AITF-Mediated Carboxylic Acid Activation for the Synthesis of Amides, Peptides, and Esters: Activation Mechanism and Applicable Scenarios

1. AITF-Mediated Carboxylic Acid Coupling Reactions

1.1 Research Sources Underlying This Article

Amide bonds, peptide bonds, and ester bonds are widely present in drug molecules, peptides, natural products, fine chemicals, and functional materials. For synthetic chemists, the key question in these reactions is usually not simply “whether the target bond can be formed,” but whether the reaction is sufficiently mild, whether the substrates are compatible, whether chirality is retained, and whether the work-up is manageable.

In 2023, Sureshbabu and co-workers published a study in Organic & Biomolecular Chemistry, a journal of the Royal Society of Chemistry (RSC), reporting 4-acetamidophenyl triflimide, namely N-(4-acetamidophenyl)bis(trifluoromethanesulfonyl)imide, abbreviated as AITF. AITF is an aryl triflimide-type carboxylic acid activating reagent. The study showed that AITF can serve as a crystalline and stable carboxylic acid-activating coupling reagent for the synthesis of amides, peptides, and esters under the reported conditions.

Based on the results of that paper and related review literature, this article focuses on why AITF can promote carboxylic acid coupling reactions and in which synthetic scenarios it may be considered as an option for condition screening.

1.2 Efficiency Limitations of Direct Carboxylic Acid Reactions

Carboxylic acids are common, readily available, and stable synthetic starting materials. However, when carboxylic acids react directly with amines or alcohols, the reaction is usually limited by insufficient reactivity. This is because, although the carbonyl group of a carboxylic acid is electrophilic, the hydroxyl group of the carboxylic acid is not a good leaving group. When an amine or alcohol directly attacks a carboxylic acid, relatively forcing conditions are often required, and the reaction can be affected by substrate steric hindrance, acid–base sensitivity, functional group interference, and side reactions.

This issue is even more pronounced in peptide synthesis. After the carboxyl group of an amino acid is activated, the α-stereocenter may undergo racemization. Once peptide impurities with undesired configurations are formed, subsequent separation and quality control become significantly more difficult. Therefore, peptide bond formation requires not only high conversion but also good retention of chirality.

1.3 The Essential Role of Coupling Reagents Is Carboxylic Acid Activation

In amidation, peptide coupling, and esterification reactions, the core function of a coupling reagent is to convert a carboxylic acid into a more reactive acylating intermediate. This intermediate then reacts with amines, amino acid esters, alcohols, or phenolic nucleophiles to form C(O)–N or C(O)–O bonds.

To evaluate whether a carboxylic acid-activating coupling reagent has practical value, the following factors should be considered:

Evaluation Dimension	Practical Significance for Synthetic Research
Activation efficiency	Whether the carboxylic acid can be rapidly converted into an effective acylating intermediate
Reaction conditions	Whether the reaction can proceed under relatively mild conditions
Substrate compatibility	Whether it is suitable for screening substrates containing protecting groups, heterocycles, or sensitive functional groups
Chirality retention	Whether it can reduce the risk of racemization in amino acid and peptide synthesis
Work-up feasibility	Whether it facilitates purification, scale-up, and process optimization

2. Why AITF Can Promote the Formation of Amides, Peptides, and Esters

2.1 Structural Features of AITF

AITF belongs to the class of aryl triflimide reagents. Its structure contains a bis(trifluoromethanesulfonyl)imide-related fragment, which has strong electron-withdrawing properties and can provide a good leaving group during activation. These structural features enable AITF to react with carboxylates, converting ordinary carboxylic acids into more reactive acylating intermediates.

In the literature report, AITF is described as a crystalline solid with good thermal stability. Differential scanning calorimetry (DSC) showed that its exothermic decomposition temperature is above 159 °C. This data indicates that AITF offers a certain degree of convenience in routine laboratory handling, but it does not mean that the reagent is “safe to use” or “free of safety risks.” In practical use, its safety should still be assessed together with reagent safety data, addition sequence, reaction exotherm, base loading, solvent system, and scale-up conditions.

2.2 Reaction Pathway of AITF-Mediated Carboxylic Acid Activation

The key to AITF-promoted formation of amides, peptides, and esters is the prior activation of the carboxylic acid, rather than direct catalysis of bond formation. According to the mechanism proposed in the literature, the process can be summarized in three steps.

