Editing Protecting group (section)

===Amine protecting groups===
[[File:Tert-Butoxycarbonyl protected Glycine Structural Formulae V.1.png|thumb|250px|BOC [[glycine]]. The ''tert''-butyloxycarbonyl group is marked <span style="color:blue;">'''blue'''</span>.]]Amines have a special importance in [[peptide synthesis]], but are a quite potent [[nucleophile]] and also relatively strong [[Base (chem)|bases]].  These characteristics imply that new protecting groups for amines are always under development.<ref>P.J. Kocieński: ''Protecting Groups'', p.&nbsp;186.</ref>

[[Amine group]]s are primarily protected through [[acylation]], typically as a [[carbamate]].  When a carbamate deprotects, it evolves [[carbon dioxide]].  The commonest-used carbamates are the ''tert''-butoxycarbonyl, benzoxycarbonyl, fluorenylmethylenoxycarbonyl, and allyloxycarbonyl compounds.

Other, more exotic amine protectors are the [[phthalimide]]s, which admit reductive cleavage,<ref>John O. Osby, Michael G. Martin, Bruce Ganem: ''An Exceptionally Mild Deprotection of Phthalimides'', in: ''[[Tetrahedron Lett.]]'', '''1984''', ''25'', pp.&nbsp;2093–2096; [[doi:10.1016/S0040-4039(01)81169-2]].</ref> and the trifluoroacetamides, which hydrolyze easily in base.  [[Indole]]s, [[pyrrole]]s und [[imidazole]]s&nbsp;— verily any aza-heterocycle&nbsp;— admit protection as ''N''{{nbh}}sulfonylamides,which are far too stable with aliphatic amines.<ref>P.J. Kocieński: ''Protecting Groups'', pp.&nbsp;220–227.</ref>  ''N''{{nbh}}benzylated amines can be removed through [[catalytic hydrogenation]] or Birch reduction, but have a decided drawback relative to the carbamates or amides: they retain a basic nitrogen.

