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| Product Name | Fmoc-Ile-OH |
|---|---|
| Synonyms | N-(9-Fluorenylmethoxycarbonyl)-L-isoleucine; Fmoc-L-isoleucine |
| Catalog No. | AS1011 |
| CAS Number | 71989-23-6 |
| Molecular Formula | C21H23NO4 |
| Molecular Weight | 353.41 g/mol |
| SMILES | CCC@HC@HC(O)=O |
| Storage Temperature | Cool, dry place (≤25°C) |
| Appearance | White powder |
| Melting Point | 140–155°C |
| Specific Rotation | -12° ± 2° (C=1 in DMF) |
| Side-Chain Protection | None required |
| Primary Application | Fmoc solid-phase peptide synthesis (SPPS) |
Product Overview
Fmoc-Ile-OH is the Fmoc-protected form of L-isoleucine and a standard building block for Fmoc-SPPS.
Isoleucine has a hydrophobic, β-branched aliphatic side chain and requires no additional side-chain protecting group.
The combination of hydrophobicity and β-branching makes Ile important both biologically and synthetically.
Fmoc-Ile-OH is widely used in:
natural peptide synthesis
hydrophobic peptide sequences
peptide libraries
receptor-binding peptides
SAR studies
modified and cyclic peptides
Applications in Peptide Synthesis
| Application | Role of Fmoc-Ile-OH |
|---|---|
| Fmoc-SPPS | Standard building block for L-isoleucine |
| Hydrophobic Peptides | Introduces a branched nonpolar side chain |
| SAR Studies | Enables controlled modification of hydrophobic packing |
| Peptide Libraries | Common natural amino-acid building block |
| Structure Optimization | Can influence local backbone and side-chain packing |
| Custom Peptide Synthesis | Used across linear, cyclic and modified peptides |
Fmoc-Ile-OH in Fmoc-SPPS
Fmoc-Ile-OH contains no reactive side-chain functionality requiring protection.
Its free α-carboxyl group is activated and coupled to the growing peptide, after which the Fmoc group is removed to permit the next elongation step.
Chemically the protecting-group strategy is straightforward.
However, the β-branched structure of isoleucine makes steric effects more important than they are for residues such as Gly or Ala.
β-Branched Amino Acids and Difficult Coupling
Isoleucine, valine and threonine are β-branched amino acids.
The additional branching near the peptide backbone can create steric congestion around the reacting groups. This becomes especially relevant when a β-branched residue is coupled adjacent to another sterically demanding residue.
Recent discussions of difficult SPPS coupling continue to identify sterically hindered resin-bound amines as a major source of slow or incomplete acylation.
In practice, difficult Ile-containing steps may benefit from:
longer coupling time
double coupling
optimized equivalents
more reactive coupling chemistry
improved resin swelling and solvation
sequence-specific synthesis optimization
Alan Scientific practical view: a positive crude-HPLC improvement after changing the Ile coupling protocol often reflects elimination of deletion sequences, rather than any problem with the chemical identity of Fmoc-Ile-OH itself.
Isoleucine, Hydrophobicity and Peptide Aggregation
Isoleucine is strongly hydrophobic.
Multiple Ile, Leu, Val, Phe or other hydrophobic residues in a sequence can increase the tendency of a growing peptide chain to form intermolecular or intramolecular associations on resin.
When this occurs, reactive amino termini may become less accessible and coupling efficiency can decline.
Therefore, a difficult Ile-containing synthesis may involve two different mechanisms simultaneously:
steric hindrance at the coupling site + sequence-dependent aggregation.
This distinction matters because simply increasing coupling reagent strength may not fully solve a problem caused by poor resin solvation.
For difficult sequences, see Custom Peptide Synthesis.
Ile vs Leu: An Important QC Detail
Isoleucine and leucine have the same molecular formula and molecular weight but different side-chain connectivity.
This means an Ile→Leu substitution does not produce a change in intact peptide molecular mass.
Therefore:
Intact MS alone cannot distinguish an Ile-containing peptide from the corresponding Leu isomer.
This is an important analytical point for high-value peptide projects.
Correct amino-acid identity depends on controlled raw materials, synthesis records and appropriate analytical strategy rather than molecular-weight confirmation alone.
This is one reason that protected amino-acid identity and supply-chain quality remain important even when final peptide MS appears 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 Amino Acids & Peptide Building Blocks.
Learn more in Solid-Phase Peptide Synthesis (SPPS): A Practical Guide.
For difficult hydrophobic or β-branched peptide 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