Fmoc-Thr(tBu)-Ser[psi(Me,Me)pro]-OH is an Fmoc-protected Thr-Ser pseudoproline building block for solid-phase peptide synthesis (SPPS). The Ser residue is incorporated in a reversible 2,2-dimethyloxazolidine pseudoproline form that temporarily changes local backbone hydrogen-bonding and conformation during chain elongation.

The preformed Thr-Ser unit introduces the sequence motif in one coupling operation. Under standard TFA-mediated final cleavage and deprotection, the acid-labile pseudoproline ring is opened and the native Ser residue is regenerated.

Product Information

Two Hydroxy Residues, Two Protection Roles

In the Thr-Ser unit, the upstream Thr(tBu) residue carries conventional tert-butyl side-chain protection, while the downstream Ser residue is incorporated as a pseudoproline. The upstream tBu group masks side-chain reactivity; the downstream oxazolidine modifies backbone behavior. This distinction is important when planning deprotection and sequence recovery. For broader process context, see our solid-phase peptide synthesis guide.

Application in Ser/Thr-Rich Difficult Sequences

Ser/Thr-rich regions can be highly polar yet still develop sequence-dependent secondary structure on resin. A pseudoproline at the downstream residue can interrupt local backbone organization without permanently modifying the final Thr-Ser sequence.

Final Acid Treatment

Standard TFA-mediated global deprotection removes the tert-butyl ether from the upstream residue and opens the pseudoproline ring at the downstream residue. The final peptide therefore recovers native hydroxyl functionality at both positions, subject to the complete protecting-group pattern of the synthesis.

When This Architecture Is Useful

We consider this reagent when a native Thr-Ser segment is part of a difficult assembly and both side-chain protection and temporary backbone disruption are desired. It is not a generic substitute for ordinary Fmoc-Ser(tBu)-OH or Fmoc-Thr(tBu)-OH in routine sequences. Related motifs can be compared in the protected pseudoproline building blocks.

Experimental Planning

When a difficult sequence contains several possible Ser/Thr pseudoproline insertion sites, placement should be assessed together with chain length, hydrophobicity, resin loading, neighboring residues, and the stage at which coupling or deprotection performance begins to decline. The presence of a Thr-Ser motif alone does not establish that this building block is required.

For projects where building-block selection needs to be evaluated with the full target sequence, our modified peptide synthesis can support integrated planning, synthesis, purification, and QC requirements.

Product Documents

MSDS - Fmoc-Thr(tBu)-Ser[psi(Me,Me)pro]-OH (AS4031)

The Safety Data Sheet provides product identification, hazard information, handling and storage guidance, exposure controls, transport information, and regulatory information for laboratory use.

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 does psi(Me,Me)pro indicate?

It denotes a dimethyl-substituted pseudoproline formed from the downstream Ser residue. The five-membered oxazolidine temporarily changes backbone behavior during synthesis.

Why is the Thr-Ser unit supplied as a preformed building block?

The amide bond immediately before the pseudoproline nitrogen is already formed, avoiding direct acylation of a sterically hindered oxazolidine nitrogen and allowing the motif to be introduced in one coupling operation.

Does the pseudoproline remain in the final peptide?

No. Standard TFA-mediated final cleavage opens the pseudoproline ring and restores the downstream Ser residue.

Are all protecting groups removed during final cleavage?

The protecting groups used here are acid-labile and are generally removed during TFA-mediated global deprotection, but the final cleavage cocktail should always be chosen for the complete sequence and its full protecting-group pattern.

Research Use Only.