β-Acyloxy Alkenyl Amides (AAAs): A New Approach to Amide Bond and Peptide Bond Construction Worth Attention

I. Key Questions at a Glance

This article is primarily based on a 2025 Science Advances paper and is cross-supported by review articles on amide bond formation, peptide coupling, and green peptide chemistry.

Cao S, Guo H, Zhong Z, Chen D, Song W, Liu Y, Wan J-P. β-Acyloxyl alkenyl amide synthesis via multiple defluorination: α-Trifluoromethyl ketone-amine as synergystic peptide coupling reagent. Science Advances. 2025;11(43):eaea4120. doi:10.1126/sciadv.aea4120.

Key Question	Key Conclusion
What does this study focus on?	It focuses on the streamlined preparation of β-acyloxy alkenyl amides (AAAs) and their applications in amide, peptide, and certain ester syntheses.
What is the real novelty?	The novelty is not simply the introduction of another amidation condition, but rather the transformation of AAAs—previously difficult to access—into intermediates that can be prepared in one step from α-trifluoromethyl ketones, amines, and carboxylic acids/amino acids.
Why is this worth attention?	Although many methods for constructing amide and peptide bonds already exist, the field still faces long-standing challenges such as side reactions, stereochemical retention, step economy, and sustainability.
What are the standout strengths of this work?	One-step AAA preparation, mild amine acylation, no observed racemization or epimerization in peptide synthesis, one-pot two-step dipeptide construction, and further extension to tetrapeptide and ester synthesis.
How should it be understood?	It should be viewed as a new method for amide bond and peptide bond construction that deserves serious attention, but it should not yet be regarded as a direct replacement for all existing coupling reagents.

II. Why Continued Research on Amide Bond and Peptide Bond Construction Matters

Amide bonds are among the most common linkages in organic chemistry, medicinal chemistry, and the life sciences. As noted in the relevant reviews, although a large number of mature methods for amide bond formation have already been developed, this field is far from “complete,” because researchers still need to deal with issues such as reagent selection, byproduct handling, compatibility with complex substrates, reaction efficiency, and the development of greener and more sustainable processes.[2][3][5][7] In peptide synthesis, the challenges become even more concentrated around stereochemical retention, racemization control, coupling efficiency, and the burden imposed by solvents and auxiliary reagents. For this reason, the search for new coupling strategies remains practically meaningful.[4][6]

Several long-standing issues that continue to attract attention in amide bond and peptide bond construction

Area of Concern	Specific Manifestation	Supporting References
There are many coupling methods, but choosing among them is not straightforward	Different systems differ significantly in activation mode, applicable substrates, cost, and side reactions	[2][3][5]
Peptide coupling demands strict stereochemical retention	Racemization or epimerization can directly affect the quality of the target peptide	[4][6]
Modern research looks beyond yield alone	Step economy, workup, reagent safety, and sustainability must also be considered simultaneously	[3][6][7]
The value of a new method lies in more than simply “forming the bond”	Its real value is whether it can demonstrate integrated advantages with complex substrates and in realistic synthetic settings	[3][5][6]

III. What This 2025 Study Accomplished

The central focus of this work is β-acyloxy alkenyl amides (AAAs). According to the paper abstract, AAAs are a class of vinylogous esters with high acylation reactivity. However, before this study, only one known synthetic route to AAAs existed, and that route required five discrete operational steps and involved a highly sensitive amino alkynone intermediate. This severely limited their application in peptide synthesis and in broader acylation chemistry.

The key advance reported in this study is the integration of successive triple defluorination, acyl migration, and a multicomponent reaction into a clearly simplified one-step AAA synthesis. The starting materials are α-trifluoromethyl ketones, amines, and carboxylic acids/amino acids, with Cs₂CO₃ used as the sole promoter; this step is typically carried out at 40 °C. This means that the study not only addressed the problem that AAAs were difficult to prepare and difficult to generalize, but also brought this highly reactive acylation intermediate into a genuinely practical synthetic setting.

The α-trifluoromethyl ketone–amine combination itself can be understood as a synergistic peptide coupling reagent, and the AAA is formed in situ within this system as the key intermediate responsible for the subsequent acyl transfer. In other words, this paper does not merely present a method for AAAs preparation in isolation; on the basis of AAAs formation, it proposes a new strategy for amide bond and peptide bond construction.