Step 1: The carboxylic acid forms a carboxylate under the action of a base.

Commonly used bases include N,N-diisopropylethylamine, abbreviated as DIPEA. After deprotonation, the carboxylic acid forms a carboxylate with enhanced nucleophilicity.

Step 2: The carboxylate attacks the electrophilic sulfur center of AITF.

The carboxylate reacts with AITF to generate a highly reactive acyl triflic anhydride-type intermediate. This intermediate undergoes acyl transfer more readily than the original carboxylic acid.

Step 3: An amine, alcohol, or amino acid ester attacks the activated intermediate.

The nucleophile attacks the activated acyl intermediate, and the target amide, peptide, or ester product is formed through an addition–elimination process.

2.3 Practical Significance of the AITF Activation Mode

The practical significance of AITF is mainly reflected in three aspects.

① Carboxylic acids can be preactivated within a relatively short time.

In the literature, AITF is used for carboxylic acid preactivation in acetonitrile (MeCN) with DIPEA, followed by the addition of an amine, alcohol, or amino acid ester. This operational mode is useful for shortening the condition-screening cycle.

② The reaction can proceed under relatively mild conditions.

Under the reported conditions, AITF-mediated amidation, peptide coupling, and esterification reactions can be achieved under relatively mild conditions. For protected amino acids, heterocycle-containing substrates, or substrates sensitive to strong acids, strong bases, or high temperatures, AITF can be considered as a candidate for mild coupling conditions.

③ The activated intermediate can be generated and consumed in situ.

Highly reactive acylating intermediates usually do not need to be isolated separately; instead, they continue to react with nucleophiles in the reaction system. This approach can reduce operational complexity and minimize the uncertainty associated with isolating highly reactive intermediates.

3. Application Value of AITF in Amidation Reactions

3.1 Amidation Reactions Are Not Evaluated Only by Yield

Amide bonds are highly important structural units in medicinal chemistry and fine synthesis. For R&D researchers, the evaluation criteria for amidation reactions are not limited to product yield. Other key considerations include whether the substrate can be readily converted, whether heterocycles and protecting groups are compatible, whether side reactions are reduced, and whether the product is easy to purify.

Common amidation reagents include 1-[bis(dimethylamino)methylene]-1H-1,2,3-triazolo[4,5-b]pyridinium 3-oxide hexafluorophosphate, abbreviated as HATU; O-(benzotriazol-1-yl)-N,N,N',N'-tetramethyluronium hexafluorophosphate, abbreviated as HBTU; N,N'-dicyclohexylcarbodiimide, abbreviated as DCC; N,N'-diisopropylcarbodiimide, abbreviated as DIC; 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide, abbreviated as EDC; and carbonyldiimidazole, abbreviated as CDI.

The significance of AITF lies in its use as a comparable coupling reagent for screening when conventional systems show insufficient reaction efficiency, unsatisfactory substrate conversion, or when mild carboxylic acid activation conditions are required.

3.2 Amidation Scenarios Where AITF Screening May Be Considered

In the 2023 paper, AITF was applied to amidation reactions involving various carboxylic acid and amine substrates, with the reported examples showing good to excellent yields. From an application perspective, the greater value of AITF lies in its provision of a carboxylic acid activation mode that differs from those of carbodiimides, uronium salts, and CDI.

Reaction Situation	Consideration for Screening AITF
Insufficient reactivity of the carboxylic acid substrate	Improving acyl transfer ability through formation of an activated acyl intermediate
Weak nucleophilicity of the amine substrate	Increasing the likelihood of the desired amidation reaction
Substrates containing heterocycles or protecting groups	Reducing side reactions associated with harsh reaction conditions by using relatively mild conditions
Unstable results with conventional coupling systems	Providing an alternative carboxylic acid activation pathway for comparative screening

It should be noted that the substrate scope reported in the literature cannot be directly extrapolated to all systems. For highly hindered carboxylic acids, weakly nucleophilic amines, or complex molecules containing multiple nucleophilic sites, small-scale testing is still required to confirm conversion, selectivity, and by-product formation.

4. Significance of AITF in Peptide Bond Formation

4.1 Why Peptide Bond Synthesis Places Greater Emphasis on Racemization Control

A peptide bond is essentially an amide bond, but peptide synthesis is more sensitive to reaction conditions. Amino acids usually contain both amino and carboxyl groups, so protecting groups are required to control the reaction site. At the same time, after the carboxyl terminus is activated, the α-stereocenter may undergo racemization under basic conditions or in the presence of highly reactive intermediates.

