- A green synthesis of quinoxalines and 2,3-dihydropyrazines
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Quinoxaline and dihydropyrazine derivatives were obtained in high yields by simple addition of 1,2-diamines and 1,2-dicarbonyl compounds in water. In some cases, the products spontaneously precipitated from the reaction mixture, making it possible to recover and reuse the mother liquor for further condensations. The very mild reaction conditions, the high yields of the products, and the absence of any catalyst make this methodology an efficient and green route to quinoxalines and dihydropyrazines. Georg Thieme Verlag Stuttgart New York.
- Delpivo, Camilla,Micheletti, Gabriele,Boga, Carla
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p. 1546 - 1552
(2013/06/27)
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- Preparation of pyrazines
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The present invention relates to a new process for the generation of pyrazines consisting in the bioconversion of hydroxyketones with 1,2-diaminopropane. New tetrahydropyrazine derivatives as well as new dihydropyrazine derivatives with high flavour and low threshold properties are disclosed. Such pyrazines compounds exhibiting roasted and earthy aroma profiles may be used in the food and bevererage industry, especially chocolate, confectionery and coffee.
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- Chemoenzymatic synthesis of aroma active 5,6-dihydro- and tetrahydropyrazines from aliphatic acyloins produced by baker's yeast
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Twenty-five acyloins were generated by biotransformation of aliphatic aldehydes and 2-ketocarboxylic acids using whole cells of baker's yeast as catalyst. Six of these acyloins were synthesized and tentatively characterized for the first time. Subsequent chemical reaction with 1,2-propanediamine under mild conditions resulted in the formation of thirteen 5,6-dihydropyrazines and six tetrahydropyrazines. Their odor qualities were evaluated, and their odor thresholds were estimated. Among these pyrazine derivatives, 2-ethyl-3,5-dimethyl-5,6-dihydropyrazine (roasted, nutty, 0.002 ng/L air), 2,3-diethyl-5-methyl-5,6-dihydropyrazine (roasted, 0.004 ng/L air), and 2-ethyl-3,5-dimethyltetrahy-dropyrazine (bread crustlike, 1.9 ng/L air) were the most intensive-smelling aroma active compounds.
- Kurniadi, Toshinari,Bel Rhlid, Rachid,Fay, Laurent-Bernard,Juillerat, Marcel-Alexandre,Berger, Ralf Guenter
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p. 3103 - 3107
(2007/10/03)
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- Dihydropyrazine derivatives as a new type of DNA strand breaking agent
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The DNA strand-breaking activity of some dihydropyrazine derivatives, 2,3-dihydro-5,6-dimethylpyrazine (3), 2,3-dihydro-2,5,6-trimethylpyrazine (4), 2,3-dihydro-2,2,5,6-tetramethylpyrazine (5), trans-2,3-dimethyl- 5,6,7,8,9,10-hexahydroquinoxaline (6), its cis-compound (7) and the mixture of 6 and 7 (8) was tested by agarose gel electrophoresis using plasmid pBR322 ccc-DNA as a substrate. The order of DNA strand-breaking activity in the presence of Cu2+ was (7)>(8)≤(5)>(2)>(6)>(4)≤(1)≤(3). 2,5-Bis(D-arabino- tetrahydroxybutyl)-2,5-dihydropyrazine (1) and 2,5-dihydro-3,6- dimethylpyrazine (2) have already been described in terms of DNA breaking activity in a previous paper. The activity was suggested to be due to the dihydropyrazine skeleton, in addition to active oxygen radicals formed in an aqueous solution. The introduction of a methyl group to the dihydropyrazine skeleton enhanced the activities of dihydropyrazine derivatives. The possible chemical basis for DNA strand breakage by dihydropyrazine derivatives, especially in the presence of Cu2+, was discussed.
- Yamaguchi, Tadatoshi,Kashige, Nobuhiro,Mishiro, Noriko,Miake, Fumio,Watanabe, Kenji
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p. 1261 - 1265
(2007/10/03)
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- Formation of tricyclic heterocycles from the condensation reaction of 1,2-diamines with 1,2-diketones
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Condensation of 1,2-diamines with 1,2-diketones yielded unexpected tricyclic heterocycles. The structures were determined by single-crystal X- ray analysis.
- Yamaguchi, Tadatoshi,Eto, Masashi,Watanabe, Kenji,Kashige, Nobuhiro,Harano, Kazunobu
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p. 1977 - 1979
(2007/10/03)
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