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Fmoc-Ser(HPO3Bzl)-OH is a protected phosphoserine derivative for introducing a defined phosphorylated serine residue during Fmoc solid-phase peptide synthesis. The alpha-amino group is Fmoc-protected, while the phosphate is partially protected with one benzyl group.
This is chemically different from ordinary Fmoc-Ser(tBu)-OH. The target state after synthesis is phosphoserine rather than serine, so the building block changes both charge and deprotection behavior in the growing peptide.
Product Information
| Product Name | Fmoc-Ser(HPO3Bzl)-OH |
| Catalog No. | AS2099 |
| CAS No. | 158171-14-3 |
| Molecular Formula | C25H24NO8P |
| Molecular Weight | 497.43 g/mol |
| Building Block Type | Fmoc-protected O-benzyl phosphoserine |
| Primary Applications | Phosphopeptide synthesis; site-specific phosphoserine incorporation; Fmoc-SPPS; kinase and phosphatase research peptides |
Why Use a Prephosphorylated Serine Building Block
Introducing phosphorylation at the building-block stage gives positional control over the phosphoserine site. Fmoc-Ser(tBu)-OH is appropriate when the final residue should be ordinary Ser, whereas Fmoc-Ser(HPO3Bzl)-OH is selected when the final peptide must contain a defined phosphate at that position.
Phosphate Protection and Fmoc-SPPS
The monobenzyl-protected phosphate is designed to tolerate standard peptide elongation while reducing the reactivity and charge of a fully unprotected phosphate. After final deprotection, the target phosphoserine functionality is regenerated. The protection state should be confirmed on the COA because mono- and di-protected phosphate reagents are not interchangeable.
A Practical Deprotection Risk
Published supplier guidance notes that phosphoserine-containing intermediates can undergo beta-elimination or piperidine-related side chemistry under unfavorable Fmoc-deprotection conditions, particularly when the phosphoserine becomes N-terminal. We consider this a reason to review deprotection conditions rather than simply extending piperidine exposure when a phosphopeptide synthesis begins to underperform.
Phosphopeptide Applications
Defined phosphopeptides are used in kinase, phosphatase, antibody-recognition and protein-interaction studies. Alan Scientific's peptide applications overview provides broader context for phosphorylation-dependent research designs.
Procurement and QC Considerations
Confirm CAS 158171-14-3, C25H24NO8P, MW 497.43 g/mol and the O-benzyl phosphate structure. For multi-phosphorylated or otherwise sensitive sequences, the full protecting-group plan should be evaluated as part of custom modified peptide synthesis.
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
Is this the same as Fmoc-Ser(tBu)-OH?
No. This building block is designed to produce phosphoserine; Fmoc-Ser(tBu)-OH produces ordinary serine.
Why is the phosphate benzyl-protected?
Partial protection reduces phosphate reactivity during synthesis while allowing final regeneration of phosphoserine.
Can it be used in standard Fmoc-SPPS?
Yes, but phosphoserine-containing sequences can require more careful deprotection control than ordinary serine sequences.
Related Technical Resources
Review common SPPS side reactions
Review the full Fmoc-SPPS workflow