Nitrite Mediated

The principal in vitro route to the formation of RSNOs is through the reaction of nitrous acid or protonated nitrite (HN02) with thiols (Eq. (1)). Since the pKa of HN02 is 3.37, this reaction is unlikely to occur in cells and tissues where the pH is maintained at 7.4. 

However, this reaction can and has led to errors in the measurement of RSNOs in biological fluids when the samples are improperly buffered to avoid the HN02 -route to S-nitrosation (Tsikas, 2003). 

Enzymatic conversion of nitrite to RSNOs has been reported. Glutathione-S-transferase catalyzed generation of RSNOs from organic nitrites was initially demonstrated in rat liver microsomes (Ji et ah, 1996). Subsequently, this activity has been identified in the rat heart and lung GSTs (Akerboom et al., 1997). 

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As an e.xtension of the oxidative carbonylation with alkyl nitrites, malonate can be prepared by the oxidative carbonylation of ketene (583)[524], Also, the acetonedicarboxylate 585 is prepared by the Pd-catalyzed, alkyl nitrite-mediated oxidative carbonylation of diketene (584)[525],... 

II. Stereospecific Ester Activation in Nitrite-Mediated Carbohydrate Epimerization... 

Figure 13. Comparison of nitrite-mediated inversion with neighboring group participation...

Table 2. Water effects in studied nitrite-mediated inversion reactions.

Dong, H. Pei, Z. C. Ramstrom, O., Stereospecrfic ester activation in nitrite-mediated carbohydrate epimerization. J. Org. Chem. 2006,71, 3306-3309. 

Recent work has demonstrated that the sodium nitrite mediated cyclization of a series of hydrazino uracil glycosides gives a range of toxoflavin glycosides together with their 4-oxide analogues, where the latter can be reduced to the former with hyposulfite. The method of cyclization is as discussed in Section 10.20.9.2.3(i) in Equations (22)-(24). 

Pannala, A.S., Rice-Evans, C.A., HaUiwell, B., and Singh, S., Inhibition of peroxy-nitrite-mediated tyrosine nitration by catechin polyphenols, Biochem. Biophys. Res. Commun., 232, 164—168, 1997. 

Kostyuk VA, Kraemer T, Sies H, Schewe T. Myeloperoxidase/nitrite-mediated lipid peroxidation of low-density lipoprotein as modulated by flavonoids. FEES Lett 2003 537 146-150. 

Cobbs et al. (2001) showed that p53, a key tumour suppressor protein, has evidence of peroxy-nitrite-mediated modifications in gliomas in vitro. 

Lei JP, Ju HX, Dceda O (2004) Catalytic oxidatitm of nitric oxide and nitrite mediated by water-soluble high-valent irrar pOTphyiins at an ITO electrode. J Electroanal Chem 567 331—338... 

Heme d,6 another isobacteriochlorin, occurs as one of two cofactors in the reductase cytochrome cdj which mediates the nitrite reduction to nitrogen monoxide (NO) and from there to dinitrogen oxide (N20) in denitrifying bacteria.7... 

Although, to our knowledge, the effects of inhalation of amyl nitrite or butyl nitrite on glutamatergic neurotransmission have not been studied, NO, the potent compound that mediates the peripheral effects of nitrites in blood vessels, if released in the CNS when nitrites are inhaled, may potentially affect the glutamatergic system. NO has been reported to act directly on the postsynaptic NMDA receptor, where it can increase or decrease NMDA-mediated currents and subsequent calcium influx (Aizenman et al. 1990 Dingledine et al. 1999 Manzoni et al. 1992). 

To our knowledge no smdies have examined the effects of nitrites on GABA neuro transmission. However, when NO, the major mediator of the peripheral effects of nitrites, was administered within the paraventricular nucleus, it caused an increase in GABA concentrations (Horn et al. 1994). 

