Pyrazine, 2-isopropyl-3-methoxy

CIC the typical sulphurous flavour is represented by the high concentration of dimethyl sulphide, combined with traces of 1,2-dithia-cyclo-pentene. The vegetable-green note results from 2-isopropyl-3-methoxy pyrazine, resembling raw potatoes, and 2-sec-butyl-3-methoxy pyrazine, a green bell pepper note. 

CIC the earthy odour of fresh potatoes is represented by 2-isopropyl-3-methoxy pyrazine. This earthy note is supported by the mushroom character of l-octen-3-ol. The key component of boiled potatoes is 3-(methylthio)-propanal, balanced with dimethyl sulphide. The high reaction temperatures in baked and fried potatoes start the Maillard reaction to form mainly heterocyclic components 2-ethyl-3,5-dimethyl pyrazine, 2-ethyl-6-vinyl pyrazine, 5-methyl-6,7-dihydro-(5H)cyclopenta-pyrazine, 2-acetyl-l,4,5,6-tetrahydro-pyridine are responsible for the roasted, nutty cracker-like flavour. The heat-induced degradation of the potato lipids and the frying oil imparts a fatty, tallowy character to the french fried potatoes. (E,E)-2,4-Decadienal, 2-octenal, octanoic acid and decanoic acid are main contributors to this fatty note. 

Red currant flavor The flavor of red currants is principally due to ( )-2- hexenal, ( )-2- hexen-l-ol, and hexanal (see alkanals). In black currants the im-pact compound 4-methoxy-2-methyl-2-butanethiol (C6H14OS, Mr 134.24, CAS [94087-83-9]) is responsible for the typical feline note. Terpene compounds such as 1,8- cineole, linalool, a-terpineol (see p-menthenols), citronellol and /S- damascenone, fruit esters (e.g., ethyl butanoate), the butter note of 2,3-butanedione, 4-methoxyacetophenone (CgHmOj, Mr 150.18, CAS [100-06-1]) and 2-isopropyl-3-methoxy-pyrazine (see pyrazines) complete the aroma. In the aroma industry buchu leaf oil is used to generate the black currant note. 

Geosmin, 2-Methyl isobomeol (MIB) and 2-isopropyl methoxy pyrazine are known to be produced by various types of actinomycete cultures (10-15). Geosmin and MIB are saturated tertiary alcohols and resist oxidation. The steric configuration of the hydroxyl and methyl groups in both compounds are believed to interact with receptors in the nose, imparting their characteristic earthy odour (16). The four compounds itemised as the key osmogenes in this odorous emission have extremely low odour threshold concentrations. Their occasional occurence in drinking water can lead to widespread complaints and are routinely monitored for within this Authority. 

Alkyl-2-methoxypyrazines exhibit a base peak at miz 124 in the mass spectrum. The peak corresponds to a molecular ion in 2-methoxy-3-methylpyrazine (24a) and to a fragment ion, resulting from a McLafferty rearrangement of an alkyl group, in 3-isopropyl-2-methoxypyrazine (24b) and 3-5cc-butyl-2-methoxy pyrazine (24d) (97). 

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

Isopropyl-2-methoxy pyrazine (2- Isopropy 1 - 3- methoxy pyrazine) och3 i i-C3H7... 

Isopropyl-5-methoxy pyrazine (5-Isopropyl-2-methoxypyrazine) i-C3H7 OCH3... 

Geosmin, 2-isopropyl, 3-methyox pyrazine, 2-isobutyl-3-methoxy-pyrazine, 2-methyl isobomeol, 2,3, 6 trichloroanisole ... 

Pseudomonas species 3-Isopropyl-2-methoxy pyrazine Green pea... 

Alkyl methoxy pyrazines are an important class of aroma compounds exhibiting intense green bean/green pea aroma notes. Reineccius s group at the University of Minnesota show that mutant strains of Pseudomonas perolens produce the isopropyl isomer to a final level of 15 mg/L of culture. Since the threshold is 2xl0 ° ppm, the reported yield is substantial. 

Musty/mouldy aroma defects in black pepper are caused by a mixture of 2,3-diethyl-5-methyl-pyrazine and 3-isopropyl-2-methoxy-pyrazine. Some samples of white pepper contain up to 2.5 mg/kg of skatole (odor threshold on starch 0.23 pg/kg), which together with 3- and 4-methylphenol can cause a fecal aroma defect. This aroma defect arises during fermentation (degradation of amino acids, e. g., tryptophan 3-methylindole), which is carried out to remove the flesh. On longer storage, this defect becomes more noticeable because intensive aroma substances, which disguise it in fresh white pepper, volatilize. 

