Mironova Labs · Protocol
SPPS Coupling Protocol
Fmoc solid-phase peptide synthesis using DMTMM·BF₄
Reagents
| Reagent | Role | Amount |
|---|---|---|
| Fmoc-amino acid | Acyl donor | 3.0 eq |
| DMTMM·BF₄ | Coupling reagent | 3.0 eq |
| NMM (N-methylmorpholine) | Base | 6.0 eq |
Conditions
Solvent
NMP or DMF/NMP mixtures (DMTMM·BF₄ has limited solubility in pure DMF)
Temperature
20–25 °C (room temperature)
Reaction Time
30–60 min per coupling
Atmosphere
Ambient (no inert gas required)
Procedure
- 1
Swell resin in DMF (5 mL/g resin) for 15 min. Drain.
- 2
Deprotect Fmoc group: treat with 20% piperidine/DMF (2 × 5 min). Wash resin with DMF (5×).
- 3
Dissolve Fmoc-amino acid (3.0 eq) and DMTMM·BF₄ (3.0 eq) in minimum DMF.
- 4
Add NMM (6.0 eq) to the solution. Mix briefly to ensure dissolution.
- 5
Add activated solution to drained resin. Agitate (shaking or N₂ bubbling) for 30–60 min.
- 6
Drain coupling solution. Wash resin with DMF (5×).
- 7
Monitor coupling completion by Kaiser test (ninhydrin) or chloranil test. Recouple if necessary.
- 8
Repeat deprotection–coupling cycle for each residue.
Expected Outcome
Coupling efficiency comparable to PyBOP/HATU. Lower epimerization than HATU/HBTU + DIPEA pairings. Crude purity typically improved vs TBTU or PyBOP in automated synthesis.
Analytical Monitoring
Kaiser/chloranil test after each coupling. HPLC and MS analysis of cleaved crude peptide.
Troubleshooting
Incomplete coupling (positive Kaiser test)
Recouple with fresh reagent solution. Extend reaction time to 90 min. For very hindered residues, increase to 5.0 eq reagent.
Elevated epimerization
Switch from DIPEA to NMM or collidine. Reduce coupling temperature to 0–10 °C for sensitive residues.
Poor resin swelling
Pre-swell in DCM before switching to DMF. Ensure DMF is fresh and dry.
Notes
- Store DMTMM·BF₄ in a desiccator. Weigh quickly to minimize moisture exposure.
- DMTMM·BF₄ has limited solubility in pure DMF. Use NMP or DMF/NMP co-solvent mixtures. Verify dissolution before adding to resin.
- For fragment condensation, 1.5 eq reagent with extended reaction time (2–4 h) is often sufficient.
- Base selection is critical for epimerization control: NMM or collidine are preferred. Epimerization advantages over uronium reagents were demonstrated in specific model systems (Kamiński et al., 2005).
- Compatible with standard Fmoc/tBu protection strategy.