3-Hydroxy-2-isobutyl-5- pyrazine

Bromination of 5-s-butyl-3-hydroxy-2-isobutylpyrazine (deoxyaspergillic acid) in aqueous solution or acetic acid gave 2-bromo-3-s-butyl-5-hydroxy-6-isobutylpyrazine (bromodeoxyaspergjllic acid) (87) bromination of 2-s-buty-3-hydroxy-5-isobutyl-pyrazine in acetic acid gave 2-bromo-6-s-butyl-5-hydroxy-3-isobutylpyrazine (93) and 3-hydroxy-2,5-diphenylpyrazine behaved similarly (282). This procedure with bromine in acetic acid was unsatisfactory when applied to simpler hydroxypyrazines (817), and bromination of 3,6(and 5,6)-disubstituted-2-hydroxypyrazines and 2-... 

Treatment of bromoaspergillic acid (3-bromo-2-s-butyl-6-hydroxy-5-isobutyl-pyrazine 1-oxide with zinc dust in acetic acid gave a product thought to be 3-5-butyl-6-isobutylpiperazine-2,5-dione (87). 

Diazotization of 2-aminopyrazine with nitrous acid in dilute or concentrated sulfuric acid gave 2 hydroxypyrazine (to 67% yield) (86, 477, 720, 818). Many such conversions have been described, mostly using nitrosylsulfuric acid in concentrated sulfuric acid solution. Preparations of hydroxypyrazines from the aminopyrazines are summarized as follows 2-hydroxy-3-methylpyrazine (sodium nitrite in concentrated sulfuric acid-acetic acid) (681), 2Jiydroxy-3,5-dimethylpyrazine (aqueous nitrous acid, then at 60°) (524), 3-hydroxy-2,5-dimethylpyrazine (477), 2,5-diethyl-3-hydroxypyrazine (aqueous nitrous acid) (478), 2-hydroxy-6-phenyl-pyrazine (365a), 24iydroxy-3,5-diphenylpyrazine (nitrous acid in N hydrochloric acid) (524), 3-hydroxy-2,5-diphenylpyrazine (282), 2-s-butyl-3-hydroxy-5-isobutyl-pyrazine (93), 5TS-butyl-3 hydroxy-2-isobutylpyrazine (92, 536), 2,5-di-s-butyl-3-hydroxypyrazine (89, 720), 3-hydroxy-2-isobutyl-5-isopropylpyrazine (103, 525), 2,3-dihydroxypyrazine (from 2 amino-3-hydroxypyrazine) (757, 1055) and its... 

Hydroxy-5-(1 -hydroxy-2 -methylpropyl)-2-isobutylpyrazine 1,4-dioxide was deoxygenated by titanium trichloride in dry tetrahydrofuran under nitrogen at room temperature to give 2-hydroxy-6-(r-hydroxy-2 -methylpropyl)-3-isobutyl-pyrazine 1 oxide (DL-neohydroxyaspergillic acid) (760a). 

Demethylation of 5-(2 -hydroxy-2 -methylpropyl)-2-isobutyl-3-methoxypyrazine occurred on refluxing with 10% hydrochloric acid to give 3-hydroxy-5-(2 -hydroxy-2 -methylpropyl)-2-isobutylpyrazine but 2-isobutyl-3-methoxy-5-(2 -methylprop-l -enyl)pyrazine and 3-hydroxy-24sobutyl-5-(2 -methylprop-l -enyl)pyrazine were also produced (113b). 

Methoxypyrazines (31) have been prepared by diazomethane methylation of 2-hydroxy-3-isobutylpyrazine (60, 311, 367), 2-hydroxy-3-isopropylpyrazine (59, 367), 2-hydroxy-3-propyl(ethyl or hexyl)pyrazine (367), 3-hydroxy-2-isobutyl-5(and 6)methylpyrazine and 2-hydroxy-3-isobutyl-5,6-dimethylpyrazine (368), 2,3-dihydroxypyrazine (832), 2-hydroxy-5-methoxy- and 2,5-dihydroxy-3,6-diphenyl-pyrazine (832), 2-hydroxy-6-methoxy(and benzyloxy)pyrazine (832), 2,6-dihydroxy-3,5-diphenylpyrazine (873), 2,3,5-trifluoro-6-hydroxypyrazine (851), 2-chloro-6-hydroxy-3,5-diphenylpyrazine (873), 2-chloro-6-hydroxy-5-methyl-3-phenylpyrazine (873), 2-chloro-6-hydroxy-3-methyl-5-phenylpyrazine (873), 5,6-dichloro-1 -cyclohexyl-34iydroxy-2-oxo-l, 2-dihydropyrazine (853), 2-chloro-5-hydroxy-3-methoxy-6-methoxycarbonylpyrazine (881), 2-(4 -amino-3, 5 -dibromo-phenylsulfonamido)-3Tiydroxy-6-methoxypyrazine (881), 2-amino-3-hydroxy-... 

Boron tribromide in dry chloroform was used to convert 3-isobutyl-6-isopropyl-1-methoxy-2-oxo-l, 2-dihydropyrazine to 2-hydroxy-3-isobutyl-6-isopropylpyrazine 1-oxide, and 6-isobutyl-3-isopropyl-l-methoxy-2-oxo-l, 2-dihydropyrazine behaved similarly (740a). Ohta (843) reports the preparation of 2-hydroxy-3,6-diisobutyl-pyrazine 1-oxide from 3,6-diisobutyl-l-methoxy-2-oxo-l, 2-dihydropyrazine (as intermediate) and hydrogen iodide. 

Chang et al. [73] and Nawar et al. [74] have identified many of the volatiles formed during deep fat frying. They have found numerous acids, alcohols, aldehydes, hydrocarbons, ketones, lactones, esters, aromatics, and a few miscellaneous compounds (e.g., pentylfuran and 1,4-dioxane) as products of deep fat frying. More recently, Wagner and Grosch [75] have studied the key contributors to French fry aroma. The list of key aroma compounds in French fries includes 2-ethyl-3,5-dimethylpyrazine, 3-ethyl-2,5-dimethylpyrazine, 2,3-diethyl-5-methylpyrazine, 3-isobutyl-2-methoxypyrazine, (E,Z), (E,E)-2,4-decadienal, trans-4,5-epoxy-(E)-2-decenal, 4-hydroxy-2,5-dimethyl-3(2H)-furanone, methylpropanal, 2- and 3-methylbutanal, and methanethiol. If one examines this list, it is obvious that the Maillard reaction (pyrazines, branched chain aldeydes, furanones, and methional), and lipid oxidation (nnsaturated aldehydes) are the primary sources of this characteristic aroma. 

---