Pyrrole is a
heterocyclic aromatic
In chemistry, aromaticity is a chemical property of cyclic ( ring-shaped), ''typically'' planar (flat) molecular structures with pi bonds in resonance (those containing delocalized electrons) that gives increased stability compared to satur ...
organic compound
In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen or carbon-carbon bonds. Due to carbon's ability to catenate (form chains with other carbon atoms), millions of organic compounds are known. Th ...
, a five-membered ring with the
formula
In science, a formula is a concise way of expressing information symbolically, as in a mathematical formula or a ''chemical formula''. The informal use of the term ''formula'' in science refers to the general construct of a relationship betwe ...
C4 H4 NH. It is a colorless volatile liquid that darkens readily upon exposure to air. Substituted derivatives are also called pyrroles, e.g., ''N''-methylpyrrole, C
4H
4NCH
3.
Porphobilinogen, a trisubstituted pyrrole, is the biosynthetic precursor to many natural products such as
heme.
Pyrroles are components of more complex macrocycles, including the
porphyrinogens and products derived therefrom, including
porphyrins of
heme, the
chlorins, bacteriochlorins, and
chlorophyll
Chlorophyll (also chlorophyl) 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 allow plants to ...
s.
Properties
Pyrrole is a colorless
volatile liquid that darkens readily upon exposure to air, and is usually purified by
distillation
Distillation, or classical distillation, is the process of separating the components or substances from a liquid mixture by using selective boiling and condensation, usually inside an apparatus known as a still. Dry distillation is the he ...
immediately before use. Pyrrole has a nutty odor. Pyrrole is a 5-membered
aromatic
In chemistry, aromaticity is a chemical property of cyclic ( ring-shaped), ''typically'' planar (flat) molecular structures with pi bonds in resonance (those containing delocalized electrons) that gives increased stability compared to satur ...
heterocycle, like
furan
Furan is a heterocyclic organic compound, consisting of a five-membered aromatic ring with four carbon atoms and one oxygen atom. Chemical compounds containing such rings are also referred to as furans.
Furan is a colorless, flammable, highl ...
and
thiophene
Thiophene is a heterocyclic compound with the formula C4H4S. Consisting of a planar five-membered ring, it is aromatic as indicated by its extensive substitution reactions. It is a colorless liquid with a benzene-like odor. In most of its reacti ...
. Unlike furan and thiophene, it has a dipole in which the positive end lies on the side of the heteroatom, with a dipole moment of 1.58
D. In CDCl
3, it has chemical shifts at 6.68 (H2, H5) and 6.22 (H3, H4). Pyrrole is an extremely weak base for an amine, with a conjugate acid p''K''
a of −3.8. The most thermodynamically stable pyrrolium cation (C
4H
6N
+) is formed by protonation at the 2 position. Substitution of pyrrole with alkyl substituents provides a more basic molecule—for example, tetramethylpyrrole has a conjugate acid p''K''
a of +3.7. Pyrrole is also weakly acidic at the N–H position, with a p''K''
a of 16.5.
As a hydrogen bonding Lewis acid it is classified as a
hard acid and the
ECW model lists its acid parameters as ''E''
A = 1.38 and ''C''
A = 0.68.
History
Pyrrole was first detected by
F. F. Runge in 1834, as a constituent of
coal tar
Coal tar is a thick dark liquid which is a by-product of the production of coke and coal gas from coal. It is a type of creosote. It has both medical and industrial uses. Medicinally it is a topical medication applied to skin to treat pso ...
. In 1857, it was isolated from the pyrolysate of bone. Its name comes from the Greek ''pyrrhos'' (, “reddish, fiery”), from the reaction used to detect it—the red color that it imparts to wood when moistened with
hydrochloric acid
Hydrochloric acid, also known as muriatic acid, is an aqueous solution of hydrogen chloride. It is a colorless solution with a distinctive pungent smell. It is classified as a strong acid. It is a component of the gastric acid in the dige ...
.
