2- -3-methoxypyrazines

Modern Methods of Plant Analysis, Vol. 18 Fruit Analysis 

Edited by H.-F. Linskens and J.F. Jackson Springer-Verlag Berlin Heidelberg 1996 

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The characteristic note of green beans is attributed to methoxypyrazines which have very low threshold values (10). The characteristic musty earthy note of robustas was recently identified as 2-methyhsobomeol [2371-42-8] (11). 

A cyano group produces practical reactivity (methanolic CH30, 66°, < 3hr) by its presence in 2-chloro-3-cyano-6-methylpyridine, opposing the deactivating effect of a methyl group, and on other 2-chloropyridines (see references 3-6 in ref. 140). The cyano group activates 3-cyano-6,6-diphenyl-2-methoxypyrazine (168) (pre-... 

Closely related compounds, even enantiomers, may not show similar binding affinities. OBP1 specifically bound 2- H-3 -isobutyl-3-methoxypyrazine, whereas OBP2 did not a derivative compound (2-isobutyl-3-methoxy-pyrazine) was unable to displace ligands from OBP-2 (Lobel et al., 1998). 

Other compounds, such as 2,4,6-trichloroanisole (TCA), 2-isopropyl-3-methoxypyrazine and 2-isobutyl-3-methoxypyrazine, were found downstream of a pulp mill effluent, and were considered as off-flavours. These compounds are by-products of chlorination, or can be produced by actinomycetes or other biota [74]. 

Minuscule quantities of naturally-occurring pyrazines have been found in some foodstuffs and are largely responsible for their flavor and aroma. For example, 3-isopropyl-2-methoxypyrazine is isolated from green peas and wine and a seasoned wine connoisseur can identify a ppt quantity. In addition, 2-methyl-6-vinylpyrazine exists in coffee. 

The specific compounds that are responsible for the "pea" flavor have not been identified. Bengtsson and Bosund (52) suggested that acetaldehyde, hexanal and ethanol were important, while Murray et al. (53) isolated three methoxypyrazines that have very low taste or recognition thresholds and might, therefore, be of major significance in pea flavor. 

Figure 8. Intervalence spectrum of Creutz-Taube ion (------) and of the corresponding ion with 1-methoxypyrazine (-----) instead of pyrazine (DtO solution,...

Aposematic species from two different families produce pungent pyrazines, presumably as an additional warning to potential predators of their toxicity. These include Oncopeltus fasciatus (Lygaeidae, seed bug family) that secretes 2-isobutyl-3-methoxypyrazine [28], and the stink bug Murgantia histrionica (Pentatomidae), that oozes froth containing 2-isobutyl- and 2-sec-butyl-3-methoxypyrazine when molested [39]. 

Attractive Compounds. While the defence chemistry of ladybird beetles has been extensively investigated, little is known about intraspecific communication. The role of chemical and behavioural cues has been described in mate recognition in Adalia bipunctata. Cuticular hydrocarbons, especially 7- and 9-methyltri-cosane seem to play an important role [301]. In Coccinella septempunctata, 2-isopropyl-3-methoxypyrazine 158 (see Scheme 17) accounting for the dis-... 

When disturbed or molested, these insects release small droplets of hemo-lymph from the tibio-femoral joints of their legs, and it is now well established that the deterrency exhibited by many species of coccinellids towards potential predators results from the presence of repellent and bitter alkaloids in that fluid [ 12,13]. In ladybirds, this unpalatability is associated with a bright aposematic coloration and a characteristic smell due to 3-alkyl-2-methoxypyrazines [14, 15]. The beetles use these molecules not only to reinforce the visual alerting signal on an olfactory level, but also as aggregation pheromones [16]. 

GERBER, N.N., Three Highly Odorous Metabolites from an Actinomycete. 2-Isopropyl-3-methoxypyrazine, Methylisobomeol, and Geosmin , J Chem Ecol 3 475 (1977). 

Solid phase microextraction (SPME) is an ideal approach to monitor volatile flavor components. This approach has been used to identify the volatile compounds in the headspace of fresh fruit during maturation [92], Using SPME fibers and GC/MS, the key flavor components are hexanal, 2-isobutyl-3-methoxypyrazine, 2,3-butanedione, 3-carene, trans-2-hexenal, and linalool (Fig. 8.1). In this study, the principal aroma compounds whose abundance varied during fruit development were specifically identified. 

Upstream migrating glass eels also swim toward compounds with earthy and green (vegetable) odors. These are pyrazines, thiazoles, and alcohols of the cyclohexanol type (Sola, 1995). One of these compounds, 2-isobutyl-3-methoxypyrazine, is common in rivers and lakes (Hwang eta/., 1984). 

The mucus of the olfactory epithelimn contains odorant-hinding proteins that are specific to various odorants, such as anisole, camphor, benzalde-hyde (cherry-almond odor), 2-isobutyl-3-methoxypyrazine (green bell pepper odor), and 5o -androst-16-en-3-one (urine odor) (summarized by Leffingwell, 2001). 

Methoxypyrazines 249 and 250 are lithiated with LiTMP as shown in the two syntheses in Scheme 123 , the first being part of a route to kelfizine and sulphalene . 

Methoxypyrazine-2-one Af-oxides 341 were prepared from oxime derivatives 340 by one-pot cyclization in the presence of DCC/DME with subsequent interaction with Me2S04/K2C03 and NaOH (equation 148) . Similar intramolecular cyclizatiou of ester and oxime O-ethers groups iu the presence of lithium arylthiolate also leads to pyrazin-2-one ring formation . ... 

Examples of the 3-lithiation of both 2- and 2,6-disubstituted chloro- and methoxypyrazines, as well as 2-thiomethylpyrazine are known (88S881 90JOC3410 91JHC765, 91JOM(412)301] (Scheme 117). As with pyridazine, LiTMP has so far been the only base employed, and this same base system has also recently been used for the directed metalation of pyrazine... 

Three 3-alkyl-2-methoxypyrazines (24b, 24c, and 24d) are detected as odor components in the monarch butterfly, Danaus plexippus (Table III). The wide variability in pyrazine content observed with this insect is correlated with similar variability in the larval food plants, Asclepias sp. It seems possible that the pyrazines may be one of the factors implicated in the food choice mechanism (69). 

Alkyl-2-methoxypyrazines exhibit a base peak at miz 124 in the mass spectrum. The peak corresponds to a molecular ion in 2-methoxy-3-methylpyrazine (24a) and to a fragment ion, resulting from a McLafferty rearrangement of an alkyl group, in 3-isopropyl-2-methoxypyrazine (24b) and 3-5cc-butyl-2-methoxy pyrazine (24d) (97). 

The use of headspace solid-phase microextraction (HS-SPME) combined with GC was effective for isolation and determination of alkylpyrazines in cocoa liquor <2004JBS267, 2004MI291>, and similarly methoxypyrazine in wine was analyzed by HS-SPME/2-D GC <2005MI1075>. 

In an initial survey at the University of Auckland in 2004 on Cabernet Sauvignon, Merlot and Malbec wines, subject to MOX in 2000-L tanks at 4-8 mg/L/month for 12 weeks post-MLF, no changes were seen in the aroma profiles of the wines (vs. controls) for a wide range of aroma compounds, including herbaceous methoxypyrazines and C6 alcohols, floral terpenes and (3-ionone, or for fruity esters and higher alcohols (Rowdon, 2005). Likewise, the concentrations of the varietal thiol 3MH,... 

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