Boc-Cys(Acm)-OSu is a Boc-protected cysteine derivative bearing an Acm (acetamidomethyl) thioether-protecting group on the side-chain sulfur and an OSu (N-hydroxysuccinimide) ester at the carboxyl terminus. The molecule contains a Boc carbamate on the amino group, a free or activated carboxyl functionality converted to an N-hydroxysuccinimide ester, and a thioamide-protected cysteine side chain that is commonly used to control chemoselectivity during peptide coupling and subsequent sulfur-directed transformations. As an activated amino acid ester, it is employed in peptide chemistry and bioconjugation workflows to introduce a cysteine residue under conditions that favor amide bond formation while deferring side-chain reactivity until deprotection or selective functionalization steps are performed.
CAT No: CP26605
CAS No:19746-38-4
Synonyms/Alias:Boc-Cys(Acm)-OSu;ZINC71788043;19746-38-4
Boc-Cys(Acm)-OSu is a Boc-protected cysteine derivative bearing an Acm-protected thiol and an activated N-hydroxysuccinimide (OSu) ester at the carboxylate. This combination is used to enable controlled cysteine handling during peptide and bioconjugation workflows, where the Acm group suppresses thiol reactivity until a deliberate deprotection step is applied. The activated OSu ester supports efficient coupling to amine-containing partners under standard peptide-chemistry conditions.
1. Peptide Segment Coupling
Boc-Cys(Acm)-OSu is used by peptide synthesis groups as an activated cysteine building block for segment condensation and targeted incorporation of a protected cysteine residue. The OSu ester form promotes reliable amide bond formation with amine-bearing fragments, while the Boc group provides N-terminal protection and the Acm group maintains thiol chemoselectivity during assembly. This reagent format is particularly valued when cysteine-containing sequences require minimized side reactions from the sulfhydryl functionality until the desired stage of synthesis.
2. Cysteine Bioconjugation Intermediates
Boc-Cys(Acm)-OSu is employed in chemical biology and bioconjugation development to generate cysteine-functional conjugates through OSu-mediated coupling to lysine or N-terminal amines on peptides, linkers, or carrier proteins. The Acm-protected thiol helps preserve a controlled "masked" cysteine handle during the initial conjugation step, supporting downstream processing where thiol unmasking is performed to enable selective conjugation, labeling, or further derivatization. Researchers developing modular conjugation strategies often choose this reagent because it integrates an activated carboxylate with thiol protection in a single, workflow-friendly intermediate.
3. Thioselective Post-Modification
Boc-Cys(Acm)-OSu is used as a cysteine source in workflows that require later, thiol-directed chemistry after the main assembly step is complete. By keeping the cysteine sulfur protected as Acm during coupling or fragment assembly, the reagent supports preparation of intermediates that can be carried forward to controlled thiol activation and subsequent transformations. This approach is common in peptide engineering and materials chemistry programs where cysteine reactivity must be deferred to a specific stage to improve reproducibility and reduce formation of undesired disulfides or thioether byproducts.
4. Analytical Reference Peptide Synthesis
Boc-Cys(Acm)-OSu is also applied in the preparation of cysteine-containing reference peptides and standards used for method development and characterization in peptide analytics. The OSu activation supports consistent incorporation of the cysteine unit into defined sequences, while the Boc and Acm protecting groups help maintain structural integrity through synthesis and purification. Analytical groups use such standards to support LC-MS method tuning, retention-time matching, and verification of cysteine-containing product identity under controlled synthetic conditions.
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