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Related Concept Videos

Esters to β-Ketoesters: Claisen Condensation Mechanism01:08

Esters to β-Ketoesters: Claisen Condensation Mechanism

Regular Claisen condensation involves the synthesis of β-ketoesters by combining identical ester molecules bearing two α hydrogens in the presence of an alkoxide base. The reaction commences with the deprotonation of the acidic α hydrogen by the base to form a resonance stabilized ester enolate. This nucleophilic ion then attacks the carbonyl center of another ester molecule to generate a tetrahedral alkoxide intermediate. Next, the expulsion of the alkoxide group from the intermediate restores...
α-Hydroxy Ketones via Reductive Coupling of Esters: Acyloin Condensation Overview01:19

α-Hydroxy Ketones via Reductive Coupling of Esters: Acyloin Condensation Overview

The pinacol and McMurry reactions involve the reductive coupling of ketones or aldehydes. Similarly, the bimolecular reductive coupling of two ester molecules in the presence of sodium metal in an aprotic solvent yields an α-hydroxy ketone product. The α-hydroxy ketone is also called acyloin, so the reaction is referred to as ‘acyloin condensation.’
Esters to β-Ketoesters: Claisen Condensation Overview01:24

Esters to β-Ketoesters: Claisen Condensation Overview

Regular Claisen condensation is a base-promoted reaction involving identical esters with two α hydrogens, condensing to produce β-ketoesters. It is a nucleophilic acyl substitution reaction wherein one of the ester molecules, upon deprotonation by the base, forms a nucleophilic enolate ion, while the other molecule serves as an electrophile.
Preparation and Reactions of Thiols02:33

Preparation and Reactions of Thiols

Thiols are prepared using the hydrosulfide anion as a nucleophile in a nucleophilic substitution reaction with alkyl halides. For instance, bromobutane reacts with sodium hydrosulfide to give butanethiol.
Alkylation of β-Diester Enolates: Malonic Ester Synthesis01:14

Alkylation of β-Diester Enolates: Malonic Ester Synthesis

Malonic ester synthesis is a method to obtain α substituted carboxylic acids from ꞵ-diesters such as diethyl malonate and alkyl halides.
Alkylation of β-Ketoester Enolates: Acetoacetic Ester Synthesis01:07

Alkylation of β-Ketoester Enolates: Acetoacetic Ester Synthesis

Acetoacetic ester synthesis is a method to obtain ketones from alkyl halides and β-keto esters. The reaction occurs in the presence of an alkoxide base that abstracts the acidic proton of the β-keto esters. The step results in an enolate ion which is doubly stabilized. The enolate then reacts with an alkyl halide via the SN2 process to produce an alkylated ester intermediate with a new C–C bond. The hydrolysis of the intermediate, followed by acidification, results in an alkylated β-keto acid.

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Constructing Thioether/Vinyl Sulfide-tethered Helical Peptides Via Photo-induced Thiol-ene/yne Hydrothiolation
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Epimerization in peptide thioester condensation.

Kenta Teruya1, Takeyuki Tanaka, Toru Kawakami

  • 1Institute for Protein Research, Osaka University, 3-2 Yamadaoka, Suita, Osaka 565-0871, Japan. teruya@koto.kpu-m.ac.jp

Journal of Peptide Science : an Official Publication of the European Peptide Society
|September 14, 2012
PubMed
Summary
This summary is machine-generated.

Minimizing epimerization during peptide synthesis is crucial. Using less polar solvents for thioester peptide condensation significantly reduces epimer content in the final peptide product.

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Area of Science:

  • Chemical Synthesis
  • Biochemistry
  • Organic Chemistry

Background:

  • Peptide segment couplings are essential in modern protein chemical synthesis.
  • Peptide thioesters are key intermediates, but the adjacent amino acid risks epimerization.
  • Silver ion-mediated condensation of C-terminal peptide thioesters is a powerful strategy.

Purpose of the Study:

  • To investigate and minimize epimerization during peptide thioester synthesis and condensation.
  • To identify reaction conditions that reduce the risk of amino acid epimerization.
  • To optimize segment condensation for producing longer peptides with high fidelity.

Main Methods:

  • Preparation of peptide thioesters using the Boc solid-phase method.
  • Evaluation of epimerization during thioester-thiol exchange reactions in aqueous and organic solvents.
  • Assessment of epimerization during segment condensation in various solvents, including DMSO and less polar alternatives.
  • Application of optimized conditions to the condensation of longer peptide segments (45 and 44 residues).

Main Results:

  • No significant epimerization was detected during peptide thioester preparation via the Boc method.
  • Epimerization occurred during thioester-thiol exchange and segment condensation in DMSO with base.
  • Thioester-thiol exchange in aqueous solutions yielded no epimerization.
  • Less polar solvents significantly suppressed epimerization during segment condensation.
  • Epimer content in an 89-residue peptide product was reduced from 27% to 6% using optimized conditions.

Conclusions:

  • Reaction conditions, particularly solvent choice, critically influence epimerization during peptide thioester chemistry.
  • Aqueous conditions for thioester-thiol exchange and less polar solvents for segment condensation are effective strategies to minimize epimerization.
  • Optimized peptide segment condensation enables the synthesis of longer peptides with reduced epimer content, enhancing protein chemical synthesis fidelity.