Phenazine-1,6-dicarboxylic acid synthesis

The cleavage of fused pyrazines represents an important method of synthesis of substituted pyrazines, particularly pyrazinecarboxylic acids. Pyrazine-2,3-dicarboxylic acid is usually prepared by the permanganate oxidation of either quinoxalines or phenazines. The pyrazine ring resembles the pyridine ring in its stability rather than the other diazines, pyridazine and pyrimidine. Fused systems such as pteridines may easily be converted under either acidic or basic conditions into pyrazine derivatives (Scheme 75). 

Another novel synthesis of phenazines was introduced by Vagg and co-workers <00JHC151>. The key step was the reaction of dicarboxylic acid 230 with various 1,2-diamines to give 231, 232, and 233. Each was a potential polydentate ligand capable of interacting with DNA via their extended phenanthroline or phenazine components. 

Observed limitations include partial decarboxylation during ring closure in the synthesis of phenazine-1,9-dicarboxylic acid as well as poor yield and very low reactivity of ketal-protected ketone diphenylamine in the cyclization step of saphenic acid synthesis. The deprotected ketone was cyclized and reduced in one step, affording the desired saphenic acid in satisfactory yields. 

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See also in sourсe #XX -- [ ]

See also in sourсe #XX -- [ , ]

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