of plane by ∼25°. Equilibrium molecular dynamics simulations on a membrane-embedded model of the cyt bo3 QH site show that these H-bond orientations are plausible but do not distinguish which H-bond, from R71 or D75, is nearly perpendicular to the quinone ring. Density functional theory calculations support the idea that the distances and geometries of the H-bonds to the ubiquinone carbonyl oxygens, along with the measured proton anisotropic hfi couplings, are most compatible with an anionic (deprotonated) ubisemiquinone.

Biotransformations versus chemical modifications: new cytotoxic analogs of marine sesquiterpene ilimaquinone

Highly biologically active marine sesquiterpene ilimaquinone was selected for chemical modifications. Its biotransformation was investigated using a combinatorial approach as an original way to screen different strains of microorganisms. Mucor circinelloides ATCC 8541 was able to structurally modify ilimaquinone into three different compounds. A stereospecific epoxidation was observed and compared to chemical epoxidation. A hydroxylation of the decalin ring was also observed as well as an unexpected substitution on the quinone ring by ethanolamine. Compounds were evaluated against several cell lines.

Structural analysis and molecular docking of trypanocidal aryloxy-quinones in trypanothione and glutathione reductases: a comparison with biochemical data

A set of aryloxy-quinones, previously synthesized and evaluated against Trypanosoma cruzi epimastigotes cultures, were found more potent and selective than nifurtimox. One of the possible mechanisms of the trypanocidal activity of these quinones could be inhibition of trypanothione reductase (TR). Considering that glutathione reductase (GR) is the equivalent of TR in humans, biochemical, kinetic, and molecular docking studies in TR and GR were envisaged and compared with the trypanocidal and cytotoxic data of a set of aryloxy-quinones. Biochemical assays indicated that three naphthoquinones (Nq-h, Nq-g, and Nq-d) selectively inhibit TR and the TR kinetic analyses indicated that Nq-h inhibit TR in a noncompetitive mechanism. Molecular dockings were performed in TR and GR in the following three putative binding sites: the catalytic site, the dimer interface, and the nicotinamide adenine dinucleotide phosphate-binding site. In TR and GR, the aryloxy-quinones were found to exhibit high affinity for a site near it cognate-binding site in a place in which the noncompetitive kinetics could be justified. Taking as examples the three compounds with TR specificity (TRS) (Nq-h, Nq-g, and Nq-d), the presence of a network of contacts with the quinonic ring sustained by the triad of Lys62, Met400′, Ser464′ residues, seems to contribute hardly to the TRS. Compound Nq-b, a naphthoquinone with nitrophenoxy substituent, proved to be the best scaffold for the design of trypanocidal compounds with low toxicity. However, the compound displayed only a poor and non-selective effect toward TR indicating that TR inhibition is not the main reason for the antiparasitic activity of the aryloxy-quinones.

Spherical Vesicles Formed by Co-Assembly of Cyclic Pentagonal Pillar[5]quinone with Cyclic Hexagonal Pillar[6]arene.

Mixing cyclic pentagonal pillar[5]quinone with cyclic hexagonal pillar[6]arene in a 12:20 molar feed ratio resulted in spontaneous production of vesicles, while assembly of pillar[6]arene and pillar[5]quinone alone produced hexagonal disks and wires, respectively. Incorporation of pentagonal pillar[5]quinone rings into hexagonal pillar[6]arene sheets gave curvature and contributed to the formation of vesicles. Conventional vesicles are generally synthesized by assembly of amphiphilic molecules containing hydrophobic and hydrophilic parts. Therefore, the co-assembly of pentagonal and hexagonal molecules to obtain spherical vesicles demonstrated in this study is a new concept based on geometric design.

Coenzyme Q biosynthesis in health and disease

Coenzyme Q (CoQ, or ubiquinone) is a remarkable lipid that plays an essential role in mitochondria as an electron shuttle between complexes I and II of the respiratory chain, and complex III. It is also a cofactor of other dehydrogenases, a modulator of the permeability transition pore and an essential antioxidant.CoQ is synthesized in mitochondria by a set of at least 12 proteins that form a multiprotein complex. The exact composition of this complex is still unclear. Most of the genes involved in CoQ biosynthesis (COQ genes) have been studied in yeast and have mammalian orthologues. Some of them encode enzymes involved in the modification of the quinone ring of CoQ, but for others the precise function is unknown. Two genes appear to have a regulatory role: COQ8 (and its human counterparts ADCK3 and ADCK4) encodes a putative kinase, while PTC7 encodes a phosphatase required for the activation of Coq7.Mutations in human COQ genes cause primary CoQ10 deficiency, a clinically heterogeneous mitochondrial disorder with onset from birth to the seventh decade, and with clinical manifestation ranging from fatal multisystem disorders, to isolated encephalopathy or nephropathy.The pathogenesis of CoQ10 deficiency involves deficient ATP production and excessive ROS formation, but possibly other aspects of CoQ10 function are implicated.CoQ10 deficiency is unique among mitochondrial disorders since an effective treatment is available. Many patients respond to oral CoQ10 supplementation. Nevertheless, treatment is still problematic because of the low bioavailability of the compound, and novel pharmacological approaches are currently being investigated. This article is part of a Special Issue entitled ‘EBEC 2016: 19th European Bioenergetics Conference, Riva del Garda, Italy, July 2–6, 2016’, edited by Prof. Paolo Bernardi.

