Formation Of Reactive Intermediates Research Articles

Seasonal and spatial variabilities in the water chemistry of prairie pothole wetlands influence the photoproduction of reactive intermediates

The hydrology and water chemistry of prairie pothole wetlands vary spatially and temporally, on annual and decadal timescales. Pesticide contamination of wetlands arising from agricultural activities is a foremost concern. Photochemical reactions are important in the natural attenuation of pesticides and may be important in limiting ecological and human exposure. Little is known, however, about the variable influence of wetland water chemistry on indirect photochemistry. In this study, seasonal water samples were collected from seven sites throughout the prairie pothole region over three years to understand the spatiotemporal dynamics of reactive intermediate photoproduction. Samples were classified by the season in which they were collected (spring, summer, or fall) and the typical hydroperiod of the wetland surface water (temporary or semi-permanent). Under photostable conditions, steady-state concentrations and apparent quantum yields or quantum yield coefficients were measured for triplet excited states of dissolved organic matter, singlet oxygen, hydroxyl radical, and carbonate radical under simulated sunlight. Steady-state concentrations and quantum yields increased on average by 15% and 40% from spring to fall, respectively. Temporary wetlands had 40% higher steady-state concentrations of reactive intermediates than semi-permanent wetlands, but 50% lower quantum yields. Computed quantum yields for reactive intermediate formation were used to predict the indirect photochemical half-lives of seven pesticides in average temporary and semi-permanent prairie pothole wetlands. As a first approximation, the predictions agree to within two orders of magnitude of previously reported half-lives.

Plasma Proteins Modified by Advanced Glycation End Products (AGEs) Reveal Site-specific Susceptibilities to Glycemic Control in Patients with Type 2 Diabetes

Protein glycation refers to the reversible reaction between aldoses (or ketoses) and amino groups yielding relatively stable Amadori (or Heyns) products. Consecutive oxidative cleavage reactions of these products or the reaction of amino groups with other reactive substances (e.g. α-dicarbonyls) yield advanced glycation end products (AGEs) that can alter the structures and functions of proteins. AGEs have been identified in all organisms, and their contents appear to rise with some diseases, such as diabetes and obesity. Here, we report a pilot study using highly sensitive and specific proteomics approach to identify and quantify AGE modification sites in plasma proteins by reversed phase HPLC mass spectrometry in tryptic plasma digests. In total, 19 AGE modification sites corresponding to 11 proteins were identified in patients with type 2 diabetes mellitus under poor glycemic control. The modification degrees of 15 modification sites did not differ among cohorts of normoglycemic lean or obese and type 2 diabetes mellitus patients under good and poor glycemic control. The contents of two amide-AGEs in human serum albumin and apolipoprotein A-II were significantly higher in patients with poor glycemic control, although the plasma levels of both proteins were similar among all plasma samples. These two modification sites might be useful to predict long term, AGE-related complications in diabetic patients, such as impaired vision, increased arterial stiffness, or decreased kidney function.

Intramolecular C-H and C-F Bond Oxygenation Mediated by a Putative Terminal Oxo Species in Tetranuclear Iron Complexes.

Herein we report the intramolecular arene C-H and C-F bond oxygenation by tetranuclear iron complexes. Treatment of [LFe3(PhPz)3OFe][OTf]2 (1) or its fluorinated analog [LFe3(F2ArPz)3OFe][OTf]2 (5) with iodosobenzene results in the regioselective hydroxylation of a bridging pyrazolate ligand, converting a C-H or C-F bond into a C-O bond. The observed reactivity suggests the formation of terminal and reactive Fe-oxo intermediates. With the possibility of intramolecular electron transfer within clusters in 1 and 5, different reaction pathways (Fe(IV)-oxo vs Fe(III)-oxo) might be responsible for the observed arene hydroxylation.

Metabolic activation and drug-induced liver injury: in vitro approaches for the safety risk assessment of new drugs.

Drug-induced liver injury (DILI) is a significant leading cause of hepatic dysfunction, drug failure during clinical trials and post-market withdrawal of approved drugs. Many cases of DILI are unexpected reactions of an idiosyncratic nature that occur in a small group of susceptible individuals. Intensive research efforts have been made to understand better the idiosyncratic DILI and to identify potential risk factors. Metabolic bioactivation of drugs to form reactive metabolites is considered an initiation mechanism for idiosyncratic DILI. Reactive species may interact irreversibly with cell macromolecules (covalent binding, oxidative damage), and alter their structure and activity. This review focuses on proposed in vitro screening strategies to predict and reduce idiosyncratic hepatotoxicity associated with drug bioactivation. Compound incubation with metabolically competent biological systems (liver-derived cells, subcellular fractions), in combination with methods to reveal the formation of reactive intermediates (e.g., formation of adducts with liver proteins, metabolite trapping or enzyme inhibition assays), are approaches commonly used to screen the reactivity of new molecules in early drug development. Several cell-based assays have also been proposed for the safety risk assessment of bioactivable compounds. Copyright © 2015 John Wiley & Sons, Ltd.

