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Fmoc-S-(3-fluorophenyl)-L-cysteine (Fmoc-Cys(S-3-F-Ph)-OH) is an Fmoc-protected L-cysteine thioether in which sulfur is bonded to a 3-fluorophenyl group. It is an S-aryl cysteine building block for noncanonical peptide synthesis, thioether-containing peptide design, and medicinal-chemistry studies.
The fluorophenyl group is attached through sulfur and should not be interpreted as a fluorinated phenylalanine side chain. This connectivity creates a distinct thioether-containing residue with different geometry, oxidation behavior, and analytical identity.
Product Information
| Product Name | Fmoc-S-(3-fluorophenyl)-L-cysteine |
| Preferred Short Name | Fmoc-Cys(S-3-F-Ph)-OH |
| Catalog No. | AS124 |
| Molecular Formula | C24H20FNO4S |
| Molecular Weight | 437.49 g/mol |
| Stereochemistry | L |
| Modification | 3-F-phenyl |
| Primary Research Use | Fmoc-SPPS and noncanonical peptide SAR research |
S-Aryl Cysteine Connectivity
The defining feature is the Cys-S-aryl bond. Exact connectivity matters because phenylalanine analogs and S-phenyl cysteine derivatives can have similar aromatic content but different heteroatom placement and peptide behavior.
For other noncanonical residue classes, see our noncanonical amino acids.
Use in Fmoc-Based Peptide Assembly
The Fmoc-protected alpha-amino group supports Fmoc-SPPS incorporation. The thioether should be considered when selecting oxidation-sensitive workup, cleavage, storage, and analytical conditions, particularly if the peptide contains additional sulfur-containing residues.
For sequence-level route planning, our SPPS coupling strategy summarizes coupling and deprotection factors that can affect nonstandard residues.
Identity and Category Fit
For procurement, verify the S-(3-fluorophenyl) connectivity, L-cysteine stereochemistry, molecular formula, purity method, and lot-specific MS data. If exact stereochemical confirmation is critical, request supporting documentation beyond nominal molecular weight.
This material is chemically an S-aryl cysteine rather than a phenylalanine or tryptophan analog. Its placement alongside aromatic amino-acid building blocks can be convenient for discovery, but the product identity should remain explicit in analytical records.
Product Documents
MSDS - Fmoc-S-(3-fluorophenyl)-L-cysteine (AS124)
The Safety Data Sheet provides product identification, hazard information, handling and storage guidance, exposure controls, transport information, and regulatory information for laboratory use.
Frequently Asked Questions
Is this a fluorinated phenylalanine?
No. It is an S-aryl cysteine derivative. The 3-fluorophenyl group is attached through sulfur.
Does the residue contain a free thiol?
No. The cysteine sulfur is present as an aryl thioether rather than a free thiol.
What analytical point is most important?
MS can support molecular identity, but the S-aryl connectivity and stereochemical assignment should be supported by the structural and lot-specific documentation used for the material.