Reagents
| Reagent | Role | Amount |
|---|---|---|
| Fatty diacid–spacer construct (e.g., C18 or C20 linker) | Acyl donor | 1.5–2.0 eq |
| DMTMM salt | Coupling reagent | 1.5–2.5 eq |
| NMM | Base | 3.0–5.0 eq |
| Peptide with free ε-lysine | Nucleophile | 1.0 eq |
Conditions
- Solvent
- DMF/water (4:1 or higher water fraction) for Cl; neat DMF or NMP for BF₄. Note: DMTMM·Cl has a half-life of ~15 min in neat DMF — use BF₄ or PF₆ if organic-phase pre-activation is required.
- Temperature
- 0–25 °C (lower temperatures reduce over-acylation)
- Reaction time
- 2–8 h
- Atmosphere
- Ambient or N₂
Procedure
- If peptide has multiple free amines, ensure orthogonal protection so that only the target ε-lysine is available for acylation.
- Dissolve fatty diacid–spacer construct (1.5–2.0 eq) in DMF or DMF/water mixture at 0–10 °C.
- Add DMTMM salt (1.5–2.5 eq) and NMM (3.0–5.0 eq). Stir for 5–10 min to pre-activate the carboxyl group.
- Add the peptide (1.0 eq, dissolved in minimum DMF or buffer) to the activated acid solution.
- Stir at 0–25 °C for 2–8 h. Monitor by analytical HPLC.
- Quench by dilution with cold water or buffer. Purify by preparative HPLC.
Expected outcome
Target: selective mono-acylation of target lysine with minimal over-acylation. These are expected outcomes based on general DMTMM coupling behavior; actual results require process-specific optimization (see notes).
Analytical monitoring
Analytical RP-HPLC (C18, gradient). LC-MS for identity confirmation. Monitor for di-acylated species and triazine adducts.
Troubleshooting
- Over-acylation (di-acylated product)
- Reduce DMTMM equivalents to 1.2 eq. Lower temperature to 0 °C. Reduce reaction time. Ensure orthogonal protection of non-target amines.
- Low conversion
- Increase DMTMM equivalents. Extend reaction time. Ensure fatty acid is fully dissolved (add DMSO if needed for solubility).
- Triazine adduct detected
- Reduce DMTMM excess. This side product is typically separable by prep HPLC but is best minimized at the reaction level.
Notes & applicability
- These conditions are chemically plausible extrapolations from general DMTMM amide coupling data. DMTMM has been demonstrated to form amide bonds to lysine ε-amino groups in protein cross-linking contexts (Leitner et al., 2014 [B18]), establishing chemical competence for carboxyl→lysine amide formation. Farkaš et al. (2013 [B22]) further demonstrated DMTMM-mediated conjugation to BSA lysine residues. However, no published study has specifically demonstrated DMTMM for GLP-1 peptide lipidation at manufacturing scale. Users should treat this as an evaluation starting point.
- For semaglutide-class molecules, the lipidation step is quality-critical. Coupling-reagent choice directly affects the impurity profile.
- DMTMM mechanistically avoids the guanidinylation risk inherent to HATU/HBTU at this step.
- Batch-to-batch reagent purity (≥99%) is important for reproducible impurity profiles at scale.