2-Methoxy-3-alkylpyrazines

Source From R.M. Seifert et al., Synthesis of Some 2-Methoxy-3-Alkylpyrazines with Strong Bell Pepper-Like Odors, J. Agr. Food Chem., Vol. 18, pp. 246-249, 1970, American Chemical Society. 

Seifert R.M., Buttery R.G., Guadagni D.G., Black D.R. and Harris J.G. (1970) Synthesis of some 2-methoxy-3-alkylpyrazines with strong bell pepper-like odors. J. Agric. Food Chem 18, 246-9. 

Figure 6.69 Proposed biosynthetic pathways of 2-methoxy-3-alkylpyrazines, (a) from valine and glyoxal and (b) from glycine, valine, and SAM.

Unlabelled 2-methoxy-3-alkylpyrazines are commercially available (Pyrazine Specialities, Inc., Atlanta, GA, USA). They can also be synthesized by the method of Murray and Whitfield (1975). The chloro compounds (8) and (9), prepared by the method of Murray and Whitfield (1975), are converted to trideuterated methoxypyrazines (6) and (7) by the action of sodium methoxide- Hj (Fig. 2 Harris et d. 1987 Lacey et d. 1991). 

Methoxy-3-alkylpyrazines are often associated with musty-earthy and potato-like odors. 2-methoxy-3-isopropylpyrazine is responsible for the musty, potato-bin odor and contributes to off-flavor notes in wines 2-methoxy-3-isobutylpyrazine is a main constituent of green bell pepper and jalapenios flavor. It is known that alkylpyrazines are formed in thermal reactions but can be also produced by microorganisms, mainly bacteria, such as Pseudomonas species [2]. 

D Kilkast. Sensory evaluation of taints and off-flavours. In MJ Saxby, ed. Food Taints and Off-Flavours. Glasgow Chapman Hall, 1993, pp. 1-32. RC Mclver, GA Reineccius. Synthesis of 2-methoxy-3-alkylpyrazines by Pseudomonas perolens. In C Parliament, R Croteau, ed. Bioformation of Flavours, ACS Symposium Series 1989, pp 266-274. 

Methoxy-3-alkylpyrazines Evocative, alerting odor to herbivores and predators — 214... 

Although most of the alkylpyrazines are formed through thermal Interactions of components in food, methoxy-substltuted pyrazlnes are mainly derived from biosynthetic pathways. 2-Isobutyl-3-methoxy-pyrazine Isolated from bell pepper by Buttery at al. (14) is one of the most significant flavor compounds discovered. This characteristic bell pepper aroma compound has an extremely low odor threshold of 0.002 ppb in water (15). 

Alkylpyrazines with other substituents have been oxidized to carboxylic acids as follows 2-acetamido-6-methylpyrazine was oxidized in aqueous magnesium sulfate with potassium permanganate to 2-acetamido-6aqueous potassium permanganate at room temperature to 2-carboxy-3-chloropyrazine, which was also obtained by oxidation of 2-chloro-3-methylpyrazine with selenium dioxide in boiling aqueous pyridine (947). Oxidations of 2-methoxy-3-methyl-... 

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