Nitrites vitamin

Epidemiologic studies in Japan indicate an increased risk of stomach cancer owing to consumption of broiled fish and meats (116). In the United States, stomach cancer incidence has steadily declined since the 1940s, whereas consumption of broiled food has increased (108). In addition, the average human intake of PAHs is only 0.002 of that required to produce cancer in half of animals fed. Test results are often contradictory (117) and many components of food, such as vitamin A, unsaturated fatty acids, thiols, nitrites, and even saUva itself, tend to inhibit the mutagenic activity of PAHs (118—120). Therefore, the significance of PAHs in the human diet remains unknown (121,109). 

Equations 4-8 illustrate some mild methods that can be used to cleave amides. Equations 4 and 5 indicate the conditions that were used by Woodward and Eschenmoser, respectively, in their synthesis of vitamin B,2- Butyl nitrite," nitrosyl chloride, and nitrosoniurn tetrafluoroborate... 

Equations 1-10 illustrate some mild methods that can be used to cleave amides. Equations 1 and 2 indicate the conditions that were used by Woodward and Eschenmoser, respectively, in their synthesis of vitamin B12. Butyl nitrite, nitrosyl chloride, and nitrosonium tetrafluoroborate (NO BF4 ) have also been used to cleave amides. Since only tertiary amides are cleaved by potassium -butoxide (eq. 3), this method can be used to effect selective cleavage of tertiary amides in the presence of primary or secondary amides.(Esters, however, are cleaved by similar conditions.) Photolytic cleavage of nitro amides (eq. 4) is discussed in a review. 

In 1973, the first naturally occurring isobacteriochlorin, iron-containing siroheme, was isolated1 from a sulfite reductase of Escherichia coli. Later it was also discovered in sulfite and nitrite reductases of numerous bacteria and plants.2 Iron-free sirohydrochlorins (also called factor II) were discovered in vitamin B12 producing bacteria.3-4 Together with factor III. a sirohydrochlorin methylated in the 20-position, the reduced forms of factor II and factor III were identified as biosynthetic intermediates in the biosynthesis of vitamin B12.5... 

Mirvish (53,54) discovered that vitamin C could inhibit ni-trosation reactions. The purely chemical interaction of ascorbic acid with nitrite has been studied for theoretical reasons and because of its importance in the preservation of foods. This interaction has received increased attention for minimizing the presence of nitrosamines and nitrosamides in the environment, and especially in foods. We have studied the relationship in gastric carcinogenesis between high levels of nitrite, including pickling, and of vitamin C as a protective and inhibiting element. 

We demonstrated that the mutagenic activity from the reaction of nitrite and Sanma was carcinogenic (48). It is quite relevant that this product induced glandular stomach cancer in rats. Since the formation of the mutagen can be blocked by vitamin C, it would seem that the formation of glandular stomach cancer can also be so Inhibited. 

Nitric oxide (NO) and nitrite were found to be oxidized by Prussian blue and indium hexacyanoferrate-modified electrodes [75-77], For pharmaceutical application oxidation of isoprenaline [78] and vitamin B-6 [79] at cupric hexacyanoferrate-modified electrodes was shown. 

Aquacobalamin (vitamin B12) does not bind NO in aqueous solution -nitrite impurities account for the reaction observed (71). 

Inhibitors of nitrosation generally function by competing with the amine for the nitrosating agent. An inhibitor would thus react with nitrite at a faster rate than with amines. The inhibition reaction has recently been reviewed ( 35). The ability of ascorbate to act as a potent inhibitor of nitrosamine formation has resulted in the use of the vitamin in nitrite-preserved foods and pharmaceuticals. Furthermore, the effectiveness of ascorbate in inhibiting nitrosamine formation is dependent on (1) the concentration of ascorbate (an excess is required) (2) pH (ascorbate is nitrosated 240 times more rapidly than ascorbic acid) (3) the reactivity of the amine toward nitrosation and (4) the extent of oxygenation of the system. 

Treatment — Patients should be decontaminated immediately prior to treatment using the decontamination method presented in Section 7.3.3. The Lilly Cyanide Antidote Kit contains amyl nitrite, sodium nitrite, and sodium thiosulfate. Dimeth-ylaminophenol, cobalt-edetate, or vitamin B12a are alternative antidotes for cyanide poisoning.5... 

