In biochemistry, a porphyrinogen is a member of a class of naturally occurring compounds with a tetrapyrrole core, a macrocycle of four pyrrole rings connected by four methylene bridges. [1] They can be viewed as derived from the parent compound hexahydroporphine by the substitution of various functional groups for hydrogen atoms in the outermost (20-carbon) ring.
Porphyrinogens are intermediates in the biosynthesis of porphyrins, cofactors with a porphine core which are found in many enzymes and proteins including myoglobin, hemoglobin, cytochromes, and chlorophylls. [2]
Porphyrins differ from porphyrinogens by having the four pyrrole rings linked by methine bridges =CH− instead of methylene bridges −CH2−, and by lacking the hydrogen atom in two of the four amine −NH− groups, turning them into imines =N−. In the biosynthesis of porphyrins, the parent porphyrinogen is dehydrogenated by protoporphyrinogen oxidase.
Because of their limited delocalization, porphyrinogens are colorless. Loss of all four central hydrogen atoms in the core yields a tetravalent anion that can act as a ligand to metal cations, creating a coordination compound. [3] Subsequent biosynthetic intermediates en route to porphyrins are deeply colored and often phytotoxic.
Porphyrogens that occur in living organisms usually have sidechains replacing some or all of the hydrogen atoms in two outermost carbon atoms of each pyrrole ring (as opposed to the hydrogen atoms in the methylene bridges).
A variety of synthetic porphyrinogens have been produced and studied in laboratories. These often have side groups that do not occur in nature, and possibly at the carbons in the methylene bridges (meso positions) instead of the pyrrole rings. The Meso-substituted porphyrinogens are intermediates in the so-called Lindsey synthesis of meso-substituted porphyrins. Oxidation turns the central hexahydroporphine core into a porphine core, yielding the desired porphyrin. [4]
Under acid catalysis, pyrrole and ketones R−(C=O)−R' or aldehydes R−(C=O)−H condense to give many oligomers, including the cyclic ones [−(CRR')−(C4H2NH)−]n\. The desired porphyrinogens (n = 4) can then be separated. [4] Meso-substituted porphyrinogens with eight non-hydrogen side chains are also called calix[4]pyrroles. These products resist dehydrogenation of the outer ring better than the natural porphyrinogens. [3]
For example, condensation with benzaldehyde C6H5−(C=O)−H yields meso-tetraphenylporphyrinogen, which can be oxidized to meso-tetraphenylporphyrin. [4] Condensation with acetone H3C−(C=O)−CH3 yields meso-octamethyporphyrinogen. [3]
Alternatively, pyrrole with sidechains substituted at carbons 3 and 4 (those not adjacent to the nitrogen) can be condensed with formaldehyde H−(C=O)−H to give porphyrinogens that more closely resemble the natural ones. For example, with 3,4-diethylpyrrole one obtains octaethylporphyrinogen, parent of octaethylporphyrin.[ citation needed ]
Pyrrole is a heterocyclic, aromatic, organic compound, a five-membered ring with the formula C4H4NH. It is a colorless volatile liquid that darkens readily upon exposure to air. Substituted derivatives are also called pyrroles, e.g., N-methylpyrrole, C4H4NCH3. Porphobilinogen, a trisubstituted pyrrole, is the biosynthetic precursor to many natural products such as heme.
Porphyrins are a group of heterocyclic, macrocyclic, organic compounds, composed of four modified pyrrole subunits interconnected at their α carbon atoms via methine bridges. In vertebrates, an essential member of the porphyrin group is heme, which is a component of hemoproteins, whose functions include carrying oxygen in the bloodstream. In plants, an essential porphyrin derivative is chlorophyll, which is involved in light harvesting and electron transfer in photosynthesis.
Diethyl malonate, also known as DEM, is the diethyl ester of malonic acid. It occurs naturally in grapes and strawberries as a colourless liquid with an apple-like odour, and is used in perfumes. It is also used to synthesize other compounds such as barbiturates, artificial flavourings, vitamin B1, and vitamin B6.
Tetrapyrroles are a class of chemical compounds that contain four pyrrole or pyrrole-like rings. The pyrrole/pyrrole derivatives are linked by, in either a linear or a cyclic fashion. Pyrroles are a five-atom ring with four carbon atoms and one nitrogen atom. Tetrapyrroles are common cofactors in biochemistry and their biosynthesis and degradation feature prominently in the chemistry of life.
Porphine or porphin is an organic compound of empirical formula C20H14N4. It is heterocyclic and aromatic. The molecule is a flat macrocycle, consisting of four pyrrole-like rings joined by four methine bridges, which makes it the simplest of the tetrapyrroles.
Porphobilinogen (PBG) is an organic compound that occurs in living organisms as an intermediate in the biosynthesis of porphyrins, which include critical substances like hemoglobin and chlorophyll.
Coproporphyrinogen III is a metabolic intermediate in the biosynthesis of many compounds that are critical for living organisms, such as hemoglobin and chlorophyll. It is a colorless solid.
Uroporphyrinogen III is a tetrapyrrole, the first macrocyclic intermediate in the biosynthesis of heme, chlorophyll, vitamin B12, and siroheme. It is a colorless compound, like other porphyrinogens.