Studies into the synthetic analogs of key intermediates, and ring precursors in the biosynthetic pathway of Coenzyme Q: Synthesis and metabolism

Coenzyme Q (ubiquinone or Q) is a redox active lipid molecule, with a fully substituted benzoquinone ring and a polyisoprenoid tail, containing up to ten isoprene units. Q is an essential component of the mitochondrial respiratory electron transport chain. The exact biosynthetic pathway has still not been completely characterized. In this study, farnesylated analogs of several Q intermediates have been been chemically synthesized. The synthesis of 2‐farnesyl‐1,4‐hydroquinone serves as an analog of 3‐hexaprenyl‐4‐hydroxyphenol, which accumulates in yeast coq6 and coq9 mutants that over‐express the Coq8 polypeptide. In addition farnesylated analogs of 5‐demethoxy‐Q3 (DMQ3), 2‐demethyl‐5‐demethoxy‐Q3 (DDMQ3), and 2‐demethyl‐5‐demethoxy‐4‐amino‐Q3 (IDDMQ3H2) were chemically synthesized. The farnesylated analogs are added to yeast cell cultures to determine whether they serve as precursors and/or intermediates in the biosynthesis of Q3. Also, other selected farnesylated substrates such as 3‐farnesyl‐4‐hydroxybenzoic acid, 3‐farnesyl‐4,5‐dihroxybenzoic acid and others are being synthesized for studying Q metabolism. These substrates can also serve as ligands in protein binding assays and as substrates with isolated enzymes. In addition, a number of different compounds are being tested in assays with mammalian cells, to analyze their roles as ring precursors for Q biosynthesis. Thereby we hope to understand and further characterize the biosynthetic and metabolic pathways responsible for Q biosynthesis and function in different living systems.Support or Funding InformationThis research was funded by NSF MCB‐1330803

An EPR and DFT study on the primary radical formed in hydroxylation reactions of 2,6-dimethoxy-1,4-benzoquinone

ABSTRACTThe quinone compound 2,6-dimethoxy-1,4-benzoquinone is hydroxylated in alkaline aqueous solution with pH above 12. Electron paramagnetic resonance experiments showed that two transient radicals are formed in this reaction. The radical appearing first is assigned to a one electron reduced 2,6-dimethoxy-1,4-benzoquinone, receiving the electron from an intermediate anionic hydroxylated species. For this primary radical, all proton couplings were determined (quinoid ring protons: 1.453 G, methyl protons: 0.795 G). The density functional theory method was applied to obtain electronic and structural information of the primary radical and a solution structure is suggested. For approaching the experimental hyperfine couplings in theoretical models, it was necessary to consider effects of external polarisation arising from water molecules near one carbonyl group, and the orientation of methoxy groups towards the quinone ring. With this approach, the secondary radical formed in the hydroxylation reaction, and the transient radicals found for other biologically important quinones (including coenzymes Q) and their hydroxylated species may become accessible.

Both idebenone and idebenol are localized near the lipid–water interface of the membrane and increase its fluidity

Idebenone is a synthetic analog of coenzyme Q; both share a quinone moiety but idebenone has a shorter lipophilic tail ending with a hydroxyl group. Differential scanning calorimetry experiments showed that both idebenone and idebenol widened and shifted the phase transition of 1,2-dipalmitoylphosphatidylcholine (DPPC) to a lower temperature and a phase separation with different concentrations of these molecules was observed. Also small angle X-ray diffraction and wide angle X-ray diffraction revealed that both, idebenone and idebenol, induced laterally separated phases in fluid membranes when included in DPPC membranes. Electronic profiles showed that both forms, idebenone and idebenol, reduced the thickness of the fluid membrane. 2H NMR measurements showed that the order of the membrane decreased at all temperatures in the presence of idebenone or idebenol, the greatest disorder being observed in the segments of the acyl chains close to the lipid–water interface. 1H NOESY MAS NMR spectra were obtained using 1-palmitoyl-2-oleoyl-phosphatidylcholine membranes and results pointed to a similar location in the membrane for both forms, with the benzoquinone or benzoquinol rings and their terminal hydroxyl group of the hydrophobic chain located near the lipid/water interface of the phospholipid bilayer and the terminal hydroxyl group of the hydrophobic chain of both compounds located at the lipid/water interface. Taken together, all these different locations might explain the different physiological behavior shown by the idebenone/idebenol compared with the ubiquinone-10/ubiquinol-10 pair in which both compounds are differently localized in the membrane.

