Benzyl chloroformate

Last updated
Benzyl chloroformate
Benzyl-chloroformate-2D-skeletal.png
Benzyl-chloroformate-3D-balls.png
Names
Preferred IUPAC name
Benzyl carbonochloridate
Other names
Benzyl chloroformate
Benzyloxycarbonyl chloride
Z-Chloride
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.007.205 OOjs UI icon edit-ltr-progressive.svg
EC Number
  • 207-925-0
PubChem CID
RTECS number
  • LQ5860000
UNII
UN number 1739
  • InChI=1S/C8H7ClO2/c9-8(10)11-6-7-4-2-1-3-5-7/h1-5H,6H2 Yes check.svgY
    Key: HSDAJNMJOMSNEV-UHFFFAOYSA-N Yes check.svgY
  • InChI=1/C8H7ClO2/c9-8(10)11-6-7-4-2-1-3-5-7/h1-5H,6H2
    Key: HSDAJNMJOMSNEV-UHFFFAOYAW
  • ClC(=O)OCc1ccccc1
Properties
C8H7ClO2
Molar mass 170.59 g·mol−1
Appearancecolorless liquid, may appear yellow due to impurities
Odor pungent
Density 1.195 g/cm3
Boiling point 103 °C (217 °F; 376 K) (20 Torr)
degrades
1.519 (589 nm)
Hazards
GHS labelling:
GHS-pictogram-skull.svg GHS-pictogram-pollu.svg
Danger
H314, H410
P260, P264, P273, P280, P301+P330+P331, P303+P361+P353, P304+P340, P305+P351+P338, P310, P321, P363, P391, P405, P501
Flash point 80 °C (176 °F; 353 K)
Safety data sheet (SDS) External MSDS
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Yes check.svgY  verify  (what is  Yes check.svgYX mark.svgN ?)

Benzyl chloroformate, also known as benzyl chlorocarbonate or Z-chloride, is the benzyl ester of chloroformic acid. It can be also described as the chloride of the benzyloxycarbonyl (Cbz or Z) group. In its pure form it is a water-sensitive oily colorless liquid, although impure samples usually appear yellow. It possesses a characteristic pungent odor and degrades in contact with water.

Contents

The compound was first prepared by Leonidas Zervas in the early 1930s who used it for the introduction of the benzyloxycarbonyl protecting group, which became the basis of the Bergmann-Zervas carboxybenzyl method of peptide synthesis he developed with Max Bergmann. [1] [2] This was the first successful method of controlled peptide chemical synthesis and for twenty years it was the dominant procedure used worldwide until the 1950s. [1] To this day, benzyl chloroformate is often used for amine group protection.

Preparation

The compound is prepared in the lab by treating benzyl alcohol with phosgene:

PhCH2OH + COCl2 → PhCH2OC(O)Cl + HCl

Phosgene is used in excess to minimise the production of the carbonate (PhCH2O)2C=O. [3]

The use of phosgene gas in the lab preparation carries a very large health hazard, and has been implicated in the chronic pulmonary disease of pioneers in the usage of the compound such as Zervas. [4]

Amine protection

Benzyl chloroformate is commonly used in organic synthesis for the introduction of the benzyloxycarbonyl (formerly called carboxybenzyl) protecting group for amines. The protecting group is abbreviated Cbz or Z (in honor of discoverer Zervas), hence the alternative shorthand designation for benzyl chloroformate as Cbz-Cl or Z-Cl.

Benzyloxycarbonyl is a key protecting group for amines, suppressing the nucleophilic and basic properties of the N lone pair. This "reactivity masking" property, along with the ability to prevent racemization of Z-protected amines, made the Z group the basis of the Begmann-Zervas synthesis of oligopeptides (1932) where the following general reaction is performed to protect the N-terminus of a serially growing oligopeptide chain: [1] [2]

Cbz to protect N-terminus.svg

This reaction was hailed as a "revolution" and essentially started the distinct field of synthetic peptide chemistry. [1] It remained unsurpassed in utility for peptide synthesis until the early 1950s when mixed anhydride and active ester methodologies were developed.

Although the reaction is no longer commonly used for peptides, it is nonetheless very widespread for amine protection in other applications within organic synthesis and total synthesis. Common procedures to achieve protection starting from benzyl chloroformate include:

Alternatively, the Cbz group can be generated by the reaction of an isocyanate with benzyl alcohol (as in the Curtius rearrangement).

Deprotection

Hydrogenolysis in the presence of a variety of palladium-based catalysts is the usual method for deprotection. [1] [7] Palladium on charcoal is typical. [8]

Cbz deprot.png

Alternatively, HBr and strong Lewis acids have been used, provided that a trap is provided for the released benzyl carbocation. [9]

When the protected amine is treated by either of the above methods (i.e. by catalytic hydrogenation or acidic workup), it yields a terminal carbamic acid which then readily decarboxylates to give the free amine.