Racemization directly affects the quality of peptide products. Peptide impurities with undesired configurations are structurally similar to the target product, making conventional separation difficult and potentially affecting subsequent activity evaluation. Therefore, the value of a peptide coupling reagent depends not only on reaction conversion but also on its ability to retain chirality under specific substrate and reaction conditions.

4.2 Application Features of AITF in the Coupling of Protected Amino Acids

In the literature, AITF was used in coupling reactions of various protected amino acids. The relevant protecting groups include 9-fluorenylmethoxycarbonyl, abbreviated as Fmoc; benzyloxycarbonyl, abbreviated as Cbz; and tert-butoxycarbonyl, abbreviated as Boc.

Under the reported conditions, AITF can be used for the synthesis of dipeptides, oligopeptides, and selected peptide fragment condensations. Its value in peptide synthesis can be understood from the following three aspects.

① It can serve as a candidate reagent for activating the carboxyl group of protected amino acids.

Protected amino acids may be sensitive to strong acids, strong bases, or high-temperature conditions. Through in situ carboxylic acid activation, AITF provides a relatively mild condition option for protected amino acid coupling.

② It shows good chirality retention in the tested systems.

In the 2023 paper, readily racemizable substrates were examined, and no obvious racemization was observed under the tested conditions. This result indicates that AITF has potential for low-racemization applications under specific peptide coupling conditions.

③ It can be used for exploring peptide fragment coupling conditions.

Peptide fragment coupling is usually more challenging than the coupling of individual amino acids because of greater steric hindrance, more complex solubility behavior, and stronger effects from local conformation. The reported use of AITF in peptide fragment condensation suggests that it can serve as a candidate screening reagent for peptide fragment ligation reactions.

5. Application of AITF in Esterification and Active Ester Preparation

5.1 Esterification Reactions Also Rely on Carboxylic Acid Activation

When carboxylic acids form esters with alcohols or phenols, the insufficient intrinsic reactivity of carboxylic acids must also be overcome. Traditional acid-catalyzed esterification is often limited by equilibrium and may not be suitable for acid-sensitive substrates. By activating the carboxylic acid with a coupling reagent, C(O)–O bond formation can be promoted under relatively mild conditions. In AITF-mediated esterification reactions, the carboxylic acid is first converted into a highly reactive acyl intermediate, which is then attacked by an alcohol or phenolic nucleophile to generate the ester product.

5.2 Practical Significance of Active Ester Preparation

In addition to ordinary esterification, the literature also reports that AITF can be used to prepare N-hydroxysuccinimide esters, abbreviated as NHS esters. NHS esters are commonly used active esters that can further react with amines to form amide bonds, and they have application value in bioconjugation, pharmaceutical intermediates, and functional molecule modification. The value of AITF in esterification and active ester preparation can be summarized as follows:

Application Need	Potential Value
Mild preparation of ordinary esters	Can serve as a candidate option for avoiding strong acids or high-temperature conditions
Preparation of NHS active esters	Provides intermediates for subsequent amine coupling, labeling, or molecular modification
Handling sensitive carboxylic acid substrates	Reduces reaction severity through in situ activation
Comparison with traditional esterification methods	Can serve as an alternative activation system in condition screening

For sterically hindered alcohols, weakly nucleophilic phenols, or substrates containing multiple reactive sites, small-scale condition screening should be prioritized, with particular attention to conversion, selectivity, and by-product formation.

6. Applicable Scenarios and Screening Recommendations for AITF

6.1 Reaction Types That May Be Prioritized

Reaction Issue	Reason for Screening AITF
Slow reaction between carboxylic acids and amines	AITF can improve acyl transfer ability through carboxylic acid activation
Unsatisfactory results with conventional coupling reagents	Provides an activation pathway different from those of carbodiimides, uronium salts, and CDI
Substrates containing protected amino acids	Can serve as a candidate for relatively mild peptide coupling conditions
Need for racemization control	Shows good chirality retention under the literature-tested conditions
Need to prepare active esters	Can be used for screening the preparation of NHS esters and related intermediates
Reactions unsuitable for high-temperature or strongly acidic conditions	The in situ activation pathway helps reduce the severity of reaction conditions

6.2 Factors Requiring Careful Evaluation

Although AITF shows good application potential under the reported conditions, the following factors should still be considered in practical use.

