Pyrazine compounds

The quaternization of pyrazine compounds has not been extensively studied, and, therefore, a detailed discussion of the effect of substituents is not possible. Recently Cheeseman has shown, from spectroscopic evidence, that 2-amino- and 2-diethylamino-pyrazine (50, Y = NH2 and NEt2) quatemize at N-4, although protonation occurs at position-1. Other substituted pyrazines from which quaternary salts of structure 51 are formed include 2-chloro- and 2-... 

The synthesis and biological testing of the pyrazine compound 123 was described by Wang et al. [34], The same benzoin intermediate 22 was formed as described in Scheme 2. A three-step reaction was then performed to obtain the desired pyrazine 123, shown in Scheme 31 (i) oxidation of Q1SO4 in aqueous pyridine, (ii) reaction with ethylenediamine in EtOH, and (iii) aromatization in the presence of elemental sulfur. 

An alternative method of synthesizing the pyrazine compounds was described by Ghosh et al, and the synthesis is shown is Scheme 32 [78]. Reaction of a 1,2-dione (124) with a 1,2-diamine (125) to form an imine intermediate followed by spontaneous oxidation of the dihydropyrazine intermediate, formed the protected pyrazine compound 126. The free phenol 127 was obtained by removal of the methyl-protecting groups with a boron trifluoride-dimethyl sulfide complex. Similar compounds were prepared via the same method by Simoni et al. [79]. 

There are two distinct classes of compounds that fit the criteria mentioned above alkene-functionalized chalcone derivatives (Fig. IB) and enone-functionalized chalcone derivatives (Fig. 1C). Within each class, both aromatic and non-aromatic compounds exist. Those compounds functionalized at the alkene include i) 3-membered heterocycles, e.g., epoxide and aziri-dine compounds, ii) 5-membered aromatic derivatives including fused and non-fused compounds, and iii) 6-membered aromatic pyrazine compounds. The enone-functionalized compounds include i) 5-membered aromatics such as pyrazole and isoxazole compounds, ii) 5-membered non-aromatic compounds for example pyrazolines and isoxazolines, and iii) 6-membered non-aromatics where a discussion of heterocyclic and non-heterocyclic compounds will be given for completeness. 

The chinning response in tree shrews, Tupaia lelangeri, is triggered by several lipophilic fractions of male urine. The combined fractions are more active than single fractions. Pyrazine compounds and a high concentration of several volatile monocarboxylic acids characterize male urine. Some pyrazine compounds and some monocarboxylic acids release the chinning response (StralendorfF, 1987). 

Moree- Testa, P., M. Donzel, M. H. Bergerol, and M. M. Luzinier. Determination of pyridinic and pyrazinic compounds in tobacco and cigarette smoke. Ann Tab Sect 1974 1(12) 27. Richter, M. Composition of essential oils in tobacco. III. Analysis of phenolic fraction. Ber Inst Tabakforsch (Dresden) 1974 21 52. 

There are two theories as to the mechanism of the formation of imidazole and pyrazine compounds, namely, (a) the prior formation of glycosylamines and aminodeoxy sugars, and (b) the fragmentation mechanism. 

Musty or potato-like flavor and aroma have been observed as a defect in milk (Hammer and Babel 1957) and Gruyere de Comte cheese (Dumont et al. 1975). This off-flavor results from the production of nitrogenous cyclic compounds by Pseudomonas taetrolens and P. perolens (Morgan 1976). Musty-flavored compounds produced by these organisms include 2,5-dimethylpyrazine and 2-methoxy-3-isopropyl-pyrazine. The Gruyere de Comte with potato off-flavor contained 3-methoxy-2-propyl pyridine, as well as alkyl pyrazine compounds (Dumont et al. 1975). Murray and Whitfield (1975) postulated that alkyl pyrazines are formed in vegetables by condensation of amino acids such as valine, isoleucine, and leucine with a 2-carbon compound. Details of the synthetic mechanism in pseudomonads are unknown. 

Pyrazine compounds. As mentioned earlier the pyrazines have been found in abundance. As a rule the alkyl derivatives of the pyrazines produce roasted—nut like odor profiles. Fifty pyrazines have been reported to occur in cooked or roasted beef (28)-... 

Found in processed truffles but absent in fresh truffles were two furans (compound 4 and 7) and a pyrazine (compound 24). Furans are well known to result from the thermal degradation of carbohydrates while alkyl pyrazines result from the reaction of amino acids and alpha-diketones. A number of methyl ketones were also observed in the canned product which were absent in the fresh product. Methyl ketones are known to result from the thermal decomposition of beta-keto acids (17-19) -... 

