peptide epimerization Peptide - Epimerizationand racemization peptides Understanding Peptide Epimerization: A Deep Dive into a Critical Challenge in Peptide Synthesis

Epimerizationof glucose Peptide epimerization is a significant and often underestimated challenge in the field of peptide synthesisEpimerization in peptide synthesis. It refers to a chemical conversion wherein an epimer transforms into another epimer or its chiral partner作者：Y Yeboue·2020·被引用次数：35—Indeed,epimerization during peptide couplingsoccurs either through direct αH- abstraction in basic medium and/or through the formation of an oxazolone .... This process fundamentally alters the stereochemistry of amino acid residues within a peptide chain, leading to the formation of diastereomers and potentially compromising the intended biological activity and purity of the synthesized peptide. Understanding the mechanisms, detection methods, and strategies to avoid epimerization is crucial for researchers and chemists working with peptides, whether for therapeutic applications, biochemical research, or other scientific endeavors.作者：S Duengo·2023·被引用次数：27—Epimerisation is basically a chemical conversionthat includes the transformation of an epimer into another epimer or its chiral partner.

The fundamental issue of epimerization arises from the inherent chemical properties of amino acids.Epimerization‐Free C‐Terminal Peptide Activation - 2013 The alpha-carbon atom in amino acids is a chiral center, meaning it has four different substituents attached. During peptide bond formation, the activation of the carboxyl group of the incoming amino acid is a necessary step.作者：S Duengo·2023·被引用次数：27—Epimerisation is basically a chemical conversionthat includes the transformation of an epimer into another epimer or its chiral partner. However, this activation process, particularly under certain conditions, can lead to the abstraction of the alpha-proton, creating a planar enolate intermediateO-to-O acyl transfer for epimerization-free peptide C- .... This intermediate can then be reprotonated from either face, resulting in a mixture of the original stereoisomer (L-amino acid) and its epimer (D-amino acid). This phenomenon is closely related to racemization, which involves the formation of a racemic mixture (equal amounts of enantiomers), although epimerization specifically refers to the change in configuration at a single chiral center, leading to a diastereomer.

Several factors can influence the rate and extent of peptide epimerization. The nature of the C-terminal residue plays a significant role; for instance, residues like Valine (Val) or Isoleucine (Ile) are known to epimerize more readily, especially in polar solvents. The coupling method employed is also a critical determinantDevelopment of Two Complementary Epimerization .... Traditional peptide coupling reagents and conditions have often been associated with a higher propensity for epimerizationThe minimization of amino acidracemizationduring coupling is also of vital importance to avoidepimerizationin the finalpeptideproduct.. For example, epimerization during peptide couplings can occur through direct alpha-H abstraction in a basic medium or via the formation of oxazolones, especially when activating amino acids with certain side chains.

The challenges associated with epimerization are particularly pronounced in the synthesis of C-terminal Cys peptide acids, as well as peptides containing racemization-prone amino acids like phenylglycine at the C terminus.Solid Phase Peptide Synthesis of the Fragment BPC 157 of Human ... The synthesis of cyclic peptides can also be affected, with C-terminal epimerization identified as a problem during chain elongation in some approaches. Furthermore, studies have shown that enhanced epimerization of glycosylated amino acids can occur under many common peptide coupling conditions used for preparing O-linked glycopeptides.

Detecting and quantifying peptide epimerization is a vital aspect of quality control in peptide synthesis. Researchers have developed various methods to identify and measure the presence of epimers.作者：S Komiya·2025—Herein, we reporttwo types of peptide fragment coupling reactionsdeveloped towards realization of highly convergent synthesis of N-alkyl-rich ... Understanding how can epimerization during peptide synthesis be detected often involves advanced analytical techniques such as High-Performance Liquid Chromatography (HPLC) with chiral stationary phases or mass spectrometry.

Fortunately, significant advancements have been made in developing epimerization-free strategies and reagents. Researchers have explored numerous innovative approaches to mitigate or eliminate this issue. These include the development of specialized coupling reagents and reaction conditions designed to minimize the formation of enolate intermediates or oxazolones.Allenone-Mediated Racemization/Epimerization-Free Peptide ... For example, the use of C-terminal pseudoproline structures and specific resins has been reported to achieve epimerization-free direct preparation of C-terminal Cys-containing peptides. Similarly, methods employing reagents like 2-(dichloromethyl)phenol have enabled the direct formation of peptide salicylaldehyde esters in an epimerization-free manner.作者：AF Spatola·1996·被引用次数：80—During our synthesis of cyclicpeptidemixtures, C-terminalepimerizationwas identified as a problem during chain elongation. This was significantly overcome ...

Other notable strategies include the development of epimerization-free C-term activation of peptide fragments through methods like ball-milling, which has shown high yields with very low epimerization. The use of Allenone as a highly effective peptide coupling reagent for epimerization-free peptide bond formation has also been documented. Furthermore, novel coupling reagents and activation strategies are continuously being developed to facilitate efficient, epimerization-free solid-phase peptide synthesis. Some innovative two types of peptide fragment coupling reactions have also been reported, aiming for highly convergent synthesis.Epimerization During Coupling to the Unnatural Amino ...

Beyond chemical synthesis, the biological context of peptide epimerization is also being explored. For instance, peptide epimerization machineries found in microorganisms are known to produce a variety of peptides containing D-amino acid residues as secondary metabolitesA New Way to Synthesize Peptides.

In summary, peptide epimerization is a fundamental chemical challenge in peptide synthesis that can significantly impact the integrity and functionality of peptides. While the epimerization mechanism can be complex, ongoing research is yielding increasingly effective solutions. From understanding the epimerization definition and examples to implementing epimerization-free activation and ligation of peptides, researchers are actively working to overcome this hurdle, paving the way for the reliable and efficient production of high-quality peptides for a wide range of applications. The quest for robust and racemization-free peptide synthesis remains a central focus in the field.作者：J Yang·2024·被引用次数：7—Remarkably, the robustness of TFPN-mediatedpeptideformation is showcased incisively by the synthesis of the pentapeptide neurotransmitter Leu-enkephalin.