Core contributions of this study

Research Aspect	Information Provided by the Paper	What It Means
Nature of AAA	AAA is a vinylogous ester with high acylation activity	It is not an ordinary structural motif, but an activated intermediate that can be used for subsequent acylation
Previous limitation	Only one five-step route had previously been reported, and it involved a sensitive intermediate	In the past, researchers “knew it was useful,” but it was “not easy to use in practice”
New method	AAA can be prepared in one step from α-trifluoromethyl ketones, amines, and carboxylic acids/amino acids, with Cs₂CO₃ as the sole promoter	This turns AAA from a high-barrier target into a more operationally accessible synthetic intermediate
Downstream applications	The generated AAA can be used in ester, amide, and peptide synthesis	The novelty lies not only in its preparation, but also in the direct validation of its downstream applications
Performance in peptide synthesis	In the peptide synthesis examples examined, no racemization or epimerization was observed	This is one of the most noteworthy strengths of the method

IV. What Specific Applications of AAAs Were Demonstrated in This Study

1. Used for Amide Synthesis

AAAs can react with amines in ethyl acetate (EA) at 30 °C to accomplish amide formation. The resulting AAAs showed good performance in the synthesis of esters, amides, and peptides. This indicates that, in this work, AAAs were used as effective acyl-transfer intermediates rather than merely as isolable and characterizable structures.

2. Used for Dipeptide Construction

Figure 4 of the paper presents the scope of dipeptide synthesis, and Figure 4B shows selected dipeptide examples together with comparative results against certain commercial coupling reagents. The abstract states that no racemization or epimerization was observed in any of the peptide synthesis examples examined. For peptide chemistry, this conclusion is of strong practical significance, because the value of a peptide coupling method depends not only on whether bond formation can be achieved, but also on whether stereochemical information can be preserved as fully as possible.[4][6]

3. Used for One-Pot, Two-Step Dipeptide Synthesis

Figure 5 of the paper further demonstrates a one-pot, two-step route to dipeptides: AAA is first generated in situ from the starting materials, and then allowed to react further with another amino acid to afford the dipeptide. The first step forms AAA at 40 °C, and the second step continues the coupling at room temperature. The significance of this design lies in its reduction of intermediate isolation steps, making it more consistent with the modern emphasis on step economy and operational simplicity in synthesis.[3][6]

4. Extended to Tetrapeptide Synthesis

Figure 6 of the paper shows the construction of a tetrapeptide and also provides the conditions for subsequent ammonolysis, deprotection, and re-preparation of peptide-derived AAA. This shows that the method does not stop at merely “making a dipeptide as a proof of concept,” but has already begun to extend toward longer peptide fragments.

5. Applicable to Ester Synthesis, but with More Demanding Conditions

AAAs can also be used for ester synthesis, but this requires the participation of DBU and a reaction temperature of 100 °C, although some reactions can be completed at 80 °C. Therefore, this system is not effective only for amines; however, based on the reported conditions, its requirements for esterification are clearly more demanding than those for amine acylation. At the current stage, the most prominent applications therefore remain amide and peptide synthesis.

A quick overview of the main application scenarios in this study:

Application Scenario	What the Paper Demonstrated	Representative Conditions or Conclusions	Significance
AAA preparation	One-step generation of various AAAs	40 °C, promoted by Cs₂CO₃	Solves the problem of “difficult-to-access intermediates”
Amide synthesis	AAA reacts with amines to give amides	EA, 30 °C, 3–24 h	Relatively mild conditions, demonstrating acyl-transfer capability
Dipeptide synthesis	AAA couples with amino acids	Figure 4 shows the substrate scope	Directly relevant to peptide chemistry applications
One-pot, two-step dipeptide synthesis	In situ generation of AAA followed by continued coupling	AAA formed at 40 °C, followed by coupling at room temperature	Improves step economy
Tetrapeptide synthesis	Figure 6 shows further extension	Conditions for ammonolysis, deprotection, and re-preparation are provided	Indicates potential for development toward longer peptide fragments
Ester synthesis	AAA reacts with alcohols/phenols to form esters	DBU, 100 °C	Shows that the method has broader acyl-transfer potential

V. Key Highlights of This Study

1. The first highlight is that it turns “AAAs is useful” into “AAAs is genuinely easier to access and can be used directly.” In many methodology papers, what truly limits application is not the reaction itself, but the fact that key intermediates are difficult to prepare, difficult to store, or difficult to scale up. This study addresses precisely that bottleneck.

2. The second highlight is that the utility of AAAs is directly connected to the construction of amides, peptides, and esters, rather than stopping at the level of “preparing a new molecule.” This continuous demonstration from intermediate preparation to downstream application gives the work greater practical value than mere structural novelty alone.

3. The third highlight is the stereochemical retention advantage it displayed in peptide synthesis. For peptide chemistry, this is a highly important strength, because modern peptide coupling methods are judged not simply by whether “the coupling succeeded,” but by whether side reactions and stereochemical loss can also be controlled in addition to achieving efficiency.

