Study on the Application of Deep Eutectic Solvents in Green Peptide Synthesis and Deprotection

Study on the Application of Deep Eutectic Solvents in Green Peptide Synthesis and Deprotection

Peptides, due to their excellent biocompatibility and structural diversity, are widely used in biomedical fields such as drug delivery and tissue engineering. NCA ring-opening polymerization is a common method for synthesizing peptide polymers; however, NCA monomers are extremely sensitive to moisture, prone to degradation, chain termination, and other side reactions, requiring strictly anhydrous operations, which limits large-scale production. Additionally, tert-butyl groups are commonly used as protecting groups in peptide synthesis, and traditional deprotection methods rely on strong acids and toxic reagents, making them environmentally unfriendly. To address these issues, Jia Yao from Tianjin University of Technology carried out research on green peptide synthesis and deprotection mediated by deep eutectic solvents, providing new approaches for efficient and eco-friendly peptide preparation.

The study first focused on solving the moisture sensitivity problem of NCA ring-opening polymerization. By screening 18 types of hydrophobic combinations, a hydrophobic deep eutectic solvent [Camphor][Decanoic acid] was successfully developed. This solvent features strong hydrophobicity and high thermal stability, with a saturated water content of only 0.023%, effectively preventing water from interfering with NCA monomers and enabling stable polymerization under open-air conditions. Experiments showed that the polymerization reaction proceeded normally even under high humidity and direct water addition conditions, with over 99% of NCA monomers remaining, far superior to traditional DMF solvents. Moreover, the system can withstand high temperatures of 85°C, significantly enhancing the polymerization rate, with an apparent activation energy of only 27.7 kJ/mol, while the product retains α-helical secondary structure with no racemization observed.

This hydrophobic deep eutectic solvent has good universality, compatible with various initiators such as benzylamine, triethylamine, and LiHMDS, enabling ring-opening polymerization of seven common NCA monomers including alanine, phenylalanine, and lysine, producing polymers with narrow molecular weight distribution. Additionally, multi-step feeding allowed for the synthesis of antimicrobial peptide polymers containing 8 alternating blocks, exhibiting high antibacterial activity against Escherichia coli and Staphylococcus aureus while maintaining good biocompatibility, providing a new pathway for functional peptide design and synthesis. The system also allows scale-up to tens of grams, achieving a yield of 75%, demonstrating its industrial production potential.

In the peptide deprotection stage, the study developed an acidic deep eutectic solvent [Camphor][Formic acid] to achieve mild, efficient, and selective removal of tert-butyl protecting groups. This solvent is gently acidic without requiring corrosive reagents such as trifluoroacetic acid. At 70°C for 18 hours, the deprotection rate of poly(γ-benzyl-L-glutamate tert-butyl ester) reached 93.8%; when the temperature was raised to 120°C, the reaction time shortened to 3 hours and the deprotection rate reached 100%, with the product structure intact and no chain cleavage or racemization.

Selectivity tests confirmed that the system removes only tert-butyl protecting groups without affecting benzyl or Fmoc groups, demonstrating excellent selectivity. Furthermore, the method is highly versatile and can achieve tert-butyl deprotection of polymers such as poly(tert-butyl acrylate) and poly(tert-butyl methacrylate), as well as various small molecule derivatives, providing high product purity and simple post-processing. Compared to traditional methods, this deprotection system is green, non-toxic, easy to operate, and cost-effective, making it an ideal alternative to conventional strong acid deprotection processes.

The two types of deep eutectic solvents developed in this study respectively address the industry pain points of NCA ring-opening polymerization being water-sensitive and severe contamination from tert-butyl deprotection, achieving greener and more efficient peptide synthesis and deprotection. The [camphor][decanoic acid] solvent overcomes the limitations of anhydrous operations and simplifies the production process; the [camphor][formic acid] solvent enables mild and selective deprotection, reducing environmental hazards. These findings not only improve the theory of green peptide synthesis but also provide technical support for the industrial production of peptide polymers, which is of great significance for promoting the sustainable development of the biomedical materials field.

Reference：Yao, J. Green and efficient peptide synthesis and deprotection in deep eutectic solvents[D]. Tianjin Polytechnic University, 2025.

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