ChemInform Abstract: The Chemistry of Silacyclopropenes

AbstractReview: [synthesis and reactions; 65 refs.

Comparative absorption and tissue distribution of 14C-benzo(a)pyrene and 14C-phenanthrene in the polar cod (Boreogadus saida) following oral administration

The Arctic is an important sink for organic pollutants such as polycyclic aromatic hydrocarbons (PAHs) long-range transported from industrial regions. With the retreat of sea ice and increasing anthropogenic activities such as the oil and gas industries, local sources of PAHs are expected to increase both through operational and accidental discharges. There is a need to increase our knowledge concerning the uptake and distribution of organic pollutants, in particular PAHs, to evaluate the risk these toxic compounds may represent for Arctic species. The absorption and tissue distribution of 14C-benzo(a)pyrene (BaP) and 14C-phenanthrene (Phen) were studied in the polar cod (Boreogadus saida), a key Arctic species. After a single oral dose of BaP (1.15 ± 0.36 mg/kg fish) or Phen (0.40 ± 0.12 mg/kg fish), corresponding to 0.12 ± 0.03 mCi/kg fish, the tissue distribution was followed through 30 days by means of whole-body autoradiography and liquid scintillation counting of liver and bile. For both compounds, radiolabeling was mainly present in the bile and the intestines throughout the study period. Phen-derived radioactivity, however, appeared to be more systemically distributed compared to BaP. Furthermore, a far higher amount of irreversibly bound BaP-derived radioactivity was present in the intestinal mucosa compared to Phen, indicating a more extensive formation of reactive intermediates from the former compared with the latter. Liquid scintillation counting confirmed that radioactivity was present in the liver at all time points for both groups although the levels were low in the BaP group. These results strongly indicated that both compounds and/or their metabolites undergo enterohepatic circulation.

Iodine-Mediated Oxidative Coupling of Hydroxamic Acids with Amines towards a New Peptide-Bond Formation

An efficient and straightforward approach for the coupling of Nα-protected hydroxamic acids with an amino component in the presence of iodine is delineated. The reaction is mediated by the formation of unstable but reactive acyl nitroso intermediates. The peptide hydroxamic acids were found to be useful substrates in coupling reactions.

The Chemistry of Silacyclopropenes

AbstractThe synthesis and reactions of silacyclopropenes are summarized. Addition of silylenes to acetylenes and photochemical isomerization of alkynyldisilanes are known as two major routes for the synthesis of silacyclopropenes. Silacyclopropenes had been thought to be highly reactive and difficult to handle until the first crystal structure of a stable one was reported in 1980. Currently, however, it is commonly accepted that those molecules are stable under ambient conditions when sufficiently bulky substituents are introduced onto the strained three‐membered ring system to stabilize it kinetically. The reactivity of silacyclopropenes is interesting and depends on the nature of substituents. They, indeed, undergo a variety of reactions, such as photolysis, thermolysis, and transition‐metal‐catalyzed reactions, leading to the formation of reactive intermediates including silylenes and silapropadienes, and their transition‐metal complexes, through which numerous transformations into silicon‐containing cyclic and acyclic compounds are possible.

Photochemical degradation of PAHs in estuarine surface water: effects of DOM, salinity, and suspended particulate matter.

The photodegradation of several polycyclic aromatic hydrocarbons (PAHs) including phenanthrene, benzo(a)pyrene, and benzo(e)pyrene was studied under different estuarine conditions to elucidate the effects of dissolved organic matter (DOM), salinity, and suspended particles on PAH photodegradation in the estuarine surface water. Besides the competitive light absorption effect, DOM can accelerate the photodegradation of small PAHs such as phenanthrene by enhancing the formation of reactive intermediates and inhibit the photodegradation of large PAHs such as benzo[a]pyrene (BaP) and benzo[e]pyrene (BeP) by binding the PAH molecules. High salinity would accelerate the photodegradation of PAHs; however, the magnitude and direction of the salt effect are complicated in the presence of DOM due to the "salting-out" effect on the binding of PAHs with DOM. Suspended particulate matter in the estuary provides an alternative solid-phase photodegradation pathway for PAHs, which proceeds faster than the aqueous phase. Particulates apparently exert different effects on the photodegradation of phenanthrene (Phe) and BaP as a result of the combined effects of light absorption, particulate organic matter, PAH surface sorption, and concentration dilution in the presence of suspended particulate matter.

