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A variety of 2-aminobenzonitriles were prepared from 2-arylindoles in good to excellent yields through tert-butylnitrite (TBN)-mediated nitrosation and sequential iron(III)-catalyzed C-C Bond cleavage in a one-pot fashion. The 2-aminobenzonitriles can be used to rapidly synthesize benzoxazinones by intramolecular condensation. The present method features an inexpensive iron(III) catalyst, gram scalable preparations, and novel C-C bond cleavage of indoles. [ABSTRACT FROM AUTHOR]

Among the variety of nitrogen heterocycles, the furoxan (1,2,5-oxadiazole 2-oxide) scaffold has attracted considerable attention owing to its ability to release NO under physiological conditions. Therefore, significant efforts of organic chemists have been directed toward the construction of new drug candidates containing the NO-donor furoxan subunit connected to a known pharmaceutical or a potential pharmacophore by C C/C N bonds or through an appropriate linker. This digest summarizes the recent information concerning both new synthetic approaches for the furoxan ring construction and various methods for the functionalized furoxan synthesis with particular focus on the last three years. Methods for the furoxan ring formation including cyclodimerization of nitrile oxides, nitrosation of unsaturated compounds, and acylation of dinitromethane sodium salt are reviewed. The functionalization of furoxan ring is represented by nucleophilic substitution of nitro and arylsulfonyl groups as well as by different condensations of cyano-, carbonyl- and carboxyfuroxan derivatives. Synthesis of hybrid structures combining NO-donor furoxan ring and some pharmacophoric moiety is also considered. [ABSTRACT FROM AUTHOR]

A two-step procedure for preparing N-nitrosodimethylamine by direct nitrosation of aqueous solutions of dialkylamines with dinitrogen dioxide was suggested. The first step involves preparation of dialkylammonium nitrite, and in the second step, on heating to 70-90°С in a weakly acidic solution, it transforms into N-nitrosodialkylamine. The yield of N-nitrosodialkylamines is 95-98% based on the converted dialkylamine. A low-waste process for N-nitrosodimethylamine production was developed. [ABSTRACT FROM AUTHOR]

The ubiquitous cellular labile iron pool (LIP) is often associated with the production of the highly reactive hydroxyl radical, which forms through a redox reaction with hydrogen peroxide. Peroxynitrite is a biologically relevant peroxide produced by the recombination of nitric oxide and superoxide. It is a strong oxidant that may be involved in multiple pathological conditions, but whether and how it interacts with the LIP are unclear. Here, using fluorescence spectroscopy, we investigated the interaction between the LIP and peroxynitrite by monitoring peroxynitrite-dependent accumulation of nitrosated and oxidized fluorescent intracellular indicators. We found that, in murine macrophages, removal of the LIP with membrane-permeable iron chelators sustainably accelerates the peroxynitritedependent oxidation and nitrosation of these indicators. These observations could not be reproduced in cell-free assays, indicating that the chelator-enhancing effect on peroxynitrite-dependent modifications of the indicators depended on cell constituents, presumably including LIP, that react with these chelators. Moreover, neither free nor ferrous-complexed chelators stimulated intracellular or extracellular oxidative and nitrosative chemistries. On the basis of these results, LIP appears to be a relevant and competitive cellular target of peroxynitrite or its derived oxidants, and thereby it reduces oxidative processes, an observation that may change the conventional notion that the LIP is simply a cellular source of pro-oxidant iron. [ABSTRACT FROM AUTHOR]

Nitrosation of hydrazinocarbonylethyl alginic acids afforded polymeric azides, and the stability of their aqueous solutions at different pH values, temperatures, and holding times was studied. [ABSTRACT FROM AUTHOR]

The chemical changes (oxidation/nitrosation) of meat proteins during digestion lead to a decrease in their nutritional value. Moreover, oxidized and nitrosated amino acids are suspected to promote various human pathologies. To investigate the mechanisms and the kinetics of these endogenous protein modifications, we used a dynamic artificial digestive system (DIDGI®) that mimics the physicochemical conditions of digestion. The combined effect of meat cooking and endogenous addition of ascorbate and nitrite was evaluated on protein oxidation (by measuring carbonyl groups), protein nitrosation (by measuring nitrosamines), and proteolysis. Considerable carbonylation was observed in the digestive tract, especially under the acidic conditions of the stomach. Nitrosamines, caused by ammonia oxidation, were formed in conditions in which no nitrite was added, although the addition of nitrite in the model significantly increased their levels. Meat cooking and nitrite addition significantly decreased protein digestion. The interactions between all the changes affecting the proteins are discussed. [ABSTRACT FROM AUTHOR]

Deterioration of neuromuscular junction (NMJ) integrity and function is causal to muscle atrophy and frailty, ultimately hindering quality of life and increasing the risk of death. In particular, NMJ is vulnerable to ischemia reperfusion (IR) injury when blood flow is restricted followed by restoration. However, little is known about the underlying mechanism(s) and hence the lack of effective interventions. New evidence suggests that mitochondrial oxidative stress plays a causal role in IR injury, which can be precluded by enhancing mitochondrial protein S- nitrosation (SNO). To elucidate the role of IR and mitochondrial protein SNO in skeletal muscle, we utilized a clinically relevant model and showed that IR resulted in significant muscle and motor nerve injuries with evidence of elevated muscle creatine kinase in the serum, denervation at NMJ, myofiber degeneration and regeneration, as well as muscle atrophy. Interestingly, we observed that neuromuscular transmission improved prior to muscle recovery, suggesting the importance of the motor nerve in muscle functional recovery. Injection of a mitochondria-targeted S -nitrosation enhancing agent, MitoSNO, into ischemic muscle prior to reperfusion reduced mitochondrial oxidative stress in the motor nerve and NMJ, attenuated denervation at NMJ, and resulted in accelerated functional recovery of the muscle. These findings demonstrate that enhancing mitochondrial protein SNO protects against IR-induced denervation at NMJ in skeletal muscle and accelerates functional regeneration. This could be an efficacious intervention for protecting neuromuscular injury under the condition of IR and other related pathological conditions. [ABSTRACT FROM AUTHOR]