==== Selection ====
Carbamates:
* [[Carbamate]] group – Removed by acid and mild heating.
* [[Carboxybenzyl|Carbobenzyloxy]] (Cbz) group&nbsp;— Removed by [[hydrogenolysis]]: [[hydrogen]] and [[palladium]] on [[activated carbon]],<ref>P.J. Kocieński: ''Protecting Groups'', p.&nbsp;195.</ref> or lithium or sodium in liquid ammonia.<ref>Robert M. Williams, Peter J. Sinclair, Dongguan Zhai, Daimo Chen: "Practical asymmetric syntheses of α-amino acids through carbon-carbon bond constructions on electrophilic glycine templates", in: ''[[J. Am. Chem. Soc.]]'', '''1988''', ''110'', p.&nbsp;1547–1557; [[doi:10.1021/ja00213a031]].</ref>
* [[Methoxybenzyl|''p''-Methoxybenzyloxycarbonyl]] (Moz or MeOZ) group – Removed by [[hydrogenolysis]], more labile than Cbz
* [[Tert-butyloxycarbonyl protecting group|''tert''-Butyloxycarbonyl]] (Boc) group&nbsp;— Removed by concentrated strong acid (such as HCl<ref>Glenn L. Stahl, Roderich Walter, Clarck W. Smith: "General procedure for the synthesis of mono-N-acylated 1,6-diaminohexanes", in: ''[[J. Org. Chem.]]'', '''1978''', ''43'', pp.&nbsp;2285–2286; [[doi:10.1021/jo00405a045]].</ref> or CF<sub>3</sub>COOH<ref>Naomi Sakai, Yasufumi Ohfune: "Total synthesis of galantin I. Acid-catalyzed cyclization of galantinic acid", in: ''[[J. Am. Chem. Soc.]]'', '''1992''', ''114'', pp.&nbsp;998–1010; [[doi:10.1021/ja00029a031]].</ref>), or by heating to >80&nbsp;°C.  Common in [[solid phase peptide synthesis]].  
* 9-Fluorenylmethyloxycarbonyl ([[Fmoc]]) group&nbsp;— Removed by base, such as 20–50&nbsp;% [[piperidine]] in [[dimethylformamide]] (DMF)<ref>Weng C. Chan, Peter D. White: ''Fmoc Solid Phase Peptide Synthesis'', pp.&nbsp;27–30.</ref> or [[N-Methyl-2-pyrrolidone|''N''-Methyl-2-pyrrolidone]],<ref>Gregg B. Fields: [http://www.renyi.hu/~stipsicz/skin/PepsynthProt/Ch_2.pdf ''Methods for Removing the Fmoc Group.''] (PDF; 663&nbsp;kB) In: Michael W. Pennington, Ben M. Dunn (eds.): ''Peptide Synthesis Protocols''  volume 35, 1995, ISBN 978-0-89603-273-6, pp.&nbsp;17–27.</ref> or 50% [[morpholine]] in DMF for sensitive [[Glycoproteins|glycopeptides]].<ref>B. Liebe, H. Kunz: ''Festphasensynthese eines tumorassoziierten Sialyl-Tn-Antigen-Glycopeptids mit einer Partialsequenz aus dem "Tandem Repeat" des MUC-1-Mucins'' In: ''Angew. Chem.'' volume 109, 1997, pp.&nbsp;629–631 (in German).</ref><ref>ChemPep Inc.: [http://www.chempep.com/ChemPep-Fmoc-Solid-Phase-Peptide-Synthesis.htm ''Fmoc Solid Phase Peptide Synthesis.''] retrieved 16 November 2013.</ref>  Common in [[solid phase peptide synthesis]]
* [[Allyloxycarbonyl group|Allyloxycarbamate]] group&nbsp;— Removed with complexes of metals like palladium(0) or [[nickel]](0).<ref>P.J. Kocieński: ''Protecting Groups'', pp.&nbsp;199–201.</ref>  
Other amides:
* [[Acetyl]] ({{vanchor|Ac}}), [[Benzoyl]] ({{vanchor|Bz}}) groups&nbsp;&mdash; common in [[Oligonucleotide synthesis#Phosphoramidite building blocks|oligonucleotide synthesis]] for protection of N<sup>4</sup> in [[cytosine]] and N<sup>6</sup> in [[adenine]].  Removed by base, often aqueous or gaseous [[ammonia]] or [[methylamine]].  Too stable to readily remove from aliphatic amides.
* [[2,2,2-Trichloroethoxycarbonyl chloride|Troc]] (trichloroethyl chloroformate ) group – Removed by Zn insertion in the presence of acetic acid
* [[Tosyl]] (Ts) group – Removed by concentrated acid (HBr, H<sub>2</sub>SO<sub>4</sub>) & strong reducing agents ([[sodium]] in liquid [[ammonia]] or [[sodium naphthalenide]])
* Other sulfonamide ([[Nosyl]] & [[Nps group|Nps]]) groups&nbsp;— Removed by [[Samarium(II) iodide|samarium iodide]], [[thiophenol]] or other soft thiol nucleophiles, or [[tributyltin hydride]]<ref>{{cite journal |last=Moussa |first=Ziad |author2=D. Romo |year=2006 |title=Mild deprotection of primary N-(p-toluenesufonyl) amides with SmI<Sub>2</sub> following trifluoroacetylation |journal=[[Synlett]] |volume=2006 |issue=19 |pages=3294–3298 |doi=10.1055/s-2006-951530}}</ref>
Benzylamines:
* [[Benzyl]] (Bn) group – Removed by [[hydrogenolysis]]
* [[p-Methoxybenzyl|''p''-Methoxybenzyl]] (PMB) – Removed by [[hydrogenolysis]], more labile than benzyl
* [[3,4-Dimethoxybenzyl]] (DMPM) – Removed by [[hydrogenolysis]], more labile than ''p''-methoxybenzyl
* [[p-methoxyphenyl|''p''-Methoxyphenyl]] (PMP) group – Removed by [[ammonium cerium(IV) nitrate]] (CAN)