ChemInform Abstract: Carbon—Fluorine Bond Activation for the Synthesis of Functionalized Molecules

AbstractReview: [39 refs.

Vapor-phase ethanol carbonylation with heteropolyacid-supported Rh

Ethanol carbonylation is a potential route to valuable C3 products. Here, Rh supported on porous, Cs-exchanged heteropolyacid Cs3PW12O40, is demonstrated as an effective catalyst for vapor-phase ethanol carbonylation, with higher selectivity and conversion to propionates than existing catalysts. Residual acidity or a Mo polyatom was strongly detrimental to yields. Propionate selectivity was maximized at 96% at 170°C and with added H2O. The catalyst displayed stable selectivity over 30h on stream and up to 77% conversion. Ethyl iodide is a required co-catalyst but at levels as low as 2% relative to ethanol. XPS and in situ XANES indicate partial Rh reduction, consistent with the formation of low-valent reactive intermediates and slow deactivation through formation of Rh nanoparticles. With further optimization and understanding, these Rh/heteropolyacid catalysts may lead to stable and selective catalysts for the production of propionates through ethanol carbonylation.

Copper(II) Complexes of 2,2′:6′,2″‐Terpyridine Derivatives for Catalytic Aerobic Alcohol Oxidations – Observation of Mixed‐Valence CuICuII Assembles

AbstractThe reactions of copper(II) salts with simple terpyridine (tpy) ligands gave mononuclear monoligand complexes 1–3, of which two new structures have been characterized by X‐ray crystallography. These complexes were applied as catalysts for the oxidation of benzylic alcohol to benzaldehyde in air in the presence of the radical 2,2,6,6‐tetramethylpiperidinyl‐1‐oxyl (TEMPO). Copper complexes 1 and 2 are efficient catalysts for the reactions in water at 70 °C with 4‐dimethylaminopyridine (DMAP) as an extra base. The influence of TEMPO on the formation of new reactive intermediates during the catalytic reactions was tentatively investigated by introducing TEMPO into the reaction solutions of tpy derivatives with copper dichloride. Two new complexes with interesting solid‐state structures resulting from these reactions have been isolated and characterized. The coordination reactions in the presence of TEMPO led to new mixed‐valence CuICuII supramolecular assembles (4 and 5), although they adopt either discrete complex or 1D polymeric structures. Further catalytic studies indicated that the mixed‐valence assembles 4 and 5 displayed higher catalytic activity than those of the mononuclear complexes under milder conditions. The relationship between the molecular structures of diverse copper complexes and their reactivity is discussed on the basis of the results obtained.

Quantum Yields for the Formation of Reactive Intermediates from Dissolved Organic Matter Samples from the Suwannee River

Photochemical properties of dissolved organic matter (DOM) are of interest due to their effects on natural and engineered systems, including the fate and transport of organic contaminants and pathogen inactivation. DOM absorbs energy and produces different reactive intermediates (RI), including the hydroxyl radical (HO·), singlet oxygen (1O2), and excited triplet states (3DOM*). Recently, a new set of DOM samples, including natural organic matter (NOM), the hydrophobic organic acid fraction (HPOA), and the transphilic acid fraction (TPIA) from the Suwannee River, were collected. Apparent quantum yields for the formation of HO·, 1O2, and 3DOM* were measured for DOM samples using a solar simulator. Values were 2.09–4.20×10−4 for triplet states, 2.74–6.54×10−2 for singlet oxygen, and 0.95–1.65×10−5 for hydroxyl radical for the different samples. In addition, fluorescence quantum yields were measured with obtained values between 0.79–1.3×10−2. In some cases, values obtained were different from older DOM samples, indicating potential changes in properties of DOM in the Suwannee River over time.

Synthesis, in Vitro Covalent Binding Evaluation, and Metabolism of (14)C-Labeled Inhibitors of 11β-HSD1.

In this letter, we reported the design and synthesis of three potent, selective, and orally bioavailable 11β-HSD1 inhibitors labeled with (14)C: AMG 456 (1), AM-6949 (2), and AM-7715 (3). We evaluated the covalent protein binding of the labeled inhibitors in human liver microsomes in vitro and assessed their potential bioactivation risk in humans. We then studied the in vitro mechanism of 2 in human hepatocytes and the formation of reactive intermediates. Our study results suggest that 1 and 3 have low potential for metabolic bioactivation in humans, while 2 has relatively high risk.

