Boc-L-cysteine is a protected amino acid derivative of L-cysteine in which the amino group is carbamylated with a tert-butoxycarbonyl (Boc) protecting group, while the molecule retains the free carboxylic acid functionality and the cysteine thiol-containing side chain. The side chain bears a sulfhydryl (-SH) group that can participate in thiol-disulfide chemistry and other nucleophilic transformations, whereas the Boc group controls chemoselectivity by reducing the reactivity of the amino functionality during peptide-coupling steps. Boc-L-cysteine is used as a precursor for preparing cysteine-containing peptides and peptide building blocks in stepwise synthesis, including solid-phase or solution-phase strategies where orthogonal protection and side-chain handling are required to manage thiol reactivity.
CAT No: CP00613
CAS No:20887-95-0
Synonyms/Alias:Boc-L-cysteine;Boc-Cys-OH;20887-95-0;N-Boc-L-Cysteine;N-tert-Butyloxycarbonylcysteine;(R)-2-((TERT-BUTOXYCARBONYL)AMINO)-3-MERCAPTOPROPANOICACID;N-ALPHA-T-BUTYLOXYCARBONYL-L-CYSTEINE;n-boc-cysteine;PubChem9978;BOC-L-CYS-OH;N-t-butoxycarbonyl-L-cysteine;SCHEMBL314569;AC1L484R;15411_FLUKA;CTK4E5391;ATVFTGTXIUDKIZ-YFKPBYRVSA-N;MolPort-003-926-781;ZINC4521267;ANW-24273;SBB066211;N-(tert-Butyloxycarbonyl)-L-cysteine;AKOS015841311;AKOS015895914;AB02619;(R)-2-((TERT-BUTOXYCARBONYL)AMINO)-3-MERCAPTOPROPANOIC ACID;L-Cysteine, N-[(1,1-dimethylethoxy)carbonyl]-;(2R)-2-[(2-methylpropan-2-yl)oxycarbonylamino]-3-sulfanylpropanoic acid;DTXSID30175033;(2R)-2-{[(tert-butoxy)carbonyl]amino}-3-sulfanylpropanoic acid;MFCD00065565;BOC-L-CYS-OH;Boc-Cys-Cysteine;DTXCID6097524;(tert-butoxycarbonyl)-cysteine-OH;BCP06688;CS-W014733;FD21262;AS-49016;DB-200472;EN300-317069;Boc-Cys-OH, for chiral derivatization, >=98.5%
Boc-L-cysteine is an L-cysteine derivative bearing an N-terminal Boc (tert-butoxycarbonyl) protecting group and a side-chain thiol that is commonly handled as a protected thiol form for peptide chemistry workflows. As a protected amino acid building block, it is used to introduce cysteine residues into peptides while controlling undesired thiol reactivity during assembly. The Boc-protected amino acid format supports standard peptide synthesis strategies used in research-grade and custom peptide manufacturing settings, where cysteine's sulfur functionality is a key feature for subsequent functionalization or disulfide formation.
1. Solid-Phase Peptide Synthesis
Boc-L-cysteine is widely used as a cysteine residue building block in solid-phase peptide synthesis workflows, especially when cysteine incorporation is required in peptide libraries or sequence-specific custom peptides. Researchers and peptide synthesis service groups rely on Boc-protected amino acid formats to manage N-terminal reactivity during stepwise chain assembly, while the cysteine side chain is kept under controlled conditions to reduce side reactions that can occur with free thiols. This makes the reagent a practical choice for constructing peptides that will later be processed for native disulfide patterns, thiol-based derivatization, or cysteine-dependent functional studies.
2. Disulfide and Thiol Chemistry
Boc-L-cysteine supports downstream sulfur chemistry in peptide and protein engineering workflows where cysteine thiols are used to generate disulfide linkages or to introduce site-specific thiol handles for further modification. In chemical biology and structural biology projects, cysteine-containing peptide intermediates are often processed to enable disulfide formation that stabilizes folded motifs or to provide reactive thiol functionality for controlled conjugation steps. Using a Boc-protected cysteine building block helps maintain synthetic control during peptide assembly, so the sulfur functionality can be carried forward into the stage where disulfide mapping or thiol-directed functionalization is performed.
3. Pharmaceutical Intermediate Development
Boc-L-cysteine is also used as a protected amino acid intermediate in medicinal chemistry and pharmaceutical intermediate development, where cysteine-derived fragments are needed to build peptidomimetic scaffolds or cysteine-containing linkers. Process chemists and API-adjacent development teams often select Boc-protected amino acid building blocks to manage chemoselectivity during multistep synthesis, keeping the amino functionality masked while the sulfur functionality is handled under conditions compatible with subsequent transformations. This positioning is particularly relevant when cysteine's thiol is a defining structural element for later coupling, cyclization, or functional group interconversion in the synthesis of larger, more complex intermediates.
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