Pyrazine occurrence

Second only to sulfur-based systems, nitrogen complexes are relatively well represented in the structural literature with 41 complexes reported. Of these, 25 are with I2 as the electron acceptor, 11 are with the interhalogen IC1, three are with Br2, and two are with IBr. As expected, in every case the halogen bond forms between the nitrogen and the softest halogen atom, i.e., iodine, in all of the complexes except those with dibromine. Most N I2 complexes, and all N Br2, N IBr, and N IC1 complexes are simple adducts, mode A. Exceptions for the diiodine complexes include bridging mode (B) observed for diazines, such as pyrazine [86], tetramethylpyrazine [86], phenazine, and quinoxaline [87], and for 9-chloroacridine [89] and the 1 1 complex of diiodine with hexamethylenetetramine [144] and amphoteric bridging mode (BA) observed for 2,2 -bipyridine [85], acridine [89], 9-chloroacridine [89], and 2,3,5,6-tetra-2/-pyridylpyrazine [91]. The occurrence of both B and BA complexes with 9-chloroacridine, and of B and A complexes and an... 

At elevated temperatures, sugars react more quickly than at lower temperatures with aqueous ammonia, to give, mainly, substituted imidazoles and pyrazines, summarized in Table IV, and a catalyst is not needed. At the higher temperatures, there is an increase in the methyl-pyrazine and -imidazole fractions and a decrease in the (hydroxymethyl)imidazole and (tetrahydroxybutyl)pyrazine fractions, indicating occurrence of thermal cleavage of the side chains.10... 

The occurrence of a large number of pyrazines as flavouring or aroma constituents and as pheromones in extremely low concentrations has led to mass spectrometry being the method of choice for determining the gross structural details of a pyrazine nucleus. The method appears to be generally applicable and relatively specific and sensitive. 

The effect of the various substituents in the 2-position of pteridine has been investigated.24 Here the (—1) substituents, which disfavour hydration of the 3,4-position, do not interfere with its occurrence in the alternative site for the pteridine nucleus, namely in the pyrazine ring. 

Pyrazine, 3-isobutyl-2-methoxy-occurrence, 3, 192-193 Pyrazine, 3-isopropyl-2-methoxy-occurrence, 3, 193... 

The general term oxypyrazine is used here to include derivatives such as the cy-cloamidic tautomeric pyrazinones (1), the alcoholic hydroxyalkylpyrazines (2), the etherial alkoxypyrazines (3-5), the cycloamidic nontautomeric pyrazinones (6), and pyrazine A-oxides (7, 8) in addition, related types like diketopiperazines, acy-loxypyrazines, pyrazine quinones, and endoperoxypyrazines are covered as appropriate. Some brief ancillary information on trivial names, natural occurrence, and biological activities of pyrazines (mainly oxy derivatives) is collected in a final Appendix section. 

Baldaccini NE, Gagliardo A, Pelosi P, Topazzini A. Occurrence of a pyrazine binding protein in the nasal mucosa of some vertebrates. Compar. Biochem. Physiol. B. 1986 84 249-253. 

A review listing the extensive occurrence of pyrazines (mostly alkylpyrazines) in foods and a discussion of the theories of pyrazine formation has been published by Maga and Sizer (69), and a review of the natural occurrence and mass spectra of pyrazines by Brophy and Cavill (69a). 

Kochi and co-workers have prepared the anion-radical 231 of [l,2,5]thiadiazolo[3,4-c][l,2,5]thiadiaz.ole. Also prepared were the anion-radicals of [l,2,5]thiadiazolo[3,4-h]pyrazine (232) and [1,2,5]thiadi-azolo[3,4-fe]quinoxaline. Hyperfine splittings are indicated for 231 and 232 in gauss. The radicals were prepared by alkali-metal reduction in THF the observation of counterion splittings indicates their occurrence in ion-pairs. Radical 231 is of interest from the point of view of the nature of the... 

There are, in fact, very few occurrences of binary hydrogen-bond-based cocrystals that do not contain a primary intermolecular interaction between the two different molecules. Two such examples include 4-nitrobenzamide pyrazine-carboxamide (1 1) [70] and 3,5-dintrobenzoic acid 4-(N,N-dimethylamino)benzoic acid (1 1) [132]. The latter is a rare example of a carboxylic acid- carboxylic acid cocrystal that contains two homomeric dimers instead of one heteromeric dimer [133]. 

Allen, M.S., Lacey, M.J., and Boyd, S. (1995). Methoxypyrazines in red wines occurrence of 2-methoxy-3-(l-methylethyl)pyrazine,/. Agric. Food Chem., 43,769-772. 

Sizer C.E., Maga J.A. and Lorenz K. (1975) The occurrence of pyrazines in white bread crust and crumb. Lebensm. Hiss. Technol. 8, 267-9,... 

Pyrazine, l,4-bis(trimethylsilyl)-l,4-dihydro-synthesis, 3, 178 Pyrazine, 3-s-butyl-2-methoxy-occurrence, 3, 193 Pyrazine, chloro-reactions... 

Although pyrolysis of selected leaf constituents generates pyrazines, the diversity and abundance of pyra-zines in smoke cannot be adequately accounted for by this mechanism alone. Maga and Sizer (2439) and Enomoto et al. (17B12) have reviewed the occurrence of pyrazines in roasted foods and proposed pathways for pyrazine formation. Their summaries present a large array of pyrazines found in the flavor fractions of a number of roasted foods. It is striking that nearly all pyrazines commonly found in tobacco smoke have been identified in at least one roasted food. For example, 2,3-dimethylpyrazine has been found in peanuts, barley, coffee, baked potatoes, mushrooms, lamb fat, and tobacco smoke (1587a). 

Martin, and A. Rodgman Effect of treatment of tobacco with ammonia or various ammonium salts on the levels of pyridines and pyrazines in smoke RDR, 1976, No. 3, January 29, see www.ijrtdocs.com 501003985 -4047. Mizusaki, S., Y. Tanabe, M. Noguchi, and E. Tamaki Phytochemical studies on tobacco alkaloids. XIV. The occurrence and properties of putrescine V-methyltransferase in tobacco roots Plant Cell Physiol. 12 (1971) 633-640. Mozayani, A. Phencychdine Effects on human performance and behavior, Eorensic Sd. Rev. 15 (2002) 61-73. Pailer, M. Chemistry of nicotine and related compounds (including biosynthetic aspects) in Tobacco alkaloids and related compounds, edited by U.S. Von Euler, MacMillan, New York, NY (1965) pp. 15-36. Pictet, A. and A. Rotschy Synthese des Nikotins [Synthesis of nicotine] Chem. Ber. 37 (1904) 1225-1235. 

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