Fmoc-Gln(Trt)-Ser[psi(Me,Me)pro]-OH is an Fmoc-protected Gln-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 Gln-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

Dual Protection Architecture

This reagent combines Trt protection on the Gln side-chain amide with a downstream Ser pseudoproline. The Trt group protects the polar side chain during assembly, while the oxazolidine temporarily changes the peptide backbone. The two protection elements solve different synthetic problems and should not be treated as interchangeable. This should be considered alongside aggregation control in SPPS when diagnosing sequence-dependent assembly problems.

Use in Polar, Aggregation-Prone Motifs

A Gln-Ser region can participate in extensive hydrogen-bonding networks as the resin-bound chain grows. The pseudoproline interrupts backbone hydrogen-bonding continuity, while Trt masks the upstream amide functionality. This combination is most useful when the complete sequence shows a genuine aggregation or accessibility problem.

Acidic Global Deprotection

Both Trt and the pseudoproline are acid-labile. Final TFA treatment removes the upstream side-chain Trt group and opens the downstream pseudoproline ring, restoring the intended Gln-Ser residues. Cleavage conditions should account for other acid-labile groups and scavenger requirements in the target peptide.

Selection Considerations

The presence of Gln-Ser is a structural prerequisite, not by itself a reason to use the reagent. We prioritize this type of building block when the motif occurs in a difficult segment and a temporary backbone disruption is expected to improve chain handling during SPPS. Related motifs can be compared in the Ser/Thr 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 Gln-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 difficult peptide project support can support integrated planning, synthesis, purification, and QC requirements.

Product Documents

MSDS - Fmoc-Gln(Trt)-Ser[psi(Me,Me)pro]-OH (AS4022)

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 Gln-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.