The choice of method depends on target length, purity, scale and environmental considerations. Here are the four main methods, plus two ligation techniques.
1. Solid-phase synthesis (SPPS)
The growing chain is anchored by its C-terminus to an insoluble polymer; amino acids are added C→N. One cycle: deprotection → wash → coupling → wash.
- Polystyrene resin (Wang, 2-chlorotrityl). Fmoc (preferred) and Boc strategies.
- Typical length: < 80 aa.
Advantages: fast, automatable. Limits: impurities on long sequences, high solvent excess.
2. Liquid-phase synthesis (LPPS)
Assembly in solution, direct HPLC monitoring and intermediate fragment purification.
- Length: < 10 aa. Greener chemistry (less solvent).
3. Chemo-enzymatic synthesis (CEPS)
Peptiligase assembles fragments under mild aqueous conditions. No side-chain protection required. Length: > 150 aa, scalable and eco-friendly.
4. Tag-assisted synthesis (TAPS)
Liquid phase + aqueous purification (Molecular Hiving™). A hydrophobic tag enables a simple extraction after each coupling. Length: < 15 aa; up to −60 % solvent.
5. Native chemical ligation (NCL)
Chemoselective coupling of unprotected fragments; requires a cysteine at the ligation site. Length: 30–150 aa.
6. Comparison table
| Method | Length | Benefits | Limits |
|---|---|---|---|
| SPPS | < 80 aa | Fast, automatable | Impurities (long sequences) |
| LPPS | < 10 aa | Intermediate purification | Solubility, slow |
| CEPS | > 150 aa | No protection, scalable | Ligation site required |
| TAPS | < 15 aa | CMR-free, low solvent | Solubility |
| NCL | 30–150 aa | Long cyclic peptides | Cysteine required |