4. The fourth highlight is that this work is aligned with the broader current trends in the field of amide bond and peptide bond construction: researchers are placing increasing emphasis on step economy, operational simplicity, substrate compatibility, and sustainability, rather than treating high yield as the only goal. The AAAs method deserves attention precisely because it offers new and discussable content across all of these dimensions.

VI. Chemical Navigation Table Related to Amide Bond and Peptide Bond Construction (Tables 1–5)

Experimental or Research Task	Recommended Table to Consult First	Why Start with This Table	Navigation Notes
Want to first understand the new method discussed in this article and see what kinds of starting materials and model substrates are typically used in this type of reaction	Table 1	Table 1 concentrates on precursors related to the AAA method, promoters, model carboxylic acids, model amines, model alcohols, and reaction media	Start by building an overall understanding of “what kinds of starting materials are typically used in this new method, which substrates are commonly chosen for validation, and within what general condition framework the chemistry is carried out.”
Want to explore AAA-related routes, defluorination transformations of fluorinated ketones, or acyl-migration-based methods	Table 1	Table 1 includes representative α-trifluoromethyl ketones, cesium carbonate, DBU, model carboxylic acids, and model acceptors	This table is most suitable for initial methodology screening, especially for assembling “precursor–base–carboxylic acid/amine/alcohol” combinations and establishing a basic reaction model.
Want to compare how the “new method” differs from traditional amide-forming or peptide-coupling methods and prepare comparative experiments	Read Table 1 first, then Table 3	Table 1 provides the precursors and model substrates for the new method, while Table 3 provides traditional and modern common coupling reagent systems	This is suitable for methodological comparison: first use Table 1 to understand the starting point of the new route, then use Table 3 to choose traditional coupling reagents for comparison of activation mode, conditions, and applicability.
Want to screen amidation conditions for ordinary small-molecule carboxylic acids and amines	Read Table 1 first, then Table 3	Table 1 provides standard model carboxylic acids and amines, while Table 3 provides different types of coupling reagents and additives	Suitable for method development or teaching-oriented experiments: first determine the substrates, then choose carbodiimide-, uronium-, phosphonium-, or triazine-based condensation systems according to substrate type.
Want to extend the study from “amide bond formation” further to the compatibility of “acylation/esterification of alcohols or phenols”	Read Table 1 first, then Table 3	Table 1 contains model acceptors such as benzyl alcohol, ethanol, and phenol, while Table 3 contains reagent systems suitable for acyl transfer or condensation	Suitable for comparative experiments on which type of acceptor—amine, alcohol, or phenol—is more suitable for bond formation, and also for expanding toward broader acyl-group-transfer studies.
Want to establish or optimize a basic Fmoc peptide synthesis workflow	Table 2	Table 2 concentrates on workflow-oriented chemicals such as Fmoc/Boc protection–deprotection reagents, DMF/NMP, piperidine, TFA, N-methylmorpholine, and DIPEA	Suitable for building a basic polypeptide synthesis system, especially for practical questions such as “which protecting-group route to choose, how to formulate the deprotection system, and how to prepare common solvents and bases.”
Want to design protection/deprotection strategies for amino, amino acid, or amine substrates	Table 2	Fmoc-Cl, Boc₂O, piperidine, and TFA in Table 2 correspond more directly to protecting-group operations	For this type of task, the emphasis is not on coupling efficiency, but on pretreatment and protection strategy; Table 2 is therefore more suitable as the first reference table.
Want to compare how different coupling reagents should be selected, especially the roles of DCC, DIC, EDC, HATU, HBTU, COMU, and DMTMM	Table 3	Table 3 is the most concentrated comparison table of coupling reagents and additives in the entire product set	Suitable for answering the question “which type of condensation reagent should be used at this step?” Whether for solution-phase amidation, peptide coupling, or comparison between new and old methods, Table 3 should be consulted first.
Want to handle difficult couplings, sterically hindered amino acids, or concerns about racemization	Table 3	Table 3 includes not only highly active systems such as HATU, HCTU, and COMU, but also additives such as HOBt and Oxyma	Suitable for situations where “the coupling is not proceeding smoothly, the conversion is low, or high stereochemical retention is required”; this is the table to consult first when moving from routine coupling to optimized coupling.
Want to select amino acids based on the properties of the target peptide segment, starting with neutral, hydrophobic, and aromatic types	Table 4	Table 4 concentrates on common neutral/hydrophobic/aromatic amino acids such as Gly, Ala, Val, Leu, Ile, Pro, Phe, Tyr, Trp, and Thr	Suitable for designing general peptide segments, hydrophobic peptide segments, aromatic-interaction peptide segments, or for comparing sequence properties; this is often the first amino acid table consulted for routine peptide construction.
Want to design peptide sequences featuring hydroxyl groups, phenolic hydroxyl groups, aromatic rings, or conformational constraints	Table 4	Thr, Tyr, Trp, Pro, and related entries in Table 4 better reflect conformational features, aromaticity, and modifiability	Suitable for extending from “amide bond/peptide bond construction” in this article to selection needs related to “peptide structure and property design.”
Want to select amino acids for building acidic, basic, polar, sulfur-containing, or more functionally rich peptide segments	Table 5	Table 5 concentrates on amino acids with more strongly functional side chains, such as Asp, Glu, Asn, Gln, Ser, Cys, Met, Arg, His, and Lys	Suitable for designing polar peptides, cationic peptides, metal-binding peptides, sulfur-containing peptide segments, and sequences in which side-chain protection requires special attention.
Want to study “how different types of amino acids affect coupling difficulty, purification behavior, and sequence properties”	Table 4 + Table 5	Tables 4 and 5 respectively cover neutral/hydrophobic/aromatic amino acids and acidic/basic/polar/sulfur-containing amino acids	Taken together, these two tables are most suitable for comparative experiments on amino acid types, and also for further extension to peptide sequence design and structure–property studies.

