biochemistry Biochemistry, or biological chemistry, is the study of chemical processes within and relating to living organisms. A sub-discipline of both chemistry and biology, biochemistry may be divided into three fields: structural biology, enzymology, a ...

, a porphyrinogen is a member of a class of naturally occurring compounds with a

tetrapyrrole Tetrapyrroles are a class of chemical compounds that contain four pyrrole or pyrrole-like rings. The pyrrole/pyrrole derivatives are linked by ( or units), in either a linear or a cyclic fashion. Pyrroles are a five-atom ring with four carbon ...

core, a

macrocycle Macrocycles are often described as molecules and ions containing a ring of twelve or more atoms. Classical examples include the crown ethers, calixarenes, porphyrins, and cyclodextrins. Macrocycles describe a large, mature area of chemistry. ...

of four

pyrrole Pyrrole is a heterocyclic, aromatic, organic compound, a five-membered ring with the formula . It is a colorless volatile liquid that darkens readily upon exposure to air. Substituted derivatives are also called pyrroles, e.g., ''N''-methylpyrrol ...

rings connected by four

methylene bridge In chemistry, a methylene bridge is part of a molecule with formula . The carbon atom is connected by single bonds to two other distinct atoms in the rest of the molecule. A methylene bridge is often called a methylene group or simply methylene, ...

s.porphyrinogens
-

IUPAC The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering Organizations working for the advancement of the chemical sciences, especially by developing nomenclature and terminology. It is ...

Gold Book The International Union of Pure and Applied Chemistry (IUPAC) publishes many books which contain its complete list of definitions. The definitions are divided initially into seven IUPAC Colour Books: Gold, Green, Blue, Purple, Orange, White, and R ...

They can be viewed as derived from the parent compound hexahydroporphine by the substitution of various

functional group In organic chemistry, a functional group is any substituent or moiety (chemistry), moiety in a molecule that causes the molecule's characteristic chemical reactions. The same functional group will undergo the same or similar chemical reactions r ...

s for

hydrogen Hydrogen is a chemical element; it has chemical symbol, symbol H and atomic number 1. It is the lightest and abundance of the chemical elements, most abundant chemical element in the universe, constituting about 75% of all baryon, normal matter ...

atoms in the outermost (20-carbon) ring. Porphyrinogens are intermediates in the

biosynthesis Biosynthesis, i.e., chemical synthesis occurring in biological contexts, is a term most often referring to multi-step, enzyme-Catalysis, catalyzed processes where chemical substances absorbed as nutrients (or previously converted through biosynthe ...

of porphyrins, cofactors with a porphine core which are found in many enzymes and proteins including

myoglobin Myoglobin (symbol Mb or MB) is an iron- and oxygen-binding protein found in the cardiac and skeletal muscle, skeletal Muscle, muscle tissue of vertebrates in general and in almost all mammals. Myoglobin is distantly related to hemoglobin. Compar ...

hemoglobin Hemoglobin (haemoglobin, Hb or Hgb) is a protein containing iron that facilitates the transportation of oxygen in red blood cells. Almost all vertebrates contain hemoglobin, with the sole exception of the fish family Channichthyidae. Hemoglobin ...

cytochrome Cytochromes are redox-active proteins containing a heme, with a central iron (Fe) atom at its core, as a cofactor. They are involved in the electron transport chain and redox catalysis. They are classified according to the type of heme and its ...

s, and

chlorophyll Chlorophyll is any of several related green pigments found in cyanobacteria and in the chloroplasts of algae and plants. Its name is derived from the Greek words (, "pale green") and (, "leaf"). Chlorophyll allows plants to absorb energy ...

s. Porphyrins differ from porphyrinogens by having the four pyrrole rings linked by methine bridges instead of methylene bridges , and by lacking the hydrogen atom in two of the four

amine In chemistry, amines (, ) are organic compounds that contain carbon-nitrogen bonds. Amines are formed when one or more hydrogen atoms in ammonia are replaced by alkyl or aryl groups. The nitrogen atom in an amine possesses a lone pair of elec ...

groups, turning them into

imine In organic chemistry, an imine ( or ) is a functional group or organic compound containing a carbon–nitrogen double bond (). The nitrogen atom can be attached to a hydrogen or an organic group (R). The carbon atom has two additional single bon ...

s . 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 A coordination complex is a chemical compound consisting of a central atom or ion, which is usually metallic and is called the ''coordination centre'', and a surrounding array of chemical bond, bound molecules or ions, that are in turn known as ' ...

