Aspartimidestructure Aspartimide formation remains a significant challenge in peptide synthesis, particularly within Fmoc-based solid-phase peptide synthesis (SPPS).Preventing aspartimide rearrangements during fmoc-based ... This undesirable side reaction, often occurring with aspartic acid residues, can lead to low yields, complex purification processes, and ultimately, inaccessible peptide sequences. Understanding the mechanisms behind aspartimide formation and implementing effective prevention strategies are crucial for researchers and chemists aiming to produce high-purity peptidesThe Problem of Aspartimide Formation During Protein ....
Aspartimide formation is an intramolecular cyclization reaction that arises from the side chain of aspartic acidAcid-Mediated Prevention of Aspartimide Formation in Solid .... Under the basic conditions frequently employed in Fmoc SPPS, such as during deprotection steps with piperidine, the carboxyl group of an aspartic acid residue can attack the activated $\alpha$-amino group of the same residue. This cyclization results in the formation of a five-membered imide ring, known as an aspartimide.
The primary issue with aspartimide formation is not just its occurrence, but the subsequent rearrangements it can undergo.作者：K Sato·2024·被引用次数：8—Aspartimide formationis one of the major obstacles that impedes the solid phasesynthesisof largepeptidesand proteins. Until now, no cost- ... Upon nucleophilic attack, the aspartimide can open to form either the desired $\alpha$-peptide bond or an undesired $\beta$-peptide bond, leading to isoaspartyl impurities. These impurities are structurally similar to the target peptide, making their separation difficult and significantly impacting the overall purity and yield of the synthesized peptide.
Several factors can influence the propensity for aspartimide formation, making it a complex challenge to overcome:
* Amino Acid Sequence: Certain sequences are more prone to aspartimide formation than others. Specifically, the Aspartic Acid, Glycine (DG) sequence is frequently cited as being highly susceptible. The presence of glycine immediately C-terminal to aspartic acid can facilitate the cyclization. Other sequences involving aspartic acid followed by small, flexible amino acids can also increase the risk.A Systematic Comparison of Different Methods to Tackle ...
* Reaction Conditions: The basic conditions used for Fmoc deprotection are a primary driver.Suppression of Aspartimide Formation during Fmoc Solid ... The choice of base, its concentration, and the duration of exposure can all play a role. Elevated temperatures can also accelerate the reaction.
* Protecting Groups: The nature of the protecting groups used for the aspartic acid side chain can influence the reactivity and susceptibility to cyclization. While some protecting groups are designed to mitigate this, their effectiveness can varyAspartimide Formation and Its Prevention in Fmoc ....
* Peptide Length and Structure: Longer peptides or those that undergo aggregation during synthesis can present unique challenges, potentially influencing the accessibility of residues and the microenvironment around aspartic acid.Aspartimide formation 1,2is caused by repeated exposure of aspartic acid-containing sequencesto bases like piperidine and can result ultimately in the ...
Given its persistent nature, numerous strategies have been developed to minimize or completely block aspartimide formation during peptide synthesis. These approaches generally fall into a few key categories:
#### 1. Modifying Protecting Group Strategies
One of the most effective methods involves the use of specific protecting groups for the aspartic acid side chain that sterically hinder or electronically disfavor the cyclization.
* $\beta$-Ester Protection: Employing $\beta$-ester protecting groups for aspartic acid is a common tactic.2023年2月6日—Aspartimide rearrangements are a particularly nasty side reaction thatcan occur during fmoc-based solid phase peptide synthesis. These groups occupy the space that would otherwise be available for intramolecular cyclization. Examples include benzyl (Bzl) or tert-butyl (tBu) esters. However, even with $\beta$-ester protection, careful consideration of reaction conditions is still necessary.
* Amide Protection: In some cases, $\beta$-amide protecting groups can also be employed.
