This new reagent makes the synthesis of amides and esters more efficient.

In organic synthesis and medicinal chemistry, amide and ester bonds are almost indispensable, from small fine chemicals and common drug molecules to large peptides. To construct these fundamental structures more efficiently and meet increasingly sophisticated synthetic demands , chemists are constantly developing new, highly efficient coupling reagents. Recently, Sureshbabu's team reported a novel coupling reagent—4-acetamidophenylbis(trifluoromethanesulfonyl)imide (AITF)—providing a highly efficient and mild new route for the synthesis of amides and esters.

I. Introduction to AITF

AITF (structure shown in Figure 1 below) is a white crystalline solid that can be stored for a long time under normal conditions. Differential scanning calorimetry (DSC) analysis shows that its exothermic decomposition temperature is above 159℃, indicating high thermal stability.

Figure 1 AITF structure

Its mechanism of action is as follows: Under alkaline conditions, carboxylic acid forms a carboxylate anion, which attacks the electrophilic sulfur center of AITF to generate an acyl trifluoromethanesulfonic anhydride active intermediate. Subsequently, amine or alcohol acts as a nucleophile to attack this intermediate, eventually forming an amide or ester, with trifluoromethanesulfonate as a byproduct (Figure 2).

Figure 2. Mechanism of action of AITF

II. Wide substrate applicability and chiral retention

Sureshbabu team optimized the reaction conditions to achieve the construction of amide and ester bonds by activating carboxylic acids with AITF at room temperature using acetonitrile as the solvent and DIPEA as the base. This system exhibits broad substrate applicability and good functional group compatibility.

1. Conventional amide synthesis

AITF is applicable to the amidation reaction of common carboxylic acids and amines (Figure 3). Aromatic acids, heterocyclic acids, and alkyl carboxylic acids, whether electron-donating (e.g., OMe) or electron-withdrawing (e.g., NO₂ ) , can react efficiently with various aromatic amines and aliphatic amines, yielding the corresponding amides in 84%-95% yield. Furthermore, sterically hindered tert-butylamines and secondary amines can also participate in the reaction smoothly.

Figure 3 AITF-mediated conventional amide reaction

2. Peptide synthesis

AITF also performed exceptionally well in peptide bond construction. Researchers tested a series of amino acids (including aliphatic , aromatic, and acid-basic side-chain amino acids) with common protecting groups such as Fmoc, Cbz, or Boc, and all of them could be successfully coupled with various amino acid esters to obtain the corresponding dipeptide products in high yield (81%-93%), demonstrating good compatibility (Figure 4).

Figure 4 AITF-mediated dipeptide synthesis

Gram-scale experiments further validated the practicality of this method: the gram-scale coupling reaction of ZL-Phe-Ala-OMe still yielded dipeptide products in yields exceeding 80%. Furthermore, this method was successfully applied to peptide fragment condensation, synthesizing tripeptides and tetrapeptides in good yields , demonstrating its potential in oligopeptide synthesis .

3. Esterification reaction

Besides amides, AITFs can also efficiently catalyze the formation of ester bonds. Various protected amino acids or aromatic acids can react with phenols, alcohols, and even N-hydroxysuccinimide (NHS) to give the corresponding esters in moderate to excellent yields (Figure 5).

Figure 5 AITF-mediated esterification reaction

For condensation reagents, racemization inhibition is also a key evaluation indicator. The research team selected easily racemic phenylglycine (Phg) as the test substrate and confirmed through chiral HPLC analysis that the peptide product synthesized under optimal conditions completely maintained chiral purity, with no racemization detected. Similarly, excellent chiral retention was also observed in esterification reactions.

III. Summary and Outlook

AITF is a highly efficient coupling reagent that is easy to store and safe to use. It can efficiently promote the synthesis of amides, peptides, and esters under mild conditions, exhibiting broad substrate applicability, excellent functional group compatibility, and outstanding racemic inhibition capabilities. However, existing literature reports post-processing steps all employ column chromatography purification, which is cumbersome and time-consuming. Furthermore, the reagent cannot be recovered and reused, resulting in low atom economy.

Overall, this research provides a reliable and practical new tool for organic synthesis, particularly in medicinal chemistry and peptide chemistry, and is expected to have wide applications in the construction of complex molecules.

Company Introduction:

Suzhou Haofan Biotech Co., Ltd. (Stock Code: 301393.SZ), founded in 2003 and headquartered in Suzhou High-tech Zone, is a national high-tech enterprise providing specialty raw materials to pharmaceutical R&D and manufacturing companies worldwide. Its products are mainly used in the synthesis of peptides, nucleotides, and pharmaceuticals, covering a wide range of products including condensing agents for specialty amide bonds, protective agents, linking agents, protein cross-linking agents for antibody-drug conjugates, molecular building blocks, liposomes, and phosphorus reagents. To date, it has cumulatively developed and produced over 1,500 different products.

After more than two decades of unremitting efforts and accumulation, Haofan Biotech has continuously cultivated its expertise in the global peptide synthesis reagent field. It has now developed into a leading enterprise with extensive customized product coverage and significant advantages in large-scale production, capable of meeting the specific needs of various customers. We sincerely invite customers interested in this product to contact us to learn more about product details and explore cooperation opportunities .

References:

[1] AITF (4-acetamidophenyl triflimide) mediated synthesis of amides, peptides and esters.

DOI: 10.1039/d3ob01351k