Porphine skeleton

There are macrocyclic ligands of biochemical interest that contain a modified porphine skeleton in varying degrees of reduction compared to the porphine nucleus one such species is tetrahydrocorrin. The reaction between (1,2-... 

There are only two major classes of metals of primary importance in the above list—the porphyrin metals and the nonporphyrin metals. The porphyrin metals belonging to (aa) have been studied widely. The nonporphyrin metals have not yet been explored. The nonporphyrin metals could be (ab), (ac), and (ad) because in these categories the porphin skeleton has lost the physical properties of a typical porphyrin due to either interrupted conjugation or increased aromaticity. The more important types of nonporphyrin metals are those of the (b) category. In summary, the following definition is applied ... 

B2y, and >42 vibrations are expected to be polarized (p), depolarized (dp), and inversely polarized (tp ), respectively. These polarization properties, together with their vibrational frequencies, were used by Spiro and his coworkers to make complete assignments of vibrational spectra of the Fe-porphin skeletons of a series of heme proteins. They showed that the resonance Raman spectrum may be used to predict the oxidation and spin states of the Fe atom in heme proteins. For example, the Fe atom in oxyhemoglobin has been shown to be low-spin Fc(IIl). It should be noted that the A2y mode, which is normally Raman inactive, is observed under the resonance condition. Although the modes are rather weak in Fig. I-19, these vibrations are enhanced markedly and exclusively by the excitation near the B band since the A-term resonance is predominant under such condition. The majority of compounds studied thus far exhibit the A-term rather than the l -term resonance. A more complete study of resonance Raman spectra involves the observation of excitation profiles (Raman intensity plotted as a function of the exciting frequency for each mode), and the simulation of observed excitation proliles based on various theories of resonance Raman spectroscopy. ... 

Fig. 1. The tilted porphin skeleton in the diacid of tetraphenylporphine (TPP) (a) and (6) represent diacids of TPP and of TPyP(IIl), respectively. Reproduced with permission from Ref. (12)...

Hydroporphyrins. H. are derived from completely unsaturated porphyrins by reduction of the double bonds in the porphine skeleton. The spectrum of naturally occurring H. ranges from the dihydro derivatives chlorin and phlorin(s) through the tetrahydro derivatives bacteriochlorin and isobacteriochlorins, the hexahydro derivatives porphyrinogens and precor-rins to the more highly reduced corphins and factor F430. 

Here, these alkaloids will be described in this chapter as alkaloids based on a porphine skeleton. Their biosynthesis is completely different from that of prodigiosin described in the chapter on alkaloids derived from proline (Chapter 5). Total synthesis of chlorophyll a was achieved [2,3], and the assignment of all resonances in the nuclear magnetic resonance (NMR) spectrum of chlorophyll b has been accomplished [4]. Also the biosynthesis and chemistry of the chlorophylls have been reviewed [5—8]. 

Hiickel molecular orbitals in porphin were investigated by Longuet-Higgins et al. (68), and the extended Hiickel molecular orbital model was applied to metalloporphyrins in attempts by Pullman et al. (93), Ohno et al. (86), and Zerner et al. (120) to explain various experimental observations. Let us briefly consider a description of cyanoferriporphin. According to the Hiickel theory all but the -orbitals of each carbon and nitrogen atom of porphin are used up to form the relatively inert skeleton of single bonds. To describe the -bonding twenty-four molecular orbitals of porphin can then be formed as linear combinations of... 

Porphyrins - Natural pigments containing a fundamental skeleton of four pyrrole nuclei united through the a-positions by four methine groups to form a macrocyclic structure (porphyrin is designated porphine in Chemical Abstracts indexes). [5]... 

Porphyrin used here signifies the alkyl substituted analogs derived from porphin, which is the parent skeleton. 

Figure i.i. Nomenclature of porphyrin system, Chlorin is the basic skeleton of natural chlorophylls. Notice the 7,8-dihydro group and pentacyclic ring V, Chlorin does not contain ring V, Porphin is the basic skeleton of porphyrins (alkyl porphins), Etioporphins contain methyl and ethyl groups in the Q-positions, etioporphyrin I is M, E, M, E,... 

It has been established by crystallographic data (12) and by H-NMR studies that the inner pyrrole hydrogens are opposite to each other. At room temperature the switch to equivalent positions is fast on the H-NMR time scale, as shown for several porphyrins dissolved in CDCI3/CS2 (22, 23). It is not known whether proton jumps are coupled to out-of-plane vibrations of the porphyrin skeleton. Double protonation to H4P2+ freezes in an out-of-plane conformation of tetraphenyl-porphin as shown in Fig. 1, which is taken from Ref. (12). Another type of distortion has been postulated recently in connection with an intermediate observed in the reaction of PtCll with haematoporphyrin IX (24). It has been argued... 

Name coined by Eschenmoser for a heterocyclic ring system with a structure between that of 001110 and that of porphine. C. structures have been detected as intermediates in vitamin B 2 biosynthesis. The participating enzymes are also able to convert unnatural substrates such as uroporphyrinogen I in vitro to C. compounds The basic skeleton of factor F 430, in-... 

The structural skeleton of I. (tetrahydroporphyrins) is formally derived from porphine by reduction of two peripheral double bonds in neighboring pyrrole rings of the porphyrin skeleton. I. are constitutional isomers of the bacteriochlorins, from which their name is derived. Natural members of this structural type are heme d, siroheme, and sirohydrochlorin. 

Porphyrins. Collective name derived from Greek porphyra=purple, purple snail, for the widely distributed purple (red) natural pigments formally prepared from the parent skeleton of porphine by substitution of the macrocylic tetrapyrrole framework with methyl, vinyl, acetic acid, propanoic acid units, or other substituents. 

Corrinoids are formed from a porphyrin precursor biosynthesized as described above, and from which one ring carbon (C-20 in the porphine nucleus) has been extruded. On the other hand, in the biosynthesis of the porphyrin skeleton in the chloroplast of a plant, glutamic acid is introduced instead of glycine [1]. Therefore, it can be said that these alkaloids are derived from glycine and glutamic acid, and contain four pyrrole rings. 

Figure 1 (a) Typical porphyrins porphine, chlorin, and corrole. (b) Some common porph3Tmoids. Note the tetrapyrrole skeleton... 

The macrocyclic tetrapyrrole skeletons of a range of natural substances can act as ligands that bind metals to form complexes. In foods, the main important types of macrocycKc tetrapyrroles are porphin (see Section 9.2) and corrin (see Section 5.13.1) derivatives. 

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