Boc-L-Cys(Fm)-OH is a protected amino acid derivative of L-cysteine in which the α-amino group is protected as a Boc carbamate and the side-chain thiol is protected as an Fm thioether (Fm group). The molecule contains both an α-carboxylic acid and a Boc-protected amino functionality, while the cysteine β-thiol is masked to prevent disulfide formation or thiol oxidation during handling and coupling, and the stereochemistry is specified as L by the product name. In peptide synthesis workflows, this protected analogue is used as a stepwise building block to support chemoselective amide bond formation at the α-carboxyl/α-amino positions while maintaining the cysteine side chain in a protected state for later deprotection and functionalization.
CAT No: CP26073
CAS No:84888-35-7
Synonyms/Alias:Boc-Cys(Fm)-OH;84888-35-7;AmbotzBAA5510;SCHEMBL8541445;Boc-S-Fluorenylmethyl-L-cysteine;CTK8F8269;MolPort-008-267-466;ZINC2554996;AKOS015998819;AJ-39662;AK-86491;KB-48256;FT-0699051;ST24030192;W8759;N-Boc-S-(9H-Fluoren-9-ylmethyl)-L-Cys-OH;A26737;N-alpha-t-Butyloxycarbonyl-S-(9-fluorenylmethyl)-L-cysteine;N-tert-Butoxycarbonyl-S-fluorenylmethyl-L-cysteine;Boc-L-Cys(Fm)-OH
Chemical Name:N-alpha-t-Butyloxycarbonyl-S-(9-fluorenylmethyl)-L-cysteine
Boc-L-Cys(Fm)-OH is a protected cysteine building block bearing a Boc-protected alpha-amino group and an Fm (formyl/methylene-type) protected thiol side chain, providing controlled reactivity during peptide assembly. This protected amino acid is commonly used in workflows where cysteine's sulfhydryl functionality must be masked to prevent side reactions such as oxidation or disulfide scrambling. The combination of Boc on nitrogen and Fm on sulfur makes it a practical intermediate for preparing cysteine-containing peptides and for generating defined cysteine residues in downstream synthetic steps.
1. Boc-Based Peptide Synthesis
Boc-L-Cys(Fm)-OH is used by peptide synthesis groups to incorporate cysteine residues into sequences while maintaining thiol protection throughout coupling and deprotection steps. Researchers performing custom peptide synthesis rely on the masked sulfhydryl to suppress oxidation and undesired disulfide formation during solid-phase or solution-phase assembly, enabling cleaner access to cysteine-containing intermediates and final peptides. The Boc-protected amino group supports established Boc-chemistry workflows, where controlled deprotection and sequential coupling are required to build longer peptide segments with cysteine positioned at defined sites.
2. Cysteine-Containing Segment Building
Boc-L-Cys(Fm)-OH is frequently selected for preparing cysteine-bearing peptide segments used in segment condensation strategies and modular peptide assembly. In medicinal chemistry and peptide development, defined cysteine placement is often required for subsequent functionalization, such as generation of a free thiol for conjugation or for controlled formation of disulfide-linked motifs. The Fm-protected side chain helps keep the cysteine residue chemically stable during intermediate handling, purification, and iterative synthesis steps, which is particularly valuable when producing peptides that will later undergo thiol-dependent transformations.
3. Thiol-Functional Intermediate Preparation
Boc-L-Cys(Fm)-OH supports the preparation of thiol-reactive peptide intermediates by providing a protected cysteine that can be converted to a defined thiol-containing species under appropriate downstream conditions. Chemical biology and biomaterials researchers often need cysteine residues that can be selectively unveiled and then used for subsequent coupling strategies, including site-directed conjugation to linkers or surfaces after the peptide scaffold has been assembled. By keeping the sulfhydryl masked during peptide construction, the reagent helps minimize side reactions that can compromise yield and reproducibility when generating thiol-bearing intermediates for later derivatization.
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