Occurrence in nature
Pyrrole itself is not naturally occurring, but many of its derivatives are found in a variety of
cofactors
Cofactor may also refer to:
* Cofactor (biochemistry), a substance that needs to be present in addition to an enzyme for a certain reaction to be catalysed
* A domain parameter in elliptic curve cryptography, defined as the ratio between the order ...
and
natural products. Common naturally produced molecules containing pyrroles include
vitamin B12, bile pigments like
bilirubin
Bilirubin (BR) ( Latin for "red bile") is a red-orange compound that occurs in the normal catabolic pathway that breaks down heme in vertebrates. This catabolism is a necessary process in the body's clearance of waste products that arise from t ...
and
biliverdin
Biliverdin ( latin for green bile) is a green tetrapyrrolic bile pigment, and is a product of heme catabolism.Boron W, Boulpaep E. Medical Physiology: a cellular and molecular approach, 2005. 984-986. Elsevier Saunders, United States. It is the ...
, and the
porphyrins of
heme,
chlorophyll
Chlorophyll (also chlorophyl) 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 allow plants to ...
,
chlorins,
bacteriochlorin
In organic chemistry, chlorins are tetrapyrrole pigments that are partially hydrogenated porphyrins. The parent chlorin is an unstable compound which undergoes air oxidation to porphine.
The name chlorin derives from chlorophyll. Chlorophylls a ...
s, and porphyrinogens.
Other pyrrole-containing secondary
metabolite
In biochemistry, a metabolite is an intermediate or end product of metabolism.
The term is usually used for small molecules. Metabolites have various functions, including fuel, structure, signaling, stimulatory and inhibitory effects on enzymes, ...
s include PQQ, makaluvamine M, ryanodine, rhazinilam, lamellarin, prodigiosin, myrmicarin, and sceptrin. The syntheses of pyrrole-containing haemin, synthesized by
Hans Fischer was recognized by the Nobel Prize.
Pyrrole is a constituent of tobacco smoke and may contribute to its toxic effects.
Synthesis
Pyrrole is prepared industrially by treatment of
furan
Furan is a heterocyclic organic compound, consisting of a five-membered aromatic ring with four carbon atoms and one oxygen atom. Chemical compounds containing such rings are also referred to as furans.
Furan is a colorless, flammable, highl ...
with
ammonia
Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous ...
in the presence of solid acid
catalyst
Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...
s, like
SiO2 and
Al2O3.
Pyrrole can also be formed by catalytic dehydrogenation of pyrrolidine.
Laboratory routes
Several syntheses of the pyrrole ring have been described.
Hantzsch pyrrole synthesis
The Hantzsch pyrrole synthesis is the reaction of β-ketoesters (1) with ammonia (or primary amines) and α-haloketones (2) to give substituted pyrroles (3).
Knorr pyrrole synthesis
The Knorr pyrrole synthesis involves the reaction of an α-amino ketone or an α-amino-β-ketoester with an activated methylene compound. The method involves the reaction of an α-
aminoketone
In organic chemistry, a ketone is a functional group with the structure R–C(=O)–R', where R and R' can be a variety of carbon-containing substituents. Ketones contain a carbonyl group –C(=O)– (which contains a carbon-oxygen double b ...
(1) and a compound containing a
methylene group
In organic chemistry, a methylene group is any part of a molecule that consists of two hydrogen atoms bound to a carbon atom, which is connected to the remainder of the molecule by two single bonds. The group may be represented as , where th ...
α to (bonded to the next carbon to) a
carbonyl group (2).
Paal–Knorr pyrrole synthesis
In the Paal–Knorr pyrrole synthesis, a 1,4-dicarbonyl compound reacts with ammonia or a primary amine to form a substituted pyrrole.
[ ][ ]
Van Leusen reaction
The Van Leusen reaction can be used to form pyrroles, by reaction of
tosylmethyl isocyanide
TosMIC (toluenesulfonylmethyl isocyanide) is an organic compound with the formula CH3C6H4SO2CH2NC. The molecule contains both sulfonyl and isocyanide groups. It is a colourless solid that, unlike many isocyanides, is odorless. It is prepared by de ...
(TosMIC) with an
enone in the presence of base, in a
Michael addition. A 5-''endo'' cyclization then forms the 5-membered ring, which reacts to eliminate the tosyl group. The last step is tautomerization to the pyrrole.
Barton–Zard synthesis
The Barton–Zard synthesis proceeds in a manner similar to the Van Leusen synthesis. An isocyanoacetate reacts with a nitroalkene in a 1,4-addition, followed by 5-''endo''-''dig'' cyclization, elimination of the
nitro group, and
tautomer
Tautomers () are structural isomers (constitutional isomers) of chemical compounds that readily interconvert.
The chemical reaction interconverting the two is called tautomerization. This conversion commonly results from the relocation of a hy ...
ization.