Despite the large number of globins recently discovered in bacteria, our knowledge of their physiological functions is restricted to only a few examples. In the microbial world, globins appear to perform multiple roles in addition to the reversible binding of oxygen; all these functions are attributable to the heme pocket that dominates functional properties. Resistance to nitrosative stress and involvement in oxygen chemistry seem to be the most prevalent functions for bacterial globins, although the number of globins for which functional roles have been studied via mutation and genetic complementation is very limited. The acquisition of structural information has considerably outpaced the physiological and molecular characterisation of these proteins. The genome of the Antarctic cold-adapted bacterium Pseudoalteromonas haloplanktis TAC125 ( Ph TAC125) contains genes encoding three distinct single-chain 2/2 globins, supporting the hypothesis of their crucial involvement in a number of functions, including protection against oxidative and nitrosative stress in the cold and O 2 -rich environment. In the genome of Ph TAC125, the genes encoding 2/2 globins are constitutively transcribed, thus suggesting that these globins are not functionally redundant in their physiological function in Ph TAC125. In the present study, the physiological role of one of the 2/2 globins, Ph -2/2HbO-2217, was investigated by integrating in vivo and in vitro results. This role includes the involvement in the detoxification of reactive nitrogen and O 2 species including NO by developing two in vivo and in vitro models to highlight the protective role of Ph -2/2HbO-2217 against reactive nitrogen species. The PSHAa2217 gene was cloned and over-expressed in the flavohemoglobin-deficient mutant of Escherichia coli and the growth properties and O 2 uptake in the presence of NO of the mutant carrying the PSHAa2217 gene were analysed. The ferric form of Ph -2/2HbO-2217 is able to catalyse peroxynitrite isomerisation in vitro , indicating its potential role in the scavenging of reactive nitrogen species. Here we present in vitro evidence for the detoxification of NO by Ph -2/2HbO-2217. [ABSTRACT FROM AUTHOR]

Aims Propofol can be applied as an anesthetic or sedative agent for septic patients. Our previous studies showed that propofol ameliorated inflammation- and nitrosative stress-induced cellular insults. This study further evaluated effects of propofol on cecal ligation and puncture (CLP)-induced septic insults to rats and its possible mechanisms. Main methods Wistar rats were administered with CLP and effects of propofol on CLP-induced liver dysfunction and rat death were evaluated. Levels of hepatic or systemic nitrogen oxides (NOx) and interleukin (IL)-6 were quantified. Sequentially, inducible nitric oxide synthase (iNOS) and IL-6 gene expressions, toll-like receptor 4 (TLR4) protein levels, and nuclear factor (NF)-κB translocation were determined. Key findings Subjecting rats to CLP led to body weight loss, liver weight gain, and death. Administration of propofol lessened CLP-induced augmentations of serum and hepatic nitrosative stress and IL-6 levels. Additionally, propofol suppressed CLP-induced enhancements in levels of hepatic iNOS protein. Furthermore, the CLP-induced iNOS and IL-6 mRNA expressions in the liver were inhibited following propofol administration. Sequentially, subjecting rats to CLP enhanced hepatic TLR4 protein levels and NF-κB translocation to nuclei, but propofol inhibited these augmentations. Significance Consequently, exposure to propofol protected against CLP-induced liver dysfunction and increased the survival rates of the animals. This study shows that propofol can protect rats against septic insults through suppression of systemic and hepatic nitrosative and inflammatory stress due to inhibition of TLR4/NF-κB-mediated iNOS and IL-6 mRNA and protein expressions. [ABSTRACT FROM AUTHOR]

Freshwater turtles (Trachemys scripta) are among the very few vertebrates capable of tolerating severe hypoxia and reoxygenation without suffering from damage to the heart. As myocardial ischemia and reperfusion causes a burst of mitochondrial reactive oxygen species (ROS) in mammals, the question arises as to whether, and if so how, this ROS burst is prevented in the turtle heart. We find here that heart mitochondria isolated from turtles acclimated to anoxia produce less ROS than mitochondria from normoxic turtles when consuming succinate. As succinate accumulates in the hypoxic heart and is oxidised when oxygen returns this suggest an adaptation to lessen ROS production. Specific S-nitrosation of complex I can lower ROS in mammals and here we show that turtle complex I activity and ROS production can also be strongly depressed in vitro by S-nitrosation. While we can detect in vivo endogenous S-nitrosated complex I in turtle heart mitochondria, these levels are unaffected upon anoxia acclimation. Thus while heart mitochondria from anoxia-acclimated turtles generate less ROS and have a lower aerobic capacity than those from normoxic turtles, this is not due to decreases in complex I activity or expression levels. Interestingly, in-gel activity staining reveals that most complex I of heart mitochondria from normoxic and anoxic turtles forms stable supercomplexes with other respiratory enzymes and, in contrast to mammals, these are not disrupted by dodecyl maltoside. Taken together, these results show that, although S-nitrosation of complex I is a potent mechanism to prevent ROS formation upon reoxygenation after anoxia in vitro, this is not a major cause of the suppression of ROS production by anoxic turtle heart mitochondria. [ABSTRACT FROM AUTHOR]

