Phenazine derivatives, formation

Dynamic quenching of the MLCT excited state of [Ru(phen)2(dppz)] " " by H" " transfer in MeCN solution occurs for proton donors with pAa values in the range 4.7-15.7. Comparisons of the quenching have been made in the presence and absence of DNA. " The addition of Cu " " to DNA-bound [Ru(bpy)2L] " " (L is the phenazine derivative (167)) leads to luminescence quenching. This is explained in terms of complexation of Cu " " with the vacant coordination site of L in [Ru(bpy)2L] " ". Formation of the [Ru(bpy)2L] " "/Cu " " complex in the presence of DNA is proposed to place one metal center in the major groove and one in the minor groove. " ... 

The nitro group can take part in the formation of heterocyclic nitrogen-containing rings. For example, one of the well known methods for the preparation of phenazine derivatives consists in heating derivatives of 2-nitro-2 -aminodiphenyl-arnine at high temperature (Kehrmann et al. [11]) ... 

The accumulation of phenazine-1,6-dicarboxylic acid (154) by mutants of Pseudomonas phenazinium148 which normally produce hydroxy-phenazine derivatives supports a role for (154) in phenazine biosynthesis. In further studies143 with Ps. phenazinium the sequence of hydroxylative steps leading to the various phenazines has been deduced143 148 to be that illustrated in Scheme 15 the biosynthesis deduced for iodinin (156) is in agreement with earlier conclusions about its formation in cultures of another organism (Brevibacterium iodinum ).146... 

Shikimic acid, an intermediate in the biosynthesis of phenazine derivatives (e.g., iodinine, pyocyanin) can act as the sole carbon source in the formation of the phenazine skeleton. 

Mention was made above that the nature of the shikimic acid derivatives involved in phenazine ring formation was unknown. In addition, little is known of which atoms of shikimic acid correspond to particular atoms in the phenazine nuclei of the various metabolites a degradation of iodinin after incorporation of [l,6- C2]shikimic acid ° was open to at least two interpretations. 

Several eburnea-ebumea bisindoles have been obtained through coupling of iminium and enamine species which are in equihbrium under the reaction conditions. For instance, treatment of dehydrovincamone (648) with acetic acid gave the dimeric compound 649. The same dimer was formed from the reaction of vincam-one-AT-oxide with acetic anhydride. Extension of the reaction to criocerine (650) and its derivatives resulted in formation of the dimer 651 (395,396). The phenazine derivative 652 was formed in 30% yield from the reaction of (-i-)-ll-aminovinca-mine 653 with iodine in CHCls/NaHCOs (397). 

The rates of formation of some phenazines by cyclization of di- and monoimines of JV-(2-aminophenyl)-l,4-benzoquinone have been determined spectrophotometrically. The reaction of 2-aminoindamines (quinoneimines) is a similar example (see Hotiben-Weyl, Vol. 7/3 b, p 330). The oxidation of benzene-1,2,4-lriamine (16) takes place through a series of intermediates, c.g. initial oxidation of 2-amino-l, 4-quinonediiminc (17) is followed by its condensation with beiizene-1,2,4-triamine (16) which leads to the formation of the indamine derivative 18 which, on further oxidation, undergoes cyclization to the amino-substituted phenazine. Different isomers of phenazinetriamines 19 can thus be formed. 

Consequently, it was considered that iodinin was derived from anthra-nilic acid, or a related intermediate, via phenazine-l,6-dicarboxylic acid. The intermediates for the formation of this alkaloid remain to be clarified. 

Becker et al. discovered the formation of alkyl-shifted phenazines 138 versus the anticipated 9-membered triazaorthocyclophane 139 when treating halotriaryl derivatives 140 with potassium diisopropylamide (Scheme 68) (13JOC3532). The reaction passes through an aryne intermediate, but the exact mechanism is still unclear. 

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