Piloty–Robinson pyrrole synthesis
The starting materials in the Piloty–Robinson pyrrole synthesis, named for
Gertrude and
Robert Robinson and
Oskar Piloty, are two equivalents of an
aldehyde
In organic chemistry, an aldehyde () is an organic compound containing a functional group with the structure . The functional group itself (without the "R" side chain) can be referred to as an aldehyde but can also be classified as a formyl gro ...
and
hydrazine
Hydrazine is an inorganic compound with the chemical formula . It is a simple pnictogen hydride, and is a colourless flammable liquid with an ammonia-like odour. Hydrazine is highly toxic unless handled in solution as, for example, hydrazine ...
. The product is a pyrrole with substituents at the 3 and 4 positions. The aldehyde reacts with the diamine to an intermediate di-
imine (R−C=N−N=C−R). In the second step, a
,3 sigmatropic rearrangement takes place between. Addition of
hydrochloric acid
Hydrochloric acid, also known as muriatic acid, is an aqueous solution of hydrogen chloride. It is a colorless solution with a distinctive pungent smell. It is classified as a strong acid. It is a component of the gastric acid in the dige ...
leads to ring closure and loss of
ammonia
Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous ...
to form the pyrrole. The
mechanism was developed by the Robinsons.
In one modification,
propionaldehyde is treated first with
hydrazine
Hydrazine is an inorganic compound with the chemical formula . It is a simple pnictogen hydride, and is a colourless flammable liquid with an ammonia-like odour. Hydrazine is highly toxic unless handled in solution as, for example, hydrazine ...
and then with
benzoyl chloride at high temperatures and assisted by
microwave irradiation:
Cycloaddition-based routes
Pyrroles bearing multiple substituents are obtained from the reaction of
münchnone
Münchnone (synonyms: 1,3-oxazolium-5-oxide; 1,3-oxazolium-5-olate; anhydro-5-hydroxy-1,3-oxazolium hydroxide; 5-hydroxy-1,3-oxazolium hydroxide, inner salt; oxido-oxazolium) is a mesoionic heterocyclic aromatic chemical compound, with the molecula ...
s and
alkyne
\ce
\ce
Acetylene
\ce
\ce
\ce
Propyne
\ce
\ce
\ce
\ce
1-Butyne
In organic chemistry, an alkyne is an unsaturated hydrocarbon containing at least one carbon—carbon triple bond. The simplest acyclic alkynes with only one triple bond and n ...
s. The reaction mechanism involves
1,3-dipolar cycloaddition followed by loss of
carbon dioxide
Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is t ...
by a retro-
Diels–Alder process. Similar reactions can be performed using azalactones.
Pyrroles can be prepared by
silver
Silver is a chemical element with the symbol Ag (from the Latin ', derived from the Proto-Indo-European ''h₂erǵ'': "shiny" or "white") and atomic number 47. A soft, white, lustrous transition metal, it exhibits the highest electrical ...
-catalyzed cyclization of alkynes with
isonitriles
An isocyanide (also called isonitrile or carbylamine) is an organic compound with the functional group –. It is the isomer of the related nitrile (–C≡N), hence the prefix is ''isocyano''.IUPAC Goldboo''isocyanides''/ref> The organic fra ...
, where R
2 is an electron-withdrawing group, and R
1 is an alkane, aryl group, or ester. Examples of disubstituted alkynes have also been seen to form the desired pyrrole in considerable yield. The reaction is proposed to proceed via a silver
acetylide intermediate. This method is analogous to the
azide–alkyne click chemistry
In chemical synthesis, click chemistry is a class of biocompatible small molecule reactions commonly used in bioconjugation, allowing the joining of substrates of choice with specific biomolecules. Click chemistry is not a single specific reactio ...
used to form azoles.
Other methods
One synthetic route to pyrrole involves the
decarboxylation
Decarboxylation is a chemical reaction that removes a carboxyl group and releases carbon dioxide (CO2). Usually, decarboxylation refers to a reaction of carboxylic acids, removing a carbon atom from a carbon chain. The reverse process, which is ...
of
ammonium mucate, the ammonium salt of
mucic acid
Mucic acid, C6H10O8 or HOOC-(CHOH)4-COOH (also known as galactaric or meso-galactaric acid) is an aldaric acid obtained by nitric acid oxidation of galactose or galactose-containing compounds such as lactose, dulcite, quercite, and most varieti ...