2-Mercaptoethanol can also be used, in the presence of potassium phosphate in dimethylacetamide. [10]

Related Research Articles

<span class="mw-page-title-main">Diphosgene</span> Chemical compound

Diphosgene is an organic chemical compound with the formula ClCO2CCl3. This colorless liquid is a valuable reagent in the synthesis of organic compounds. Diphosgene is related to phosgene and has comparable toxicity, but is more conveniently handled because it is a liquid, whereas phosgene is a gas.

<span class="mw-page-title-main">Protecting group</span> Group of atoms introduced into a compound to prevent subsequent reactions

A protecting group or protective group is introduced into a molecule by chemical modification of a functional group to obtain chemoselectivity in a subsequent chemical reaction. It plays an important role in multistep organic synthesis.

<span class="mw-page-title-main">Peptide synthesis</span> Production of peptides

In organic chemistry, peptide synthesis is the production of peptides, compounds where multiple amino acids are linked via amide bonds, also known as peptide bonds. Peptides are chemically synthesized by the condensation reaction of the carboxyl group of one amino acid to the amino group of another. Protecting group strategies are usually necessary to prevent undesirable side reactions with the various amino acid side chains. Chemical peptide synthesis most commonly starts at the carboxyl end of the peptide (C-terminus), and proceeds toward the amino-terminus (N-terminus). Protein biosynthesis in living organisms occurs in the opposite direction.

<span class="mw-page-title-main">Curtius rearrangement</span> Chemical reaction

The Curtius rearrangement, first defined by Theodor Curtius in 1885, is the thermal decomposition of an acyl azide to an isocyanate with loss of nitrogen gas. The isocyanate then undergoes attack by a variety of nucleophiles such as water, alcohols and amines, to yield a primary amine, carbamate or urea derivative respectively. Several reviews have been published.

<span class="mw-page-title-main">Knorr pyrrole synthesis</span> Chemical reaction

The Knorr pyrrole synthesis is a widely used chemical reaction that synthesizes substituted pyrroles (3). The method involves the reaction of an α-amino-ketone (1) and a compound containing an electron-withdrawing group α to a carbonyl group (2).

Di-<i>tert</i>-butyl dicarbonate Chemical compound

Di-tert-butyl dicarbonate is a reagent widely used in organic synthesis. Since this compound can be regarded formally as the acid anhydride derived from a tert-butoxycarbonyl (Boc) group, it is commonly referred to as Boc anhydride. This pyrocarbonate reacts with amines to give N-tert-butoxycarbonyl or so-called Boc derivatives. These carbamate derivatives do not behave as amines, which allows certain subsequent transformations to occur that would be incompatible with the amine functional group. The Boc group can later be removed from the amine using moderately strong acids. Thus, Boc serves as a protective group, for instance in solid phase peptide synthesis. Boc-protected amines are unreactive to most bases and nucleophiles, allowing for the use of the fluorenylmethyloxycarbonyl group (Fmoc) as an orthogonal protecting group.

<i>tert</i>-Butyloxycarbonyl protecting group Protecting group used in organic synthesis

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{{Infobox scientist | name = Max Bergmann | image = | caption = | birth_date = 12 February 1886 | birth_place = Fürth, Germany | nationality = | death_date = 7 November 1944 (aged 58) | death_place = New York City, United States | field = peptide chemistry | work_institution = Kaiser Wilhelm Institute for Leather Research
Rockefeller Institute for Medical Research | alma_mater = Ludwig Maximilian University of Munich, Friedrich Wilhelm University | doctoral_advisor = Ignaz Bloch | doctoral_students = Leonidas Zervas | known_for = Carboxybenzyl protecting group | spouse = Emmy Bergmann [[:de:Emmy Bergmann | children = Peter Bergmann (physicist) }} Max Bergmann was a Jewish-German biochemist. Together with Leonidas Zervas, the discoverer of the group, they were the first to use the carboxybenzyl protecting group for the synthesis of oligopeptides.

<span class="mw-page-title-main">Bergmann azlactone peptide synthesis</span>

The Bergmann azlactone peptide synthesis is a classic organic synthesis process for the preparation of dipeptides.

The Bergmann degradation is a series of chemical reactions designed to remove a single amino acid from the carboxylic acid (C-terminal) end of a peptide. First demonstrated by Max Bergmann in 1934, it is a rarely used method for sequencing peptides. The later developed Edman degradation is an improvement upon the Bergmann degradation, instead cleaving the N-terminal amino acid of peptides to produce a hydantoin containing the desired amino acid.

<span class="mw-page-title-main">Mukaiyama Taxol total synthesis</span>

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<span class="mw-page-title-main">Achmatowicz reaction</span> Organic synthesis

The Achmatowicz reaction, also known as the Achmatowicz rearrangement, is an organic synthesis in which a furan is converted to a dihydropyran. In the original publication by the Polish Chemist Osman Achmatowicz Jr. in 1971 furfuryl alcohol is reacted with bromine in methanol to 2,5-dimethoxy-2,5-dihydrofuran which rearranges to the dihydropyran with dilute sulfuric acid. Additional reaction steps, alcohol protection with methyl orthoformate and boron trifluoride) and then ketone reduction with sodium borohydride produce an intermediate from which many monosaccharides can be synthesised.