tert-Butyl nitrite (TBN) is an important metal-free reagent that is widely applied in various organic transformations. Besides its traditional applications in nitrosation and diazotization, its ability to activate molecular oxygen to enable the initiation of radical reactions, including nitration, oximation, oxidation, and so on, has attracted extensively attention in the past decade. This review highlights recent advances in this field to promote further exploration of this versatile compound. 1 Introduction 2 Reactions Involving TBN 2.1 Nitrosation 2.2 Oximation 2.3 Diazotization 2.4 Nitration 2.5 Oxidation 2.6 Other Reactions 3 Conclusion and Perspective [ABSTRACT FROM AUTHOR]

Endogenous and dietary nitrite produces reactive nitrogen species (RNS) that react with DNA causing mutations. The nitrosation of 2′-deoxyguanosine (dGuo) and DNA with nitrite was studied under different conditions, and the reaction and degradation products identified and analysed by HPLC-DAD-MS. Nitrosative deamination of dGuo produced xanthine along with 2′-deoxyxanthosine whereas DNA afforded xanthine. Formation of xanthine increased with nitrite concentration and in low pH such as that of stomach. Xanthine was measured as a marker of nitrosation of dGuo and DNA, and it was subsequently used to study the antinitrosating activity of β-carboline alkaloids, and selected antioxidants. Food-occurring tetrahydro-β-carbolines (THβCs) decreased nitrosative deamination of dGuo and DNA under conditions simulating the stomach. Antinitrosating activity was also evidenced for flavonoids (catechin, quercetin) and indole (melatonin) antioxidants. Among THβCs the most active antinitrosating compounds were 1,2,3,4-tetrahydro-β-carboline-3-carboxylic acids (THβC-3-COOHs) that reacted with nitrite to give N -nitroso derivatives as main products along with 3,4-dihydro-β-carboline-3-carboxylic acids and aromatic β-carbolines (norharman and harman). Antinitrosating activity of THβCs correlated well with the formation of N -nitroso-THβC-3-COOHs. These N -nitroso derivatives were stable at pH 7 but degraded in acid conditions affording nitrosating species. [ABSTRACT FROM AUTHOR]

Abstract: A simple and practical method for the denitrosation of aryl N‐nitrosamines to secondary amines is reported under metal‐free conditions using iodine and triethylsilane. Several reduction‐susceptible functional groups such as alkene, alkyne, nitrile, nitro, aldehyde, ketone and ester were found to be very stable during the denitrosation, which is remarkable. Broad substrate scope, room temperature reactions and excellent yields are the additional features of the current methodology. [ABSTRACT FROM AUTHOR]

Obesity is associated with elevated intracellular nitric oxide (NO) production, which promotes nitrosative stress in metabolic tissues such as liver and skeletal muscle, contributing to insulin resistance. The onset of obesity-associated insulin resistance is due, in part, to the compromise of hepatic autophagy, a process that leads to lysosomal degradation of cellular components. However, it is not known how NO bioactivity might impact autophagy in obesity. Here, we establish that S-nitrosoglutathione reductase (GSNOR), a major protein denitrosylase, provides a key regulatory link between inflammation and autophagy, which is disrupted in obesity and diabetes. We demonstrate that obesity promotes S-nitrosylation of lysosomal proteins in the liver, thereby impairing lysosomal enzyme activities. Moreover, in mice and humans, obesity and diabetes are accompanied by decreases in GSNOR activity, engendering nitrosative stress. In mice with a GSNOR deletion, diet-induced obesity increases lysosomal nitrosative stress and impairs autophagy in the liver, leading to hepatic insulin resistance. Conversely, liver-specific overexpression of GSNOR in obese mice markedly enhances lysosomal function and autophagy and, remarkably, improves insulin action and glucose homeostasis. Furthermore, overexpression of S-nitrosylation-resistant variants of lysosomal enzymes enhances autophagy, and pharmacologically and genetically enhancing autophagy improves hepatic insulin sensitivity in GSNOR-deficient hepatocytes. Taken together, our data indicate that obesity-induced protein S-nitrosylation is a key mechanism compromising the hepatic autophagy, contributing to hepatic insulin resistance. [ABSTRACT FROM AUTHOR]

