Protecting group

(Redirected from Protecting groups)
Jump to navigation Jump to search

Please Take Over This Page and Apply to be Editor-In-Chief for this topic: There can be one or more than one Editor-In-Chief. You may also apply to be an Associate Editor-In-Chief of one of the subtopics below. Please mail us [1] to indicate your interest in serving either as an Editor-In-Chief of the entire topic or as an Associate Editor-In-Chief for a subtopic. Please be sure to attach your CV and or biographical sketch.

WikiDoc Resources for Protecting group

Articles

Most recent articles on Protecting group

Most cited articles on Protecting group

Review articles on Protecting group

Articles on Protecting group in N Eng J Med, Lancet, BMJ

Media

Powerpoint slides on Protecting group

Images of Protecting group

Photos of Protecting group

Podcasts & MP3s on Protecting group

Videos on Protecting group

Evidence Based Medicine

Cochrane Collaboration on Protecting group

Bandolier on Protecting group

TRIP on Protecting group

Clinical Trials

Ongoing Trials on Protecting group at Clinical Trials.gov

Trial results on Protecting group

Clinical Trials on Protecting group at Google

Guidelines / Policies / Govt

US National Guidelines Clearinghouse on Protecting group

NICE Guidance on Protecting group

NHS PRODIGY Guidance

FDA on Protecting group

CDC on Protecting group

Books

Books on Protecting group

News

Protecting group in the news

Be alerted to news on Protecting group

News trends on Protecting group

Commentary

Blogs on Protecting group

Definitions

Definitions of Protecting group

Patient Resources / Community

Patient resources on Protecting group

Discussion groups on Protecting group

Patient Handouts on Protecting group

Directions to Hospitals Treating Protecting group

Risk calculators and risk factors for Protecting group

Healthcare Provider Resources

Symptoms of Protecting group

Causes & Risk Factors for Protecting group

Diagnostic studies for Protecting group

Treatment of Protecting group

Continuing Medical Education (CME)

CME Programs on Protecting group

International

Protecting group en Espanol

Protecting group en Francais

Business

Protecting group in the Marketplace

Patents on Protecting group

Experimental / Informatics

List of terms related to Protecting group

Overview

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.

Acetal protection of a ketone during reduction of an ester

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 aluminum 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.

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.

Common protecting groups

Alcohol protecting groups

Protection of alcohols:

  • Acetyl (Ac) - Removed by acid or base. (see Acetoxy_group)
  • β-Methoxyethoxymethyl ether (MEM) - Removed by acid.
  • Methoxymethyl ether (MOM) - Removed by acid.
  • p-Methoxybenzyl ether (PMB) [2] - Removed by acid, hydrogenolysis, or oxidation.
  • Methylthiomethyl ether - Removed by acid.
  • Pivaloyl (Piv) - Removed by acid, base or reductant agents. It is stronger than other acyl protecting groups.
  • Tetrahydropyran (THP) - Removed by acid.
  • Silyl ether (most popular ones include trimethylsilyl (TMS), tert-butyldimethylsilyl (TBDMS), and triisopropylsilyl (TIPS) ethers) - Removed by acid or fluoride ion. (such as NaF or TBAF (Tetra-n-butylammonium fluoride))
  • Methyl Ethers (cleavage is by TMSI in DCM or MeCN or Chloroform the other method to cleave methyl ethers is BBr3 in DCM)

Amine protecting groups

Protection of amines:

Carbonyl protecting groups

Protection of carbonyl groups:

  • Acetals and Ketals - Removed by acid. Normally, the cleavage of acyclic acetals is easier than of cyclic acetals.
  • Acylals - Removed by Lewis acids.
  • Dithianes - Removed by metal salts or oxidizing agents.

Carboxylic acid protecting groups

Protection of carboxylic acids:

  • Methyl esters - Removed by acid or base.
  • Benzyl esters - Removed by hydrogenolysis.
  • tert-Butyl esters - Removed by acid, base and some reductants.
  • Silyl esters - Removed by acid, base and organometallic reagents

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]:

Orthogonal protection Application In Photochemistry

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.

External links

References

  1. Merrifield, R. B.; Barany, G.; Cosand, W. L.; Engelhard, M.; Mojsov, S. Pept.: Proc. Am. Pept. Symp. 5th 1977
  2. 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

Template:SIB

de:Schutzgruppe sv:Kemisk skyddsgrupp Template:WH Template:WS Template:Jb1