Reactivity of hypotaurine and cysteine sulfinic acid toward carbonate radical anion and nitrogen dioxide as explored by the peroxidase activity of Cu,Zn superoxide dismutase and by pulse radiolysis

Hypotaurine and cysteine sulfinic acid are known to be readily oxidized to the respective sulfonates, taurine and cysteic acid, by several oxidative agents that may be present in biological systems. In this work, the relevance of both the carbonate anion and nitrogen dioxide radicals in the oxidation of hypotaurine and cysteine sulfinic acid has been explored by the peroxidase activity of Cu,Zn superoxide dismutase (SOD) and by pulse radiolysis. The extent of sulfinate oxidation induced by the system SOD/H2O2 in the presence of bicarbonate (CO3•– generation), or nitrite (•NO2 generation) has been evaluated. Hypotaurine is efficiently oxidized by the carbonate radical anion generated by the peroxidase activity of Cu,Zn SOD. Pulse radiolysis studies have shown that the carbonate radical anion reacts with hypotaurine more rapidly (k = 1.1 × 109 M−1s−1) than nitrogen dioxide (k = 1.6 × 107 M−1s−1). Regarding cysteine sulfinic acid, it is less reactive with the carbonate radical anion (k = 5.5 × 107 M−1s−1) than hypotaurine. It has also been observed that the one-electron transfer oxidation of both sulfinates by the radicals is accompanied by the generation of transient sulfonyl radicals (RSO2•). Considering that the carbonate radical anion could be formed in vivo at high level from bicarbonate, this radical can be included in the oxidants capable of performing the last metabolic step of taurine biosynthesis. Moreover, the protective effect exerted by hypotaurine and cysteine sulfinate on the carbonate radical anion-mediated tyrosine dimerization indicates that both sulfinates have scavenging activity towards the carbonate radical anion. However, the formation of transient reactive intermediates during sulfinate oxidation by carbonate anion and nitrogen dioxide radical may at the same time promote oxidative reactions.

Metabolism and Pharmacokinetics of Allitinib in Cancer Patients: The Roles of Cytochrome P450s and Epoxide Hydrolase in its Biotransformation

Allitinib, a novel irreversible selective inhibitor of the epidermal growth factor receptor (EGFR) 1 and human epidermal receptor 2 (ErbB2), is currently in clinical trials in China for the treatment of solid tumors. It is a structural analog of lapatinib but has an acrylamide side chain. Sixteen metabolites of allitinib were detected by ultra-high-performance liquid chromatography/quadrupole time-of-flight mass spectrometry. The pharmacologically active α,β-unsaturated carbonyl group was the major metabolic site. The metabolic pathways included O-dealkylation, amide hydrolysis, dihydrodiol formation, hydroxylation, and secondary phase 2 conjugation. The metabolite of amide hydrolysis (M6) and 27,28-dihydrodiol allitinib (M10) were the major pharmacologically active metabolites in the circulation. The steady-state exposures to M6 and M10 were 11% and 70% of that of allitinib, respectively. The biotransformation of allitinib was determined using microsomes and recombinant metabolic enzymes. In vitro phenotyping studies demonstrated that multiple cytochrome P450 (P450) isoforms, mainly CYP3A4/5 and CYP1A2, were involved in the metabolism of allitinib. Thiol conjugates (M14 and M16) and dihydrodiol metabolites (M5 and M10) were detected in humans, implying the formation of reactive intermediates. The formation of a glutathione conjugate of allitinib was independent of NADPH and P450 isoforms, but was catalyzed by glutathione-S-transferase. P450 enzymes and epoxide hydrolase were involved in M10 formation. Overall, our study showed that allitinib was metabolized by the O-dealkylation pathway similar to lapatinib, but that amide hydrolysis and the formation of dihydrodiol were the dominant metabolic pathways. The absorbed allitinib was extensively metabolized by multiple enzymes.

Importance of analytical determination of reactive intermediates and their reaction products with biomacromolecules: a mini review.

Metabolic reactive intermediates can react with biomolecules such as DNA and proteins to produce adducts. Recently, research has shown that such adducts can act as precursors of some chronic diseases (cancer, Parkinson's, immunologic system diseases, etc.), and their determination is important because they are biomarkers of undesirable health effects. These compounds are produced at very low concentrations, but the development and dissemination of sensitive new analytical tools, especially those based on chromatography coupled to other analytical instruments, make such determinations possible. This mini review is focused on the formation of reactive intermediates, their reaction with biomolecules, and the importance of their determination.