Cruciferous vegetables belong to the mustard family of plants such as Brussels sprouts, kale, broccoli, cabbage and cauliflower. They are well known for their cancer prevention properties which are due to high content of bioactive compounds, isothiocyanates (ITCs). This study was aimed to investigate nitrosation inhibition ability of the cruciferous vegetables commonly consumed with meat products namely, broccoli, cauliflower and cabbage. Aqueous extracts of fresh and steamed (2 and 4 min) vegetables were subjected to determination of antioxidant capacity (DPPH and FRAP assay) and chemical composition i.e. total phenolic and isothiocyanate (ITC) content. It was found that TPC, DPPH and FRAP values of raw vegetables were different in each vegetable and ranged from 17.12-38.91 mg GAE/100 ml, 44.09-63.31% and 1.36-6.81 mg TE/100 ml, respectively. Among three types of cruciferous vegetable, broccoli had the highest PEITC content being 0.21 mmol/100 g compared to cauliflower (0.15 mmol/100 g) and cabbage (0.06 mmol/100 g). Moreover, it was found that steaming process significantly enhanced antioxidant activity, TPC as well as PEITC content in a timedependent manner up to 4 min (p<0.05). Nitrosation reaction was stimulated in vitro at pH 3.0 and spectrophotometric method was used to determine formation of nitrosodimethylamine (NDMA) in the presence and absence of cruciferous vegetable extracts. The highest NDMA inhibition was found in broccoli and steaming could promote the effect in all vegetables. Prevention of DNMA was believed to be a result of PEITC content in the vegetables because when anti-nitrosation ability of synthesized isothiocyanates was determined, PEITC acted as a potent inhibitor with 89.28% inhibition whereas that of ascorbic acid (positive control) was 88.57% and allyl isothiocyanate had the least effect (53.21%) at the same concentration. This study infers that the concomitant consumption of cruciferous vegetables may possess toxicity reduction of nitrosamine and these effects can be enhanced by a common heating process of the vegetables. [ABSTRACT FROM AUTHOR]

Objective: The objective was to compare the complex formation of flavones (luteolin, apigenin), flavonols (morin, quercetin, and rutin), flavanones (naringenin), flavanonols (dihydroquercetin), caffeic, and ferulic acids with aluminum ion using two spectrophotometric methods and the application of these methods to estimate the flavonoid content in the angionorm herbal product. Materials and Methods: Method 1 included direct complex formation with aluminum chloride, and Method 2 involved preliminary nitrozation and subsequent complex formation of nitroso-derivatives with aluminum chloride. 2,4-dinitrophenylhydrazine method was also tested. Results: The conjugation system increase in the chromophore structure of nitroso derivatives is reflected by the hyperchromic effect of all substances (from 1.4 to 4-fold). The largest bathochromic shift of nitroso derivatives was seen for rutin, luteolin, and dihydroquercetin (to 510–530 nm). The total flavonoids estimation in the extract of the four herbs mixture, which constitute angionorm preparation active ingredient, depends on the chosen reference substance (3.49% calculated as luteolin when measured by Method 1 or 8.71% by Method 2; 7.97% calculated as dihydroquercetin when measured by Method 1 and 4.14% by Method 2. Conclusion: The complex formation according to Methods 1 and 2 does not allow the identification of the selective spectral regions typical for the certain flavonoids subgroups and hydroxycinnamic acids. Neither method of complex formation is suitable for the assay of total flavonoids in unknown samples or for the flavonoid content comparison in the different herbal material. [ABSTRACT FROM AUTHOR]

Aims: This study was designed to explore the neuroprotective potential of inorganic nitrite as a new therapeutic avenue in Parkinson's disease (PD). Results: Administration of inorganic nitrite ameliorates neuropathology in phylogenetically distinct animal models of PD. Beneficial effects are not confined to prophylactic treatment and also occur if nitrite is administered when the pathogenic cascade is already active. Mechanistically, the effect is mediated by both complex I S-nitrosation, which under nitrite administration is favored over formation of other forms of oxidation, and down-stream activation of the antioxidant Nrf2 pathway. Nitrite also rescues respiratory reserve capacity and increases proton leakage in LRRK2 PD patients' dermal fibroblasts. Innovation: The study proposes an unprecedented approach based on the administration of the nitrosonium donor nitrite to contrast complex I and redox anomalies in PD. Dysfunctional mitochondrial complex I propagates oxidative stress in PD, and treatments mitigating this defect may, therefore, limit disease progression. Therapeutic complex I targeting has been successfully achieved in ischemia/reperfusion by using nitrosonium donors such as nitrite to reversibly modify its subunits and protect from oxidative damage after reperfusion. This evidence led to the innovative hypothesis that nitrite could exert protective effects also in pathological conditions where complex I dysfunction occurs in normoxia, such as in PD. Conclusions: Overall, these results demonstrate that administration of inorganic nitrite improves mitochondrial function in PD, and it, therefore, represents an amenable intervention to hamper disease progression. Antioxid. Redox Signal. 28, 44-61. [ABSTRACT FROM AUTHOR]

The styryl ketonic Mannich base 2 has been used as a precursor in the synthesis of 2‐pyrazolines having a basic side chain at C‐3 and a phenolic Mannich base at C‐5. Treatment of the bis(styryl ketonic bases) 6a and 8a with phenylhydrazine affords the bis(3‐functionalized 2‐pyrazolines) 7 and 9. The transamination between the styryl keto base 10 and 4‐aminoantipyrine leads to 12, which reacts with piperazine to give 13. N‐Nitrosation of the sec‐Mannich bases 15a–d followed by reductive cyclization affords 2‐pyrazolines 17a–d. The keto base 14b has been used for the synthesis of 2‐pyrazolines having a phenolic Mannich base at C‐3 and its reaction with 3,5‐dimethyl‐1H‐pyrazole affords 23. The alkylation of 3‐methyl‐1‐phenyl‐2‐pyrazolin‐5‐one with the bis(Mannich base) 25 was investigated. [ABSTRACT FROM AUTHOR]

