2,5-Dimethyl-3,6-diphenylpyrazine 1-oxide

Dimethyl-3,6-diphenylpyrazine 1-oxide 1,3-Dimethyl-5,6-diphenyl-2(177)-pyrazinone... 

The reactions of 2,5-dimethyl-3,6-diphenyl-2,5-dihydropyrazine 1,4-dioxide and 3,6-diphenyl-2,5-dihydropyrazine 1,4-dioxide with acetic anhydride and a small amount of sulfuric acid afforded 2,5-dimethyl-3,6-diphenylpyrazine 1-oxide and... 

Recently, some interesting photochemical reactions of 2,5-dimethyl-and 2,5-diphenylpyrazine 1-oxide have been reported. Irradiation of a nitrogen-stirred benzene suspension of 2,5-dimethylpyrazine 1-oxide gives 5% 2-acetyl-4-methylimidazole (220) and 15% 2,4-dimethyl -imidazole (221). When the irradiation is carried out in aqueous solution, 10% 2-hydroxy 3,0-dimethylpyrazine (126) and 20% 1-acet-amido-2-formamido-l-propene (222) is formed. The mechanisms in Scheme 49 are suggested for these transformations. 

Ethoxy-3,6-dimethylpyrazine 4-oxide 5-Ethoxy-l,3-dimethyl-2(177)-pyrazinone 2-Ethoxy-3,6-diphenylpyrazine... 

Methyl 6-amino-5-cyano-3-methyl-2-pyrazinecarboxylate 1-oxide Methyl 3-amino-5-cyclohexyl-2-pyrazinecarboxylate Methyl 3-amino-6-cyclohexyl-2-pyrazinecarboxylate Methyl 3-amino-6-cyclopropyl-2-pyrazinecarboxylate Methyl 3-amino-5,6-dichloro-2-pyrazinecarboxylate Methyl 3-amino-5-dimethylamino-6-methyl-2-pyrazinecarboxylate Methyl 3-amino-5-dimethylamino-6-phenyl-2-pyrazinecarboxylate Methyl 3-amino-5-dimethylamino-2-pyrazinecarboxylate Methyl 3-amino-5,6-dimethyl-2-pyrazinecarboxylate 2-Methylamino-3,5-diphenylpyrazine 2-Methylamino-3,6-diphenylpyrazine... 

Having obtained and described a suitable sample, the next stage is to analyse the material for the presence of cathinone and cathine. In addition to these drugs, other structurally similar compounds found in the C. edulis plant include norephedrine (3). It is well accepted that cathinone is converted into this compound by the process of enzymatic reduction. Furthermore, the oxidation product, 1-phenyl-1,2-propanedione (4), and the cathinone dimer, 3,6-dimethyl-2,5-diphenylpyrazine (5), may also be identified. These, however, are reported to form as artefacts of the isolation and analytical processes [6]. 

Ethoxypyrazine 1-oxide refluxed with 40% alcoholic hydrogen chloride yielded 2-ethoxy-5-hydroxypyrazine (1069). Ultraviolet irradiation of 2,5-dimethyl-pyrazine 1-oxide in water afforded 3-hydroxy-2,5-dimethylpyrazine (10%) and 2,5-diphenylpyrazine 1-oxide in benzene gave 3-hydroxy-2,5-diphenylpyrazine (3%) (742). A small yield of 2-ethyI-5-hydroxy-3,6-dimethylpyrazine has been isolated as by-product from the reaction of 2,5-dimethylpyrazine with ethyllithium in ether (615). 

Hydrolysis of l,4-diacetyl-2,3-diphenyl-l,4-dihydropyrazine with potassium hydroxide in ethylene glycol produced 2,3-diphenylpyrazine (probably formed by air oxidation of the dihydropyrazine) (1562). l,4-Dimethyl-2,6-diphenyl-l,4-dihydropyrazine reacts with methanol to give 2-methoxy-1,4-dimethyl-3,5-diphenyl-1,2,3,4-tetrahydropyrazine (57) (1536). 

These effects are produced mostly by phenylpropanolamines present in the leaves. These include cathinone [4] (5 -a-aminopropiophenone), cathine [5] [(-)-IS, 2S-norpseudoephedrine] and (-) -IR, 2S-norephedrine (8). These substances have pharmacological properties similar to those of amphetamine [6] (81), as they induce the release and inhibit the uptake of dopamine and norepinephrine in CNS (82). In addition to the known phenylpropylamines, the presence of other amines such as meracathine, pseudomeracathine and meracathinone have been identified (83, 84). Cathinone, being a ketoamine base, is extremely unstable and, in particular, it can be transformed into (+)-norpseudoephedrine and (-)-norephedrine by an enzymatic reduction. It can also be oxidized to give 1-phenyl-l,2-propandione, while the cathinone dimers, such as 3,6-dimethyl-2,5-diphenylpyrazine are purely artifacts of the isolation (85). 

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