Nitrous oxide can react with vitamin B12, preventing its use in red blood cell development and resulting in anemia. Use of nitrites can rapidly result in fatal methemoglobinemia, a condition that reduces the ability of the blood to transport oxygen. In 1944,11 men were admitted to a New York hospital with bluish discoloration of the skin due to methemoglobinemia. The city toxicologist and the health department eventually determined that salt shakers in a food establishment visited by all of the men contained sodium nitrite instead of table salt, sodium chloride. 

Treatment of cyanide poisoning includes rapid administration of activated charcoal (although charcoal binds cyanide poorly, it can reduce absorption) and general supportive care. The conventional antidote kit available in the USA includes two forms of nitrite (amyl nitrite and sodium nitrite) and sodium thiosulfate. The nitrites induce methemoglobinemia, which binds to free CI T creating the less toxic cyanomethemoglobin thiosulfate is a cofactor in the enzymatic conversion of CN to the much less toxic thiocyanate (SCINT). Recently, the FDA approved a concentrated form of hydroxocobalamin, which is now available as the Cyanokit (EMD Pharmaceuticals, Durham, North Carolina). Hydroxocobalamin (one form of vitamin B12) combines rapidly with CN to form cyanocobalamin (another form of vitamin B12). 

Several macrocyclic ligands are shown in Figure 2. The porphyrin and corrin ring systems are well known, the latter for the cobalt-containing vitamin Bi2 coenzymes. Of more recent interest are the hydroporphyrins. Siroheme (an isobacteriochlorin) is the prosthetic group of the sulfite and nitrite reductases which catalyze the six-electron reductions of sulfite and nitrite to H2S and NH3 respectively. The demetallated form of siroheme, sirohydrochlorin, is an intermediate in the biosynthesis of vitamin Bi2, and so links the porphyrin and corrin macrocycles. Factor 430 is a tetrahydroporphyrin, and as its nickel complex is the prosthetic group of methyl coenzyme M reductase. F430 shows structural similarities to both siroheme and corrin. 

The oxidation of terminal alkenes with an EWG in alcohols or ethylene glycol affords acetals of aldehydes chemoselectively. Acrylonitrile is converted to 3,3-dimethoxypropionitrile (38), which is produced commercially as an intermediate of vitamin Bi in MeOH using methyl nitrite (37) as a unique reoxidant of Pd(0). Methyl nitrite (37) is regenerated by oxidation of NO with oxygen in MeOH. Methyl nitrite is a gas, which can be separated easily from water formed by the oxidation [la],... 

If k2 >> k, then reaction (4) is mostly complete before (3) starts. Large doses of vitamin C have been observed to protect rats from liver tumors induced by aminopyrine and sodium nitrite (26). This inhibition is thought to result, in part, from blockage of in vivo nitrosation, which forms dimethylnitrosamine. 

Acetals result from oxidative coupling of alcohols with electron-poor terminal olefins followed by a second, redox-neutral addition of alcohol [11-13]. Acrylonitrile (41) is converted to 3,3-dimethoxypropionitrile (42), an intermediate in the industrial synthesis of thiamin (vitamin Bl), by use of an alkyl nitrite oxidant [57]. A stereoselective acetalization was performed with methacrylates 43 to yield 44 with variable de [58]. Rare examples of intermolecular acetalization with nonactivated olefins are observed with chelating allyl and homoallyl amines and thioethers (45, give acetals 46) [46]. As opposed to intermolecular acetalizations, the intramolecular variety do not require activated olefins, but a suitable spatial relationship of hydroxy groups and the alkene[13]. Thus, Wacker oxidation of enediol 47 gave bicyclic acetal 48 as a precursor of a fluorinated analogue of the pheromone fron-talin[59]. 

Chemical preservatives include free radical scavengers (also known as antioxidants), such as vitamin C and compounds such as BHA (butylated hydroxyanisole), and bacterial growth inhibitors, such as benzoic acid, sulfur dioxide, and sodium nitrite (NaN02). Ethanol (CH3CH2OH) has long been used as a preservative, both of itself (as in wine), and of other foods (e.g., fruits stored in brandy). Some chemical preservatives may be harmful Sulfur dioxide (often used to preserve wines) is irritating to the bronchial tubes of persons who have asthma, and nitrites have been implicated as carcinogens. 

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