Table 1 | AAA-Method-Related Precursors, Promoters, Model Substrates, and Reaction Media

Category	CAS No.	Aladdin Cat. No.	Name	Grade or Purity	Product Features and Applications
AAA precursor: representative α-trifluoromethyl ketone	434-45-7	T106660	2,2,2-Trifluoroacetophenone	≥98%(GC)	A representative α-trifluoromethyl ketone substrate that can be used to construct active acylation intermediates such as β-acyloxy alkenyl amides; it is also suitable as a model substrate for studies on defluorination transformations and acyl migration involving fluorinated ketones.
AAA precursor: substituted representative α-trifluoromethyl ketone	394-59-2	T162002	2,2,2-Trifluoro-4'-methylacetophenone	≥97%(GC)	A representative para-methyl-substituted α-trifluoromethyl ketone, suitable for examining how electron-donating substitution on the aryl ring affects defluorination transformations, formation of active acylation intermediates, and subsequent acyl-transfer reactions.
Inorganic base / promoter for AAA generation	534-17-8	C432848	Cesium carbonate	purum p.a., ≥98%(T)	A strongly basic inorganic base commonly used in dehalogenation, defluorination, condensation, and acid–base activation processes; it is also suitable for promoting the synergistic reaction of carboxylic acids, amines, and fluorinated ketone substrates in multicomponent transformations.
Strong organic base / esterification-promoting base	6674-22-2	D106478	1,8-Diazabicyclo[5.4.0]undec-7-ene (DBU)	≥99%	A strong non-nucleophilic organic base suitable for acyl transfer, esterification, elimination, deprotection, and related processes; it is especially useful in systems that require strong basicity while minimizing nucleophilic side reactions.
Solvent for amidation-related reactions and workup	141-78-6	E116139	Ethyl acetate	For protein sequencing, ≥99.5%	A commonly used medium-polarity organic solvent suitable as a reaction medium for amidation, esterification, and related processes; it is also widely used for post-reaction extraction, washing, and crude-product handling.
Simple aliphatic carboxylic acid model substrate / acidity-adjusting reagent	64-19-7	A116166	Acetic acid	Guaranteed reagent, ≥99.5%	One of the most basic aliphatic carboxylic acid model substrates, suitable for establishing basic reaction models for amidation and esterification; it may also be used as an acidity-adjusting reagent or as a reference acetyl source.
Aromatic carboxylic acid model substrate	65-85-0	B433248	Benzoic acid	Suitable for synthesis	A classic aromatic carboxylic acid model substrate, suitable for screening carboxylic acid activation conditions, comparing bond-forming behavior between aromatic and aliphatic carboxylic acids, and serving as a standard substrate in methodology studies on amide bond construction.
Primary amine model acceptor	100-46-9	B108477	Benzylamine	AR, ≥99%	A representative primary amine nucleophile with relatively good reactivity, commonly used for rapid evaluation of the applicability of carboxylic acid activation systems, coupling reagents, and novel acylation intermediates toward amine acceptors.
Cyclic secondary amine model substrate	110-91-8	M109058	Morpholine	Distilled grade, ≥99.5%	A classic cyclic secondary amine substrate, suitable for examining the reactivity and selectivity of secondary amines in amidation; morpholine amide motifs are also common in pharmaceuticals and bioactive molecules.
Aromatic amine model acceptor	62-53-3	A112122	Aniline	ACS, ≥99%	A representative aromatic amine substrate suitable for evaluating the performance of less nucleophilic amines in amidation, acyl transfer, and new coupling systems; it is also suitable for comparison with substrates such as benzylamine and morpholine to assess bond-forming efficiency and applicability across different types of amine acceptors.
Alcohol nucleophile / model esterification substrate	100-51-6	B163018	Benzyl alcohol	Pharmaceutical grade, PharmPure™	A common primary alcohol model substrate suitable for esterification and acyl-transfer studies; it is also a common alcohol source for constructing benzyl ester protecting derivatives.
General alcohol solvent / model alcohol substrate	64-17-5	E111989	Ethanol	Guaranteed reagent, water≤0.3%	A commonly used organic solvent and simple model alcohol substrate, suitable for esterification, transesterification, and operations such as sample cleaning, precipitation, and workup.
Phenolic model acceptor / analytical standard	108-95-2	P100767	Phenol	Analytical standard, ≥99.5%	A representative phenolic substrate suitable for studying the acylation reactivity of phenolic hydroxyl groups, the ability to form phenolic esters, and selectivity differences between alcohol and phenol acceptors.
Alcohol solvent related to peptide/amino acid analytical pretreatment	67-56-1	M433272	Methanol solution	MS grade, UltraPureChrom™, UHPLC grade, ≥99.5%, contains 0.10% (v/v) formic acid	MS-grade methanol containing formic acid, suitable for LC-MS mobile-phase preparation, sample reconstitution, and pretreatment analysis of amino acids, peptides, and amide-containing samples.