Chloroformic acid is a chemical compound with the formula ClCO2H. It is the single acyl-halide derivative of carbonic acid. Chloroformic acid is also structurally related to formic acid, in a way that the non-acidic hydrogen of formic acid is replaced by chlorine. Despite the similar name, it is very different from chloroform. It is described as unstable.

<span class="mw-page-title-main">Chloroformate</span>

Chloroformates are a class of organic compounds with the formula ROC(O)Cl. They are formally esters of chloroformic acid. Most are colorless, volatile liquids that degrade in moist air. A simple example is methyl chloroformate, which is commercially available.

<span class="mw-page-title-main">2,2,2-Trichloroethoxycarbonyl chloride</span> Chemical compound

Trichloroethyl chloroformate is used in organic synthesis for the introduction of the trichloroethyl chloroformate (Troc) protecting group for amines, thiols and alcohols. It readily cleaves vs other carbamates and can be used in an overall protecting group strategy.

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<span class="mw-page-title-main">Fluorenylmethyloxycarbonyl protecting group</span>

The fluorenylmethoxycarbonyl protecting group (Fmoc) is a base-labile protecting group used in organic synthesis.

Leonidas Zervas was a Greek organic chemist who made seminal contributions in peptide chemical synthesis. Together with his mentor Max Bergmann they laid the foundations for the field in 1932 with their major discovery, the Bergmann-Zervas carboxybenzoxy oligopeptide synthesis which remained unsurpassed in utility for the next two decades. The carboxybenzyl protecting group he discovered is often abbreviated Z in his honour.

Iphigenia Photaki was a Greek organic chemist remembered for her contributions in peptide chemical synthesis, especially in the synthesis of biologically/enzymatically active peptides.

References

  1. 1 2 3 4 5 Katsoyannis, P. G., ed. (1973). The Chemistry of Polypeptides. New York: Plenum Press. doi:10.1007/978-1-4613-4571-8. ISBN   978-1-4613-4571-8. S2CID   35144893. Archived from the original on 2022-10-13. Retrieved 2021-04-01.
  2. 1 2 3 Bergmann, Max; Zervas, Leonidas (1932). "Über ein allgemeines Verfahren der Peptid-Synthese" [On a general method of peptide synthesis]. Berichte der deutschen chemischen Gesellschaft . 65 (7): 1192–1201. doi:10.1002/cber.19320650722.
  3. Hough, L.; Priddle, J. E. (1961). "Carbonate derivatives of methyl α-D-mannopyranoside and of D-mannose". J. Chem. Soc. 1961: 3178–3181. doi:10.1039/JR9610003178.
  4. Theodorakopoulos, I.; Tsatsas, G. (1981). "Dedication to Prof. L. Zervas (from the Minutes of the Academy of Athens)". Laboratory of Organic Chemistry (in Greek). University of Athens, Department of Chemistry. Archived from the original on 2021-12-19. Retrieved 31 Mar 2021.
  5. Dymicky, M. (1989-02-01). "Preparation of Carbobenzoxy-L-Tyrosine Methyl and Ethyl Esters and of the Corresponding Carbobenzoxy Hydrazides". Organic Preparations and Procedures International. 21 (1): 83–90. doi:10.1080/00304948909356350. ISSN   0030-4948.
  6. Aggarwal, Varinder K.; Humphries, Paul S.; Fenwick, Ashley (1999). "A Formal Asymmetric Synthesis of Anatoxin-a Using an Enantioselective Deprotonation Strategy on an Eight-Membered Ring". Angewandte Chemie International Edition. 38 (13–14): 1985–1986. doi:10.1002/(SICI)1521-3773(19990712)38:13/14<1985::AID-ANIE1985>3.0.CO;2-7. PMID   34182674.
  7. Jakubke, Hans-Dieter; Sewald, Norbert (2008). Peptides from A to Z: A Concise Encyclopedia. John Wiley & Sons. ISBN   978-3-527-62117-0.
  8. Felpin, François-Xavier; Fouquet, Eric (2010-11-02). "A Useful, Reliable and Safer Protocol for Hydrogenation and the Hydrogenolysis of O-Benzyl Groups: The In Situ Preparation of an Active Pd0/C Catalyst with Well-Defined Properties". Chemistry – A European Journal. 16 (41): 12440–12445. doi:10.1002/chem.201001377. ISSN   1521-3765. PMID   20845414.
  9. Theodora W. Greene; Peter G. M. Wuts (1999). Protecting Groups in Organic Synthesis (3 ed.). J. Wiley. ISBN   978-0-471-16019-9.
  10. Scattolin, Thomas; Gharbaoui, Tawfik; Chen, Cheng-yi (2022). "A Nucleophilic Deprotection of Carbamate Mediated by 2-Mercaptoethanol". Organic Letters . 24 (20): 3736–3740. doi:10.1021/acs.orglett.2c01410. PMID   35559611. S2CID   248776636.