① Work-up methods still require optimization.

Many products in the literature rely on column chromatography for purification. For small-scale research reactions, this approach is acceptable. However, for gram-scale or larger-scale preparation, it is necessary to further develop purification methods more suitable for scale-up, such as crystallization, extraction, washing, trituration, or salting-out.

② The reagent is not recoverable, and atom economy is limited.

AITF participates in carboxylic acid activation as a stoichiometric coupling reagent and generates corresponding by-products. If the goal is low-cost, low-waste, or green process development, the reagent loading, removal of by-products, waste-liquid treatment, and overall material cost should be comprehensively evaluated.

③ Substrate applicability cannot be extrapolated without limitation.

The high yields and low racemization reported in the literature were obtained with specific substrates and reaction conditions. For highly hindered carboxylic acids, highly hindered amines, weakly nucleophilic alcohols, acid- or base-sensitive substrates, substrates containing multiple nucleophilic sites, or complex natural product fragments, experimental validation is still required.

④ Thermal stability is not equivalent to scale-up safety.

The crystalline stability and thermal stability of AITF indicate that it offers a certain degree of operational convenience. However, when used on scale, reaction exotherm, addition sequence, local concentration, solvent selection, and by-product handling still require careful attention.

7. Representative Chemicals Related to Carboxylic Acid Activation and Coupling Reactions

Table 1. Reaction Solvents and Basic Auxiliary Reagents

Category	CAS No.	Aladdin Cat. No.	Name	Specification or Purity	Product Features and Applications
Organic base	109-02-4	M104644	N-Methylmorpholine	For protein sequencing, ≥99.8% (GC)	Used for screening basic auxiliary conditions in protected amino acid coupling, carboxylic acid activation, and peptide bond formation reactions
Organic base	121-44-8	T431607	Triethylamine	For protein sequencing, ≥99.5% (GC), ampoule	Used for acid scavenging and basicity adjustment in amidation, esterification, and protecting group introduction reactions
Reaction solvent	109-99-9	T120775	Tetrahydrofuran (THF)	Anhydrous grade, ≥99.9%, containing 250 ppm BHT as stabilizer	Used for screening anhydrous reaction media in carboxylic acid activation, amidation, and esterification reactions
Reaction solvent	75-05-8	A1521124	Acetonitrile (ACN)	Extra-dry grade, ≥99.9%, water ≤30 ppm	Used in AITF-mediated carboxylic acid activation, amidation, peptide coupling, and esterification reaction systems
Reaction solvent	75-09-2	D433565	Dichloromethane	Anhydrous grade, ≥99.8%, containing 40–150 ppm pentene as stabilizer	Used for screening anhydrous solvents in acylation, esterification, protecting group introduction, and coupling reactions
Reaction solvent	68-12-2	D119450	N,N-Dimethylformamide (DMF)	Anhydrous grade, ≥99.8%	Used in peptide coupling, amidation, and carboxylic acid activation reactions involving polar substrates
Reaction solvent	872-50-4	M119668	N-Methyl-2-pyrrolidone (NMP)	Anhydrous grade, ≥99.5%	Used in solid-phase peptide synthesis, difficult couplings, and protected amino acid condensation reactions
Organic base	7087-68-5	N433364	N,N-Diisopropylethylamine solution	Suitable for peptide synthesis, ~2 M in 1-methyl-2-pyrrolidinone	Used for basic assistance and acid scavenging in carboxylic acid preactivation, peptide coupling, and amidation reactions
Sterically hindered organic base	108-75-8	T108942	2,4,6-Trimethylpyridine	≥99%	Used for coupling of acid-sensitive substrates, acylation reactions, and screening conditions involving sterically hindered bases
Acylation auxiliary reagent	1122-58-3	D109207	4-Dimethylaminopyridine	≥99%	Used to promote acyl transfer in esterification, acylation, and carboxylic acid derivatization reactions

