Phenazines, active

Conflicting reports on the nitration of phenazine have appeared, but the situation was clarified by Albert and Duewell (47MI21400). The early work suggested that 1,3-dinitroph-enazine could be prepared in 66% yield under standard nitration conditions however, this proved to be a mixture of 1-nitrophenazine and 1,9-dinitrophenazine (24). As with pyrazines and quinoxalines, activating substituents in the benzenoid rings confer reactivity which is in accord with valence bond predictions thus, nitration of 2-methoxy- or 2-hydroxy-phenazine results in substitution at the 1-position. 

Pyrazine and quinoxaline fV-oxides generally undergo similar reactions to their monoazine counterparts. In the case of pyridine fV-oxide the ring is activated both towards electrophilic and nucleophilic substitution reactions however, pyrazine fV-oxides are generally less susceptible to electrophilic attack and little work has been reported in this area. Nucleophilic activation generally appears to be more useful and a variety of nucleophilic substitution reactions have been exploited in the pyrazine, quinoxaline and phenazine series. 

In the case of substituted phenazine fV-oxides some activation of substituents towards nucleophilic substitution is observed. 1-Chlorophenazine is usually very resistant to nucleophilic displacements, but the 2-isomer is more reactive and the halogen may be displaced with a number of nucleophiles. 1-Chlorophenazine 5-oxide (56), however, is comparable in its reactivity with 2-chlorophenazine and the chlorine atom is readily displaced in nucleophilic substitution reactions. 2-Chlorophenazine 5,10-dioxide (57) and 2-chlorophenazine 5-oxide both show enhanced reactivity relative to 2-chlorophenazine itself. On the basis of these observations, similar activation of 5- or 6-haloquinoxaline fV-oxides should be observed but little information is available at the present time. 

As might be expected from a consideration of electronic effects, an amino substituent activates pyrazines, quinoxalines and phenazines to electrophilic attack, usually at positions ortho and para to the amino group thus, bromination of 2-aminopyrazine with bromine in acetic acid yields 2-amino-3,5-dibromopyrazine (Scheme 29). 

Phenazine [92-82-0] M 180.2, m 171°, pKj -4.9 (aq H2SO4), pK 1.21. Crystd from EtOH, CHCI3 or ethyl acetate, after pre-treatment with activated charcoal. It can be sublimed in vacuo, and zone refined. 

It is notable that pyridine is activated relative to benzene and quinoline is activated relative to naphthalene, but that the reactivities of anthracene, acridine, and phenazine decrease in that order. A small activation of pyridine and quinoline is reasonable on the basis of quantum-mechanical predictions of atom localization encrgies, " whereas the unexpected decrease in reactivity from anthracene to phenazine can be best interpreted on the basis of a model for the transition state of methylation suggested by Szwarc and Binks." The coulombic repulsion between the ir-electrons of the aromatic nucleus and the p-electron of the radical should be smaller if the radical approaches the aromatic system along the nodal plane rather than perpendicular to it. This approach to a nitrogen center would be very unfavorable, however, since the lone pair of electrons of the nitrogen lies in the nodal plane and since the methyl radical is... 

Beifuss U, Tietze M (2005) Methanophenazine and Other Natural Biologically Active Phenazines. 244 77-113 Belisle H,see Bussiere G (2004) 241 97-118... 

Laursen, J.B and Nielsen, J., Phenazine natural products biosynthesis, synthetic analogues, and biological activity, Chem. Rev., 104, 1663, 2004. 

The book is divided into seven chapters. Chapter 1 describes photo-chromic materials which have critical applications in memory technology. These compounds generally are activated by light. Chapter 2 covers leuco quinones which, in many cases, when oxidized, have their absorption maxima in the near-infrared region. Chapter 3 describes leuco dyes of a common group of compounds—oxazine, thiazine, and phenazines—that have found applications in color photography. Chapters 4-6 describe arylmethine-type compounds that can be triggered to dyes by common chemistry. Chapter 7 describes a special class of leuco dyes, namely, tetra-... 

On the other hand various nonphysiological chemicals were identified as inhibitors of PHA synthases such as, for example, phenazine methosulfonate. None of these chemicals specifically inhibit PHA synthases and they are therefore not suitable for application in strategies to enrich mutants with altered PHA metabolism or altered PHA synthase activity. These inhibitors are only interesting in that they reveal some biochemical features of the enzymes. 

Methanophenazine and Other Natural Biologically Active Phenazines... 

As the key enzymes of the two electron transport systems with the electron carriers 9 and rac-10 almost exhibit the same specific activity, we may assume that the phenazine system is wholly responsible for the redox process and that the sole function of the terpenoid side chain in 10 is to anchor the electron carrier in the membrane. 

The more recently discovered and most unusual structures include the dimeric phenazine derivatives esmeraldin A (52) and esmeraldin B (53), which are produced by Streptomyces antibioticus Tii 2706 together with 49 [54]. Esmeraldins exhibit no antibacterial activity but 53 is effective against tumor cells. Much effort has been directed to the elucidation of the biosynthesis of the esmeraldins [55]. Some rare L-quinovose esters (55a-d) of saphenic acid have... 

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