Table 2 | Common Solvents, Acids/Bases, and Protecting/Deprotecting Reagents in Peptide Chemistry (Including Reagents Related to Analysis and Sample Pretreatment)

Category	CAS No.	Aladdin Cat. No.	Name	Grade or Purity	Product Features and Applications
Acidification reagent for peptide/protein analytical pretreatment	76-05-1	T433653	Trifluoroacetic acid (TFA)	For protein sequencing, 25% solution in water	A 25% aqueous TFA solution, more suitable for peptide/protein sample acidification, pretreatment, ion-pairing, or protein-sequencing-related analytical scenarios; it can be used for LC-MS/HPLC sample treatment and acidification operations.
Organic base / acid scavenger for peptide coupling	109-02-4	M104644	N-Methyl morpholine	For protein sequencing, ≥99.8%(GC)	A commonly used tertiary amine base that can serve as an acid scavenger/basic additive in amidation, activated-ester reactions, or protection reactions; it is commonly used in conjunction with condensation systems.
Organic base / acid scavenger for peptide coupling	7087-68-5	D109322	N,N-Diisopropylethylamine	Distilled grade, ≥99.5%	A commonly used tertiary amine base and acid scavenger, widely used in coupling systems such as HATU, HBTU, COMU, TBTU, and PyBOP; it promotes amide bond formation after carboxylic acid activation and helps reduce interference from acidic byproducts.
Common coupling/deprotection solvent in Fmoc peptide chemistry	68-12-2	D119450	N,N-Dimethylformamide (DMF)	Anhydrous, ≥99.8%	One of the core solvents in Fmoc peptide chemistry, suitable for amino acid coupling, resin swelling, and 20% piperidine deprotection of Fmoc; it is compatible with a variety of coupling reagent systems.
Common coupling/deprotection solvent in Fmoc peptide chemistry	872-50-4	M119668	1-Methyl-2-pyrrolidinone (NMP)	Anhydrous, ≥99.5%	A commonly used polar aprotic solvent that can serve as an alternative or supplement to DMF in systems involving Fmoc amino acid derivatives, coupling reagents, and certain difficult sequences.
Fmoc amino-protecting reagent	28920-43-6	F106534	Fmoc chloride	For HPLC derivatization, ≥99%(HPLC)	A classic amino-protecting reagent used for preparing Fmoc-protected amino acids or amine derivatives, and an important reagent for preparing upstream building blocks in Fmoc peptide chemistry.
Boc amino-protecting reagent	24424-99-5	D106159	Di-tert-butyl dicarbonate	≥99%	A classic Boc-protecting reagent used for amino protection of amines and amino acids, and an important basic reagent in substrate pretreatment and protection–deprotection strategies before amidation.
Fmoc deprotection working solution	110-89-4	P1506348	Piperidine solution	Suitable for polypeptide synthesis, 20% in DMF	A classic deprotection system in Fmoc SPPS. A 20% piperidine/DMF solution efficiently removes Fmoc and serves as a key working solution directly matched to Fmoc-protected amino acids and Fmoc-Cl systems.

