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Di-Fmoc-seleno-L-cystine is the diselenide-linked dimer of Fmoc-protected selenocysteine. Its two selenium atoms replace the sulfur atoms of a cystine-type disulfide while the two α-amino groups remain protected with Fmoc.
This reagent belongs to the broader class of noncanonical amino-acid building blocks used when selenium chemistry is intentionally introduced into a peptide or peptide-derived intermediate. It should be treated as a redox-active specialty building block, not as a direct biological reagent.
Product Information
| Product Name | Di-Fmoc-seleno-L-cystine |
| Catalog No. | AS4158 |
| CAS No. | 1639843-33-6 |
| Molecular Formula | C36H32N2O8Se2 |
| Molecular Weight | 778.60 g/mol |
| Building Block Type | Di-Fmoc-protected selenocystine diselenide |
| Primary Applications | Selenocysteine chemistry; diselenide-containing peptide design; redox and ligation research; specialty peptide synthesis |
Why Selenium Changes the Chemistry
Selenium is larger and more polarizable than sulfur, and Se-Se/Se-S redox chemistry can behave differently from conventional disulfides. In peptide research, that difference can be used to study redox behavior, folding pathways, ligation chemistry, or selenocysteine-containing analogs. The final outcome depends on sequence, solvent, oxidation state, and downstream conditions.
Dimeric Diselenide Identity Matters
The product is a diselenide dimer, not a monomeric free selenol. Formula C36H32N2O8Se2 and MW 778.60 g/mol reflect two protected amino-acid units joined through Se-Se. Procurement should confirm the dimeric structure as well as CAS identity.
Fmoc Protection and Route Planning
Both α-amino groups are Fmoc-protected. Converting the diselenide into a sequence-ready selenocysteine strategy may require reduction, selective handling, or other route-specific operations. We recommend planning selenium redox chemistry together with peptide assembly rather than treating it as a routine cysteine substitution.
Analytical and Handling Considerations
Confirm CAS 1639843-33-6, the two-selenium molecular formula, and the diselenide structure. Selenium-containing materials can show isotope-rich MS patterns, which should be interpreted against the expected elemental composition. Lot-specific purity and storage documentation remain important.
Procurement and QC Considerations
Projects using selenocysteine, diselenides, or mixed Se/S linkages can be evaluated through custom peptide synthesis with specialty residues.
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 Di-Fmoc-seleno-L-cystine the same as Fmoc-Cys(Trt)-OH?
No. This is a selenium-containing diselenide dimer, whereas Fmoc-Cys(Trt)-OH is a sulfur-containing monomeric cysteine building block.
Why are there two Fmoc groups?
The molecule contains two amino-acid units, each with an Fmoc-protected α-amino group.
Can routine LC-MS confirm the selenium composition?
LC-MS supports molecular identity, and the selenium isotope pattern can provide additional evidence, but lot-specific structural documentation should also be reviewed.
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