Pyrazine trimethyl

Trimethyl pyrazine 3-ethyl 2,5-dimethyl pyrazine FIG. 8 Flavor compounds in roasted flaxseed observed by Meyers et al. (2004). 

The reactions of the isomeric dimethylpyrazines and trimethyl-pyrazine with methyllithium have been studied in order to gain insight into the factors involved in the competition between ring methylation and side-chain metalation.189 The major product from the reaction of 2,5-dimethylpyrazine and ethereal methyllithium was shown to be trimethylpyrazine, thus confirming Klein and Spoerri s earlier observation.190,191 Tetramethylpyrazine was also formed as a by-product. Proof of side-chain metalation was obtained by treatment of the reaction mixture with methyl benzoate and isolation of 2-methyl-5-phenacylpyrazine. Evidence for the presence of dihydro-and tetrahydropyrazine intermediates is derived from the infrared spectrum of the crude product obtained on hydrolysis of the reaction mixture which shows C=N and N-H absorptions (see Scheme 17). 

CIC Non-enzymatic-browning compounds 2,5- and 2,6-dimethyl pyrazines, trimethyl pyrazine impart the fresh, green, nutty character, 2-methyl-6,7-dihydro-5H-cy-clo-penta-pyrazine is responsible for the roasted-nutty note and 2,5-dimethyl-4-hy-droxy-furan-3(2H)-one supports the caramel like, sweet overall impression. 

Pyrazines are generally associated with nonenzymatic browning. However, pyrazines have also been found as a result of microbial action. Bacillus subtilis was the first organism found to produce a pyrazine (tetramethyl pyrazine [105]). Since that time, several pyrazines (2-acetyl, dimethyl, 2-methoxy-3-ethyl, 2,5 or 2,6-diethyl-3-methyl, trimethyl, tetramethyl, and trimethyl pyrazine) have been identified in aged cheese [16,106-109]. While some of these pyrazines may be formed via the Maillard reaction during aging of the cheese, it is likely that they were formed via microbial action. 

Elemental composition analysis (and some idea of the volatile composition of colfee) strongly suggested that this ion corresponded to a pyrazine. It did not, however, allow us to distinguish between trimethyl pyrazine and ethyl methyl pyrazine, isomers that consequently have the same molecular weight. Accurate mass may therefore allow us to discriminate between some molecules or molecular classes but will be of little value in the analysis of mixtures of isomers, such as systems containing a wide range of terpenes. 

Dioxopiperazines are amongst the most ubiquitous of natural products (75FOR(32)57) and they are formally derived by the cyclodimerization of a-amino acids (69CCC4000) or their esters. A number of methods are available for their oxidation to the corresponding pyrazines. Treatment of 2,5-dioxopiperazines with triethyl- or trimethyl-oxonium fluorobor-ate followed by oxidation with DDQ, chloranil or iodine results in pyrazine formation, usually in high yields (Scheme 63) (72JCS(P1)2494). 

Imidazo[4,5-6]pyrazin-2(3H)-one, 1,5,6-trimethyl-chlorination, 5, 626 lmidazo[ 1,2-a ]pyrazin-3(2H) -ones synthesis, 5, 642... 

Isolation and identification of pyrazine alkaloids (Table III) have been achieved in most cases by a combination of gas chromatography and mass spectrometry (35,36,38,69,97,142). Methyl-, 2,3,6-trimethyl-, and tetramethylpyrazines (23a, 21a, and 22a) from the melon fly are identified by utilizing a solid sampling technique in conjunction with gas chromatography-mass spectroscopy (147). Methylpyrazines show the molecule ion as a base peak. Fragmentation proceeds mainly by the loss of HCN or CH3CN from the molecular ion (141). Eth-... 

The synthesis of the trimethyl analogue of (70-6) represents the most direct approach to the pyrazine system. In this case, condensation of /, 5-alaninamide (71-1) with diacetyl gives the pyrazinol (71-2) directly. The hydroxyl group is then converted to the corresponding dimethylamine by the same sequence as above [71]. The product, triampyzine (71-3), shows predominantly anticholinergic activity. 

In Figure 3, as in Figure 2, samples isolated from oats with 7.4% and 8.3% lipid content were different with regard to chemical composition. Since the oil itself may play several roles, for example as generator of aroma compounds as well as solvent for other volatile compounds, it is of interest to follow the aroma pattern in the abovementioned samples. The amount of heterocycles decreased in most cases when the initial oat lipid content increased. Compounds such as pyrazine derivatives (methyl, 2,5-dimethyl, 2,6-dimethyl, 2-ethyl-5-methyl, trimethyl, 2,5-methyl-3-ethyl), furfural, 5-... 

N-Heterocycles Pyridine Pyrazines Unsubstituted, 2,3-Dimethyl, MARM ++ 2,5-Dimethyl-3-ethyl, Methyl, 2-Ethyl-6-methyl, 2,5-Dimethyl, 2-Ethyl-5-methyl, 2,6-Dimethyl, Acetylmethyl, 2-(2-Furyl), Ethyl, 2-Methyl-5-(methylethyl), Trimethyl Pyrroles 2-Acetyl, N-Methyl-2-furyl, 1-Formyl, 1-Furfury 1-2-formyl, 5-Methvl-2-formvl Trimethylpyrazine (TMPy) (RV = 0.989)... 

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