Table 3 | Traditional and Modern Amide/Peptide Coupling Reagents and Additives

Category	CAS No.	Aladdin Cat. No.	Name	Grade or Purity	Product Features and Applications
Water-soluble carbodiimide coupling reagent	25952-53-8	A638729	Aladdin™ EDC	Analytical standard	A representative water-soluble carbodiimide coupling reagent, commonly used for condensation of carboxylic acids with amines and also frequently seen in aqueous-phase or bioconjugation systems; suitable for understanding the difference between traditional carboxylic-acid activation methods and new active-acyl-intermediate strategies.
Carbodiimide coupling reagent	538-75-0	D106074	N,N′-Dicyclohexylcarbodiimide	≥99%	A classic carboxylic-acid activation reagent that can be used together with additives such as HOBt and Oxyma to accomplish amide bond formation; an important representative for understanding traditional condensation-reagent systems.
Carbodiimide coupling reagent	693-13-0	N420184	N,N'-Diisopropylcarbodiimide	≥98.5%	A commonly used liquid carbodiimide reagent, often employed together with additives such as HOBt and Oxyma, and suitable for solid-phase peptide synthesis as well as routine amidation systems.
Imidazole-type carboxylic-acid activation reagent	530-62-1	C109315	N,N'-Carbonyldiimidazole (CDI)	≥99%	A classic carbonyl-activation reagent that can convert carboxylic acids into more reactive acyl imidazole intermediates for the construction of amides, ureas, carbamates, and related bond types.
Acyl-transfer catalyst	1122-58-3	D109207	4-Dimethylaminopyridine	≥99%	A classic acyl-transfer catalyst that can accelerate acyl transfer between activated carboxylic acids and alcohols/amines; commonly used in esterification, carbonate formation, and some auxiliary amidation systems.
Highly active uronium-type peptide coupling reagent	148893-10-1	H109327	HATU	≥99%	One of the highly efficient coupling reagents in modern peptide chemistry, especially suitable for sterically hindered substrates or difficult coupling steps, and commonly used together with DIPEA to improve peptide bond formation efficiency.
Uronium-type peptide coupling reagent	94790-37-1	H106174	HBTU	≥99%	A commonly used peptide coupling reagent suitable for rapid condensation of carboxylic acids with amines/amino acids, and highly representative in both solution-phase peptide synthesis and solid-phase peptide synthesis.
Uronium-type peptide coupling reagent	125700-67-6	T109338	TBTU	≥98%	A commonly used uronium-type coupling reagent suitable for routine peptide bond construction and small-molecule amidation, and can be used together with bases such as DIPEA.
Uronium-type peptide coupling reagent	330645-87-9	C106175	O-(6-Chlorobenzotriazol-1-yl)-N,N,N′,N′-tetramethyluronium hexafluorophosphate	≥98%	A highly active HCTU-type uronium coupling reagent suitable for efficient peptide bond formation, and a common peptide-coupling option alongside HBTU and HATU.
Oxyma-type uronium coupling reagent	1075198-30-9	C340003	COMU	≥98%	A modern Oxyma-type coupling reagent that combines high coupling efficiency with good racemization control, and is often used in peptide synthesis as an alternative or upgraded choice relative to HATU/HBTU.
Phosphonium-type peptide coupling reagent	128625-52-5	P109336	1H-Benzotriazol-1-yloxytripyrrolidinophosphonium Hexafluorophosphate	≥98%	A typical phosphonium-type coupling reagent commonly used for efficient peptide bond construction, suitable as a representative traditional highly active coupling system for comparison alongside uronium-type reagents.
Triazine-type condensation reagent	3945-69-5	D110326	4-(4,6-Dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride hydrate (DMTMM)	≥97%	A representative triazine-type condensation reagent suitable for condensation of carboxylic acids with amines or alcohols, and particularly valuable in some mild or water-containing systems; an important methodological representative alongside carbodiimide, uronium, and phosphonium systems.
Coupling additive / activation auxiliary	80029-43-2	H157386	1-Hydroxybenzotriazole Monohydrate	≥97%(T)	A classic coupling additive, commonly used together with DCC, DIC, EDC, and related reagents to improve the stability of activated intermediates and suppress racemization; an important component of traditional peptide coupling systems.
Coupling additive / racemization suppressor	3849-21-6	E138773	Ethyl (hydroxyimino)cyanoacetate	≥98%	A representative Oxyma-type additive, commonly used together with DIC, EDC, and related reagents; it can improve coupling efficiency and reduce racemization risk, making it a highly important auxiliary reagent in modern peptide coupling systems.

