2,3,5,6-Tetramethylpyrazine

Second only to sulfur-based systems, nitrogen complexes are relatively well represented in the structural literature with 41 complexes reported. Of these, 25 are with I2 as the electron acceptor, 11 are with the interhalogen IC1, three are with Br2, and two are with IBr. As expected, in every case the halogen bond forms between the nitrogen and the softest halogen atom, i.e., iodine, in all of the complexes except those with dibromine. Most N I2 complexes, and all N Br2, N IBr, and N IC1 complexes are simple adducts, mode A. Exceptions for the diiodine complexes include bridging mode (B) observed for diazines, such as pyrazine [86], tetramethylpyrazine [86], phenazine, and quinoxaline [87], and for 9-chloroacridine [89] and the 1 1 complex of diiodine with hexamethylenetetramine [144] and amphoteric bridging mode (BA) observed for 2,2 -bipyridine [85], acridine [89], 9-chloroacridine [89], and 2,3,5,6-tetra-2/-pyridylpyrazine [91]. The occurrence of both B and BA complexes with 9-chloroacridine, and of B and A complexes and an... 

Besides ruthenium porphyrins (vide supra), several other ruthenium complexes were used as catalysts for asymmetric epoxidation and showed unique features 114,115 though enantioselectivity is moderate, some reactions are stereospecific and treats-olefins are better substrates for the epoxidation than are m-olcfins (Scheme 20).115 Epoxidation of conjugated olefins with the Ru (salen) (37) as catalyst was also found to proceed stereospecifically, with high enantioselectivity under photo-irradiation, irrespective of the olefmic substitution pattern (Scheme 21).116-118 Complex (37) itself is coordinatively saturated and catalytically inactive, but photo-irradiation promotes the dissociation of the apical nitrosyl ligand and makes the complex catalytically active. The wide scope of this epoxidation has been attributed to the unique structure of (37). Its salen ligand adopts a deeply folded and distorted conformation that allows the approach of an olefin of any substitution pattern to the intermediary oxo-Ru species.118 2,6-Dichloropyridine IV-oxide (DCPO) and tetramethylpyrazine /V. V -dioxide68 (TMPO) are oxidants of choice for this epoxidation. 

Rhetsinine (2), isolated from the hot water extract of Evodia rutae-carpa (family Rutaceae), was found to inhibit aldose reductase with an IC50 value of 24.1 /rM furthermore, the isolate inhibited sorbitol accumulation by 79.3% at 100 This compound could find potential use in the treatment of diabetic complications. Tetramethylpyrazine (3), one of the active components in Qing Huo Yi Hao, displayed strong antioxidant and endothelial protective effects, which can be comparable as Qing Huo Yi Hao this result indicated that some therapeutic potential of Qing Huo Yi Hao for vascular complications of diabetes may be attributed to the presence of tetramethylpyrazine (3). ... 

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-... 

Epoxidation of propene and oct-l-ene was effected with tran5-Ru(0)j(TMP)/ O ll atm)/water-CH2Cl2. After some 40 turnovers in a day, the deactivated form of the complex, Ru(C0)(TMP).H20 was detected (vide infra). Use of (l-( C)-oct-l-ene suggest that, in part at least, the carbon atom of the Ru(CO)(TMP) formed derives from the first C atom of the octene [591]. For styrene epoxidation by trans-Ru(0)2(TMP)/(LN0)/CgH (LNO=N-oxides of 2,3,5,6-tetramethylpyrazine, acridine, 2-methylquinoline and 3,6-dichloropyridazine) the mono- and bis-A-oxides of tetramethylpyrazine were the most effective co-oxidants [586]. 

Jatropha podagrica Hooker San Hu You Tong (stem bark) Tetramethylpyrazine, steroids, n-hexacosane, beta-amirine, lupeol palmitate, beta-sitosterol, rutin, flavonoids, quercetin, apigenin, vitexin, isovitexin.57-207 208 This herb is toxic. Detoxicant, hypotensive, neuromuscular and cardiovascular actions, antibacterial, relieve swelling, pain, externally treat snakebite, infection. 

Ligusticum chuanziang Hort. Chuan Xiang (rhizome) Tetramethylpyrazine, perlolyrine, leucylphenylalanine anhydride, cnidilide, neocnidilide, ligustilide, acetylsalicylic acid, phthalide, benzoquinone.33-226-419-420 Promote blood flow, remove blood stasis and relieve pain. 

Ojewole, J. A. O. 1980. Studies on the pharmacology of tetramethylpyrazine from the stem of Jatmpha podagrica. Plants Med. 39 238. 

Tetramethylpyrazine combines with 3 moles of DMAD and loses methanol, giving product 252 or the isomer 253.336... 

Phenyl- and 2,3-diphenyl-quinoxalines in methanol with DMAD give 1 1 1 adducts (453),410 whereas 2-methyl- and 2,3-dimethyl-quinoxalines in acetonitrile form as major products cyclobutapyrroles (454),337 earlier described432 as azepines. By-products in the last two cases are, respectively, the r-7a,(-9,e-9a-isomer of 454 and a compound analogous to that formed from 2,3,5,6-tetramethylpyrazine. 

The crystal structure of the related molecule tetramethylpyrazine (48) was solved by Cromer et al. (1951) and refined by Fourier methods. Cromer (1957) has carried the refinement further by least-squares... 

Polarographic studies on pyrazine and methylpyrazines indicate that 1 4-dihydropyrazines are the products of reduction. The reduction of pyrazine itself at the dropping mercury electrode proceeds reversibly. The substitution of methyl groups makes the reduction more difficult with an increased number of methyl groups an increased tendency toward irreversible reduction is noted.102-104 The half-wave reduction potentials for pyrazine, methylpyrazine, 2,6-dimethyl-pyrazine, and tetramethylpyrazine are 2.17, 2.23, 2.28, and 2.50 eV, respectively. Pyrazine is thus more easily reduced than pyridine which has a half-wave potential of 2.76 eV, and less easily reduced than quinoxaline which has a half-wave potential of 1.80 eV.105... 

The mass spectra of pyrazine, methylpyrazine, 2,5- and 2,6-dimethylpyrazine have been reported.106 The base peak in the mass spectrum of tetramethylpyrazine corresponds to the loss of two molecules of methyl cyanide.107 The mass spectra of 2,5-bis(p-fluorophenyl)-3,6-diphenylpyrazine,108 2-hydroxy-3- alkylpyrazines, and their N- and O-methyl derivatives have also been reported.30... 

Pyrazines form diquaternary salts on treatment with triethyloxonium fluoroborate. Using this reagent the 1,4-diethylpyrazinium difluoro-borates of pyrazine, 2,5-dimethyl-, and 2,6-dimethylpyrazines have been obtained in 96, 97, and 46% yield, respectively. The reaction is subject to considerable steric hindrance since the yield of diquaternary salt from tetramethylpyrazine is only 6%. The diquaternary salts are extremely reactive substances and that of the parent compound is shown by ESR measurements to be readily reducible to the radical cation [Eq. (7)].150... 

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