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Fmoc-Ser(tBu)-Ile-OH is a protected Ser-Ile dipeptide in which the serine amino terminus carries Fmoc and the serine side-chain hydroxyl is protected as a tert-butyl ether. The C-terminal isoleucine carboxyl group remains available for further activation.
This fragment combines a polar, protected Ser residue with beta-branched Ile. Its practical value is to supply the Ser-Ile bond as a preformed unit, which can be useful when a route would otherwise place that coupling in a more crowded or aggregation-prone stage.
Product Information
| Product Name | Fmoc-Ser(tBu)-Ile-OH |
| Catalog No. | AS4136 |
| Molecular Formula | C28H36N2O6 |
| Molecular Weight | 496.60 g/mol |
| Chemical Identity | Fmoc-L-Ser(tBu)-L-Ile-OH; protected Ser-Ile dipeptide fragment |
| Building Block Type | Fmoc/tBu-protected dipeptide |
| Primary Applications | Protected Ser-Ile fragment coupling, convergent peptide synthesis, beta-branched sequence assembly and route development |
Stepwise Alternative: Ser(tBu) + Ile
A conventional route can assemble the same motif from Fmoc-Ser(tBu)-OH and Fmoc-Ile-OH. Choosing the preformed fragment removes one downstream coupling and can simplify impurity attribution. We consider this a route-efficiency decision rather than a universal quality improvement.
Why Isoleucine Needs Stereochemical Attention
Isoleucine contains two stereocenters, so L-Ile and allo-Ile variants cannot be distinguished by nominal molecular mass. The fragment name should therefore be supported by a structure record and lot-specific stereochemical documentation. This is especially important when the material is used as a sequence standard or in SAR work.
Beta-Branched Residues Can Increase Coupling Demand
Ile's beta branching increases steric congestion near the peptide backbone. In longer hydrophobic sequences, beta-branched residues can also contribute to slower coupling and aggregation. The SPPS side-reaction and difficult-coupling guide explains why sequence-level behavior can remain challenging even when one local dipeptide bond is already preformed.
Procurement and QC Considerations
Confirm the Fmoc-L-Ser(tBu)-L-Ile sequence, L-Ile stereochemistry, Ser O-tBu protection, HPLC purity and MS on the lot-specific COA.
For Ser/Ile-rich or otherwise sterically demanding sequences, custom synthesis for beta-branched and difficult peptide sequences can be evaluated before scale-up.
Product Documents
A Safety Data Sheet (SDS / MSDS) is available for this product to support laboratory handling, storage and safety assessment.
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
What is Fmoc-Ser(tBu)-Ile-OH used for?
It is used as a protected Ser-Ile dipeptide fragment for peptide extension and convergent assembly.
Which group protects the serine side chain?
The serine hydroxyl is protected as a tert-butyl ether.
Why does isoleucine stereochemistry need separate QC?
Isoleucine has two stereocenters, and nominal mass does not distinguish L-Ile from stereoisomeric alternatives such as allo-Ile.
Related Technical Resources
Use the monomer links above to compare stepwise assembly with the preformed fragment. For other protected dipeptides, see the specialty peptide building-block collection.