Quinoxaline dihydroxy

E. Reactions of Quinoxalin-2-ones and Quinoxaline-2,3-diones (2-Hydroxy- and 2,3-Dihydroxy-quinoxalines) ... 

Abbreviations N-methyl-D-aspartate (NMDA), alpha-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid (AMPA), L(+)-2 amino-3-phosphonopropionic acid (L-AP3), 6-cyano-7-nitroqninoxaline (CNQ5Q, 2,3-dihydroxy-6-nitro-7-sulfamyl-benzo-f-quinoxaline (NBQX), 3-(2-carboxypiperazin-4-yl)-propyl-l-phosphonic acid (CPP), 7 Chlorokynnreic... 

AA and lAA can be easily detected nsing UV or ED. Compared to AA, DHAA has a weak UV absorption and no response on ED. Therefore, derivatization prior to or after the chromatographic separation is needed to increase sensitivity. Different strategies can be applied (a) DHAA may be rednced to AA, prior to HPLC by L-cysteine [547] or dithiothreitol [548], or using a postanalyti-cal colnmn for a solid-state redaction [549] (b) DHAA may be derivatized with o-phenyldiamine to form the flnorophore 3(l,2-dihydroxy-ethyl)furo[3,4- ]quinoxaline-l-one (DFQ) [550] (c) AA may be oxidized to DHAA by an on-line postcolnmn oxidation with Cn + or Hg + followed by derivatization with o-phenyldiamine [551,552]. 

Zn(II) complexes with glycine, Ai-acetyl, and At-benzoyl glycine were investigated in DMSO, CH3CN, and DME solutions [105]. Voltammetric study of the redox chemistry of 2,3-dihydroxy-quinoxaline and its zinc complexes in nonaqueous medium was also presented [106]. 

The second synthetic route to PAE containing quinoxaline units involved the reaction of an aromatic dihydroxy quinoxaline or aromatic bis(hydroxy-quinoxaline) with activated aromatic difluoro compounds (Eq. (3)) [15]. The dihydroxy quinoxaline and bis(hydroxyquinoxaline) monomers were readily prepared from the condensation of 1,2-diaminobenzene with 4,4 -dihydroxyben-zil and aromatic bis(o-diamines) with 4-hydroxybenzil, respectively. The Tgs of a series of PAE containing quinoxaline units are presented in Tables 3 and 4. For these polymers, the trend for the Tg is sulfone > carbonyl > terephthaloyl-> isophthaloyl. This trend holds for most polymer families when polymers of similar molecular weights are compared. Several polyphenylquinoxalines of the same chemical structure as those in Table 3 were also prepared by the poly-... 

Attention was then turned to aromatic heterocyclic ladder polymers other than BBL. Due to the complexities in their synthesis, ladder polymers were not reported extensively in the literature at that time. A sample of polyfluoflavine (I) having an inherent viscosity in methanesulfonic acid of 2.5 was obtained from professor C. S. Marvel at the University of Arizona. The ladder polymer was prepared [5] from the A-B polycondensation of 2,3-dihydroxy-6,7-diamino-quinoxaline hydrochloride in PPA. Transparent blue sheets were observed on precipitation of this polymer from methanesulfonic acid, and when collected and dried, it formed gold films much like the color of the BBL films. It was felt at that time that all ladder polymers of sufficient molecular weight would form precipitated films. 

A few extensions of the Conrad-Limpach synthesis have been applied to the synthesis of 4,7-phenanthrolines. Unlike o-phenylenediamine, which gives a quinoxaline derivative, p-phenylenediamine reacts with excess of ethyl ethoxalylpropionate to give an intermediate bisanil, which cyclizes in hot diphenyl ether to afford 3,8-dicarboethoxy-l,10-dihydroxy-2,9-dimethyl-4,7-phenanthroline in high yield.237 With diethyl ethoxymethylenemalonate as condensing agent, 6-amino-8-methoxy-quinoline has been converted into 2-carboethoxy-l-hydroxy-6-methoxy-4,7-phenanthroline.238 A related condensation affording 1-... 

Furthermore, some fused tropolones give typical reactions of o-dihydroxy or o-diketo (389) tautomers they form o-dimethoxy compounds (e.g., 418a) or derivatives of dicarbonyl compounds (dioximes and quinoxalines like 513), respectively (65MI3). Another diketone exhibits remarkable stability against enolization to form indolotropolone 324 (Scheme 83), due to steric interaction (78BCJ3579). 

NBQX (=2,3-Dihydroxy-6-nitro- 7-sulfamoyl-benzo(f)quinoxaline)] (quinoxaline)... 

Sheardown, M.J., Nielsen, E.O., Hansen, A.J., Jacobsen P., Honore, T. (1990). 2,3-Dihydroxy-6-nitro-7-sulfamoyl-benzo(F)quinoxaline a neuroprotectant for cerebral ischemia. Science 247 571-4. 

Bredereck and Schmotzer (1044), from diaminomaleonitrile (DAMN hydrogen cyanide tetramer) and oxalyl chloride, prepared 2,3-dicyano-5,6-dihydroxy-pyrazine but Stetten and Fox (1049) could not prepare 23-diamino-5-hydroxy-pyrazine from glycine amide and oxamide. Section 11.3 lists preparations from a, -diamino or a, -diimino compounds and reagents other than a,0-dicarbonyl compounds (384) with additional data (1050) and oxidation of 23-dichloro-quinoxaline with hot aqueous potassium permanganate gave 23-dicarboxy-5,6-dihydroxypyrazine (1051). 

Both the acid and the ester could be reacted with or Ao-phenylenediamine under acidic conditions at 150 °C in 5 and 10 minutes, respectively, to give an 87% yield of 2,3-dihydroxy quinoxaline with the carbon-11 label in the aromatic ring (equation 76). 

C1sHi0N2O, (1)Benzoxepino[2,3-b]quinoxaline, 44B, 342 C16H10N2O, (3)Benzoxepino[1,2-b]quinoxaline, 44B, 342 C1gHi5CIN2O3, 8-Chloro-4a,14a-epoxy-1,2,3,4,5,14-hexahydrophthal-azino[2,3-b]-phthalazine-7,12-dione, 45B, 342 ClsHi5NO3, cis-4,5-Dihydroxy-3,4-diphenyl-5-methyl-2-isoxazoline, 46B, 382... 

A new series of quinoxaline derivatives have been efficiently synthesized with an environment-friendly catalyst, i.e., enzyme, mainly the laccase isolated from Ganoderma sp. rckk-02. This methodology provides an alternative route safest for the synthesis of quinoxalines. 1,2- and 1,4-Dihydroxy benzenes were used for the first time in the synthesis of quinoxalines (Kidwai et al. 2012) (Scheme 2.43). 

For the mechanistic aspects of this new transformation, the first oxidation of the dihydroxy benzene to the corresponding ketone was assumed to occur followed by an electron-deficient site reaction with diamine. Although intermediate is a 1,2-diketone but in this case, it does not react in a same manner as for quinoxaline synthesis via the classical method (Xu et al. 2007 Kunamneni et al. 2008 Witayakran and Ragauskas 2009 Ma et al. 2009 He et al. 2010 Guncheva and Zhiryakova 2011). In this case its electron-deficient site is more prone to be attacked by amine (Scheme 2.44). 

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