Porphyrinogen, structure

As implied above, the success enjoyed with the texaphyrins has inspired the synthesis of several other [1 + 1] Schiff base systems (e.g., 9.92, 9.93, and 9.95 Schemes 9.1.14 and 9.1.15). One of these, an anthracene-derived expanded porphyrinogen (structure 9.95 Scheme 9.1.15) is considered particularly noteworthy. ... 

Figure 32-1 Porphyrin and porphyrinogen structures numbers I to 8 represent various substituents, the nature and order of which determine the type of porphyrin or porphyrinogen Table 32-1). Numbering system and ring designations are based on the Fischer system. A revised system formulated by the International Union of Pure and Applied Chemistry-international Union of Biochemistry (lUPAC-lUB) joint Commission on Biochemical Nomenclature is appropriate for more complex needs.

The enzymatic methylations correspond with biomimetic investigations on the structural types of pyrrocorphin (11) and porphyrinogen (9) which were performed by Eschenmoser et al. (7, 13, 14). From these experiments it was concluded that the tetrapyrrolic porphyrinogen structure (9) can be transformed by methylation reactions into the thermodynamically less stable, tautomeric, but similarly hexahydropor-phyrinoid corphin type structure (10), in which the methyl groups fix the corphin chromophore. 

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. 

Figure 96 The structure of the porphyrinogen complex Bu8N4Ba2(rje-clurene)2 182 (butyl groups have been removed for clarity).

The acid-catalyzed addition of aliphatic ketones to 2,3,4- or 2,3,5-trisubstituted pyrroles generally produces bispyrrolylalkanes, analogous in structure to the products of the corresponding reactions with aldehydes, whereas 2,5-disubstituted pyrroles react with acetone to form a 2 3 adduct (113). Pyrrole and 3,4-disubstituted pyrroles react with aliphatic ketones to give porphyrinogens (114), which, unlike the macrocycles obtained from the... 

Molecular self-assembly will not be considered here (see [9.2]) in fact, it is a special type of synthetic procedure where several reactions between several reagents occur in one experimental operation to yield the final covalent structure it is subject to control by the intramolecular conformational features of intermediates and by the stereochemistry of the reaction(s) the efficient assembly of a covalent structure may require that the connecting reaction(s) be reversible so as to allow searching for the final structure. Examples are found in the generation of macropolycyclic structures by multiple (amine-aldehyde) condensations (see Section 4.1) or of porphyrinogens, porphyrins and phthalocyanins (see also in [9.13a]. 

Sessler, J.L. et al. (1987) Synthesis and crystal structure of a novel tripyrrane-containing porphyrinogen-like macrocycle, J. Org. Chem. 52, 4394-4397. 

Meso-porphyrinogens formally represent the structural transition between pyrroles and porphyrins. Stimulated by the work of Floriani et al. [251], porphyrinogens were considered as alternative ligand sets in lanthanide chemistry by Jubb and Teuben [68,252]. The tetraamide ligand offers a coordination environment which is obviously sterically and electronically more flexible than that provided by the standard Cp2Ln- fragment. The conformational flexibility... 

Figure 1 shows the general structure of calixpyrroles. The basic ring structure resembles that of porphyrin. In the past, four pyrrole rings linked by methylene groups to form colourless macrocycles (that feature in the biosynthetic pathways to pyrrole pigments) were referred to as porphyrinogens [22], The term calix[4]pyrrole was later ascribed to these macrocycles and their synthetic derivatives because of their relation to calix[4]arenes [23],... 

Compared with metal enolates, there have been very few reports on the direct structural analysis and theoretical studies of ynolates. An X-ray crystal structure of a vanadium complex of lithium ynolate with a porphyrinogen ligand (56) is reported. This metal complex was incidentally formed from VCl3(THF)3 with tetralithium salt of the octaethyl-porphyrinogen ligand. In this complex, the lithium cation seems to interact with the 7T-electrons of the ynolate. The four atoms of the ynolate group in 56 are not collinear due to a partial sp character of the group in this complex. 

Crystal structure and substrate binding modeling of the uro-porphyrinogen-III decarboxylase from Nicotiana tabacum. Impli- 35. 

Zhang et al. [36] combine DFT-based conformation analysis with quantitative structure-activity relationship (QSAR) analysis. They looked at bioactive conformations for 25 cyclic imide derivatives as proto-porphyrinogen oxidase (PPO) inhibitors. PPO is the last common enzyme in the biosynthetic... 

Porphyrins were named from the Greek root for purple (porphyra) and owe their color to the conjugated doublebond structure of the tetrapyrrole ring. The porphyrinogens... 

The porphyrinogen-metal complexes 1-4, which are isostructuraH (see the structure in Figure 3), and complex 5 have some remarkable structural characteristics, particularly helpful for understanding their chemistry. 

The introduction of a cyclopropane moiety in the porphyrinogen skeleton causes a very little conformational change, as can be judged from the structure of 8 (Figure 6),... 

The existence of 15 which possesses structural parameters close to those of 13 (Figure 8), proves the stability of the uncomplexed biscyclopropane porphyrinogen skeleton. 

Of additional interest with regard to the porphyrinogenic action of mercury is the observation from animal studies that prolonged mercury exposure is characterized by the excretion in the urine of an atypical porphyrin, not normally found in urine of unexposed subjects, which elutes on HPLC approximately mid-way between the 5- and 4-carboxyl porphyrins (Woods et al. 1991). This porphyrin has been referred to as precopro-porphyrin in several previous publications (Bowers et al. 1992 Woods et al. 1993) and appears to be unique to mercury exposure. Absorption and electrospray ionizing mass spectroscopic analyses have suggested that this atypical porphyrin shares structural properties of a keto derivative of isocoproporphyrin. However, the precise structural characteristics as well as the biochemical etiology of this porphyrin remain to be established. This porphyrin has been detected in urine both of mercury-exposed animals and human subjects (Woods et al. 1991, 1993). 

The exact stage at which oxidation of the porphyrinogen to porphyrin occurs is not yet known. Protoporphyrin was sjrnthesized by Fischer and co-workers (4) in a classic work. Its structure (Fig. 2) was proven by reduction and esterification to a mesoporphyrin dimethyl ester, which was shown to be identical with the ninth isomer in Fischer s table of the fifteen possible isomers of mesoporphyrin. 

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