Peptide Synthesis Using Weaker Acids for High Purity
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Solution Overview
Problem
Existing methods for synthesizing peptides with N-alkylated amino acids face challenges such as side reactions during cleavage and deprotection steps using TFA, leading to low purity and yield, and difficulties in industrial-scale synthesis.
Innovation Solution
The use of weaker acids like 2,2,2-trifluoroethanol (TFE) or hexafluoro-2-propanol (HFIP) instead of TFA for cleavage from the solid phase, along with the selection of protecting groups that are not deprotected under basic conditions but can be deprotected under weakly acidic conditions, to minimize side reactions and improve peptide solubility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If TFA is used for cleavage from solid phase and deprotection of side-chain functional groups, then cleavage and deprotection can be performed simultaneously under mild conditions, but side reactions such as acid hydrolysis via oxazolonium and N- to O-acyl shift occur, resulting in low purity and yield
Solution Approach 1:
The patent divides the simultaneous cleavage and deprotection process into two separate sequential steps: first performing cleavage from the solid phase using TFA, then performing deprotection of side-chain functional groups using a different acid system. This segmentation prevents the side reactions that occur when both processes happen simultaneously under TFA conditions, thereby improving peptide purity while maintaining operational feasibility.
Solution Approach 2:
The patent introduces an intermediary protecting group strategy where side-chain functional groups are protected with groups that are stable to TFA during the cleavage step, but can be subsequently removed under milder acidic conditions. This intermediary protection approach prevents N- to O-acyl shift and hydrolysis during cleavage, allowing high purity peptide synthesis while enabling subsequent deprotection.
2Adaptability or versatility
If conventional Fmoc method is used for synthesizing N-alkylated peptides, then standard peptide synthesis procedures can be applied, but peptide chain cleavage occurs via oxazolonium mechanism during TFA treatment
Solution Approach 1:
The patent applies preliminary protection strategies where N-alkylated amino acid residues are pre-protected with protecting groups that prevent oxazolonium formation during subsequent TFA treatment. This preliminary protective action allows the use of standard Fmoc synthesis procedures while preventing peptide chain cleavage, thereby maintaining both method versatility and peptide stability.
3Temperature
If TFA is used for deprotection, then deprotection can be performed under relatively mild conditions compared to Boc method, but N- to O-acyl shift reaction occurs in peptides containing Q-hydroxy group amino acids
Solution Approach 1:
The patent changes the chemical parameters of the deprotection system by selecting protecting groups for Q-hydroxy group amino acids that have different acid-lability characteristics. Instead of using protecting groups removed by TFA, the patent employs protecting groups that require milder or different acidic conditions for removal, thereby preventing N- to O-acyl shift while maintaining deprotection efficiency and peptide structural integrity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach allows for the synthesis of peptides with high purity and high synthetic yield, reducing side reactions such as hydrolysis and N- to O-acyl shift, and facilitating industrial-scale production by improving solubility and work-up processes.
Implementation Method 1
deprotecting the protecting group having an Fmoc skeleton by using a base to expose the amino group
Implementation Method 2
cleaving the peptide obtained in step 4) off from the solid phase under a condition of weaker acidity than TFA
Implementation Method 3
reducing side reactions such as hydrolysis
Implementation Method 4
reducing side reactions such as hydrolysis and N- to O-acyl shift
Data Source
AI summary
Methods of producing a peptide containing an N-substituted amino acid or N-substituted amino acid analog of the present invention include the steps of: preparing an Fmoc-protected amino acid, an Fmoc-protected amino acid analog, or an Fmoc-protected peptide; deprotecting a protecting group which have an Fmoc skeleton of the Fmoc-protected amino acid and such by using a base; and forming an amide bond by adding a new Fmoc-protected amino acid and such; and when the peptide is produced by a solid-phase method, the obtained peptide is cleaved off from the solid phase under conditions of weaker acidity than TFA. Furthermore, at least one side chain of the obtained peptide has a protecting group that is not deprotected under basic conditions and is deprotected under conditions of weaker acidity than TFA.