Reconstitution of the interplay between cytochrome P450 and human glutathione S-transferases in clozapine metabolism in yeast

Clozapine, an often-prescribed antipsychotic drug, is implicated in severe adverse drug reactions (ADRs). Formation of reactive intermediates by cytochrome P450s (CYPs) has been proposed as a possible explanation for these ADRs. Moreover, a protective role for human glutathione S-transferases (hGSTs) was recently shown using purified enzymes. We investigated the interplay between CYP bioactivation and GST detoxification in a reconstituted cellular context using recombinant yeast expressing a bacterial CYP BM3 mutant (M11), mimicking the drug-metabolizing potential of human CYPs, combined with hGSTA1-1, M1-1 or P1-1. Clozapine and the N-desmethylclozapine metabolite caused comparable growth inhibition and reactive oxygen species (ROS) formation, whereas the clozapine-N-oxide metabolite was clearly less toxic. Clozapine metabolism by BM3 M11 and the hGSTs in yeast was confirmed by identification of stable clozapine metabolites and hGST isoform-specific glutathione-conjugates. Oxidative metabolism of clozapine by BM3 M11 increased ROS formation and growth inhibition. Co-expression of hGSTP1-1 protected yeast from BM3 M11 induced growth inhibition in presence of clozapine, whereas similar expression levels of hGSTA1-1 and hGSTM1-1 did not. ROS formation was not lowered by hGSTP1-1 co-expression and was unrelated to mitochondrial electron transport chain (mETC) activity. We present a novel cellular model to study the effect of CYP and GST interplay in drug toxicity.

Chlorine Gas Exposure on Human Bronchial Cells Decreases Mitochondrial Quality and Activates Autophagy

Chlorine (Cl2) can cause significant morbidity and mortality when inhaled due to the formation of reactive intermediates. We hypothesized that mitochondria of lung epithelial cells are injured by Cl2 causing decreased bioenergetic capacity of these organelles and membrane depolarization. Human epithelial cells (H441) were exposed to Cl2 (100 ppm for 15 min) and returned to the incubator with air/5% CO2. Measurements of mitochondrial oxygen consumption rate (OCR) using extracellular flux analysis showed a significant reduction of maximal OCR and bioenergetic reserve capacity at 1h post exposure, the values returning to air controls 6 h later. Mitochondrial ROS production, assessed by MitoSOX fluorescence (both by fluorescent microscopy and FACS analysis) showed increased signals at 1 and 6 h post Cl2 exposure. Furthermore, mitochondrial membrane potential showed a 30% decrease when compared with controls at 1h but not 6 h post exposure, indicative of significant but reversible mitochondrial injury (TMRM assay). The recovery of mitochondrial membrane potential at 6h post exposure was accompanied by increased levels of autophagy protein LC3‐II which increased even more 24h post exposure. Taken together these data support the hypothesis that mitochondrial quality is decreased by Cl2 exposure and suggests that autophagy may play a regulatory role in this process. Supported by 5U01ES015676

Efficient Oxidative Degradation of Azo Dyes by a Water‐Soluble Manganese Porphyrin Catalyst

AbstractDyes in wastewater severely affect the nature and quality of water by inhibiting the sunlight penetration into the stream, which thereby reduces the photosynthesis reaction. This poses a serious environmental threat in many developing countries. Recently, new methods for the treatment of colored dye effluent streams have attracted much attention. The [MnIII(tmpyp)]/H2O2 system (tmpyp=meso‐tetrakis(1‐methylpyridinium‐4‐yl)porphyrinato) was now found to degrade various azo dyes with remarkably high efficiency under ambient conditions in aqueous solution at certain pH values. Main products of the catalytic degradation of the dye amaranth by [MnIII(tmpyp)]/H2O2 were analyzed. The reaction mechanism was studied in more detail by using rapid‐scan stopped‐flow spectrophotometry as a function of pH, [catalyst], [H2O2], [dye], and [surfactants]. Spectral analyses and kinetic data suggested rapid formation of an intermediate [MnIII(tmpyp)(OOH)] (a compound 0‐type intermediate), followed by the formation of a relatively stable trans‐dioxomanganese(V) porphyrin complex, [MnV(O)2(tmpyp)] (a compound I analog). The one‐electron reduction of [MnV(O)2(tmpyp)] to [MnIV(O)(tmpyp)] (a compound II analog) was accelerated greatly by amaranth. On the basis of the kinetic and spectroscopic data, a reaction mechanism of the formation of reactive intermediates [MnIII(tmpyp)(OOH)], [MnV(O)2(tmpyp)], and [MnIV(O)(tmpyp)] was proposed.