Pyrazines are heterocyclic compound with two nitrogen atoms in the 1,4 position of the benzene ring. Pyrazine is an isomer of pyrimidine and pyridazine, which has a weak aromatic property, similar to pyridine. For pyrazine compounds, Electrophilic substitution is difficult to occur, but it is easy to react with nucleophiles. When the hydrogen on the carbon atom is replaced by methyl group or halogen, the hydrogen on the halogen or a halogen is active. In nature, few of its pure products exist, but its structure is found in folic acid, which makes up the part of the trexate. In industry, ethanolamine is dehydrogenated under the condition of gas phase catalysis to obtain pyrazines.
Pyrazine derivatives are widely used in various fields, such as dibenzopyrazine is an important dye and phenazine is known for its anti-tumor, antibacterial and diuretic properties. Tetramethylpyrazine, on the other hand, has been reported to trap superoxide anions and reduce the production of nitrogen oxides in human granulocytes. Citrate of hexahydropyrazine (or piperazine) is a commonly used livestock repellent that is particularly effective against roundworms. 2, 5-diketopiperazine is a reagent for the preparation of peptide compounds. Pyrazine spices generally have roasted aroma, nutty aroma, popcorn, coffee and other aroma characteristics.
Pyrazine compounds play an essential role in the pharmaceutical field. After a lot of research and experiments, a large part of these compounds can be used as raw materials or drug intermediates for the synthesis of many drugs. Benzodiazepines, for example, are a class of azacyclic compounds with broad-spectrum antibacterial activity. These compounds also act as inhibitors of DNA topoisomerases, which have anticancer activity and allow DNA to be embedded.
Fig. 1 Chemical structures of pyrazine derivatives in pharmaceutical field (Bioorganic & Medicinal Chemistry, 2011, 19, 693-701.)
Pyrazines are widely used in the field of organic electrochemistry because of their high charge carrier fluidity. Because of their low LUMO energy and high charge carrier fluidity, quinoxaline compounds have a broad development prospect. The larger aromatic heterocyclic ring has an efficient and stable n-orbital and p-orbital electron structure, and π-π unique intermolecular stacking makes it a good bipolar semiconductor in FETs (field effect transistor).The medium size aromatic heterocyclic ring can be applied to metal ion sensing according to its fluorescence property.
Fig. 2 Synthesis of pyrazine compounds (Dyes and Pigments, 2019, 174, 108030)
Because the benzene ring can be connected between orthogonal structures by simple chemical bonds, the structural planeness of benzodiazepines are greatly enhanced, and intermolecular aggregation and charge transfer are also facilitated. Furthermore, the π-conjugated structure developed by benzopyrazine makes it a stronger electron acceptor with a smaller band gap with the corresponding polymer. It has been reported that a new polymer was synthesized by combining benzodithiophene with two benzopyrazines. This novel pyrazine compound has a photoelectric conversion efficiency of 6.24%, making it a pyrazine solar cell with a high conversion rate.
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