Cyclic GMP is made from GTP by the enzyme gua-nylyl cyclase, which exists in soluble and membrane-bound forms. Each of these isozymes has unique physiologic properties. The atriopeptins, a family of peptides produced in cardiac atrial tissues, cause natriuresis, diuresis, vasodilation, and inhibition of aldosterone secretion. These peptides (eg, atrial natriuretic factor) bind to and activate the membrane-bound form of guanylyl cyclase. This results in an increase of cGMP by as much as 50-fold in some cases, and this is thought to mediate the effects mentioned above. Other evidence links cGMP to vasodilation. A series of compounds, including nitroprusside, nitroglycerin, nitric oxide, sodium nitrite, and sodium azide, all cause smooth muscle re-... 

J.M. Zen, A.S. Kumar, and H.W. Chen, Electrochemical behavior of stable cinder/Prussian blue analogue and its mediated nitrite oxidation. Electroanalysis 13, 1171-1178 (2001). 

One of the important purposes for the study of the direct electron transfer of protein is to construct the mediator-free protein-based biosensors. These biosensors can determine many small molecules like H202, 02, NO, nitrite, small organic peroxide, and so on. They also can determine glucose, alcohol, and amino acids by... 

It has been proposed [91] that nitric dioxide radical formation during the oxidation of nitrite by HRP or lactoperoxidase (LPO) can contribute to tyrosine nitration and be involved in cell and tissue injuries. This proposal was supported in the later work [92] where it has been shown that N02 formed in peroxide-catalyzed reactions is able to enter cells and induce tyrosyl nitration. Reszka et al. [93] demonstrated that N02 mediated the oxidation of biological electron donors and antioxidants (NADH, NADPH, cysteine, glutathione, ascorbate, and Trolox C) catalyzed by lactoperoxidase in the presence of nitrite. 

Free radicals are supposed to have a significant role in the progression of acute pancreatitis. The involvement of free radicals was firstly demonstrated in many animal models [355,356], Later on, it has been shown that the levels of superoxide and lipid peroxides increased in the blood from patients with acute pancreatitis [357], Rahman et al. [358] found enhanced urinary nitrite excretion in patients with severe acute pacreatitis. It was suggested that this fact is not simply a reflection of systemic inflammation but probably a consequence of the endotoxin-mediated upregulation of inducible NO synthase. 

Several approaches to the 1,2,3-triazole core have been published in 2000. Iodobenzene diacetate-mediated oxidation of hydrazones 152 led to fused 1,2,3-triazoloheterocycles 153 <00SC417>. Treatment of oxazolone 154 with iso-pentyl nitrite in the presence of acetic acid gave 1,2,3-triazole 155, a precursor to 3-(W-l,2,3-triazolyl)-substituted a,P-unsaturated a amino acid derivatives <00SC2863>. Aroyl-substituted ketene aminals 156 reacted with aryl azides to provide polysubstituted 1,23-triazoles 157 <00HC387>. 2-Aryl-2T/,4/f-imidazo[43-d][l,2,3]triazoles 159 were prepared from the reaction of triethyl AM-ethyl-2-methyl-4-nitro-l//-imidazol-5-yl phosphoramidate (158) with aryl isocyanates <00TL9889>. 

Romanin, C., Kukovetz, W. R., Guanylate cyclase activation by organic nitrates is not mediated via nitrite. J. Mol. Cell Cardiol. 20 (1988), p. 389-396... 

Given that hydroxylamine reacts rapidly with heme proteins and other oxidants to produce NO [53], the hydrolysis of hydroxyurea to hydroxylamine also provides an alternative mechanism of NO formation from hydroxyurea, potentially compatible with the observed clinical increases in NO metabolites during hydroxyurea therapy. Incubation of hydroxyurea with human blood in the presence of urease results in the formation of HbNO [122]. This reaction also produces metHb and the NO metabolites nitrite and nitrate and time course studies show that the HbNO forms quickly and reaches a peak after 15 min [122]. Consistent with earlier reports, the incubation ofhy-droxyurea (10 mM) and blood in the absence of urease or with heat-denatured urease fails to produce HbNO over 2 h and suggests that HbNO formation occurs through the reactions of hemoglobin and hydroxylamine, formed by the urease-mediated hydrolysis of hydroxyurea [122]. Significantly, these results confirm that the kinetics of HbNO formation from the direct reactions of hydroxyurea with any blood component occur too slowly to account for the observed in vivo increase in HbNO and focus future work on the hydrolytic metabolism of hydroxyurea. 

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