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| Product Name | Fmoc-Lys(Boc)-OH |
|---|---|
| Synonyms | Nα-Fmoc-Nε-Boc-L-lysine |
| Catalog No. | AS0890 |
| CAS Number | 71989-26-9 |
| Molecular Formula | C26H32N2O6 |
| Molecular Weight | 468.54 g/mol |
| Appearance | White to off-white powder |
| Reference Melting Point | 123–130°C |
| Specific Rotation | Approximately -12° (C=1 in DMF) |
| Side-Chain Protection | Boc-protected ε-amino group |
| Primary Application | Fmoc-SPPS |
Product Overview
Fmoc-Lys(Boc)-OH is one of the most widely used protected lysine derivatives in Fmoc-SPPS.
The α-amino group is protected by Fmoc, while the lysine side-chain ε-amino group is protected by Boc. This orthogonal arrangement permits repeated basic Fmoc removal while maintaining side-chain protection throughout peptide elongation.
During final acidic cleavage, Boc is removed and the native lysine ε-amino group is regenerated.
Applications in Peptide Synthesis
| Application | Role of Fmoc-Lys(Boc)-OH |
|---|---|
| Fmoc-SPPS | Standard L-lysine building block |
| Lys-Containing Peptides | Protects the ε-amino group during chain elongation |
| Cationic Peptides | Generates a positively charged Lys side chain after deprotection |
| Peptide Libraries | Enables routine incorporation of lysine |
| Conjugated Peptides | Lys can provide a post-synthesis modification handle |
| SAR Studies | Supports investigation of charge and side-chain length |
| Custom Peptides | Used in linear, cyclic and modified peptide synthesis |
Fmoc-Lys(Boc)-OH in Fmoc-SPPS
The Fmoc α-amino protecting group is removed under basic conditions, whereas the Boc side-chain protecting group remains intact during routine synthesis.
Final TFA-based cleavage removes Boc and restores the ε-amino group.
This Fmoc/Boc orthogonality is why Fmoc-Lys(Boc)-OH is the default lysine building block for many conventional peptide sequences.
Why Protect the Lysine ε-Amine with Boc?
An unprotected lysine side chain contains a reactive primary amine that could compete with the intended N-terminal amine during coupling.
Boc prevents:
unwanted side-chain acylation
peptide branching
cross-linking
modification at an unintended lysine site
After synthesis, removal of Boc regenerates the lysine side-chain amine.
Boc Is Not Always the Best Lys Protecting Group
Boc is ideal when the goal is simply to obtain native lysine after final cleavage.
It is less suitable when the ε-amino group must be selectively exposed while the peptide remains attached to the resin.
For applications such as:
site-selective fluorophore labeling
lipidation
biotinylation
branched peptide synthesis
side-chain cyclization
orthogonal protecting groups such as Dde, ivDde or Alloc may be more appropriate.
Alan Scientific practical view: protecting-group selection should be driven by the order in which functional groups must become available, not merely by which protected amino acid is most common.
Lysine as a Peptide Modification Handle
Once deprotected, lysine provides a primary ε-amine that can be used for a wide range of conjugation reactions.
However, a peptide containing several lysines presents a selectivity problem after global deprotection. If modification must occur at one defined Lys residue, an orthogonal side-chain protecting strategy is usually preferable.
For modified sequences, see Custom Peptide Synthesis.
Product Documents
A Safety Data Sheet (SDS / MSDS) is available for this product to support laboratory handling, storage and safety assessment.
📎 MSDS_Fmoc-Lys(Boc)-OH_AS0890.pdf
Related Technical Resources
Browse Standard Fmoc-Amino Acids.
Read Choosing Fmoc-Protected Amino Acids for Peptide Synthesis.
Explore Amino Acids & Peptide Building Blocks.
Why Source Peptide Building Blocks from Alan Scientific?
Alan Scientific supplies standard and specialized protected amino acids for conventional and modification-intensive peptide synthesis projects.
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