Mycobacterium tuberculosis ( M.tb. ), the causative agent of tuberculosis (TB), cannot synthesize GSH, but synthesizes two major low molecular weight thiols namely mycothiol (MSH) and ergothioneine (ERG). Gamma-glutamylcysteine (GGC), an intermediate in GSH synthesis, has been implicated in the protection of lactic acid bacteria from oxidative stress in the absence of GSH. In mycobacteria, GGC is an intermediate in ERG biosynthesis, and its formation is catalysed by EgtA (GshA). GGC is subsequently used by EgtB in the formation of hercynine-sulphoxide-GGC. In this study, M.tb. mutants harbouring unmarked, in-frame deletions in each of the fives genes involved in ERG biosynthesis ( egtA , egtB , egtC , egtD and egtE ) or a marked deletion of the mshA gene (required for MSH biosynthesis) were generated. Liquid chromatography tandem mass spectrometry analyses (LC-MS) revealed that the production of GGC was elevated in the MSH-deficient and the ERG-deficient mutants. The ERG-deficient ΔegtB mutant which accumulated GGC was more resistant to oxidative and nitrosative stress than the ERG-deficient, GGC-deficient ΔegtA mutant. This implicates GGC in the detoxification of reactive oxygen and nitrogen species in M.tb . [ABSTRACT FROM AUTHOR]

Dinitrogen trioxide, N2O3, is readily prepared and stabilized in high concentrations in dry organic solvents at normal working temperatures. These conditions allow for facile acid and water free nitrosation and nitration reactions for which three examples are given here: the preparation of benzenediazonium nitrite, [PhN2][NO2]; nitrosyl chloride, NOCl, and nitrosylsulfuric acid, (ONOSO3H). [ABSTRACT FROM AUTHOR]

Decades of chemical, biochemical and pathophysiological research have established the relevance of post-translational protein modifications induced by processes related to oxidative stress, with critical reflections on cellular signal transduction pathways. A great deal of the so-called 'redox regulation' of cell function is in fact mediated through reactions promoted by reactive oxygen and nitrogen species on more or less specific aminoacid residues in proteins, at various levels within the cell machinery. Modifications involving cysteine residues have received most attention, due to the critical roles they play in determining the structure/function correlates in proteins. The peculiar reactivity of these residues results in two major classes of modifications, with incorporation of NO moieties (S-nitrosation, leading to formation of protein S-nitrosothiols) or binding of low molecular weight thiols (S-thionylation, i.e. in particular S-glutathionylation, S-cysteinylglycinylation and S-cysteinylation). A wide array of proteins have been thus analyzed in detail as far as their susceptibility to either modification or both, and the resulting functional changes have been described in a number of experimental settings. The present review aims to provide an update of available knowledge in the field, with a special focus on the respective (sometimes competing and antagonistic) roles played by protein S-nitrosations and S-thionylations in biochemical and cellular processes specifically pertaining to pathogenesis of cardiovascular diseases. [ABSTRACT FROM AUTHOR]

The prevalence of neurodegenerative diseases, including Alzheimer’s disease (AD) and Parkinson’s disease (PD), is currently a major public health concern due to the lack of efficient disease-modifying therapeutic options. Recent evidence suggests that mitochondrial dysfunction and nitrosative/oxidative stress are key common mediators of pathogenesis. In this review, we highlight molecular mechanisms linking NO-dependent post-translational modifications, such as cysteine S-nitrosylation and tyrosine nitration, to abnormal mitochondrial metabolism. We further discuss the hypothesis that pathological levels of NO compromise brain energy metabolism via aberrant S-nitrosylation of key enzymes in the tricarboxylic acid (TCA) cycle and oxidative phosphorylation, contributing to neurodegenerative conditions. A better understanding of these pathophysiological events may provide a potential pathway for designing novel therapeutics to ameliorate neurodegenerative disorders. [ABSTRACT FROM AUTHOR]

[Display omitted] • The non-heme containing iron enzyme SznF provides a novel approach to achieve N-nitrosation reaction with biosynthetic strategy. • A modified L-Arg with methyl nitrogen deprotonation (L-DHMA d) is treated as the substrate of N-nitrosation reaction catalyzed by SznF enzyme, which has not yet been investigated. • The reaction mechanism of the critical N-nitrosation reaction toward L-DHMA d catalyzed by the cupin domain of SznF enzyme is investigated, through the combined quantum mechanics/molecular mechanics method. • Attribute to the methyl nitrogen deprotonation of L-DHMA d , the superoxo addition could induce the C-N bond cleave of L-DHMA d simultaneously on the rate-determining step, which promote the whole N-nitrosation reaction. The SznF enzyme provides a novel approach to synthesize the N-nitrosourea pharmacophore. In this work, the modified L-Arg with methyl nitrogen deprotonation(L-DHMA d), a not yet studied substrate's reaction mechanism of the critical N-nitrosation reaction catalyzed by the cupin domain of SznF enzyme is investigated, through the combined quantum mechanics/molecular mechanics method. Basis on our calculation results, the optimal N-nitrosation reaction pathway can be divided in to three reaction steps:1) superoxo addition with accompanying of Cε-Nω bond cleavage; 2) O1-O2 bond heterolytic cleavage; 3) N Me -N ω bond coupling. The first reaction step is the rate-determining step of the entire optimal reaction with an energy barrier of 20.6 Kcal/mol. Significantly, C ε -N ω bond could be homolytic cleaved spontaneously during the Cε-O2 bond formation in the first reaction step. This appearance mainly attributes to the Cε-Nω single bond of the L-DHMA d, which could be more feasible to cleave to maintain the C ε sp2 hybridization within the superoxo addition. The subsequent reaction step is the O1-O2 bond heterolytic cleavage, which involves a minimum energy crossing point to form the stable intermediate with Fe(IV) = O1 species at quintet state. Finally, N Me and N ω of L-DHMA d are very energetic favorable to coupling to form the N-nitroso product. This is consist with the experimental observations that two nitrogen atoms of the N-nitroso product are both from the same arginine substrate. Our work could contribute to the deeper understanding of the N-nitrosation reaction catalyzed by SznF enzyme, and might enlighten further studies of biomimetic chemistry of SznF enzyme. [ABSTRACT FROM AUTHOR]

