Peptide Coupling
Rob Brown
Special Topic – 25/01/112
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Peptide Coupling
The Amide Bond – Biological Importance
-Key chemical bond in proteins:
-Enzymes (biological catalysis)
- Structural and mechanical function
-Cell signalling
-Immune response
-Cell adhesion
- Amide-containing pharmaceuticals:
Combining the strengths of UMIST and
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Peptide Coupling
The Peptide Bond – Biological Synthesis
- Ribosomal Protein Translation
- DNA → RNA → Peptides/Proteins
-Chemical Synthesis? - Solid Phase
- Solution Phase
Combining the strengths of UMIST and
The Victoria University of Manchester
Peptide Coupling
The Peptide Bond – Chemical Synthesis
Problem:
Solution:
Combining the strengths of UMIST and
The Victoria University of Manchester
Peptide Coupling
The Peptide Bond – Chemical Synthesis
Combining the strengths of UMIST and
The Victoria University of Manchester
Peptide Coupling
Chemical Synthesis – Racemization
Combining the strengths of UMIST and
The Victoria University of Manchester
Peptide Coupling
Chemical Synthesis – Racemization
Combining the strengths of UMIST and
The Victoria University of Manchester
Peptide Coupling
Chemical Synthesis – Racemization
Combining the strengths of UMIST and
The Victoria University of Manchester
Peptide Coupling
Chemical Synthesis – Racemization
Combining the strengths of UMIST and
The Victoria University of Manchester
Peptide Coupling
Chemical Synthesis – Common Side Reactions
Combining the strengths of UMIST and
The Victoria University of Manchester
Peptide Coupling
Coupling reagent comparison
Published epimerisation tests:
Combining the strengths of UMIST and
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Peptide Coupling
Carbodiimide coupling
Combining the strengths of UMIST and
The Victoria University of Manchester
Peptide Coupling
Carbodiimide coupling
Combining the strengths of UMIST and
The Victoria University of Manchester
Peptide Coupling
Carbodiimide coupling
Combining the strengths of UMIST and
The Victoria University of Manchester
Peptide Coupling
Carbodiimide coupling
Combining the strengths of UMIST and
The Victoria University of Manchester
Peptide Coupling
Carbodiimide coupling
Combining the strengths of UMIST and
The Victoria University of Manchester
Peptide Coupling
Carbodiimide coupling
Combining the strengths of UMIST and
The Victoria University of Manchester
Peptide Coupling
Carbodiimide reagents:
Additives:
Combining the strengths of UMIST and
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Peptide Coupling
HOXt-based coupling reagents
Combining the strengths of UMIST and
The Victoria University of Manchester
Peptide Coupling
HOXt-based coupling reagents
Combining the strengths of UMIST and
The Victoria University of Manchester
Peptide Coupling
HOXt-based coupling reagents
Combining the strengths of UMIST and
The Victoria University of Manchester
Peptide Coupling
HOXt-uronium/aminium salts
Combining the strengths of UMIST and
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Peptide Coupling
HOXt-uronium/aminium salts
Combining the strengths of UMIST and
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Peptide Coupling
HOXt-phosphonium salts
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Peptide Coupling
HOXt-immonium salts
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Peptide Coupling
Other HOXt-derived reagents
Combining the strengths of UMIST and
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Peptide Coupling
Acid Halide-generating reagents
-Harsh activation method
-Lack of functional group compatibility
-Works well with hindered amino acids
-Racemization a major problem
e.g.
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Peptide Coupling
Acid Halide-generating reagents: Triazines
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Peptide Coupling
Acid Halide-generating reagents: Halo-uronium & phosphonium salts
Combining the strengths of UMIST and
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Peptide Coupling
Pentafluorophenol-based reagents
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Peptide Coupling
HODhbt-reagents
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Peptide Coupling
HOSu-reagents
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Peptide Coupling
Phosphorus-reagents
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Peptide Coupling
Mixed carbonic anhydrides
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Peptide Coupling
Polymer-supported reagents
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Peptide Coupling
Newer approaches to amide bond fomation
Combining the strengths of UMIST and
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Peptide Coupling
Conclusions
-Most reagents are not broadly applicable, relatively narrow uses.
-Specialized, expensive reagents work well for SPPS
-High yields required, by products can be washed out
-Simpler, cheaper all-purpose reagents better for solution phase:
- HATU & HBTU – general and excellent reactivity.
- HATU favoured for quick coupling times
- DIC/HOBt still among the best combinations
- Substitute EDC when inseparable by-products become problematic
- For hindered couplings: PyBrop for N-Me amino acids
PyBop for hindered tertiary amino acid couplings
Triazines for hindered quaternary amino acids
- PS-IIDQ and PS-Mukaiyama reagents best for library synthesis
-Finally, keep it simple, don’t be mislead by needlessly expensive reagents
Main refs:
E.Valeur, M. Bradley; Chem. Soc. Rev., 2009, 38, 606-631
A. El-Faham, F. Albericio; Chem. Rev., 2011, 111, 6557-6602
Combining the strengths of UMIST and
The Victoria University of Manchester