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Fmoc-His(Boc)-OH is an L-histidine building block with Fmoc protection on the α-amino group and Boc protection on an imidazole nitrogen. It provides an alternative side-chain protection pattern to the more conventional Fmoc-His(Trt)-OH.
The two histidine reagents should not be chosen only by price or molecular weight. Boc and Trt change imidazole protection, acid sensitivity and potentially the practical behavior of the residue during coupling and cleavage.
Product Information
| Product Name | Fmoc-His(Boc)-OH |
| Catalog No. | AS2052 |
| CAS No. | 81379-52-4 |
| Molecular Formula | C26H27N3O6 |
| Molecular Weight | 477.51 g/mol |
| Building Block Type | Fmoc-protected L-histidine with N-imidazole Boc protection |
| Primary Applications | Fmoc-SPPS; histidine-containing peptides; alternative imidazole protection; specialized route development |
Why Histidine Protection Matters
Histidine's imidazole is nucleophilic, basic and capable of metal coordination. Protecting it during chain assembly reduces unwanted side reactions and helps standardize coupling behavior.
Boc Versus Trt on Histidine
Boc- and Trt-protected histidine derivatives differ in steric bulk and acid lability. The better option depends on cleavage conditions, neighboring residues and the broader protecting-group strategy.
Racemization Remains the Main Stereochemical Risk
Changing the imidazole protecting group does not remove histidine's susceptibility to epimerization during activation. Prolonged preactivation, strong base and elevated temperature can increase risk. This is why the current SPPS side-reaction guide treats histidine stereochemical control as a process issue, not just a raw-material specification.
Procurement and QC
PubChem confirms CAS 81379-52-4, C26H27N3O6 and MW 477.5 g/mol for Fmoc-His(Boc)-OH. Confirm L stereochemistry and the position of Boc protection on the lot-specific structure. For high-purity His-containing peptides, coupling conditions should be reviewed together with the building block. Alan Scientific can support this through custom 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
How does Fmoc-His(Boc)-OH differ from Fmoc-His(Trt)-OH?
They use different imidazole protecting groups and therefore different steric and deprotection profiles.
Does Boc protection prevent histidine racemization?
No. Coupling conditions still strongly influence epimerization risk.
Can LC-MS detect a D-His epimer in the final peptide?
Not by mass alone; epimers have the same molecular weight.
Related Technical Resources
Review common SPPS side reactions