Table 4 | Common Neutral, Hydrophobic, and Aromatic Amino Acid Substrates (Free Form)

Category	CAS No.	Aladdin Cat. No.	Name	Grade or Purity	Product Features and Applications
Most fundamental amino acid (free form)	56-40-6	G432934	Glycine	UltraBio™, molecular biology grade, ultrapure, ≥99%(NT)	The simplest α-amino acid, and a classic substrate source for building Gly residues, establishing dipeptide/amidation model systems, and comparing different coupling conditions.
Simple aliphatic amino acid (free form)	56-41-7	A118860	L-Alanine	Animal-origin-free, USP, JP, Moligand™, Ph.Eur., for cell culture, ≥98.5%	Ala is one of the most fundamental aliphatic amino acids and is often used as a benchmark residue, model substrate, or source of sequence-simplification sites in peptide chemistry.
Hydrophobic aliphatic amino acid (free form)	61-90-5	L774643	L-Leucine	Animal-origin-free, USP, JP, Moligand™, Ph.Eur., for cell culture, ≥98.5%	A source of Leu residues, commonly used to construct hydrophobic peptide segments or as a model amino acid to study the effects of hydrophobic side chains on coupling and purification behavior; in routine peptide synthesis, its protected derivatives are more commonly used directly.
β-Branched hydrophobic amino acid (free form)	73-32-5	I115775	L-Isoleucine	Animal-origin-free, USP, JP, Moligand™, Ph.Eur., for cell culture, ≥98.5%	Ile is a source of β-branched hydrophobic residues and is suitable for studying how more sterically hindered amino acids affect coupling efficiency, sequence aggregation, and purification behavior.
β-Branched hydrophobic amino acid (free form)	72-18-4	V139523	L-Valine	Animal-origin-free, USP, JP, Moligand™, Ph.Eur., for cell culture, ≥98.5%	Val is a classic source of β-branched hydrophobic residues and is often used to examine the effect of steric hindrance on coupling efficiency and the tendency to form difficult sequences.
Secondary amino acid (free form)	147-85-3	P120032	L-Proline	Animal-origin-free, USP, Ph.Eur., for cell culture, ≥99%	Pro is a secondary amino acid whose residue conformation has a pronounced effect, making it an important amino acid source for studying peptide-chain turns, cis–trans isomerism, and specific coupling difficulties.
Aromatic hydrophobic amino acid (free form)	63-91-2	P110425	L-Phenylalanine	Animal-origin-free, USP, JP, Moligand™, Ph.Eur., for cell culture, ≥98.5%	Phe is a source of aromatic hydrophobic residues and is suitable for constructing hydrophobic peptide segments, sequences involving aromatic interactions, and studies on small-molecule–peptide recognition.
Phenolic hydroxyl aromatic amino acid (free form)	60-18-4	T115962	L-Tyrosine	Animal-origin-free, USP, JP, Moligand™, Ph.Eur., for cell culture, ≥99%	Tyr is a source of aromatic phenolic-hydroxyl residues and is suitable for studying peptide segments that combine aromaticity with modifiable side chains; in routine peptide synthesis, protection of the phenolic hydroxyl group is usually considered.
Aromatic heterocyclic amino acid (free form)	73-22-3	T118579	L-Tryptophan	Animal-origin-free, USP, JP, Moligand™, Ph.Eur., for cell culture, ≥99%	Trp is a source of aromatic heterocyclic residues and is commonly used to study peptide hydrophobicity, spectroscopic properties, and molecular recognition; compatibility of its indole side chain requires attention during synthesis and workup.
β-Hydroxy branched amino acid (free form)	72-19-5	T108222	L-Threonine	Animal-origin-free, USP, JP, Moligand™, Ph.Eur., for cell culture, ≥99%	Thr possesses both a β-branched framework and a hydroxyl-bearing side chain, and is often regarded as one of the more representative challenging residues in peptide coupling; side-chain protection is usually required before entering routine peptide synthesis.

Table 5 | Common Acidic, Basic, Polar, and Sulfur-Containing Amino Acid Substrates (Free Form)