Synthesis and Characterization of Nanofibrous Polyaniline Thin Film Prepared by Novel Atmospheric Pressure Plasma Polymerization Technique.

This work presents a study on the preparation of plasma-polymerized aniline (pPANI) nanofibers and nanoparticles by an intense plasma cloud type atmospheric pressure plasma jets (iPC-APPJ) device with a single bundle of three glass tubes. The nano size polymer was obtained at a sinusoidal wave with a peak value of 8 kV and a frequency of 26 kHz under ambient air. Discharge currents, photo-sensor amplifier, and optical emission spectrometer (OES) techniques were used to analyze the plasma produced from the iPC-APPJ device. Field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), gas chromatography-mass spectrometry (GC-MS), and gel permeation chromatography (GPC) techniques were used to analyze the pPANI. FE-SEM and TEM results show that pPANI has nanofibers, nanoparticles morphology, and polycrystalline characteristics. The FT-IR and GC-MS analysis show the characteristic polyaniline peaks with evidence that some quinone and benzene rings are broken by the discharge energy. GPC results show that pPANI has high molecular weight (Mw), about 533 kDa with 1.9 polydispersity index (PDI). This study contributes to a better understanding on the novel growth process and synthesis of uniform polyaniline nanofibers and nanoparticles with high molecular weights using the simple atmospheric pressure plasma polymerization technique.

Reactivity of 1.4-benzoquinone with trinuclear ruthenium and osmium clusters: Facile hydrogenation of the quinoid fragment

The reaction of [H2Os3(CO)10] with 1,4-benzoquinone yields initially a complex where the quinone bonds to the metal framework, both through a carbon atom of the ring and through an oxygen atom. Evidence suggests that this complex is a kinetic product which then transforms into complexes in which the quinone bonds through the oxygen atom. In one case, an oxygen atom of a hydroquinone moiety, bridges one of the metal–metal bonds, and in the other, a benzoquinone group acts, coordinated through the oxygen atoms, as a bridge between two trinuclear fragments. Similar products are obtained from the reaction of [Ru3(CO)12] with the same quinone in a hydrogen atmosphere although the presence of hydrogen leads to a partial hydrogenation of the benzoquinone ring. The reaction of [Os3(CO)10(MeCN)2] with the same quinone, formed a compound where the quinone is coordinate η2 through one of the double bonds of the ring to one of the osmium atoms. The products were characterized spectroscopically and; for four of the compounds; by X-ray crystallography.

Reactivity measurement in estimation of benzoquinone and benzoquinone derivatives' allergenicity.

Benzoquinone (BQ) and benzoquinone derivatives (BQD) are used in the production of dyes and cosmetics. While BQ, an extreme skin sensitizer, is an electrophile known to covalently modify proteins via Michael Addition (MA) reaction whilst halogen substituted BQD undergo nucleophilic vinylic substitution (SNV) mechanism onto amine and thiol moieties on proteins, the allergenic effects of adding substituents on BQ have not been reported. The effects of inserting substituents on the BQ ring has not been studied in animal assays. However, mandated reduction/elimination of animals used in cosmetics testing in Europe has led to an increased need for alternatives for the prediction of skin sensitization potential. Electron withdrawing and electron donating substituents on BQ were assessed for effects on BQ reactivity toward nitrobenzene thiol (NBT). The NBT binding studies demonstrated that addition of EWG to BQ as exemplified by the chlorine substituted BQDs increased reactivity while addition of EDG as in the methyl substituted BQDs reduced reactivity. BQ and BQD skin allerginicity was evaluated in the murine local lymph node assay (LLNA). BQD with electron withdrawing groups had the highest chemical potency followed by unsubstituted BQ and the least potent were the BQD with electron donating groups. The BQD results demonstrate the impact of inductive effects on both BQ reactivity and allergenicity, and suggest the potential utility of chemical reactivity data for electrophilic allergen identification and potency ranking.

Saccharothrixones A-D, Tetracenomycin-Type Polyketides from the Marine-Derived Actinomycete Saccharothrix sp. 10-10.

