Pyrido phenazines

The X-ray crystal structures of pyrazine V.JV -dioxide (134) <02AX(E)1253>, the P-polymorph of phenazine (135) <02AX(C)181>, cobalt(III) complexes of pyrazine-2,6- and pyridine-2,6-dicarboxylic acids <02JIC458>, and bis-urea-substituted phenazines <02ZN(B)937> were reported. Fluorescent pyrido[l,2-a]quinoxalines 136 prepared as pH indicators were examined by X-ray crystallography <02JCS(P2)181>, as were macrocyclic quinoxaline-bridged porphyrinoids obtained from the condensation of dipyrrolylquinoxalines 137 and 1,8-diaminoanthracene... 

To circumvent the complicated mixtures of enantiomers and diastereomers resulting from complexation of metal centers using tetra-pyrido[3,2-a 2, 3 -c 3",2"-h,3,-j]phenazine (tpphz) (41c) a method of synthesis has been developed in which the bridge is formed after the precursors are bound to chiral monometallic synthons.123... 

The pyrazine ring is stable to permanganate oxidation, and this accounts for a variety of pyrazinecarboxylic acids that have been prepared from quinoxalines, benzo-fused quinoxalines including phenazines, and pyrido-fused pyrazines . In other fused systems, particularly pter-idines, the pyrimidine ring is easily hydrolyzed under either acidic or basic conditions to give numerous 3-aminopyrazinecarboxylic acid derivatives. 

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