Peptide Folding¶
Disulfide Bond Formation¶
Purpose¶
Many bioactive peptides require specific disulfide bond patterns for correct three-dimensional structure and biological activity.
Cysteine Protection Strategies¶
| Protecting Group | Cleavage | Compatible With |
|---|---|---|
| Trt (trityl) | TFA cleavage (standard) | Most SPPS |
| Acm (acetamidomethyl) | I₂, Tl(OCOCF₃)₃ | Selective disulfide pairing |
| tBu (tert-butyl) | TFA | Orthogonal to Acm |
| StBu (S-tert-butyl) | Thiolysis | Stepwise disulfide formation |
Disulfide Bond Formation Methods¶
Air Oxidation (pH 7–8)¶
- Simple, no additional reagents
- Slow (hours to days)
- Low selectivity with multiple disulfides
Iodine Oxidation¶
- Removes Acm protecting group
- Simultaneous cyclization
- Quick (minutes)
- Can modify sensitive residues
Glutathione Redox System¶
- Oxidized/reduced glutathione (GSSG/GSH)
- Controlled redox potential
- Higher yield for complex peptides
Dimethyl Sulfoxide (DMSO)¶
- 10–20% DMSO in water
- pH 6–8
- Mild and selective
Regioselective Disulfide Formation¶
For peptides with multiple disulfide bonds:
- First pair: Use Trt protection, form during cleavage
- Second pair: Acm protection, orthogonal deprotection
Example Strategy (2 disulfide bonds)¶
| Step | Action |
|---|---|
| 1 | Synthesize with Cys¹(Trt), Cys²(Trt), Cys³(Acm), Cys⁴(Acm) |
| 2 | Cleave with TFA — Cys¹–Cys² disulfide forms |
| 3 | Purify monocyclic product |
| 4 | I₂ oxidation — removes Acm, forms Cys³–Cys⁴ |
| 5 | Purify bicyclic product |
Folding Optimization¶
| Parameter | Typical Range |
|---|---|
| Peptide concentration | 0.1–1 mg/mL |
| pH | 7.0–8.5 |
| Temperature | 4–25 °C |
| Time | 2–24 hours |
| Buffer | 0.1 M NH₄HCO₃ or Tris-HCl |
- Disulfide Bond Formation — Review the section above for key parameters, methods, and quality criteria.
- Cysteine Protection Strategies — Review the section above for key parameters, methods, and quality criteria.
- Disulfide Bond Formation Methods — Review the section above for key parameters, methods, and quality criteria.
- Regioselective Disulfide Formation — Review the section above for key parameters, methods, and quality criteria.
Key Takeaways¶
- Disulfide Bond Formation — Review the section above for key parameters, methods, and quality criteria.
- Cysteine Protection Strategies — Review the section above for key parameters, methods, and quality criteria.
- Disulfide Bond Formation Methods — Review the section above for key parameters, methods, and quality criteria.
- Regioselective Disulfide Formation — Review the section above for key parameters, methods, and quality criteria.
🔗 Related: Purification | Custom Synthesis | LC-MS Testing | Popular Research Peptides Guide