Fmoc-Ile-Ile-OH is a preassembled, Fmoc-protected L-isoleucyl-L-isoleucine (Ile-Ile, II) dipeptide with a free C-terminal carboxylic acid. Both isoleucine residues are beta-branched and stereochemically defined, making this fragment particularly relevant to hydrophobic peptide synthesis and routes where consecutive Ile couplings are synthetically demanding.

Public structure records identify this material as Fmoc-L-Ile-L-Ile-OH with (2S,3S) stereochemistry at each isoleucine residue. This is a high-value procurement detail because isoleucine contains two stereocenters, and allo-isoleucine-containing isomers can have the same formula and nominal molecular weight.

Product Information

Why Consecutive Isoleucine Residues Can Be Difficult

Isoleucine is beta-branched, which places steric bulk close to the reacting peptide backbone. Coupling at or adjacent to consecutive Ile residues can therefore be slower than coupling less hindered amino acids, especially in hydrophobic sequences where resin-bound peptide aggregation also develops.

A preassembled Ile-Ile dipeptide can bypass one direct Ile-to-Ile peptide-bond-forming step and may simplify fragment-based approaches for sequences containing this motif.

Stereochemistry: L-Ile vs Allo-Ile

Each isoleucine contains two stereocenters. The standard L-isoleucine residue is (2S,3S), while allo-isoleucine has a different configuration at the beta carbon. Because these stereoisomers have the same molecular formula and molecular weight, identity cannot be confirmed by MS alone.

For stereochemically demanding projects, procurement should rely on exact CAS/structure documentation and, where required, chiral or optical-rotation data in addition to routine chemical purity.

Application Scope

Fmoc-Ile-Ile-OH is useful for synthesis of hydrophobic peptides, beta-branched sequence motifs, peptidomimetic fragments and SAR libraries investigating side-chain packing or local conformational effects.

After incorporation into a complete peptide, the Ile-Ile motif may influence binding, membrane interaction, aggregation or proteolysis depending on sequence context. These properties should be measured on the final peptide.

Purchasing and QC Considerations

Verify L-Ile-L-Ile identity, both isoleucine stereocenters, CAS number, Fmoc protection and chemical purity. For a building block with multiple stereocenters, a chemically clean HPLC trace is not by itself proof of stereochemical purity.

Product Documents

A Material Safety Data Sheet (MSDS) is available for this product to support laboratory handling, storage and safety assessment.

MSDS_Fmoc-Ile-Ile-OH_AS4067

Certificates of Analysis (COAs) are batch-specific. Please contact us to request the COA for your product, and we will provide it by email.

Frequently Asked Questions

Why use Fmoc-Ile-Ile-OH instead of coupling two Ile residues separately?

A preassembled dipeptide can bypass one sterically demanding Ile-Ile coupling and provides a defined stereochemical fragment.

Is Fmoc-Ile-Ile-OH the same as an allo-Ile-containing dipeptide?

No. Allo-Ile differs at a stereocenter even though molecular formula and mass can be identical.

What assays can Ile-Ile-containing peptides be used in?

Depending on the final sequence, they may be studied in binding, enzyme, membrane, cell-based or in vivo assays after full synthesis and characterization.

Related Technical Resources

Explore additional Specialty Peptide Building Blocks for protected fragments, linker motifs and peptide-synthesis intermediates.

For sequence-specific synthesis, protected-fragment assembly and modified peptide projects, see our Chemical Peptide Synthesis service.

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