While the biological role of nitric oxide (NO) synthase (NOS) is appreciated, several fundamental aspects of the NOS/NO-related signaling pathway(s) remain incompletely understood. Canonically, the NOS-derived NO diffuses through the (inter)cellular milieu to bind the prosthetic ferro(Fe 2+ )-heme group of the soluble guanylyl cyclase (sGC). The formation of ternary NO-ferroheme-sGC complex results in the enzyme activation and accelerated production of the second messenger, cyclic GMP. This paper argues that cells dynamically generate mobile/exchangeable NO-ferroheme species, which activate sGC and regulate the function of some other biomolecules. In contrast to free NO, the mobile NO-ferroheme may ensure safe, efficient and coordinated delivery of the signal within and between cells. The NO-heme signaling may contribute to a number of NOS/NO-related phenomena (e.g. nitrite bioactivity, selective protein S-(N-)nitrosation, endothelium and erythrocyte-dependent vasodilation, some neural and immune NOS functions) and predicts new NO-related discoveries, diagnostics and therapeutics. [ABSTRACT FROM AUTHOR]

Nitrosative stress results from an increase in reactive nitrogen species (RNS) within the cell. Though the RNS - nitric oxide (·NO) and peroxynitrite (ONOO-) - play pivotal physiological roles, at elevated concentrations, these moieties can be poisonous to both prokaryotic and eukaryotic cells alike due to their capacity to disrupt a variety of essential biological processes. Numerous microbes are known to adapt to nitrosative stress by elaborating intricate strategies aimed at neutralizing RNS. In this review, we will discuss both the enzymatic systems dedicated to the elimination of RNS as well as the metabolic networks that are tailored to generate RNS-detoxifying metabolites - a-keto-acids. The latter has been demonstrated to nullify RNS via non-enzymatic decarboxylation resulting in the production of a carboxylic acid, many of which are potent signaling molecules. Furthermore, as aerobic energy production is severely impeded during nitrosative stress, alternative ATP-generating modules will be explored. To that end, a holistic understanding of the molecular adaptation to nitrosative stress, reinforces the notion that neutralization of toxicants necessitates significant metabolic reconfiguration to facilitate cell survival. As the alarming rise in antimicrobial resistant pathogens continues unabated, this review will also discuss the potential for developing therapies that target the alternative ATP-generating machinery of bacteria. [ABSTRACT FROM AUTHOR]

Quantum chemistry calculations and kinetic modeling were performed to investigate the nitrosation mechanism and kinetics of diamine piperazine (PZ), an alternative solvent for widely used monoethanolamine in postcombustion CO 2 capture (PCCC), by two typical nitrosating agents, NO 2 − and N 2 O 3 , in the presence of CO 2 . Various PZ species and nitrosating agents formed by the reactions of PZ, NO 2 − , and N 2 O 3 with CO 2 were considered. The results indicated that the reactions of PZ species having NH group with N 2 O 3 contribute the most to the formation of nitrosamines in the absorber unit of PCCC and follow a novel three-step nitrosation mechanism, which is initiated by the formation of a charge-transfer complex. The reactions of all PZ species with NO 2 − proceed more slowly than the reactions of PZ species with ONOCO 2 − , formed by the reaction of NO 2 − with CO 2 . Therefore, the reactions of PZ species with ONOCO 2 − contribute more to the formation of nitrosamines in the desorber unit of PCCC. In view of CO 2 effect on the nitrosation reaction of PZ, the effect through the reaction of PZ with CO 2 shows a completely different tendency for different nitrosating agents. More importantly, CO 2 can greatly accelerate the nitrosation reactions of PZ by NO 2 − through the formation of ONOCO 2 − in the reaction of CO 2 with NO 2 − . This work can help to better understand the nitrosation mechanism of diamines and in the search for efficient methods to prevent the formation of carcinogenic nitrosamines in CO 2 capture unit. [ABSTRACT FROM AUTHOR]

A new, simple, and general method for the synthesis of 6-R-7 H -tetrazolo[5,1- b ][1,3,4]thiadiazines (R = Ar, Het, Alk) has been developed. The described method is based on the one-pot condensation of α-haloketones with thiocarbohydrazide, nitrosation of the formed hydrazinylthiadiazine using NaNO 2 /HCl, and intramolecular cyclization of the nitrosation product via azide-tetrazole tautomerism. Spectroscopic and structural investigations revealed that the azide-tetrazole equilibrium is completely shifted to the tetrazole form both in solution and the solid state. [ABSTRACT FROM AUTHOR]

