NationMaster - Encyclopedia: Protecting group

A protecting group or protective group is introduced into a molecule by chemical modification of a functional group in order to obtain chemoselectivity in a subsequent chemical reaction. It plays an important role in multistep organic synthesis. In organic chemistry, functional groups (or moieties) are specific groups of atoms within molecules, that are responsible for the characteristic chemical reactions of those molecules. ... Chemical reactions are defined usually in small contexts (only up to a small number of neighbouring atoms), such generalizations are a matter of utility. ... Organic synthesis is the construction of organic molecules via chemical processes. ...

In many preparations of delicate organic compounds, some specific parts of their molecules cannot survive the required reagents or chemical environments. Then, these parts, or groups, must be protected. For example, lithium aluminium hydride is a highly reactive but useful reagent capable of reducing esters to alcohols. It will always react with carbonyl groups, and this cannot be discouraged by any means. When a reduction of an ester is required in the presence of a carbonyl, the attack of the hydride on the carbonyl has to be prevented. For example, the carbonyl is converted into an acetal, which does not react with hydrides. The acetal is then called a protecting group for the carbonyl. After the step involving the hydride is complete, the acetal is removed (by reacting it with an aqueous acid), giving back the original carbonyl. This step is called deprotection. Lithium aluminium hydride (LiAlH4), commonly abbreviated to LAH, is a powerful reducing agent used in organic chemistry. ... For other uses, see Ester (disambiguation). ... This article does not cite any references or sources. ... Carbonyl group In organic chemistry, a carbonyl group is a functional group composed of a carbon atom double-bonded to an oxygen atom : C=O. The term carbonyl can also refer to carbon monoxide as a ligand in an inorganic or organometallic complex (a metal carbonyl, e. ... An acetal is a functional group or molecule containing the functional group of a carbon bonded to two -OR groups. ...

Protecting groups are more commonly used in small-scale laboratory work and initial development than in industrial production processes because their use adds additional steps and material costs to the process. However, the availability of a cheap chiral building block can overcome these additional costs (e.g. shikimic acid for oseltamivir). Shikimic acid, more commonly known as its anionic form shikimate, is an important biochemical intermediate in plants and microorganisms. ... Oseltamivir (INN) (IPA: ) is an antiviral drug that is used in the treatment and prophylaxis of both Influenzavirus A and Influenzavirus B. Like zanamivir, oseltamivir is a neuraminidase inhibitor. ...

Common protecting groups

Alcohol protecting groups

Protection of alcohols: In general usage, alcohol (from Arabic al-khwl الكحول, or al-ghawl الغول) refers almost always to ethanol, also known as grain alcohol, and often to any beverage that contains ethanol (see alcoholic beverage). ...

Acetyl is the radical of acetic acid. ... The Acetoxy group, abbreviated AcO or OAc, is a chemical functional group of the structure CH3-C(=O)-O-. It differs from the acetyl group CH3-C(=O)- by the presence of one additional oxygen atom. ... In organic chemistry a methylthiomethyl (MTM) ether is a protective group for hydroxyl groups. ... Tetrahydropyran, or oxane, is the organic compound consisting of a saturated six-membered ring containing five carbon atoms and one oxygen atom. ... Silyl ethers are a group of chemical compounds sharing a common functional group in which a silicon atom is covalently bonded to an alkoxy group. ... Chemical structure of a Trimethylsilyl group A trimethylsilyl group (abbreviated TMS) is a functional group in organic chemistry. ... Fluoride is the ionic form of fluorine. ... Tetra-n-butylammonium fluoride or TBAF is a quaternary ammonium salt with the chemical formula (CH3CH2CH2CH2)4N+F-. It is commercially available as the trihydrate and as a solution in tetrahydrofuran. ...

Amine protecting groups

Protection of amines: The general structure of an amine Amines are organic compounds and a type of functional group that contain nitrogen as the key atom. ...

Hydrogenolysis is a chemical reaction in which a compound is decomposed -- a molecule is broken into smaller molecules by the reaction of hydrogen. ... Di-tert-butyl dicarbonate is a reagent widely used in organic synthesis. ... It has been suggested that this article or section be merged into peptide synthesis. ... In organic chemistry, peptide synthesis is the creation of peptides, which are organic compounds in which multiple amino acids bind via peptide bonds which are also known as amide bonds. ... It has been suggested that this article or section be merged into peptide synthesis. ... R-phrases , , Related Compounds Related compounds pyridine pyrrolidine piperazine Except where noted otherwise, data are given for materials in their standard state (at 25 Â°C, 100 kPa) Infobox disclaimer and references Piperidine is an organic compound with the molecular formula C5H11N. It is a heterocyclic amine with a six-membered... Benzyl is the Organic chemistry term for the radical C6H5CH2-. It is obtained by removing a proton from benzene. ... Hydrogenolysis is a chemical reaction in which a compound is decomposed -- a molecule is broken into smaller molecules by the reaction of hydrogen. ... Ammonium cerium(IV) nitrate, also called ceric ammonium nitrate or CAN, is a compound of cerium that is widely used as an oxidising agent. ...

Carbonyl protecting groups

Protection of carbonyl groups: Carbonyl group In organic chemistry, a carbonyl group is a functional group composed of a carbon atom double-bonded to an oxygen atom : C=O. The term carbonyl can also refer to carbon monoxide as a ligand in an inorganic or organometallic complex (a metal carbonyl, e. ...

