In organic chemistry, an active ester is an esterfunctional group 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. Typical modifications call for electronegative substituents. Active esters are employed in both synthetic and biological chemistry.
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 to hydrolysis, for example. Of great interest is the enhanced reactivity of active esters toward amines to give amides.[1][2]
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.[4]
Simplified version of the steroid synthesis pathway with the active ester intermediates isopentenyl pyrophosphate (IPP), dimethylallyl pyrophosphate (DMAPP), geranyl pyrophosphate (GPP) and squalene shown. Some intermediates are omitted.
Synthetic chemistry
Use of hydroxybenzotriazole to form an active ester.
Classically, activated esters are derivatives of nitrophenols and pentafluorophenol. 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.[7]
^El-Faham, Ayman; Albericio, Fernando (2011). "Peptide Coupling Reagents, More than a Letter Soup". Chemical Reviews. 111 (11): 6557–6602. doi:10.1021/cr100048w. PMID21866984.
^El-Faham, Ayman; Albericio, Fernando (2011). "Peptide Coupling Reagents, More than a Letter Soup". Chemical Reviews. 111 (11): 6557–6602. doi:10.1021/cr100048w. PMID21866984.
^Anindita Das; Patrick Theato (2016). "Activated Ester Containing Polymers: Opportunities and Challenges for the Design of Functional Macromolecules". Chem. Rev. 116 (3): 1434–1495. doi:10.1021/acs.chemrev.5b00291. PMID26305991.