3-Acetyl-4,6-diaryl-2-methylaminopyridines were synthesized via rearrangement of quaternary 4,6-diaryl-3-cyano-2-methylpyridinium salts. Annulation of the pyrazole ring of pyrazolo[3,4- b]pyridines was achieved by N-nitrosation of the methylamino group of the pyridine and reduction of N-nitroso group to the hydrazine group with simultaneous intramolecular closure of the pyrazole ring. [ABSTRACT FROM AUTHOR]

iNitrate (NO3-) and nitrite (NO2-) are known to be cardioprotective and to alter energy metabolism in vivo. NO3- action results from its conversion to NO2- by salivary bacteria, but the mechanism(s) by which NO2- affects metabolism remains obscure. NO2- may act by S-nitrosating protein thiols, thereby altering protein activity. But how this occurs, and the functional importance of S-nitrosation sites across the mammalian proteome, remain largely uncharacterized. Here we analyzed protein thiols within mouse hearts in vivo using quantitative proteomics to determine S-nitrosation site occupancy. We extended the thiol-redox proteomic technique, isotope-coded affinity tag labeling, to quantify the extent of NO2--dependent S-nitrosation of proteins thiols in vivo. Using this approach, called SNOxICAT (S-nitrosothiol redox isotope-coded affinity tag), we found that exposure to NO2- under normoxic conditions or exposure to ischemia alone results in minimal S-nitrosation of protein thiols. However, exposure to NO2- in conjunction with ischemia led to extensive S-nitrosation of protein thiols across all cellular compartments. Several mitochondrial protein thiols exposed to the mitochondrial matrix were selectively S-nitrosated under these conditions, potentially contributing to the beneficial effects of NO2- on mitochondrial metabolism. The permeability of the mitochondrial inner membrane to HNO2, but not to NO2-, combined with the lack of S-nitrosation during anoxia alone or by NO2- during normoxia places constraints on how S-nitrosation occurs in vivo and on its mechanisms of cardio-protection and modulation of energy metabolism. Quantifying S-nitrosated protein thiols now allows determination of modified cysteines across the proteome and identification of those most likely responsible for the functional consequences of NO2- exposure. [ABSTRACT FROM AUTHOR]

An efficient method for the synthesis of 1-benzyl/arylindazole 2-oxides via a bis(dibenzylideneacetone)palladium(0) [Pd(dba)2]/ tert-butyl nitrite (TBN)-catalyzed reaction of o-alkynylaniline derivatives with TBN is reported. The overall transformation involves the formation of three new bonds via N-nitrosation (N-NO), 5- exo-dig cyclization (C-N) and oxidation (C=O). The notable features are the mild reaction conditions, broad substrate scope and dual role of TBN as an NO source and redox co-catalyst. This strategy was implemented for the synthesis of indazole-3-carbaldehyde derivatives and the formal syntheses of pharmaceutically active YC-1, an anticancer agent (lonidamine), and the male contraceptive experimental drugs AF-2785 and adjudin (AF-2364). [ABSTRACT FROM AUTHOR]

Some reactions (e.g., oxidation of nitrite, denitrification of ammonium) are accelerated in freeze-concentrated solution (FCS) compared to those in aqueous solution. Ice is highly intolerant to impurities, and the ice excludes those that would accelerate reactions. Here we show the acceleration of the N-nitrosation reaction of dimethylamine (DMA) with nitrite to produce N-nitrosodimethylamine (NDMA) in FCS. NDMA is a carcinogenic compound, and this reaction is potentially accelerated in frozen fish/meat. The eaction rate of the N-nitrosation reaction becomes fastest at specific pH. This means that it is a third-order reaction. Theoretical pH values of the peak in the third-order reaction are higher than the experimental one. Freeze-concentration of acidic solution causes pH decrement; however, the freeze-concentration alone could not explain the difference of pH values. The theoretical value was obtained under the assumption that no solute took part in ice. However, solutes are incorporated in ice with a small distribution coefficient of solutes into ice. This small incorporation enhanced the decrement of pH values. Using the distribution coefficient of chloride and sodium ion and assuming those of nitrite and DMA to explain the enhancement, we succeeded in estimating the distribution coefficients of nitrite: 2 × 10-3 and DMA: 3 × 10-2. [ABSTRACT FROM AUTHOR]

Schizosaccharomyces pombe Pap1, a bZIP transcription factor, is highly homologous to the mammalian c-Jun protein that belongs to the AP1 family of transcriptional regulators. The role of transcription factor Pap1 has been extensively studied under oxidative stress. Two cysteine residues in Pap1p namely, C278 and C501 form disulfide linkage under oxidative stress resulting in nuclear accumulation. We first time showed the involvement of Pap1 in the protection against nitrosative stress. In the present study we show that pap1 deletion makes growth of S. pombe sensitive to nitrosative stress. pap1 deletion also causes delayed recovery in terms of mitotic index under nitrosative stress. Our flow cytometry data shows that pap1 deletion causes slower recovery from the slowdown of DNA replication under nitrosative stress. This is the first report where we show that Pap1 transcription factor is localized in the nucleus under nitrosative stress. From our study it is evident that nuclear localization of Pap1 under nitrosative stress was not due to reactive oxygen species formation. [ABSTRACT FROM AUTHOR]