Protoporphyrinogen IX is an organic chemical compound which is produced along the synthesis of porphyrins, a class of critical biochemicals that include hemoglobin and chlorophyll. It is a direct precursor of protoporphyrin IX.
Hydroxymethylbilane, also known as preuroporphyrinogen, is an organic compound that occurs in living organisms during the synthesis of porphyrins, a group of critical substances that include haemoglobin, myoglobin, and chlorophyll. The name is often abbreviated as HMB.
Protoporphyrin IX is an organic compound, classified as a porphyrin, that plays an important role in living organisms as a precursor to other critical compounds like heme (hemoglobin) and chlorophyll. It is a deeply colored solid that is not soluble in water. The name is often abbreviated as PPIX.
In organic chemistry, bilane is a compound with the formula C19H20N4 or [(C4H4N)−CH2−(C4H3N)−]2CH2. It is a tetrapyrrole, a class of compounds with four independent pyrrole rings. Specifically, the molecule can be described as four pyrrole molecules C4H5N connected in an open chain by three methylene bridges −CH2− at carbons adjacent to the nitrogens, replacing the respective hydrogens.
The biosynthesis of cocaine has long attracted the attention of biochemists and organic chemists. This interest is partly motivated by the strong physiological effects of cocaine, but a further incentive was the unusual bicyclic structure of the molecule. The biosynthesis can be viewed as occurring in two phases, one phase leading to the N-methylpyrrolinium ring, which is preserved in the final product. The second phase incorporates a C4 unit with formation of the bicyclic tropane core.
Tetraphenylporphyrin, abbreviated TPP or H2TPP, is a synthetic heterocyclic compound that resembles naturally occurring porphyrins. Porphyrins are dyes and cofactors found in hemoglobin and cytochromes and are related to chlorophyll and vitamin B12. The study of naturally occurring porphyrins is complicated by their low symmetry and the presence of polar substituents. Tetraphenylporphyrin is hydrophobic, symmetrically substituted, and easily synthesized. The compound is a dark purple solid that dissolves in nonpolar organic solvents such as chloroform and benzene.
The Rothemund reaction is a condensation/oxidation process that converts four pyrroles and four aldehydes into a porphyrin. It is based on work by Paul Rothemund, who first reported it in 1936. The method underpins more modern synthesis such as those described by Adler and Longo and by Lindsey. The Rothemund reactions is common in university teaching labs.
Chlorophyllide a and Chlorophyllide b are the biosynthetic precursors of chlorophyll a and chlorophyll b respectively. Their propionic acid groups are converted to phytyl esters by the enzyme chlorophyll synthase in the final step of the pathway. Thus the main interest in these chemical compounds has been in the study of chlorophyll biosynthesis in plants, algae and cyanobacteria. Chlorophyllide a is also an intermediate in the biosynthesis of bacteriochlorophylls.
2,2'-Dipyrromethene, often called just dipyrromethene or dipyrrin, is a chemical compound with formula C
9H
8N
2 whose skeleton can be described as two pyrrole rings C
5N connected by a methyne bridge =CH– through their nitrogen-adjacent (position-2) carbons; the remaining bonds being satisfied by hydrogen atoms. It is an unstable compound that is readily attacked by nucleophilic compounds above −40 °C.
Hexahydroporphine is an organic chemical compound with formula C20H20N4. The molecule consists of four pyrrole rings connected by methylene bridges −CH2− into a larger (non-aromatic) macrocycle ring, which makes it one of the simplest tetrapyrroles, and the simplest "true" one. As indicated by the name, it may be viewed as derived from porphine by the addition of six hydrogen atoms: four on the methine bridges, and two on the nitrogen atoms.
meso-Octamethylporphyrinogen, usually referred to simply as octamethylporphyrinogen, is an organic compound with the formula (Me2C-C4H2NH)4 (Me = CH3. It is one of the simplest porphyrinogens, a family of compounds that occur as intermediates in the biosynthesis of hemes and chlorophylls. In contrast to those rings, porphyrinogens are colorless since they lack extended conjugation. The prefix meso-octamethyl indicates that the eight methyl groups are located on the carbon centers that interconnect the four pyrrole rings. Also unlike porphyrins, the porphyrinogens are highly ruffled.
Phosphorus-centered porphyrins are conjugated polycyclic ring systems consisting of either four pyrroles with inward-facing nitrogens and a phosphorus atom at their core or porphyrins with one of the four pyrroles substituted for a phosphole. Unmodified porphyrins are composed of pyrroles and linked by unsaturated hydrocarbon bridges often acting as multidentate ligands centered around a transition metal like Cu II, Zn II, Co II, Fe III. Being highly conjugated molecules with many accessible energy levels, porphyrins are used in biological systems to perform light-energy conversion and modified synthetically to perform similar functions as a photoswitch or catalytic electron carriers. Phosphorus III and V ions are much smaller than the typical metal centers and bestow distinct photochemical properties unto the porphyrin. Similar compounds with other pnictogen cores or different polycyclic rings coordinated to phosphorus result in other changes to the porphyrin’s chemistry.