Uroporphyrin III

In connection with this development it is worth mentioning that uroporphyrinogen III (8), the reduced form of uroporphyrin III (9), is the key building block of all naturally occurring porphinoid structures known at present. 

Figure 32-2. Uroporphyrin III. A (acetate) = —CHjCOOH P (propionate) =—CHjCHjCOOH.

Acetate (A) and propionate (P) are reversed in ring D of uroporphyrin III compared with uroporphyrin I. Only type III porphyrins are physiologically important in humans. 

Structures of uroporphyrin I and uroporphyrin III. [Note A = acetate and P = propionate.]... 

Subsequently both a monomethyl and a trimethyl isobacteriochlorin, factors I (78) and III (79), have been isolated from P. shermanii and shown by radiolabelling experiments to act as precursors of cobyrinic acid in cell-free systems. While sirohydrochlorin (77) and factor III (79) are incorporated when administered in their oxidized forms, factor I (78) and uroporphyrin III (80) (the oxidized form of uroporphyrinogen III) are only effectively incorporated when added in the reduced forms (78a) and (70), suggesting that the four compounds are intermediates only at their reduced levels and that a cellular reductase system exists which is capable of reducing (77) and (79) but not (78) and (80). 

Other metalloporphyrins can also be found in Nature, though they do not seem to perform any vital physiological function. For example, the copper(II) complex of uroporphyrin-III (Table 1) occurs in high concentrations in the wing feathers of Turacus indicus, and is the source of most commercial samples of uroporphyrin-III. Chlorophyll degradation products, as the nickel and vanadium complexes, are found in oil shales and as a troublesome contaminant in crude petroleum oils. 

Methods using condensations of two dipyrrolic units suffer from inherent symmetry restrictions, though these are of course less serious than those involved in the use of monopyrrole tetramerization. Thus the routes through dipyrroles are limited to synthesis of porphyrins which are centrosymmetrically substituted (by way of self-condensation of a suitably activated dipyrrole), or to porphyrins which possess subunit symmetry in one or both halves of the molecule. It is very fortunate that this latter restriction is not serious for the synthesis of porphyrins from natural materials because rings c and d of uroporphyrin-III, coproporphyrin-III and protoporphyrin-IX (Table 1), for example, are symmetrically substituted about the C-15 atom. 

Coproporphyrins III (20c) and IV have been synthesized by the a-oxobilane route.A range of other porphyrins have also been synthesized by the b-oxo-bilane route including protoporphyrin-I, pemptoporphyrin, isopemptopor-phyrin, chlorocruoroporphyrin, rhodoporphyrin, and deuteriomethyl protoporphyrin IX (required for nmr studies of haemoproteins), S-411 porphyrin, harderoporphyrin, and hepta-, hexa-, and pentacarboxylic porphyrins related to uroporphyrins III and I. 

Mg-PPIX, or Mg-PPIXME. Furthermore, neither of the photodynamic precursors of PPIX, coproporphyrinogen nor uroporpophyrinogen (extracted as coproporphyrin III and uroporphyrin III) accumulate in diphenyl ether herbicide-treated plant tissues (Table IV). All of our data are consistent with the view that PPIX is the primary photodynamic pigment involved in the mechanism of action of these herbicides. 

Uroporphyrinogen III, a biosynthetic intermediate of heme, is also biosynthesized through PBG via 5-aminolevulinic acid, as in the case of uroporphyrinogen I. However, in the biosynthesis of uroporphyrinogen III, after the tetramerization of PBG, a second enzyme, a cosynthetase, is involved in the reaction, and uroporphyrinogen III is formed by the transformation of an intermediate. Uroporphyrinogen III is then oxidatively transformed into uroporphyrin III. 

The labeling pattern of uroporphyrin III shown in the figure was reported using the uroporphyrin III formed by a multienzyme complex obtained from chicken blood or euglena Euglena gracilis) of algae. That is to say, PBG doubly labeled with (90%) is diluted with PBG (4-fold) without the label, and is administered to the enzyme reaction system. 

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