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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.
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 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.