5-Isobutyl-2-isopropyl-3-methoxypyrazine

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]. 

Hydroxypropyl)-5-isobutyl-6-methoxypyrazine (157, R = Hu ) gave 2-isobutyl-3-methoxy-5-(3-phthalimidopropyl)pyrazine (158, R = Hu ) (phthal-imide, Et02CN=NC02Et, Ph3P, A, 20°C, 12 h 93%), and thence 2-(3-amino-propyl)-5-isobutyl-6-methoxypyrazine (159, R = Hu ) (H2NNH2.H20, EtOH, reflux, 4 h 83%) 295 2-(3-aminopropyl)-5-isopropyl-6-methoxypyrazine (159, R = Pfl)298 and other homologues295,298 were made similarly. 

Three extremely odorous pyrazines, 3-isopropyl-2-methoxypyrazine, 2-s-butyl-3-methoxypyrazine, and 2-isobutyl-3-methoxypyrazine have been shown to be present in green peas, and are likely to be of major significance in the flavor of peas (59). The volatile oil of green bell peppers has been found to contain 2-isobutyl-3-methoxypyrazine as a major component (60,61). The alkylpyrazines in potato chips (62,63) and roasted peanuts (63) have been examined. 2-Isopropyl-3-methoxypyrazine has been characterized in the vacuum steam volatile oil of potatoes (64), 2-ethyl-3-methoxypyrazine in cooked potato (65), and 3-ethyl-2,5-dimethylpyrazine and 2-ethyl-3,5-dimethylpyTazine as the components important to the aroma of baked potato (66). A variety of alkylpyrazines have been identified in roasted sesame seeds (67) and 21 pyrazines have been identified in the aroma components isolated from roasted green tea (68). 

Recent work has shown the presence of pyrazine and 2,6-dimethylpyrazine in leek (75), pyrazine and alkylpyrazines in the volatile constituents of tamarind (76), five alkylpyrazines in soong-neung (extract of cooked and roasted rice) (77) and in shoyu (soy sauce) (78), and alkylpyrazines in white bread (79). Murray and Whitfield (80) have examined vegetable tissue for 2-isopropyl-, 2is-butyl-, and 2-isobutyl-3-methoxypyrazines and observed at least one of these compounds in 23 of the 27 samples studied. 2-Methylpyrazine and 2,5- and 2,6-dimethylpyrazines have been determined in black tobacco and in the smoke of nonfilter cigarettes made from these tobaccos (81). 

Figure 4.10. Extracted ion chromatograms of GC/IT-MS/MS analysis of a 1 2.5 diluted wine spiked with four methoxypyrazines at 0.25 ng/L and two ethoxypyrazines at 45 ng/L as internal standards. The chromatographic conditions are described in Table 4.3. (49) 3-Ethyl-2-methoxypyrazine (m/z 119) (50) 3-isopropyl-2-methoxypyrazine (IPMP) (m/z 109) (51) 3-ethyl-2-ethoxypyrazine (internal standard 1) (m/z 124) (52) 3-isopropyl-2-ethoxypyrazine (I.S. 2) (m/z 123) (53) 3-seobutyl-2-methoxypyrazine (SBMP) (m/z 81) (54) 3-isobutyl-2-methoxypyrazine (IBMP) (m/z 109).

Ethylmethoxypyrazine. Unlike the isobutyl-, isopropyl- and sec-butyl methoxypyrazines, the existence of 2-ethyl-3-methoxypyrazine (4) (ethylmethoxypyrazine) in fruits and vegetables has not been consistently confirmed in the past. While evidence for its existence was found, unambiguous identification by mass spectrometry was prevented by the trace concentration of this component. Of all the methoxypyrazines so far mentioned, it has an aroma most similar to raw potatoes 16) and synthetic material adds potato flavor to processed potato products (18). It is also described as earthy 15), and it has a sensory detection threshold of 425 ng/L (17). Given its aroma, it is not surprising that its possible occurrence in potatoes has been the subject of several studies. 

The aroma of green peas is derived fiom aldehydes and pyrazines (3-isopropyl-, 3-sec-butyl- and 3-isobutyl-2-methoxypyrazine). 

Methoxypyrazines 3-isobutyl-2-methoxy-pyrazine, 3-isopropyl-2-methoxypyrazine Strong X No ... 

Chloro-5-isobutylpyrazine 6-Chloro-5-isobutyl-2-pyrazinecarbothioamide 6-Chloro-5-isobutyl-2-pyrazinecarboxamide 2-Chloro-3-isobutylpyrazine 4-oxide 2-Chloro-5-isopentyl-3,6-dimethylpyrazine 2-Chloro-3-isopropenyl-6-isopropyl-5-methoxypyrazine 5-Chloro-6-isopropenyl-3-isopropyl-l-methyl-2(177)-pyrazinone... 

Isobutyl-5-isopropyl-6-methoxypyrazine 6-Isobutyl-3-isopropyl-5-methyl-20 //)-... 

The odorants of dry sweet bell pepper powder have been analysed in detail [84, 85]. Omission experiments established ethyl methylpropanoate, methyl 2- and 3-methylb-utanoate, ethyl 2- and 3-methylbutanoate, 3-isopropyl-, 3-isobutyl- and 3-sec-butyl-2-methoxypyrazine as character impact odorants. 

For Vitzthum et al. (1976), methoxypyrazines were the main source for the green coffee odor. Becker et al. (1988), when tracking the compounds responsible for the undesirable flavor of peasy coffee beans (other defects being present in stinker and Rio beans) that gave to the brews a flavor of fresh green peas, found that the isobutyl derivative (0.77) was much less important than the peasy isopropyl derivative (0.75). 

Green peas (raw) 2-alkyl-3-methoxypyrazines (2-isopropyl-, 2-isobutyl-, and 2-sec-butyl-, see pyrazines) together with ( )-2-nonenal (see alkenals) ( ,Z)-2,6- nonadienal, ( , )- 2,4-decadienal, hexan-l-ol, and (Z)-3- hexen-l-ol. 

Unroasted peanut seeds Arachis hypogaea, Fabaceae) contain about 75 volatiles, and in roasted seeds around 320 volatiles have been identified. The compounds of the greatest importance for the aroma of raw seeds are 2-isopropyl-3-methoxypyrazine (earthy and pea-like), 2-isobutyl-3-methoxypyrazme (bell pepper-like and earthy), and (E)-4,5-epoxy-dec-2-enal (metallic). Aroma components... 

---