. The salt is typically heated in a
distillation
Distillation, or classical distillation, is the process of separating the components or substances from a liquid mixture by using selective boiling and condensation, usually inside an apparatus known as a still. Dry distillation is the he ...
setup with
glycerol
Glycerol (), also called glycerine in British English and glycerin in American English, is a simple triol compound. It is a colorless, odorless, viscous liquid that is sweet-tasting and non-toxic. The glycerol backbone is found in lipids known ...
as a
solvent
A solvent (s) (from the Latin '' solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a solution. A solvent is usually a liquid but can also be a solid, a gas, or a supercritical fluid. Water is a solvent for ...
.
Biosynthesis of pyrroles
The de novo biosynthesis of pyrrole rings begins with
aminolevulinic acid
δ-Aminolevulinic acid (also dALA, δ-ALA, 5ALA or 5-aminolevulinic acid), an endogenous non-proteinogenic amino acid, is the first compound in the porphyrin synthesis pathway, the pathway that leads to heme in mammals, as well as chlorophyll in p ...
(ALA), which is synthesized from
glycine and
succinyl-CoA. ALA dehydratase catalyzes the condensation of two ALA molecules via a
Knorr-type ring synthesis to form
porphobilinogen (PBG). This later reacts to form, for example, the macrocycles
heme and
chlorophyll
Chlorophyll (also chlorophyl) 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 allow plants to ...
.
.
Proline
Proline (symbol Pro or P) is an organic acid classed as a proteinogenic amino acid (used in the biosynthesis of proteins), although it does not contain the amino group but is rather a secondary amine. The secondary amine nitrogen is in the p ...
is
biosynthetically derived from the amino acid
L-
glutamate
Glutamic acid (symbol Glu or E; the ionic form is known as glutamate) is an α-amino acid that is used by almost all living beings in the biosynthesis of proteins. It is a non-essential nutrient for humans, meaning that the human body can synt ...
.
Glutamate-5-semialdehyde is first formed by
glutamate 5-kinase (ATP-dependent) and
glutamate-5-semialdehyde dehydrogenase (which requires NADH or NADPH). This can then either spontaneously cyclize to form
1-pyrroline-5-carboxylic acid
1-Pyrroline-5-carboxylic acid (systematic name 3,4-dihydro-2H-pyrrole-2-carboxylic acid) is a cyclic imino acid. Its conjugate base and anion is 1-pyrroline-5-carboxylate (P5C). In solution, P5C is in spontaneous equilibrium with glutamate-5-se ...
, which is reduced to proline by
pyrroline-5-carboxylate reductase (using NADH or NADPH), or turned into
ornithine by
ornithine aminotransferase, followed by cyclisation by
ornithine cyclodeaminase to form proline.
Proline can be used as precursor of aromatic pyrroles in secondary natural products, as in prodigiosins.
The biosynthesis of Prodigiosin
involves the convergent coupling of three pyrrole type rings (labeled A, B, and C in figure 1) from
L-proline,
L-serine,
L-methionine, pyruvate, and 2-octenal.
Ring A is synthesized from
L-proline through the nonribosomal peptide synthase (NRPS) pathway (figure 2), wherein the pyrrolidine ring of proline is oxidized twice through FAD
+ to yield pyrrole ring A.
Ring A is then expanded via the polyketide synthase pathway to incorporate
L-serine into ring B (figure 3). Ring A fragment is transferred from the peptidyl carrier protein (PCP) to the Acyl Carrier Protein (ACP) by a KS domain, followed by transfer to malonyl-ACP via decarboxylative Claisen condensation. This fragment is then able to react with the masked carbanion formed from the PLP mediated decarboxylation of
L-serine, which cyclizes in a dehydration reaction to yield the second pyrrole ring. This intermediate is then modified by methylation (which incorporates a methyl group from
L-methionine onto the alcohol at the 6 position) and oxidation of the primary alcohol to the aldehyde to yield the core A–B ring structures.
Reactions and reactivity
Due to its
aromatic character, pyrrole is difficult to
hydrogenate
Hydrogenation is a chemical reaction between molecular hydrogen (H2) and another compound or element, usually in the presence of a catalyst such as nickel, palladium or platinum. The process is commonly employed to reduce or saturate organ ...