Category	CAS No.	Aladdin Cat. No.	Name	Grade or Purity	Product Features and Applications
Acidic amino acid (free form)	56-84-8	L476204	L-Aspartic acid	UltraBio™, ultrapure, ≥99.5%(T)	A source of Asp residues, bearing an additional carboxylic-acid side chain, suitable for studying selectivity, protection requirements, and side-reaction control for polycarboxylic-acid substrates in amidation and peptide coupling.
Acidic amino acid (free form)	56-86-0	L1509602	L-Glutamic Acid Solution (0.2 mol/L, sterile)	Sterile-filtered, BioReagent, for cell culture, 0.2 mol/L	A source of acidic amino acids that can be used for Glu-residue studies, as a carboxylic-acid substrate, or as a component of culture systems; the free form is more suitable for substrate/formulation studies, whereas protected derivatives are more commonly used in routine peptide synthesis.
Amide-side-chain amino acid (free form)	70-47-3	L478521	L-Asparagine	Moligand™, BioReagent, for cell culture, for insect cell culture	A source of Asn residues, with an amide side chain, suitable for studying how polar amide side chains affect peptide solubility, coupling compatibility, and sequence properties.
Amide-side-chain amino acid (free form)	56-85-9	L1509609	L-Glutamine Solution (0.1 mol/L, Sterile)	Sterile-filtered, BioReagent, for cell culture, 0.1 mol/L	A source of Gln residues, suitable for substrate studies related to amide side chains or for use in culture systems; in routine peptide synthesis, it is usually introduced in the form of protected Gln derivatives.
Polar hydroxyl amino acid (free form)	56-45-1	L476400	L-Serine	Animal-origin-free, USP, Moligand™, Ph.Eur., for cell culture, ≥98.5%	Ser residues carry a hydroxyl group and are suitable for studying how polar side chains affect coupling compatibility, protection strategies, and the potential for subsequent modification; side-chain protection is usually required before peptide synthesis.
Sulfur-containing amino acid (free form)	52-90-4	L755721	L-Cysteine	UltraBio™, ≥98.5%(RT)	Cys contains a thiol group and is a highly important yet relatively sensitive residue source in peptide chemistry; it is commonly used to study how sulfur-containing side chains affect coupling, oxidative stability, and protection strategies.
Sulfur-containing amino acid (free form)	63-68-3	M101131	L-Methionine	Animal-origin-free, USP, JP, Moligand™, Ph.Eur., for cell culture, ≥99%	Met is a source of sulfur-containing hydrophobic residues and is suitable for studying how sulfur-containing side chains affect peptide hydrophobicity, oxidation sensitivity, and sequence behavior.
Basic guanidino amino acid (free form)	74-79-3	A118651	L-Arginine	Animal-origin-free, USP, Moligand™, Ph.Eur., for cell culture, ≥98.5%	Arg is a source of strongly basic residues and is suitable for studies on cationic peptides, binding-site peptide segments, and highly polar sequences; in routine peptide synthesis, its side chain usually requires dedicated protection.
Heterocyclic basic amino acid (free form)	71-00-1	H108261	L-Histidine	Animal-origin-free, USP, Moligand™, Ph.Eur., for cell culture	His contains an imidazole side chain and is a common residue source for metal-binding sites, catalytic sites, and pH-responsive peptide segments; in peptide synthesis, side-chain protection and sequence compatibility often need to be considered.
Basic diamino amino acid (free form)	56-87-1	L598932	L-Lysine	Moligand™, ≥98%, Metal＜500ppm	A source of Lys residues, containing both an α-amino group and an ε-amino group, commonly used to study selectivity among multiple amine sites, side-chain protection, and branched-peptide construction; orthogonal protection is usually required in routine peptide synthesis.

Note: The above are representative Aladdin products. For more product specifications, please refer to the product list at the end of the article or search on the Aladdin official website using the product name/CAS/catalog number.

References

1. Cao S, Guo H, Zhong Z, Chen D, Song W, Liu Y, Wan J-P. β-Acyloxyl alkenyl amide synthesis via multiple defluorination: α-Trifluoromethyl ketone-amine as synergystic peptide coupling reagent. Science Advances. 2025;11(43):eaea4120. doi:10.1126/sciadv.aea4120.

2. Valeur E, Bradley M. Amide bond formation: beyond the myth of coupling reagents. Chemical Society Reviews. 2009;38:606–631. doi:10.1039/B701677H.

3. Pattabiraman VR, Bode JW. Rethinking amide bond synthesis. Nature. 2011;480(7378):471–479. doi:10.1038/nature10702.

4. El-Faham A, Albericio F. Peptide coupling reagents, more than a letter soup. Chemical Reviews. 2011;111(11):6557–6602. doi:10.1021/cr100048w.

5. de Figueiredo RM, Suppo J-S, Campagne J-M. Nonclassical Routes for Amide Bond Formation. Chemical Reviews. 2016;116(19):12029–12122. doi:10.1021/acs.chemrev.6b00237.

6. Ferrazzano L, Catani M, Cavazzini A, Martelli G, Corbisiero D, Cantelmi P, Fantoni T, Mattellone A, De Luca C, Felletti S, Cabri W, Tolomelli A. Sustainability in peptide chemistry: current synthesis and purification technologies and future challenges. Green Chemistry. 2022;24(3):975–1020. doi:10.1039/D1GC04387K.

7. Lubberink M, Finnigan W, Flitsch SL. Biocatalytic amide bond formation. Green Chemistry. 2023;25(8):2958–2970. doi:10.1039/D3GC00456B.

For more related articles, see below:

A Complete Guide to Choosing Resins for SPPS (Solid-Phase Peptide Synthesis): Fmoc/Boc Routes, C-Terminal Acid/Amide, and a Key-Parameter Navigator

Greener Methods: Catalytic Amide Bond Formation

Suitable for peptide synthesis

Peptide Basics