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| Product Name | Fmoc-Leu-OH |
|---|---|
| Synonyms | Nα-Fmoc-L-leucine; Fmoc-L-leucine |
| Catalog No. | AS0304 |
| CAS Number | 35661-60-0 |
| Molecular Formula | C21H23NO4 |
| Molecular Weight | 353.41 g/mol |
| Appearance | White powder |
| Melting Point | 148–163°C |
| Specific Rotation | -25° ± 2° (C=1 in DMF) |
| Storage Temperature | Cool, dry place (≤25°C) |
| Side-Chain Protection | None required |
| Primary Application | Fmoc solid-phase peptide synthesis (SPPS) |
Product Overview
Fmoc-Leu-OH is the Fmoc-protected form of L-leucine and a standard building block for Fmoc-based solid-phase peptide synthesis (SPPS).
Leucine contains a hydrophobic branched aliphatic side chain that does not require additional protection during routine peptide assembly. The Fmoc group protects the α-amino group while the free carboxyl group remains available for activation and coupling.
Fmoc-Leu-OH is widely used in natural peptides, hydrophobic peptide sequences, peptide libraries, receptor-binding peptides and structure–activity relationship studies.
Applications in Peptide Synthesis
| Application | Role of Fmoc-Leu-OH |
|---|---|
| Fmoc-SPPS | Standard building block for incorporation of L-leucine |
| Hydrophobic Peptides | Introduces a nonpolar branched aliphatic side chain |
| SAR Studies | Supports systematic modification of hydrophobic interactions |
| Peptide Libraries | Common proteinogenic amino-acid building block |
| Helical Peptides | Frequently occurs in hydrophobic faces of α-helical sequences |
| Custom Peptide Synthesis | Used in linear, cyclic and modified peptides |
Fmoc-Leu-OH in Fmoc-SPPS
Fmoc-Leu-OH requires no side-chain protecting group.
The α-carboxyl group is activated and coupled to the resin-bound amino terminus. Subsequent base-mediated Fmoc removal exposes the amino group for the next elongation cycle.
For a broader overview, see Solid-Phase Peptide Synthesis (SPPS): A Practical Guide.
Leucine, Hydrophobicity and Difficult Sequences
Leucine is strongly hydrophobic. One or two Leu residues are usually straightforward to incorporate, but sequences containing clusters of Leu, Ile, Val, Phe and other hydrophobic residues can become progressively more difficult during SPPS.
The growing resin-bound peptide may associate through hydrophobic interactions, reducing solvent penetration and accessibility of reactive termini.
In difficult sequences, incomplete coupling can therefore reflect sequence-dependent aggregation rather than insufficient amino-acid reactivity alone.
Practical responses may include improved resin swelling, longer coupling times, double coupling or alternative synthesis conditions.
Leu vs Ile: An Important Analytical Limitation
Leucine and isoleucine have the same elemental composition and molecular mass but different side-chain connectivity.
Consequently:
An Ile↔Leu substitution in a peptide does not change the intact peptide molecular mass.
Routine intact MS therefore cannot by itself distinguish a peptide containing Leu from the corresponding Ile isomer.
Alan Scientific practical view: for isobaric amino acids such as Leu and Ile, raw-material identity, synthesis records and orthogonal analytical control remain important even when the final peptide MS is correct.
Product Documents
A Safety Data Sheet (SDS / MSDS) is available for this product to support laboratory handling, storage and safety assessment.
Related Technical Resources
Explore Standard Fmoc-Amino Acids.
Read more about Amino Acids & Peptide Building Blocks.
For difficult hydrophobic sequences, visit Custom Peptide Synthesis.
Why Source Peptide Building Blocks from Alan Scientific?
Alan Scientific supplies protected amino acids and specialized peptide building blocks for research-scale peptide synthesis, supported by flexible ordering and peptide synthesis technical expertise.
Research Use Only