The formation of 4-nitroso-sulfamethoxazole and 4-nitro-SMX, two transformation products (TPs) of sulfamethoxazole (SMX) was investigated under batch soil slurry experiments and in a field study. Due to their low occurrence levels (ng/L) in environmental waters, a suitable analytical method based on liquid chromatography – high resolution – mass spectrometry was developed. Consequently, field observations revealed, for the first time, the occurrence of 4-nitroso-SMX in groundwater at concentrations as high as 18 ng/L.Nitric oxide (NO ) steady-state concentrations were determined in soil slurry experiments because this reactive specie accounted for the formation of 4-nitroso-SMX and 4-nitro-SMX. Measurements revealed that environmental SMX concentrations (0.2–2 μg/L) at neutral pH induced the accumulation of nitric oxide. Under acidic conditions (pH < 6), nitrous acid (HONO) was the major source of nitric oxide while under neutral/basic conditions nitric oxide release was related to the inhibition of denitrification processes. Under laboratory experiments, SMX nitration reaction appeared to be an irreversible transformation pathway, while 4-nitroso-SMX was slowly transformed over time. The occurrence of 4-nitroso-SMX conditions was therefore unexpected in the field study but could be due to its continuous input from soil and/or its relative persistence under anoxic conditions. A mechanism for 4-nitroso-SMX formation was proposed involving a nitrosative desamination pathway through a phenyl radical. [ABSTRACT FROM AUTHOR]

Background Myocardial infarction remains the single leading cause of death worldwide. Upon reperfusion of occluded arteries, deleterious cellular mediators particularly located at the mitochondria level can be activated, thus limiting the outcome in patients. This may lead to the so-called ischemia/reperfusion (I/R) injury. Calpains are cysteine proteases and mediators of caspase-independent cell death. Recently, they have emerged as central transmitters of cellular injury in several cardiac pathologies e.g. hypertrophy and acute I/R injury. Methods Here we investigated the role of cardiac calpains in acute I/R in relation to mitochondrial integrity and whether calpains can be effectively inhibited by posttranslational modification by S -nitrosation. Taking advantage of the a cardiomyocyte cell line (HL1), we determined S -nitrosation by the Biotin-switch approach, cell viability and intracellular calcium concentration after simulated ischemia and reoxygenation - all in dependence of supplementation with nitrite, which is known as an ‘hypoxic nitric oxide (NO) donor’. Likewise, using an in vivo I/R model, calpain S -nitrosation, calpain activity and myocardial I/R injury were characterized in vivo . Results Nitrite administration resulted in an increased S -nitrosation of calpains, and this was associated with an improved cell-survival. No impact was detected on calcium levels. In line with these in vitro experiments, nitrite initiated calpain S -nitrosation in vivo and caused an infarct sparing effect in an in vivo myocardial I/R model. Using electron microscopy in combination with immuno-gold labeling we determined that calpain 10 increased, while calpain 2 decreased in the course of I/R. Nitrite, in turn, prevented an I/R induced increase of calpains 10 at mitochondria and reduced levels of calpain 1. Conclusion Lethal myocardial injury remains a key aspect of myocardial I/R. We show that calpains, as key players in caspase-independent apoptosis, increasingly locate at mitochondria following I/R. Inhibitory post-translational modification by S -nitrosation of calpains reduces deleterious calpain activity in murine cardiomyocytes and in vivo . [ABSTRACT FROM AUTHOR]

Foods are mixed with saliva in the oral cavity and swallowed. While staying in the stomach, saliva is contentiously provided to mix with the ingested foods. Because a salivary component of nitrite is protonated to produce active nitrous acid at acidic pH, the redox reactions of nitrous acid with phenolic compounds in foods become possible in the stomach. In the reactions, nitrous acid is reduced to nitric oxide (●NO), producing various products from phenolic compounds. In the products, stable hydroxybezoyl benzofuranone derivatives, which are produced from quercetin and its 7-O-glucoside, are included. Caffeic acid, chlorogenic acid, and rutin are oxidized to quinones and the quinones can react with thiocyanic acid derived from saliva, producing stable oxathiolone derivatives. 6,8-Dinitrosocatechis are produced from catechins by the redox reaction, and the dinitrocatechins are oxidized further by nitrous acid producing the quinones, which can make charge transfer complexes with the dinitrosocatechin and can react with thiocyanic acid producing the stable thiocyanate conjugates. In this way, various products can be produced by the reactions of salivary nitrite with dietary phenolic compounds, and reactive and toxic quinones formed by the reactions are postulated to be removed in the stomach by thiocyanic acid derived from saliva. [ABSTRACT FROM AUTHOR]

Mitochondrial complex I (NADH: ubiquinone oxidoreductase; CI) is central to the electron transport chain (ETC), oxidative phosphorylation, and ATP production in eukaryotes. CI is a multi-subunit complex with a complicated yet organized structure that optimally connects electron transfer with proton translocation and forms higher-order supercomplexes with other ETC complexes. Efforts to understand the molecular genetics, expression profile of subunits, and structure-function relationship of CI have increased over the years due to the direct role of the complex in human diseases. Although mutations in the nuclear and mitochondrial genes of CI and altered expression of subunits could potentially lower CI activity leading to mitochondrial dysfunction in many diseases, oxidative post-translational modifications (PTMs) have emerged as an important mechanism contributing to altered CI activity. These mainly include reversible and irreversible cysteine modifications, tyrosine nitration, carbonylation, and tryptophan oxidation that are generated following exposure to reactive oxygen species/reactive nitrogen species. Interestingly, oxidative PTMs could contribute either to CI damage, mitochondrial dysfunction, and ensuing cell death or a response mechanism with potential cytoprotective effects. This has also emerged as a promising field for structural biologists since analysis of PTMs could assist in understanding the structure-function relationship of the complex and correlate electron transfer mechanism with energy production. However, analysis of PTMs of CI and their contribution to CI function are incomplete in many physiological and pathological conditions. This review aims to highlight the role of oxidative PTMs in modulating CI activity with implications toward pathobiology of CNS diseases and novel therapeutics. [ABSTRACT FROM AUTHOR]