, does not easily react as a
diene
In organic chemistry a diene ( ) (diolefin ( ) or alkadiene) is a covalent compound that contains two double bonds, usually among carbon atoms. They thus contain two alk''ene'' units, with the standard prefix ''di'' of systematic nomenclature. ...
in
Diels–Alder reactions, and does not undergo usual
olefin
In organic chemistry, an alkene is a hydrocarbon containing a carbon–carbon double bond.
Alkene is often used as synonym of olefin, that is, any hydrocarbon containing one or more double bonds.H. Stephen Stoker (2015): General, Organic, a ...
reactions. Its reactivity is similar to that of
benzene
Benzene is an organic chemical compound with the molecular formula C6H6. The benzene molecule is composed of six carbon atoms joined in a planar ring with one hydrogen atom attached to each. Because it contains only carbon and hydrogen atoms ...
and
aniline
Aniline is an organic compound with the formula C6 H5 NH2. Consisting of a phenyl group attached to an amino group, aniline is the simplest aromatic amine. It is an industrially significant commodity chemical, as well as a versatile starti ...
, in that it is easy to alkylate and acylate. Under acidic conditions, pyrroles
polymerize easily, and thus many
electrophilic
In chemistry, an electrophile is a chemical species that forms bonds with nucleophiles by accepting an electron pair. Because electrophiles accept electrons, they are Lewis acids. Most electrophiles are positively charged, have an atom that carr ...
reagents that are used in benzene chemistry are not applicable to pyrroles. In contrast, substituted pyrroles (including
protected
Protection is any measure taken to guard a thing against damage caused by outside forces. Protection can be provided to physical objects, including organisms, to systems, and to intangible things like civil and political rights. Although th ...
pyrroles) have been used in a broad range of transformations.
Reaction of pyrrole with electrophiles
Pyrroles generally react with electrophiles at the α position (C2 or C5), due to the highest degree of stability of the protonated intermediate.
Pyrroles react easily with
nitrating (e.g.
HNO3/
Ac2O),
sulfonating (
Py·SO3), and
halogen
The halogens () are a group in the periodic table consisting of five or six chemically related elements: fluorine (F), chlorine (Cl), bromine (Br), iodine (I), astatine (At), and tennessine (Ts). In the modern IUPAC nomenclature, this grou ...
ating (e.g.
NCS,
NBS,
Br2,
SO2Cl2, and
KI/
H2O2) agents. Halogenation generally provides polyhalogenated pyrroles, but monohalogenation can be performed. As is typical for electrophilic additions to pyrroles, halogenation generally occurs at the 2-position, but can also occur at the 3-position by silation of the nitrogen. This is a useful method for further functionalization of the generally less reactive 3-position.
Acylation
Acylation generally occurs at the 2-position, through the use of various methods. Acylation with
acid anhydrides and
acid chlorides can occur without a catalyst; alternatively, a
Lewis acid may be used. 2-Acylpyrroles are also obtained from reaction with nitriles, by the
Houben–Hoesch reaction
The Hoesch reaction or Houben–Hoesch reaction is an organic reaction in which a nitrile reacts with an arene compound to form an aryl ketone. The reaction is a type of Friedel-Crafts acylation with hydrogen chloride and a Lewis acid catalyst.
...
. Pyrrole aldehydes can be formed by a
Vilsmeier–Haack reaction
The Vilsmeier–Haack reaction (also called the Vilsmeier reaction) is the chemical reaction of a substituted amide (1) with phosphorus oxychloride and an electron-rich arene (3) to produce an aryl aldehyde or ketone (5). The reaction is named aft ...
. ''N''-Acylation of simple pyrrole does not occur.
Alkylation
Electrophilic alkylation of simple pyrrole is uncommon. Alkylation to form enones at C2 has been seen.
Reaction of deprotonated pyrrole
The NH proton in pyrroles is moderately acidic with a
p''K''a of 16.5. Pyrrole can be deprotonated with strong bases such as
butyllithium and
sodium hydride
Sodium hydride is the chemical compound with the empirical formula Na H. This alkali metal hydride is primarily used as a strong yet combustible base in organic synthesis. NaH is a saline (salt-like) hydride, composed of Na+ and H− ions, in ...
