Fmoc-Lys(Mtt)-OH, identified by CAS number 167393-62-6, is a sophisticated building block in the field of peptide chemistry. Its nomenclature, N-alpha-Fmoc-N-epsilon-(4-methyltrityl)-L-lysine, clearly indicates its structural components: the N-terminal Fmoc (9-fluorenylmethyloxycarbonyl) protecting group and the side-chain Mtt (4-methyltrityl) protecting group on the lysine residue. Understanding the chemistry of these groups is fundamental to harnessing the full potential of this reagent in peptide synthesis.

Chemical Structure and Properties:

The molecule features a chiral alpha-amino group protected by the base-labile Fmoc group, which is standard for most Fmoc-based peptide synthesis strategies. The lysine side chain possesses a primary amine at the epsilon position. The Mtt group is a bulky, acid-labile trityl derivative specifically chosen for its differentiated stability compared to other protecting groups. This difference in lability is the cornerstone of its utility in complex synthesis pathways.

Key Properties and Reactivity:

  • Fmoc Deprotection: The Fmoc group is readily removed by treatment with a mild base, typically a solution of piperidine in dimethylformamide (DMF). This reaction liberates the alpha-amino group for coupling with the next amino acid in the peptide sequence.
  • Mtt Deprotection: The Mtt group on the epsilon-amino functionality is sensitive to mild acidic conditions. Treatment with dilute TFA (e.g., 1-5% TFA in DCM) or other mild acidic reagents selectively cleaves the Mtt group. This selectivity is crucial as it leaves other protecting groups, such as tBu or Boc, intact, allowing for precise manipulation of the lysine side chain.
  • Solubility and Stability: Fmoc-Lys(Mtt)-OH is typically supplied as an off-white powder, soluble in common organic solvents used in peptide synthesis like DMF and DCM. Its stability under appropriate storage conditions (cold, dry) is generally good, ensuring its efficacy for laboratory use.

Applications in Modern Peptide Synthesis:

The unique selective deprotection characteristic of Fmoc-Lys(Mtt)-OH makes it invaluable for several advanced synthetic applications:

  • Branched Peptide Synthesis: Researchers can selectively deprotect the Mtt group on lysine residues incorporated into a growing peptide chain. The exposed epsilon-amino group then serves as an attachment point for a second peptide sequence, creating complex, multi-branched structures vital for some drug delivery systems or vaccine development.
  • Site-Specific Conjugation: The ability to selectively deprotect the Mtt group allows for the precise attachment of labels, tags, cytotoxic agents, or pharmacokinetic modifiers to the lysine side chain. This is fundamental in creating antibody-drug conjugates (ADCs), peptide-drug conjugates (PDCs), and peptides for imaging or diagnostic purposes.
  • Cyclic Peptide Formation: For synthesizing cyclic peptides where lysine is involved in the cyclization (e.g., lactam bridges), the Mtt group provides a handle for controlled deprotection, enabling targeted ring closure reactions.

When considering sourcing this reagent, it is vital to buy Fmoc-Lys(Mtt)-OH from a trusted manufacturer. The CAS number 167393-62-6 guarantees the identity, but consistent purity and reliable supply are the hallmarks of a good supplier. Exploring options for bulk purchase from a reputable manufacturer in China can offer significant advantages for large-scale projects.

In summary, Fmoc-Lys(Mtt)-OH is a powerful tool for peptide chemists, offering a strategic advantage through its orthogonal protecting group. Its unique properties enable the synthesis of complex and functional peptides, driving innovation in pharmaceuticals and biotechnology.