An acetal is a functional group or molecule containing the functional group of a carbon bonded to two -OR groups. ... An ketal is a functional group or molecule containing the functional group of a carbon bonded to two -OR groups. ... In chemistry, a Lewis acid can accept a pair of electrons and form a coordinate covalent bond, after the American chemist Gilbert Lewis. ... A dithiane is a heterocyclic compound comprised of a cyclohexane core structure with two methylene units replaced by sulfur. ...

Carboxylic acid protecting groups

Protection of carboxylic acids: Structure of a carboxylic acid The 3D structure of the carboxyl group A space-filling model of the carboxyl group Carboxylic acids are organic acids characterized by the presence of a carboxyl group, which has the formula -C(=O)OH, usually written -COOH or -CO2H. [1] Carboxylic acids are Bronsted...

In chemistry a methyl-group is a hydrophobic Alkyl functional group which is derived from methane (CH4). ... Benzyl is the Organic chemistry term for the radical C6H5CH2-. It is obtained by removing a proton from benzene. ... Silane is a chemical compound with chemical formula SiH4. ... Organometallic have classically been compounds having bonds between one or more metal atoms and one or more carbon atoms of an organyl group. ...

Miscellaneous

Orthogonal protection

Orthogonal protection is a strategy allowing the deprotection of multiple protective groups one at the time each with a dedicated set of reaction conditions without affecting the other. It was introduced in the field of peptide synthesis by Robert Bruce Merrifield in 1977 ^[1]. As a proof of concept orthogonal deprotection is demonstrated in a photochemical transesterification by trimethylsilyldiazomethane utilizing the kinetic isotope effect ^[2]: In organic chemistry, peptide synthesis is the creation of peptides, which are organic compounds in which multiple amino acids bind via peptide bonds which are also known as amide bonds. ... Robert Bruce Merrifield (July 15, 1921 â€“ May 14, 2006) was an American biochemist who won the Nobel Prize in Chemistry in 1984. ... A proof of concept is a short and/or incomplete realization of a certain method or idea(s) to demonstrate its feasibility. ... Photochemistry is the study of the interaction of light and chemicals. ... In organic chemistry, transesterification is the process of exchanging the alkoxy group of an ester compound by another alcohol. ... The kinetic isotope effect (KIE) is a variation in the reaction rate of a chemical reaction when an atom in one of the reactants is replaced by one of its isotopes. ...

Due to this effect the quantum yield for deprotection of the right-side ester group is reduced and it stays intact. Significantly by placing the deuterium atoms next to the left-side ester group or by changing the wavelength to 254 nm the other monoarene is obtained. The Quantum Yield of a radiation-induced process is the number of times that a defined event (usually a chemical reaction step) occurs per photon absorbed by the system. ...

Criticism

In a 2007 paper ^[3] Phil Baran notes that even though the textbooks state that the use of protective groups is unavoidable and ideally easy added and removed, in practical terms in organic synthesis their use adds two synthetic steps in a chemical sequence and sometimes dramatically lower chemical yield. Crucially, added complexity impedes the use of synthetic total synthesis in drug discovery. In contrast biomimetic synthesis does not employ protective groups. As an alternative, Baran presented a novel protective-group free synthesis of the compound hapalindole U. The previously published synthesis ^[4] ^[5] ^[6] according to Baran, contained 20 steps with multiple protective group manipulations (two confirmed): Yield in chemistry, also known as chemical yield and reaction yield, is the amount of product obtained in a chemical reaction. ... In medicine, biotechnology and pharmacology, drug discovery is the process by which drugs are discovered and/or designed. ...

The tosylate group with a generic R group attached A tosyl group (abbreviated Ts or Tos) combines the toluene and sulfonyl functional groups. ...

External links

References

^ Merrifield, R. B.; Barany, G.; Cosand, W. L.; Engelhard, M.; Mojsov, S. Pept.: Proc. Am. Pept. Symp. 5th 1977
^ Isotope Effects in Photochemistry: Application to Chromatic Orthogonality Aurélien Blanc and Christian G. Bochet Org. Lett.; 2007; 9(14) pp 2649 - 2651; (Letter) doi:10.1021/ol070820h 10.1021/ol070820h
^ Total synthesis of marine natural products without using protecting groups Phil S. Baran, Thomas J. Maimone1 & Jeremy M. Richter Nature 446, 404-408 (22 March 2007) doi:10.1038/nature05569
^ Synthetic studies of marine alkaloids hapalindoles. Part 3 Total synthesis of (±)-hapalindoles H and U Tetrahedron, Volume 46, Issue 18, 1990, Pages 6351-6360 Hideaki Muratake, Harumi Kumagami and Mitsutaka Natsume doi:10.1016/S0040-4020(01)96007-7
^ Synthetic studies of marine alkaloids hapalindoles. Part I Total synthesis of (±)-hapalindoles J and M Tetrahedron, Volume 46, Issue 18, 1990, Pages 6331-6342 Hideaki Muratake and Mitsutaka Natsume doi:10.1016/S0040-4020(01)96005-3
^ Synthetic studies of marine alkaloids hapalindoles. Part 2. Lithium aluminum hydride reduction of the electron-rich carbon-carbon double bond conjugated with the indole nucleus Tetrahedron, Volume 46, Issue 18, 1990, Pages 6343-6350 Hideaki Muratake and Mitsutaka Natsume doi:10.1016/S0040-4020(01)96006-5

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Contents

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