Solid Phase Peptide Synthesis — Complete Process¶

TL;DR¶

The SPPS cycle consists of: resin preparation → loading → deprotection → coupling → washing (repeated per residue) → final cleavage → purification. Each cycle is monitored by Kaiser test.

SPPS is the standard method for peptide production. A peptide chain is assembled stepwise on insoluble resin beads, with excess reagents removed by simple filtration.

1. Resin Loading¶

Purpose¶

Attach the first (C-terminal) amino acid to the solid support via a cleavable linker.

Common Resins¶

Key Parameters¶

• Loading capacity: 0.3–1.5 mmol/g (vendor-specified)
• Swelling solvent: DCM or DMF (5–10 mL/g resin)
• Swelling time: 30–60 minutes before first coupling
• First amino acid attachment: Via symmetric anhydride or pre-activated ester

2. Coupling Reaction¶

Purpose¶

Sequentially add Fmoc-protected amino acids to the growing peptide chain.

Materials¶

• Fmoc-amino acids (2–5 fold molar excess)
• Activator (HBTU, HATU, DIC, or PyBOP)
• Base (DIEA or NMM)
• Solvent (DMF or NMP)

Activation Chemistry¶

graph LR
    A[Fmoc-AA-OH] --> B[+ Activator];
    B --> C[Active Ester];
    C --> D[+ NH2-Peptide-Resin];
    D --> E[Coupled Peptide-Resin];
    E --> F[+ Wash];

Key Parameters¶

Monitoring Methods¶

• Kaiser test (ninhydrin): Blue = free amine (incomplete coupling)
• Chloranil test: For secondary amines (Proline)
• UV monitoring: Track Fmoc removal for coupling efficiency

3. Deprotection¶

Purpose¶

Remove the Fmoc protecting group from the N-terminal amino acid before the next coupling.

Standard Deprotection¶

• Reagent: 20–25% piperidine in DMF
• Time: 5–15 minutes
• Temperature: Room temperature (or 40–50 °C with microwave)

Mechanism¶

1. Piperidine removes the Fmoc group
2. Releases dibenzofulvene (UV-active)
3. Dibenzofulvene is trapped by piperidine as a stable adduct

Monitoring¶

• UV absorption: Measure dibenzofulvene at 301 nm
• Quantitative: Track deprotection efficiency per cycle

4. Cleavage¶

Purpose¶

1. Release the peptide from the resin
2. Remove side-chain protecting groups (global deprotection)

Standard Cocktail¶

Process¶

1. Add cleavage cocktail to resin-bound peptide
2. Stir 1.5–4 hours at room temperature
3. Filter to remove resin beads
4. Precipitate peptide in cold diethyl ether or MTBE
5. Centrifuge/wash × 2–3
6. Dry under nitrogen or vacuum

5. Purification¶

Purpose¶

Remove deletion sequences, truncated peptides, and other impurities from crude product.

Method: Preparative HPLC¶

See full details: Purification Process

6. Lyophilization¶

Purpose¶

Remove water and organic solvents to produce stable peptide powder.

Process Steps¶

1. Freeze peptide solution (-40 to -80 °C)
2. Primary drying: Sublime ice under vacuum (0.1–0.5 mbar)
3. Secondary drying: Remove bound water (elevated temperature)

Expected Outcome¶

• White to off-white amorphous powder
• Residual moisture: <5% (target <2%)
• Shelf-stable at -20 °C for 2+ years

See full details: Lyophilization Process

Process Time Reference¶

• 1. Resin Loading — Review the section above for key parameters, methods, and quality criteria.
• 2. Coupling Reaction — Review the section above for key parameters, methods, and quality criteria.
• 3. Deprotection — Review the section above for key parameters, methods, and quality criteria.
• 5. Purification — Review the section above for key parameters, methods, and quality criteria.

🔗 Related: Peptide Synthesis Overview | Manufacturing Workflow | Resin Loading | Coupling Reaction | Purification | Peptide Quality Control Guide

Key Takeaways¶

• 1. Resin Loading — Review the section above for key parameters, methods, and quality criteria.
• 2. Coupling Reaction — Review the section above for key parameters, methods, and quality criteria.
• 3. Deprotection — Review the section above for key parameters, methods, and quality criteria.
• 4. Cleavage — Review the section above for key parameters, methods, and quality criteria.