Porphyrinogen oxidized

Wetmur JG, Lehnert G, Desnick RJ (1991) The (5-aminolevulinate dehydrase polymorphism higher blood lead levels in lead workers and environmentally exposed children with the 1-2 and 2-2 isozymes. Environ Res 56 109-119 Woods JS (1988a) Attenuation of porphyrinogen oxidation by glutathione and reversal by porphyrinogenic trace metals. Biochem Biophys Res Commun 152 1428-1434... 

Woods JS, Calas CA (1989) Iron stimulation of free radical-mediated porphyrinogen oxidation by hepatic and renal mitochondria. Biochem Biophys Res Comm 160 101-108... 

Woods JS, Calas CA, Aicher LD (1990a) Stimulation of porphyrinogen oxidation by mercuric ion. II. Promotion of oxidation from the interaction of mercuric ion. 

Woods JS, Galas CA, Aicher LD, Robinson BH, Mailer C (1990b) Stimulation of porphyrinogen oxidation by mercuric ion. I. Evidence of free radical formation in the presence of thiols and hydrogen peroxide. Mol Pharmacol 38 253-260 Yamamoto H, Ishii K, Meguro T, Taketa K, Ogata M (1992) Impaired in vitro accumulation of mercury in erythrocytes of acatalasemic mice. Acta Med Okayama 46 67-73... 

Cyclization of 5, for entropic reasons via conformer 5, yields a porphyrinogen 6. Porphyrinogens 6 are extremely sensitive to oxidation so that even aereal oxidation gives the desired porphyrin 7 (contaminated sometimes by the cyclized dihydroporphyrin, i.e. chlorin 8). 

The synthesis of porphyrins from bilanones is free of all symmetry restraints.77 The oxo function is necessary to stabilize the bilane system by its electron-withdrawing effect. The synthesis of porphyrins from the parent bilane without the oxo function and with /3-substituents is possible,54 but the method gives rise to preparative problems due to the sensitivity of these compounds to oxidation, to electrophiles and to acids. Nature circumvents these problems in the cellular environment by exclusion of oxygen, when porphyrinogens, the precursors of porphyrins, are produced from bilanes55 in the course of their biosynthesis. 

During the systematic investigation of the tautomerization of octacthyl porphyrinogen 2110 it was observed that hexahydroporphyrins 22 could be oxidized in the presence of air to bac-teriochlorins 23 and isobactcriochlorins 24 (both tetrahydroporphyrins) on complexation with nickel(II) acetate. 

Transformations of isobacteriochlorins are rare. The hydrogenation of isobacteriochlorins, e.g. 1,llb-24 ieacjs t0 dihydroisobacteriochlorins, e.g. 2. which are on the same oxidation level as hexahydroporphyrins or porphyrinogens. The dihydrogenated forms of sirohydrochlorin and 20-methylsirohydrochlorin (which are also called precorrin 2 and precorrin 3, respectively) have been identified as important intermediates in the biosynthesis of vitamin B, 2.5... 

CHj—), which do not form a conjugated ring system. Thus, these compounds are colorless (as are all porphyrinogens). However, the porphyrinogens are readily auto-oxidized to their respective colored porphyrins. These oxidations are catalyzed by light and by the porphyrins that are formed. 

Porphyrinogens are cyclic tetrapyrrole precursors which give rise to three basic groups of molecules, discriminated by their state of oxidation porphyrins, dihydroporphyrins and tetrahydroporphryins the basic structures are depicted in Figure 2.1.1. 

Porphyrinogens (5,10,15,20,22,24-hexahydroporphyrins) are formed as intermediates in some porphyrin syntheses or by catalytic hydrogenation of porphyrins.2 They are easily oxidized to porphyrins unless the methylene bridges are blocked by substituents. 

Alternative approaches for substituted porphyrins have been devised in which pre-functionalized dipyrromethane derivatives 3 are condensed with similar diformyl dipyrromethanes 4 through a "2+2" condensation to form meso-tetraarylporphyrins 5 (Scheme 3). Such condensations are usually catalyzed by acids and the intermediate porphyrinogens are oxidized by air to obtain porphyrins. In a similar "3+1" synthetic approach, tripyrranes 6 are condensed with 2,5-diformylpyrroles to form etioporphyrin 5 (1996CEJ1197). 

An alternative "2+2" approach (Scheme 4) involves the acid-catalyzed condensation of a-free dipyrromethanes 3 (1994T11427,05T6614,05SC929) with aldehydes to form porphyrinogens, which are then oxidized to obtain porphyrins 7. This methodology is considerably more versatile for array formation, and is frequently higher yielding and produces more soluble products as well as allows better control over substitution at the mcso-positions. 

An acid catalyzed double Schiff-base condensation of 5 with o-phenylenediamine, 6, then gives the cyclic non-aromatic sp3 texaphyrin ring 7, a macrocyclic product that can be viewed as being an expanded porphyrinogen [24], The sp3 form can be oxidized with ferrocenium ion to give the corresponding aromatic derivative, namely the metal-free sp2 form 8 (Scheme 2) [25],... 

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