Table 2. Carboxylic Acid Activation and Coupling Reagents

Category	CAS No.	Aladdin Cat. No.	Name	Specification or Purity	Product Features and Applications
Carbodiimide coupling reagent	538-75-0	D106074	N,N′-Dicyclohexylcarbodiimide (DCC)	≥99%	Used for condition screening in carboxylic acid activation, amidation, esterification, and peptide coupling reactions
Carbodiimide coupling reagent	693-13-0	N420184	N,N′-Diisopropylcarbodiimide (DIC)	≥98.5%	Used in solution-phase and solid-phase peptide coupling, protected amino acid condensation, and amide bond formation
Carbonyl activation reagent	530-62-1	C109315	N,N′-Carbonyldiimidazole (CDI)	≥99%	Used for carboxylic acid activation to generate acyl imidazole intermediates, suitable for amide, ester, and intermediate preparation
Uronium salt coupling reagent	148893-10-1	H109327	O-(7-Azabenzotriazol-1-yl)-N,N,N′,N′-tetramethyluronium hexafluorophosphate (HATU)	≥99%	Used for protected amino acid coupling, amidation of sterically hindered substrates, and screening of peptide bond formation reactions
Uronium salt coupling reagent	94790-37-1	H106174	O-(Benzotriazol-1-yl)-N,N,N′,N′-tetramethyluronium hexafluorophosphate (HBTU)	≥99%	Used in peptide coupling and amidation reactions, participating in the formation of activated ester-type intermediates
Carbodiimide coupling reagent	25952-53-8	E106172	1-Ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride	≥98%	Used for amidation, bioconjugation, and active ester preparation in aqueous or mixed-solvent systems
Phosphonium salt coupling reagent	128625-52-5	P109336	1H-Benzotriazol-1-yloxytris(pyrrolidino)phosphonium hexafluorophosphate	≥98%	Used in protected amino acid condensation, peptide fragment coupling, and amide bond formation
Benzotriazine coupling reagent	165534-43-0	D100524	3-(Diethoxyphosphoryloxy)-1,2,3-benzotriazin-4(3H)-one (DEPBT)	≥98%	Used for peptide coupling, amidation reactions, and condition screening for chiral substrate condensation
Uronium salt coupling reagent	330645-87-9	C106175	O-(6-Chlorobenzotriazol-1-yl)-N,N,N′,N′-tetramethyluronium hexafluorophosphate	≥98%	Used for protected amino acid coupling, amidation of sterically hindered substrates, and peptide bond formation reactions
Uronium salt coupling reagent	1075198-30-9	C340003	COMU	≥98%	Used in peptide coupling and amidation reactions, suitable for screening low-racemization conditions
Uronium salt coupling reagent	125700-67-6	T109338	O-(Benzotriazol-1-yl)-N,N,N′,N′-tetramethyluronium tetrafluoroborate	≥98%	Used for protected amino acid coupling, amide bond formation, and carboxylic acid activation reaction screening
Phosphonium salt coupling reagent	56602-33-6	B106161	Castro’s reagent (BOP)	≥98%	Used in peptide coupling and amidation reactions, and can serve as a reference condition for phosphonium salt-mediated condensation
Uronium salt coupling reagent	105832-38-0	T106185	O-(N-Succinimidyl)-N,N,N′,N′-tetramethyluronium tetrafluoroborate (TSTU)	≥97%	Used in active ester preparation, amidation reactions, and carboxylic acid derivatization studies

Table 3. Coupling Additives and Reagents for Active Ester Preparation

Category	CAS No.	Aladdin Cat. No.	Name	Specification or Purity	Product Features and Applications
Reagent for active ester preparation	100-02-7	P572406	p-Nitrophenol	≥99%, contains ~3% water	Used for preparing p-nitrophenyl ester intermediates, supporting research on acyl transfer and active ester reactions
Coupling additive	39968-33-7	H109328	1-Hydroxy-7-azabenzotriazole (HOAt)	≥99%	Used in peptide coupling and carboxylic acid activation systems, participating in activated ester formation and assisting in racemization control
Coupling additive	2592-95-2	H684271	1-Hydroxybenzotriazole (HOBt)	≥99%	Used in carbodiimide coupling systems to assist in activated ester formation and improve peptide coupling performance
Reagent for active ester preparation	771-61-9	P106717	Pentafluorophenol	≥99%	Used for preparing pentafluorophenyl active esters, suitable for research on intermediates in amidation and peptide fragment coupling
Coupling additive	3849-21-6	E138773	Ethyl 2-cyano-2-(hydroxyimino)acetate	≥98%	Used in carbodiimide-based peptide coupling systems to assist condensation reactions and control racemization
Coupling additive	26198-19-6	C109318	6-Chloro-1-hydroxybenzotriazole	≥98%	Used in protected amino acid coupling systems, participating in activated ester formation and amide bond construction
Reagent for active ester preparation	6066-82-6	H109330	N-Hydroxysuccinimide (NHS)	≥98%	Used to convert carboxylic acids into succinimidyl active esters, suitable for subsequent amine coupling reactions
Water-soluble reagent for active ester preparation	106627-54-7	H109337	N-Hydroxysulfosuccinimide sodium salt (Sulfo-NHS)	≥98%	Used for preparing water-soluble succinimidyl active esters and for carboxylic acid activation reactions related to bioconjugation
Coupling additive	123333-53-9	H106176	1-Hydroxybenzotriazole monohydrate	≥97%	Used in carbodiimide-based amidation and peptide coupling systems to assist in the formation of activated ester intermediates