. Subsequent biosynthetic intermediates en route to porphyrins are deeply colored and often phytotoxic.

Natural porphyrinogens

Porphyrogens that occur in living organisms usually have sidechains replacing some or all of the

atoms in two outermost

carbon Carbon () is a chemical element; it has chemical symbol, symbol C and atomic number 6. It is nonmetallic and tetravalence, tetravalent—meaning that its atoms are able to form up to four covalent bonds due to its valence shell exhibiting 4 ...

atoms of each

ring (as opposed to the hydrogen atoms in the methylene bridges). File:Uroporphyrinogen III skeletal.svg,

Uroporphyrinogen III Uroporphyrinogen III is a tetrapyrrole, the first macrocycle, macrocyclic intermediate in the biosynthesis of heme, chlorophyll, vitamin B12, and siroheme. It is a colorless compound, like other porphyrinogens. Structure The molecular structure of ...

, precursor to coproporphyrinogen III. File:Coproporphyrinogen III.svg, coproporphyrinogen III, precursor to protoporphyrinogen IX. File:Protoporphyrinogen IX.svg,

Protoporphyrinogen IX Protoporphyrinogen IX is an organic compound, 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. ...

, precursor to protoporphyrin IX.

Non-natural porphyrinogens

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. Under

acid catalysis In acid catalysis and base catalysis, a chemical reaction is catalyzed by an acid or a base. By Brønsted–Lowry acid–base theory, the acid is the proton (hydrogen ion, H+) donor and the base is the proton acceptor. Typical reactions catalyz ...

and

ketone In organic chemistry, a ketone is an organic compound with the structure , where R and R' can be a variety of carbon-containing substituents. Ketones contain a carbonyl group (a carbon-oxygen double bond C=O). The simplest ketone is acetone ( ...

s or

aldehyde In organic chemistry, an aldehyde () (lat. ''al''cohol ''dehyd''rogenatum, dehydrogenated alcohol) is an organic compound containing a functional group with the structure . The functional group itself (without the "R" side chain) can be referred ...

s condense to give many oligomers, including the cyclic ones . The desired porphyrinogens (''n'' = 4) can then be separated. Meso-substituted porphyrinogens with eight non-hydrogen side chains are also called calix yrroles. These products resist

dehydrogenation In chemistry, dehydrogenation is a chemical reaction that involves the removal of hydrogen, usually from an organic molecule. It is the reverse of hydrogenation. Dehydrogenation is important, both as a useful reaction and a serious problem. At ...

of the outer ring better than the natural porphyrinogens. For example, condensation with

benzaldehyde Benzaldehyde (C6H5CHO) is an organic compound consisting of a benzene ring with a formyl substituent. It is among the simplest aromatic aldehydes and one of the most industrially useful. It is a colorless liquid with a characteristic almond-li ...

yields meso-tetraphenylporphyrinogen, which can be oxidized to meso-tetraphenylporphyrin. Condensation with

acetone Acetone (2-propanone or dimethyl ketone) is an organic compound with the chemical formula, formula . It is the simplest and smallest ketone (). It is a colorless, highly Volatile organic compound, volatile, and flammable liquid with a charact ...

yields ''meso''-octamethyporphyrinogen. Alternatively, pyrrole with sidechains substituted at carbons 3 and 4 (those not adjacent to the nitrogen) can be condensed with

formaldehyde Formaldehyde ( , ) (systematic name methanal) is an organic compound with the chemical formula and structure , more precisely . The compound is a pungent, colourless gas that polymerises spontaneously into paraformaldehyde. It is stored as ...

to give porphyrinogens that more closely resemble the natural ones. For example, with 3,4-diethylpyrrole one obtains octaethylporphyrinogen, parent of octaethylporphyrin. File:Me8porphyrinogen.svg, ''meso''-Octamethylporphyrinogen.

References

{{Tetrapyrroles Tetrapyrroles