Alkylpyrazine A-oxides

Infrared absorption spectra of pyrazine A -oxides and alkylpyrazine A -oxides have been recorded and discussed (575, 625, 626). The ligand 2,3-bis(pyridin-2 -yl)pyrazine 1,4-dioxide and its complexes with cobalt(II), nickel(II), and copper(II) have been prepared and are polymeric octahedral in structure (754). 

D. From Alkylpyrazine A -Oxides with Acetic Anhydride Followed by... 

Whereas pyrazine and alkylpyrazines exhibit an absorption at about 260-270 nm in water, their mono A -oxides show two peaks, one about 215 nm, and the other about 260 nm, which are characteristic of the presence of an A -oxide function (838). The u.v. absorption maxima of pyrazine A -oxide moved to shorter wavelengths from that in heptane as the polarity was increased in ethanol and water (1481). Band analyses of pyrazine mono- and di-A -oxides have been carried out (627). 

Proton magnetic resonance techniques have been used for the measurement of rates of hydrogen-deuterium exchange of pyrazine (in CHsOD-CHsONa at 164.6") (591) for a study of protonation of pyrazine (1472) for analysis of the reaction mixture from quatemization of 2-substituted pyrazines with methyl iodide (666) for elucidation or confirmation of the structures of alkylpyrazines obtained by alkylation of pyrazines with aldehydes and ketones in the presence of a solution of an alkali or alkaline earth metal in liquid ammonia, or a suspension of these metals in other solvents (614) for a study of changes in chemical shifts produced on ionization of 2-methyl and 2-amino derivatives of pyrazine in liquid ammonia (665) for characterization of methoxymethylpyrazines (686) for the determination of the position of the A -oxide function in monosubstituted pyrazine V-oxides and the analysis of V-oxidation reactions (838) for a study of the structure of the cations of fV-oxides of monosubstituted pyrazines (1136) and for the determination of the structure of the products of peroxyacetic and peroxysulfuric acid iV-oxidation of phenyl- and chlorophenylpyrazines (733b). 

Direct oxidation of ethylpyrazines to the corresponding acetylpyrazines may also be carried out in favourable circumstances using hot chromic acid (75JOC1178). Treatment of 2-ethyl-3-alkylpyrazines with chromic acid yields the corresponding 2-acetyl-3-alkyl-pyrazines in yields of 50-70%. In the absence of the 3-alkyl substituent the yields fall dramatically to less than 10%. Acetylpyrazines are more generally prepared by the inverse addition of a Grignard reagent to a cyanopyrazine. 

Lipid-Protein-Carbohydrate Interactions. Evidence for such complex interaction was recently reported by Huang et al (36) who observed that the addition of corn lipids to zein and corn carbohydrates enhanced the formation of alkylpyrazines, indicating that lipid-derived free radicals may accelerate the rate of Maillard reactions. Two of the alkylpyrazines, identified in such mixtures after heating for 30 minutes at 180°C, have 5-carbon alkyl substitution at the pyrazine ring and could only be explained by interaction of lipid or lipid decomposition products. These authors suggested that condensation of amino ketones, formed by protein-carbohydrate interaction, may yield 3,6-dihydropyrazine which would in turn react with pentanal, a lipid oxidation product, to form 2,5-dimethyl-3-pentylpyrazine. 

These compounds are formed by addition of lithium alkyls to alkylpyrazines, followed by hydrolysis (see Section V,A). They readily oxidize to pyrazines on exposure to air. Some early examples of 1,4-dihydropyrazines have recently been shown to have 1,2-dihydro structures.384 ... 

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