Ethyl hydroxyiminocyanoacetate

Structural formula
Structural formula of the ( E ) isomer
General
Surname	Ethyl hydroxyiminocyanoacetate
other names	Ethyl 2-cyano-2- (hydroxyimino) acetate Ethyl isonitrosocyanoacetate Ethyl cyanoglyoxylate 2-oxime Oxyma Oxyma Pure
Molecular formula	C 5 H 6 N 3 O 3
Brief description	off-white to white or beige crystalline solid
External identifiers / databases
CAS number 3849-21-6 EC number 223-351-3 ECHA InfoCard 100.021.230 PubChem 6399475 Wikidata Q27236286
properties
Molar mass	142.11 g mol −1
Physical state	firmly
Melting point	127-133 ° C
pK s value	4.60
solubility	soluble in dimethylformamide , N -methylpyrrolidone , acetonitrile , dichloromethane and water, as well as in methanol and dimethyl sulfoxide
safety instructions
GHS labeling of hazardous substances Caution H and P phrases H: 302 P: 264-270-301 + 312-330-501
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Hydroxyiminocyanessigsäureethylester ( Oxyma ) is the oxime of the cyanoacetate and is used as an additive for carbodiimides , such as. B. Dicyclohexylcarbodiimide (DCC) in peptide synthesis . Due to its pronounced acidity (pK _S  4.60), it functions as a neutralizing reagent for the basicity or nucleophilicity of the DCC and suppresses base-induced side reactions, in particular racemization .

Occurrence and representation

Ethyl 2-cyano-2- (hydroxyimino) acetate is obtained in 87% yield from the reaction of ethyl cyanoacetate and nitrous acid (from sodium nitrite and acetic acid ).

Because of the tendency of the ester to hydrolyze, the reaction should be carried out at pH 4.5, the product being obtained in a virtually quantitative yield in buffered phosphoric acid .

The compound can be purified by recrystallization from ethanol or ethyl acetate .

Compared to the benzotriazole derivatives 1-hydroxybenzotriazole (HOBt) and 1-hydroxy-7-azabenzotriazole (HOAt), which are widely used as peptide linking reagents and are considered to be explosive , hydroxyiminocyanoacetate ethyl ester shows a significantly slower thermal decomposition when heated.

properties

Ethyl 2-cyano-2- (hydroxyimino) acetate is a white solid that is found in many solvents commonly used in the synthesis of peptides, such as e.g. B. dichloromethane (DCM) or dimethylformamide (DMF), is soluble.

As a crystalline substance, the compound is present as an oxime , while in anionic form as a salt or in a strongly basic solution it predominantly exists as a tautomeric nitrosoisomer.

Applications

Due to the simple preparative accessibility, the uncritical behavior at temperatures below 80 ° C. and in particular because of the high yields and the low racemization of the peptides obtained, ethyl hydroxyiminocyanoacetate has meanwhile found wider use as an additive in peptide syntheses.

Hydroxyiminocyanoacetate ethyl ester can be used as a coupling additive in conventional peptide linkage in solution, as in automated Merrifield synthesis on a solid support resin ( solid-phase peptide synthesis (SPPS) ) together with coupling reagents such as carbodiimides, e.g. B. dicyclohexylcarbodiimide (DCC), diisopropylcarbodiimide (DIC) or the water-soluble 1-ethyl-3- (3-dimethylaminopropyl) carbodiimide hydrochloride (EDCI) can be used.

The step-by-step liquid phase synthesis of the dipeptide Z- L -Phg- L -Val-OMe from Z- L - α-phenylglycine and L- valine methyl ester with the benzyloxycarbonyl group (Z group) N-protected with the coupling reagent DIC and the additive Hydroxyiminocyanoacetate ethyl ester a product yield ( LL -dipeptide) of 81-84%, which is free from racemic DL -dipeptide.

Recently, a variety of derivatives of the hydroxyiminocyanoacetate (Oxyma) have been developed as acylating reagents, such as. B. Fmoc-Oxyma to transfer the fluorenylmethoxycarbonyl protective group

or the coupling reagent COMU , which is readily soluble as dimethylmorpholine uronium salt and which, like Oxyma, is superior to the standard additive HOBt in terms of suppression of racemization and acylation efficiency and is comparable to HOAt without presenting an explosion risk like the benzotriazoles.

Even for the linking of protected amino acids to oligopeptides in water, water-soluble derivatives of hydroxyiminocyanoacetate (glyceroacetonide-oxyma) as an additive and DIC as a coupling reagent in a weakly basic aqueous solution with the model substances Z- L -Phg-OH and L -H-Pro- NH ₂

possible with a chemical yield of 95% and a diastereomer excess of> 99%.