Musty or potato-like flavor and aroma have been observed as a defect in milk (Hammer and Babel 1957) and Gruyere de Comte cheese (Dumont et al. 1975). This off-flavor results from the production of nitrogenous cyclic compounds by Pseudomonas taetrolens and P. perolens (Morgan 1976). Musty-flavored compounds produced by these organisms include 2,5-dimethylpyrazine and 2-methoxy-3-isopropyl-pyrazine. The Gruyere de Comte with potato off-flavor contained 3-methoxy-2-propyl pyridine, as well as alkyl pyrazine compounds (Dumont et al. 1975). Murray and Whitfield (1975) postulated that alkyl pyrazines are formed in vegetables by condensation of amino acids such as valine, isoleucine, and leucine with a 2-carbon compound. Details of the synthetic mechanism in pseudomonads are unknown. 

Pyrazine, 3-isobutyl-2-methoxy-occurrence, 3, 192-193 Pyrazine, 3-isopropyl-2-methoxy-occurrence, 3, 193... 

Methoxy-3-isopropyl-5-methyl-pyrazine OCH3 i-C3H7 ch ... 

Methoxy -3-isopropyl-6-methyl-pyrazine OCH3 i-C3H7 ch3... 

Maltol Isobutyrate 2-Methoxy 3-(or 5- or 6-) Isopropyl Pyrazine 5H-5-Methyl-6,7 -dihydrocyclopenta[b]pyrazine 5-Methyl Furfural Methyl Furoate Methyl Hexanoate Methyl Isovalerate 5-Methyl 2-Phenyl 2-Hexenal Methyl Thiobutyrate Methyl Valerate P-Naphthyl Ethyl Ether Phenyl Ethyl Cinnamate Phenyl Ethyl Propionate Propyl Formate Propyl Mercaptan Salicylaldehyde 8-T etradecalactone 2-Tridecanone... 

Isopropyl-3-methoxy-5-methylpyrazine gave 2-isopropyl-3-methoxy-5-[3-(pyran-2-yloxy)propyl]pyrazine (289) [2-(3-bromopropoxy)pyran, PT2NK (made in situ), THF, A, -78°C, 3 h 83%] 298 also analogues likewise.295,298... 

Isopropyl-3,6-dihydro-2,5(l//,4//)-pyrazinedionc (74) gave a separable 1 2 mixture of 6-isopropyl-5-methoxy- (72) and 3-isopropyl-5-methoxy-3,6-dihydro-2(l//)-pyrazinonc (73) [Me3OBF4 (1 mol), CH2C12, 20°C, N2, 6 h 60% (mixture)] or 2-isopropyl-3,6-dimethoxy-2,5-dihydro pyrazine (75) [Me3OBF4 (excess), CH2C12, 20°C, N2, 4 days 85%].1351... 

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. 

Isobutyl-6-isopropyl-2(17/)-pyrazinone 6-Isobutyl-3-isopropyl-2(17/)-pyrazinone 2-Isobutyl-3-methoxy-5,6-dimethylpyrazine 2-Isobutyl-3-methoxy-5-(2-methy]prop-1 -enyl)pyrazine... 

Replacement of the chloro substituent by methoxide has been observed in the following pyrazines 2-chloro-3-methoxycarbonyl (at <5°) (867) 2-chloro-6-methoxycarbonyl (870) 2-chloro-3-methoxycarbonyl-5,6-diphenyl (371, 837) 2-carboxy-6-chloro (869, 871) 2-carbamoyl-5( )-chloro (839) 2-carbamoyl-6-chloro (805, 839) 2-chloro-6-(4 -morpholinocarbonyl) (870) 2-chloro-3-cyano (810, 811) 5-chloro-3-cyano-2-methoxy (reflux 14h) (881) 2-chloro-5-methoxy-3,6-dimethyl (844) 2-chloro-5-isopropyl-6-methoxy-3-methyl (50, 844) 2-chloro-5-methoxy-3,6-diphenyl (1.1 equivalents of 20% methanolic sodium methoxide at 135° for 20h) (797) 2-benzyloxy-6-chloro(at reflux) (832, cf. 883) 2-chloro-3-pyridinio(pyrazine)chloride (or tosylate) (to give 2,3-dimethoxypyrazine) (765) ... 

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. 

A 2-amino-5-substituted-pyrazine refluxed with p-toluenethiol, 2-methoxy-ethanol, and 2-amino-6-formyl-4-hydroxypteridine followed by heating with acetic anhydride gave the 2-amino-4-hydroxy-6-[A -(5 -substituted-pyrazin-2 -yl)-acetamidomethyl]pteridine (34) (1244). 2-Amino-5-phenylpyrazine with isobutyral-dehyde in ether at room temperature gave 2-(3-isopropyl-6, 6-dimethyl-5, 6-dihydro-l, 2, 4 -trioxin-5 -yl)aniino-5-phenylpyrazine (35) (1245). 

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