Saccharothrixones A-C (1-3), three new aromatic polyketide seco-tetracenomycins, and saccharothrixone D (4), a new tetracenomycin analogue possessing opposite configurations at all of the stereogenic centers, were isolated from the marine-derived actinomycete Saccharothrix sp. 10-10. Compounds 1-3 represent the first examples of seco-tetracenomycins where the quinone ring B is cleaved and re-formed into a furanone ring. Their structures were elucidated by spectroscopic analyses and ECD calculations. The absolute configuration of 4 was confirmed by single-crystal X-ray diffraction analysis. Saccharothrixone D (4) showed in vitro cytotoxic activity against the HepG2 cancer cell line with an IC50 value of 7.5 μM.

Studies into the farnesylated analogs of key intermediates in the biosynthetic pathway of Coenzyme Q: Synthesis and metabolism

Coenzyme Q (ubiquinone or Q) is a redox active lipid molecule, with a fully substituted benzoquinone ring and a polyisoprenoid tail, containing up to ten isoprene units. Q is an essential component...

Identification of Coq11, a New Coenzyme Q Biosynthetic Protein in the CoQ-Synthome in Saccharomyces cerevisiae

Coenzyme Q (Q or ubiquinone) is a redox active lipid composed of a fully substituted benzoquinone ring and a polyisoprenoid tail and is required for mitochondrial electron transport. In the yeast Saccharomyces cerevisiae, Q is synthesized by the products of 11 known genes, COQ1-COQ9, YAH1, and ARH1. The function of some of the Coq proteins remains unknown, and several steps in the Q biosynthetic pathway are not fully characterized. Several of the Coq proteins are associated in a macromolecular complex on the matrix face of the inner mitochondrial membrane, and this complex is required for efficient Q synthesis. Here, we further characterize this complex via immunoblotting and proteomic analysis of tandem affinity-purified tagged Coq proteins. We show that Coq8, a putative kinase required for the stability of the Q biosynthetic complex, is associated with a Coq6-containing complex. Additionally Q6 and late stage Q biosynthetic intermediates were also found to co-purify with the complex. A mitochondrial protein of unknown function, encoded by the YLR290C open reading frame, is also identified as a constituent of the complex and is shown to be required for efficient de novo Q biosynthesis. Given its effect on Q synthesis and its association with the biosynthetic complex, we propose that the open reading frame YLR290C be designated COQ11.

Chemisorption and Electrochemical Activity of Thiophenols at Well-Defined Pd(111) Surfaces: Studies by LEED, AES, HREELS, and Electrochemistry

The chemisorption and electrochemical activity of 2 ,5 -dihydroxythiophenol (DHT) and 2-(8mercaptooctyl)-1,4-benzenediol (DHOT) on well-defined Pd(111) surfaces were studied by Auger electron spectroscopy (AES), low energy electron diffraction (LEED), high resolution electron energyloss spectroscopy (HREELS), and electrochemistry (EC). Results confirm that DHT is chemisorbed in two discrete orientations such that at low concentrations, DHT is oxidatively bound to the surface through the diphenol and mercapto groups as quinonoid and S moieties, respectively, whereas at high concentrations, the molecule is coordinated oxidatively through the –SH group in a vertical S- η 1

Valence tautomeric dinuclear adducts of Co(II) diketonates with redox-active diquinones for the design of spin qubits: computational modeling.

The possibility of employing the mechanism of intramolecular electron transfer between metal and ligand centers in the valence tautomeric complexes formed as electrically neutral 2 : 1 adducts of Co(II) diketonates and redox-active tetradentate di-o-quinones, for quantum information processing, has been computationally studied using the DFT B3LYP*/6-311++G(d,p) method. It has been shown that by the proper choice of a linker group bridging the quinone rings and substituents in the diketonate fragments, complexes with the properties required in 2-qubit quantum gates (sufficiently narrow energy gaps between the spin states and weakly coupled paramagnetic centers) can be designed, in order to realize the mechanism of thermally driven migration of paramagnetic centers between the o-quinone fragments and metal atoms. These are exemplified by the adduct of bis-(hexafluoroacetylacetonate)Co(ii) with a diquinone containing dimethylene linker. Valence tautomerism is considered as a new, promising mechanistic paradigm for the molecular design of 2-qubit molecular systems.

ChemInform Abstract: Free‐Radical Selective Functionalization of 1,4‐Naphthoquinones by Perfluorodiacyl Peroxides.

Abstract Perfluoroalkyl radicals, generated by thermal decomposition of perfluorodiacyl peroxides, react selectively with quinone rings of 1,4-naphthoquinones. In the presence of a non-conjugated alkene such as 1-hexene, perfluoroalkyl radicals add to the double bonds of the olefin forming a radical adduct, which selectively adds to the naphthoquinone ring. Several perfluorodiacyl peroxides have been synthesized and used for the direct and alkene-mediated functionalization of naphthoquinones. Geometrical parameters and electron density topology of all perfluorodiacyl peroxides have been calculated by the density functional formalism and quantum theory of atoms in molecules to attempt a rationalization of the experimental reactivity.