When coupling amino acids frequently occurring side reactions such. B. Formation of symmetrical acid anhydrides , racemization and epimerization or cyclization to oxazolinones or - especially of dipeptides - to 2,5- diketopiperazines are largely suppressed by the coupling additive ethyl 2-cyano-2- (hydroxyimino) acetate.

Individual evidence

1. ↑ ^{a b c d e} F. Albericio, R. Subirós-Funosas: Ethyl 2-Cyano-2- (hydroxyimino) acetate . In: e-EROS Encyclopedia of Reagents for Organic Synthesis . 2012, doi : 10.1002 / 047084289X.rn01377 .
2. ↑ ^{a b} Data sheet Hydroxyimino-cyanoacetic acid ethyl ester from Sigma-Aldrich , accessed on October 5, 2016 ( PDF ).
3. ↑ ^{a b c} data sheet Ethyl isonitrosocyanoacetate 97% at AlfaAesar, accessed on June 16, 2017 ( PDF )(JavaScript required) .
4. ↑ Entry on Ethyl cyano (hydroxyimino) acetate at TCI Europe, accessed on October 5, 2016.
5. ↑ M. Itoh: Peptides. IV. Racemization suppression by the use of ethyl 2-hydroxyimino-2-cyanoacetate and its amide . In: Bull. Chem. Soc. Jpn. tape 46 , 1973, p. 2219-2221 , doi : 10.1246 / bcsj.46.2219 .
6. ↑ Entry on Ethyl Cyano (hydroxyimino) acetate at Toronto Research Chemicals , accessed on October 5, 2016 ( PDF ).
7. ↑ ^{a b c} R. Subirós-Funosas, R. Prohens, R. Barbas, A. El-Faham, F. Albericio: Oxyma: An efficient additive for peptide synthesis to replace the benzotriazole-based HOBt and HOAt with a lower risk of explosion . In: Chem. Eur. J. Band 15 , no. 37 , 2009, p. 9394-9403 , doi : 10.1002 / chem.200900614 .
8. ↑ M. Conrad, A. Schulze: About nitroso-cyanoacetic acid derivatives . In: Chem. Ber. tape 42 , no. 1 , 1909, p. 735-742 , doi : 10.1002 / cber.190904201117 .
9. ↑ Patent US5166394 : Coupling reagent for peptide synthesis. Registered on May 21, 1991 , published on November 2, 1992 , applicant: Hoechst AG, inventor: G. Breipohl, W. König. ‌
10. ↑ ^{a b c} R. Subirós-Funosas, SN Khattab, L. Nieto-Rodriguez, A. El-Faham, F. Albericio: Advances in acylation methodologies enabled by Oxyma-based reagents . In: Aldrichimica Acta . tape 46 , no. 1 , 2013, p. 21–41 ( ub.edu [PDF]).
11. ↑ Coupling Reagents Bachem. (PDF; 1.9 MB) In: bachem.com. Global Marketing, Bachem Group, 2015, accessed on October 10, 2016 . 
12. ↑ A. El-Faham, Z. Al Marhoon, A. Abdel-Megeed, F. Albericio: OxymaPure / DIC: An Efficient Reagent for the Synthesis of a Novel Series of 4- [2- (2-acetylamino) -2- oxo-acetylamino] Benzoyl Amino Acid Ester Derivatives . In: Molecules . tape 18 , 2013, p. 14747-14759 , doi : 10.3390 / molecules181214747 .
13. ↑ ^{a b} R. Subirós-Funosas, A. El-Faham, F. Albericio: Low-epimerization peptides Bond Formation with Oxyma Pure: Preparation of ZL-Phg-Val-OMe In: Organic Synthesis . 90, 2013, pp. 306-315, doi : 10.15227 / orgsyn.090.0306 ( PDF ).
14. ↑ A. El-Faham, F. Albericio: Peptide coupling reagents, morethan a letter soup . In: Chem. Rev. Band 111 , no. 11 , 2011, p. 6557-6602 , doi : 10.1021 / cr.100048w .
15. ↑ SN Khattab, R. Subirós-Funosas, A. El-Faham, F. Albericio: Oxime Carbonates: Novel Reagents for the Introduction of Fmoc and Alloc Protecting Groups, Free of Side Reactions . In: Eur. J. Org. Chem. Volume 17 , 2010, p. 3275-3280 , doi : 10.1002 / ejoc.201000028 .
16. ^ Q. Wang, Y. Wang, M. Kurosu: A new Oxyma derivative for nonracemizable amide-forming reactions in water . In: Org. Lett. tape 14 , no. 13 , 2012, p. 3375-3375 , doi : 10.1021 / o3013556 .