. The resulting alkali pyrrolide is
nucleophilic. Treating this conjugate base with an electrophile such as
iodomethane gives ''N''-methylpyrrole. ''N''-Metalated pyrrole can react with electrophiles at the N or C positions, depending on the coordinating metal. More ionic nitrogen–metal bonds (such as with lithium, sodium, and potassium) and more solvating solvents lead to ''N''-alkylation. Nitrophilic metals, such as MgX, lead to alkylation at C (mainly C2), due to a higher degree of coordination to the nitrogen atom.
In the cases of ''N''-substituted pyrroles, metalation of the carbons is more facile. Alkyl groups can be introduced as electrophiles, or by cross-coupling reactions.
Substitution at C3 can be achieved through the use of ''N''-substituted 3-bromopyrrole, which can be synthesized by bromination of ''N''-silylpyrrole with
NBS.
Reductions
Pyrroles can undergo reductions to
pyrrolidines and to
pyrrolines. For example,
Birch reduction
The Birch reduction is an organic reaction that is used to convert arenes to cyclohexadienes. The reaction is named after the Australian chemist Arthur Birch and involves the organic reduction of aromatic rings in an amine solvent (traditionally ...
of pyrrole esters and amides produced pyrrolines, with the regioselectivity depending on the position of the electron-withdrawing group.
Cyclization reactions
Pyrroles with ''N''-substitution can undergo
cycloaddition
In organic chemistry, a cycloaddition is a chemical reaction in which "two or more unsaturated molecules (or parts of the same molecule) combine with the formation of a cyclic adduct in which there is a net reduction of the bond multiplicity" ...
reactions such as
+2,
+2, and
+1cyclizations. Diels-Alder cyclizations can occur with the pyrrole acting as a diene, especially in the presence of an electron-withdrawing group on the nitrogen. Vinylpyrroles can also act as dienes.
Pyrroles can react with
carbene
In organic chemistry, a carbene is a molecule containing a neutral carbon atom with a valence of two and two unshared valence electrons. The general formula is or where the R represents substituents or hydrogen atoms.
The term "carbene" m ...
s, such as
dichlorocarbene, in a
+1cycloaddition. With
dichlorocarbene, a dichlorocyclopropane intermediate is formed, which breaks down to form
3-chloropyridine (the Ciamician–Dennstedt rearrangement).
Commercial uses
Polypyrrole is of some commercial value. ''N''-Methylpyrrole is a precursor to ''N''-methylpyrrolecarboxylic acid, a building-block in pharmaceutical chemistry.
Pyrroles are also found in several drugs, including
atorvastatin
Atorvastatin is a statin medication used to prevent cardiovascular disease in those at high risk and to treat abnormal lipid levels. For the prevention of cardiovascular disease, statins are a first-line treatment. It is taken by mouth.
Common ...
,
ketorolac
Ketorolac, sold under the brand names Toradol, and Biorolac among others, is a nonsteroidal anti-inflammatory drug (NSAID) used to treat pain. Specifically it is recommended for moderate to severe pain. Recommended duration of treatment is less ...
, and
sunitinib
Sunitinib, sold under the brand name Sutent, is a medication used to treat cancer. It is a small-molecule, multi-targeted receptor tyrosine kinase (RTK) inhibitor that was approved by the FDA for the treatment of renal cell carcinoma (RCC) and i ...
. Pyrroles are used as lightfast red, scarlet, and carmine pigments.
Analogs and derivatives
Structural analogs of pyrrole include:
*
Pyrroline, a partially saturated analog with one double bond
*
Pyrrolidine
Pyrrolidine, also known as tetrahydropyrrole, is an organic compound with the molecular formula (CH2)4NH. It is a cyclic secondary amine, also classified as a saturated heterocycle. It is a colourless liquid that is miscible with water and most ...
, the saturated hydrogenated analog
Derivatives of pyrrole include
indole, a derivative with a fused
benzene
Benzene is an organic chemical compound with the molecular formula C6H6. The benzene molecule is composed of six carbon atoms joined in a planar ring with one hydrogen atom attached to each. Because it contains only carbon and hydrogen atoms ...
ring.
See also
*
Simple aromatic rings
*
Tetrapyrrole
*
Polypyrrole
*
Azonine
Azonine is an unsaturated heterocycle of nine atoms, with a nitrogen replacing a carbon at one position. A variety of derivatives have been synthesised. It is considered to possess a considerable amount of aromatic stability. It and C9H9– are ...
References
Further reading
*
*
External links
Synthesis of pyrroles (overview of recent methods)Substitution reaction mechanisms of nitrogen-containing heteroaromatics
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