The pH of the steam distillate was 6.2 in all cases. The total flavor isolate (by SDE) of plain cashews had, on the whole, a strong pungent and green aroma, reminiscent of the cashew nut testa and cashew shell, whereas the flavor isolates from roasted samples had the characteristic mildly nutty aroma also. The flavor fractions obtained by selective extraction method gave some information about the chemical nature of compounds responsible for the characteristic flavor notes. Accordingly, the basic fraction of roasted nuts, (both oven-and oil-roasted), had the typical nutty aroma associated with pyrazine. compounds. The basic fraction of plain cashews did not have any characteristic flavor in particular. 

The problem of developing desirable meat flavor in the presence of vegetable protein has been clearly demonstrated in the literature. Physical measurements after heating a meat model system with soy proteins have shown a dramatic reduction in the concentration of alkyl pyrazine compounds due to interaction with the soy proteins. These interactions have been defined in terms of stoichiometry and binding energies from measurements on pure standards of the methyl pyrazines. 

P. E. Koehler and G. V. Odell, Factors affecting the formation of pyrazine compounds in sugar-amine reactions, J. Agric. Food Chem., 1970, 18, 895-898. 

The lone set of dimers in Table II, [M(C5Me5)2]2(M Pyraz ne) (Fig. 20 M = Ba), were synthesized from the base-free metallocenes by addition of pyrazine to MCp (1 2), analogous to the dioxane reaction for the amide compounds (Fig. 8).103 The pyrazine compounds are intensely colored owing to both charge transfer and intraligand electronic transitions. The pyrazine ligand has been shown to be labile by uv-vis spectroscopy. 

In acetic acid, some 3 -oxopyrazine nucleosides undergo an unusual rearrangement to form pyrido[2,3-A]pyrazine compounds.137... 

Ionization constants of pyrazine compounds are summarized by Barlin (B-82MI 603-0l>. The basicity constants of pyrazine and its methyl derivatives in water have also been measured, and show a linear inverse relationship with polarographic half-wave potentials <85JHC1143>. 

The same authors (1987c) also identified the three isomers when heating serine and threonine with or without sucrose. 0.34 and/or 0.35 are the pyrazinic compounds formed in the reaction of 2,3-pentane-dione with alanine at 150-160 °C (Rizzi, 1972). 

Koehler P.E., Mason M.E. and Newell J.A. (1969) Formation of pyrazine compounds in sugar-amino acid model systems. J. Agric. Food Chem. 17, 393-6. 

Koehler P.E., Mason M.E. and Odell G.V. (1971) Odor threshold levels of pyrazine compounds and assessment of their role in the flavor of roasted foods. J. Food Sci. 36, 816-18. 

Winter M., Gautschi F., Flament I., Stoll M. and Goldman I.M. (Firmenich Cie) (1975g) Flavoring agents pyrazine compounds. US Patent 3917872. 

Enomoto, Y., H. Masuda, and M. Yoshida Pyrazine compounds. Recent progress in the studies of pyrazine compounds Koryo 128 (1980) 91-110. 

As a general rule, channels blocked by the pyrazine compounds are found only in tight but not leaky epithelia. Thus pyrazine carboxamides block sodium entry into the cells of the kidney distal tubule [149], salivary duct [150], colon [ISl] and epididymis [152], but not into the cells of the small intestine of kidney proximal tubule. Sodium channels sensitive to pyrazine carboxamides are not confined either to epithelia or to mammalian cells. For example, sodium entry into the cells of frog skin epithelium [153], toad urinary bladder [154], chicken coprodeum, fish gills of some species [ISS], body wall of the leech [155] and crustacean gills [155] are also sensitive. In addition, there are reports that sodium entry sites in ova [3] and erythrocytes [156] are also susceptible to the effects of the pyrazine derivatives. 

All the pyrazine compounds were tested for their ability to increase the urinary Na/K ratio in DOCA-treated adrenalectomised rats. Compounds which produced a 50% reversal of the DOCA effect at a dose of less than 10 pg per rat were given a score of 4. Scores of 3 were achieved with a dose of 10—50 pg, 2 with a dose of 50—100 pg, 1 with a dose of 100—800 pg and with a dose of more than 800 pg, the scores given in Table 1.2 being derived in this way. 

As shown in Table IV, many pyrazine compounds were generated in IMP and deoxyalliin as well as in the IMP and alliin model systems. Pyrazines are widely distributed in thermally processed foods, such as roasted beef, roasted peanut, and roasted barley. The Maillard reaction, which involves the interactions of reducing carbonyl compounds and amino-containing compounds, has been shown to be the major mechanism for the formation of pyrazines (26). 

The compound in question, fMn2(dicyanamide)j(N03)(inethylpyrazine)2], forms the net shown in Figure 9.34 [30]. This net has vertex symbols 4-4-444444-62-62 62-62-, 4444-62-62 and is thus clearly topologically different from the fsg net. It was noted that the introduction of a methyl group on the pyrazine ring induced a shift in 3D-net from the peu-net (a-polonium) of the [Mn(dicyanamide)2(pyrazine)] compounds [30]. 

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