* Blocking Groups on the $\alpha$-Nitrogen: As mentioned in some literature, incorporating a blocking group on the $\alpha$-nitrogen of the preceding amino acid in the peptide sequence can also help prevent aspartimide formation.
#### 2. Optimizing Reaction Conditions
Fine-tuning the conditions of the peptide synthesis process can significantly reduce the risk of aspartimide formation.
* Milder Deprotection Conditions: Using milder bases or reducing the concentration and exposure time of deprotection reagents can limit the opportunity for cyclization.
* Lower Temperatures: Conducting reactions at lower temperatures can slow down the kinetics of aspartimide formation.
* Acidic Conditions: While basic conditions are the primary culprit, some literature suggests that certain acidic conditions can also play a role or be used in prevention. For instance, acid-mediated prevention strategies are being explored.作者：K Toney·1993·被引用次数：21—This cytosolic enzyme is known to preferentially methylate L-isoaspartyl residues within model substrates. Control experiments in which JP was incubated in the ...
* Microwave-Assisted Synthesis: While microwave irradiation can accelerate peptide synthesis, it can also, in some instances, exacerbate side reactions like aspartimide formation if not carefully controlled. Specific strategies are being developed for microwave-assisted protocols.
#### 3. Alternative Synthesis Methodologies
For particularly challenging sequences, alternative approaches to SPPS or fragment coupling might be considered.
* Native Chemical Ligation (NCL): For synthesizing very large peptides and proteins, NCL can be a powerful tool.Aspartimideformation is an intramolecular cyclization reactionthat occurs under both acidic and, more commonly, basic conditions used during solid-phase ... Adopting "good NCL practices" can involve restricting ligation steps or employing specific strategies that minimize the conditions favoring aspartimide formation in the joining peptide sequences.作者：E Nicolás·1989·被引用次数：149—Piperidine showed a marked tendency to form aspartimides during Fmoc deprotection. The behaviour of protected H Val Lys Asp Gly Tyr Ile OH towards imide ...
#### 4.2015年6月24日—The use of the aspartic acid derivatives according to the present invention leads to the minimization of base catalyzedaspartimide formation... Sequence Design and Analysis
Proactive peptide design can mitigate the risk from the outset.
* Sequence Analysis: Identifying sequences known to be prone to aspartimide formation, such as Asp-Gly (DG) dipeptides, allows for targeted interventionAspartic Acid, Glycine (DG) is the most prone to cause aspartimide formation. Limiting the number of DG combos is a peptide can greatly simplify the ....
* Minimizing Prone Sequences: If possible, redesigning the peptide to minimize the occurrence of highly susceptible sequences can simplify synthesis.
Detecting and quantifying aspartimide formation and its resulting impurities is crucial for quality control. Techniques such as High-Performance Liquid Chromatography (HPLC) coupled with Mass Spectrometry (MS) are indispensable for identifying these sequence impuritiesAspartimide formationis a persistent challenge in Fmoc-based solid-phasepeptide synthesis(SPPS), leading to sequence impurities, .... Understanding the mass difference introduced by aspartimide formation can aid in their identification.
Aspartimide formation is a persistent and often frustrating obstacle in peptide synthesis, directly impacting the yield and purity of synthetic peptides. The reaction is driven by the inherent chemistry of aspartic acid residues and is exacerbated by the basic conditions common in Fmoc SPPS作者：D Flora·2005·被引用次数：31—In summary, we have demonstrated thataspartimide formation is predominant in the standard Fmoc peptide synthesisusing an allyl ester as the side chain .... However, by understanding the factors that promote its formation, researchers can implement a range of effective strategies. These include judicious selection of protecting groups, careful optimization of reaction conditions, and in some cases, employing alternative synthesis methodologies or thoughtful peptide design.Formation of aspartimide peptides in Asp-Gly sequences Continuous research into novel protecting groups and refined protocols aims to further mitigate this challenge, paving the way for more efficient and successful synthesis of complex peptides.
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