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organic chemistry
Organic chemistry is a subdiscipline within chemistry involving the science, scientific study of the structure, properties, and reactions of organic compounds and organic matter, organic materials, i.e., matter in its various forms that contain ...
, an active ester is an ester
In chemistry, an ester is a compound derived from an acid (either organic or inorganic) in which the hydrogen atom (H) of at least one acidic hydroxyl group () of that acid is replaced by an organyl group (R). These compounds contain a distin ...
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 ...
that is highly susceptible toward nucleophilic attack. Activation can be imparted by modifications of the acyl or the alkoxy components of a normal ester, say ethyl acetate
Ethyl acetate commonly abbreviated EtOAc, ETAC or EA) is the organic compound with the formula , simplified to . This flammable, colorless liquid has a characteristic sweet smell (similar to pear drops) and is used in glues, nail polish removers, ...
. Typical modifications call for electronegative substituents. Active esters are employed in both synthetic and biological chemistry.
Reactivity
Active esters are mainly used as acylating agents. They undergo the same reactions as their unactivated analogues but do so more rapidly. They are prone tohydrolysis
Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution reaction, substitution, elimination reaction, elimination, and solvation reactions in which water ...
, for example. Of great interest is the enhanced reactivity of active esters toward 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 ...
s to give amide
In organic chemistry, an amide, also known as an organic amide or a carboxamide, is a chemical compound, compound with the general formula , where R, R', and R″ represent any group, typically organyl functional group, groups or hydrogen at ...
s.
Examples
Biochemistry
120px, 3'-Phosphoadenosine-5'-phosphosulfate is an active ester of sulfate. Active esters are prominent in biochemistry. Glutamine synthetase is an enzyme that forms an active ester from the terminal carboxylate of glutamic acid. This activation, imparted by phosphorylation, facilitates the conversion of the carboxylate to an amide called glutamine.
Thioester
In organic chemistry, thioesters are organosulfur compounds with the molecular structure . They are analogous to carboxylate esters () with the sulfur in the thioester replacing oxygen in the carboxylate ester, as implied by the thio- prefix ...
s are prominent active esters, as illustrated by the esters of coenzyme A
Coenzyme A (CoA, SHCoA, CoASH) is a coenzyme, notable for its role in the Fatty acid metabolism#Synthesis, synthesis and Fatty acid metabolism#.CE.B2-Oxidation, oxidation of fatty acids, and the oxidation of pyruvic acid, pyruvate in the citric ac ...
.
Terpene
Terpenes () are a class of natural products consisting of compounds with the formula (C5H8)n for n ≥ 2. Terpenes are major biosynthetic building blocks. Comprising more than 30,000 compounds, these unsaturated hydrocarbons are produced predomi ...
s and terpenoids are generated from active esters. Some biosynthetically significant active esters include isopentenyl pyrophosphate, dimethylallyl pyrophosphate, and geranyl pyrophosphate.
Synthetic chemistry
Hydroxybenzotriazole is used in peptide synthesis by forming an active ester from acyl isoureas. Classically, activated esters are derivatives of nitrophenols andpentafluorophenol
Pentafluorophenol is the organofluorine compound (specifically a fluoroalcohol) with the formula . This is the perfluorinated analogue of phenol. It is a white solid that melts just above room temperature, and smells of phenol. With a pKa, p''K''a ...
. These esters react with nucleophiles much more rapdily than the related aryl and especially alkyl esters.
Active esters of acrylic acid are precursors to polymers with reactive side chains.{{cite journal, title=Activated Ester Containing Polymers: Opportunities and Challenges for the Design of Functional Macromolecules, author1=Anindita Das , author2=Patrick Theato, journal=Chem. Rev., year=2016, volume=116, issue=3 , pages=1434–1495, doi=10.1021/acs.chemrev.5b00291, pmid=26305991
The concept of active esters extends to esters of phosphoric and sulfuric acid
Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid (English in the Commonwealth of Nations, Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen, ...
s. One such case is dimethylsulfate, a strong methylating agent.
References