Table 4. Protecting Group Introduction Reagents and Protected Amino Acids

Category	CAS No.	Aladdin Cat. No.	Name	Specification or Purity	Product Features and Applications
Protecting group introduction reagent	28920-43-6	F106533	9-Fluorenylmethyl chloroformate	≥98%	Used for protection of amino acids and amine substrates, supporting the preparation of protected amino acid coupling substrates
Protecting group introduction reagent	24424-99-5	D106159	Di-tert-butyl dicarbonate	≥99%	Used for amino group protection and preparation of protected amino acids, supporting pretreatment of peptide coupling substrates
Protected amino acid	15761-38-3	B109000	Boc-L-alanine	≥98%	Used in peptide bond formation, protected amino acid condensation, and carboxylic acid activation/coupling studies
Protected amino acid	35661-39-3	F105469	Fmoc-L-alanine	≥98%	Used in peptide synthesis and protected amino acid coupling reactions, suitable for screening peptide bond formation conditions
Protected amino acid	35661-40-6	F105472	Fmoc-L-phenylalanine	≥98%	Used for introducing hydrophobic amino acid fragments, peptide coupling, and chirality retention studies
Protected amino acid	29022-11-5	F103019	Fmoc-glycine	≥98%	Used in peptide chain elongation, protected amino acid condensation, and amide bond formation studies
Protected amino acid	1161-13-3	C108998	N-Benzyloxycarbonyl-L-phenylalanine	≥98%	Used for protected amino acid coupling, peptide fragment synthesis, and carboxylic acid activation reaction screening
Protecting group introduction reagent	501-53-1	B105737	Benzyl chloroformate	≥96%, contains 0.1% sodium carbonate as stabilizer	Used for amino group protection and preparation of benzyloxycarbonyl-protected amino acids, supporting the synthesis of peptide coupling substrates

Table 5. Triflimide-Related Reagents

Category	CAS No.	Aladdin Cat. No.	Name	Specification or Purity	Product Features and Applications
Triflimide-type reagent	145100-51-2	C121606	N-(5-Chloro-2-pyridyl)bis(trifluoromethanesulfonyl)imide	≥99%	Used in triflylation and activation reaction studies, and relevant to understanding the structural type of AITF and carboxylic acid activation
Triflimide-type reagent	37595-74-7	P107033	N-Phenylbis(trifluoromethanesulfonyl)imide	≥98%	Used in triflylation reactions and related activation systems, and can serve as an extended product related to AITF-type reagents
Triflimide-type reagent	82113-65-3	B106753	Bis(trifluoromethanesulfonyl)imide	≥95%	Used in studies of triflimide-related reactions and for understanding the structures of carboxylic acid activating reagents and method development

Note: The products listed above are representative Aladdin products related to scientific research and formulation research. For more information on product specifications, grades, and COA information, please search by “product name/CAS/catalog number” on the Aladdin website.

References

[1] E. Chetankumar, S. Bharamawadeyar, C. Srinivasulu, V. V. Sureshbabu. AITF (4-acetamidophenyl triflimide) mediated synthesis of amides, peptides and esters. Organic & Biomolecular Chemistry, 2023, 21, 8875–8882. DOI: 10.1039/D3OB01351K.

[2] Daniel E. Bonn, William D. G. Brittain. Recent developments in the use of fluorinated esters as activated intermediates in organic synthesis. Chemical Communications, 2025, 61, 17060–17071. DOI: 10.1039/D5CC04851F.

[3] American Chemical Society Green Chemistry Institute Pharmaceutical Roundtable. Amidation. Synthetic Toolbox, American Chemical Society.

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