Peptide Modifications
Peptide Modifications
Post-synthesis modifications expand the chemical diversity of peptides beyond the 20 proteinogenic amino acids.
Fluorescent Labels
| Dye | Excitation (nm) | Emission (nm) | Application |
|---|---|---|---|
| <strong>FAM</strong> | 495 | 520 | Green fluorescent label |
| <strong>TAMRA</strong> | 555 | 580 | Red fluorescent label |
| <strong>Cy5</strong> | 649 | 670 | NIR fluorescent label |
| <strong>FITC</strong> | 494 | 518 | General fluorescence |
Cyclization Strategies
Head-to-Tail Cyclization
- Method: PyBOP/DIEA activation on-resin or in solution
- Requirements: Orthogonal protecting group strategy
Disulfide Cyclization
- Oxidation methods: Air (slow), DMSO, iodine, potassium ferricyanide
- Multiple disulfides: Requires regioselective protection (Acm, tBu)
Unnatural Amino Acids
| Abbreviation | Structure | Application |
|---|---|---|
| <strong>Aib</strong> | alpha-aminoisobutyric acid | Helix stabilization |
| <strong>Nle</strong> | Norleucine | Met replacement (oxidation resistant) |
| <strong>Cha</strong> | Cyclohexylalanine | Hydrophobic substitution |
| <strong>pNA</strong> | p-nitroaniline | Colorimetric substrates |
See [[Solid Phase Peptide Synthesis]], [[Amino Acid Reference]], [[Peptide Science Overview]]