Boc-Cys(Bzl)-ONp is a protected cysteine derivative bearing an N-terminal Boc protecting group and a side-chain benzyl thioether substituent, with the carboxyl functionality converted to an ONp ester (p-nitrophenyl ester) rather than a free acid. The molecule contains a thioether side chain derived from cysteine, an N-Boc carbamate that masks the amino group, and an activated ester that presents a leaving group on the carboxylate for subsequent acyl transfer chemistry, while the stereochemical configuration is not specified in the provided name. Boc-Cys(Bzl)-ONp is used as a stepwise peptide synthesis intermediate or amino-acylating reagent in contexts where controlled handling of the amino and carboxyl functionalities is required, including the preparation of more complex cysteine-containing amino acid and peptide derivatives.
CAT No: CP27049
CAS No:3560-17-6
Synonyms/Alias:3560-17-6;4-nitrophenyls-benzyl-n-(tert-butoxycarbonyl)-l-cysteinate;Boc-Cys(Bzl)-ONp;BOC-CYS-ONP;AC1L40EL;AC1Q60ZQ;MolPort-006-115-430;ZINC2575527;EINECS222-622-3;AR-1G4103;Boc-S-Benzyl-L-cysteine4-nitrophenylester;p-NitrophenylS-benzyl-N-(tert-butoxycarbonyl)-L-cysteinate;(4-nitrophenyl)(2R)-3-benzylsulfanyl-2-[(2-methylpropan-2-yl)oxycarbonylamino]propanoate;N-[(1,1-Dimethylethoxy)carbonyl]-S-(phenylmethyl)-L-cysteine4-nitrophenylester
Boc-Cys(Bzl)-ONp is a protected cysteine building block designed for peptide coupling workflows, featuring an N-terminal Boc protecting group and a side-chain benzyl thioether (Bzl) that maintains cysteine's sulfur in a non-thiol state during assembly. The C-terminal ONp ester provides an activated carboxylate equivalent, enabling efficient segment condensation in solution-phase or pre-activated peptide intermediate strategies. This reagent is commonly selected when cysteine-containing sequences require controlled handling of the thioether-protected side chain and reliable coupling performance from an ester-activated form.
1. Solution-Phase Peptide Coupling
Boc-Cys(Bzl)-ONp is used by peptide synthesis groups to assemble cysteine-containing peptide segments through activated ester condensation, supporting workflows where peptide fragments are coupled in solution rather than on resin. Researchers in custom peptide manufacturing and medicinal chemistry frequently rely on ONp-activated amino acid derivatives to promote consistent coupling during fragment joining, particularly when building blocks must remain protected to avoid side reactions. The Boc group and Bzl thioether protection help preserve the N-terminus and sulfur side chain throughout the coupling step, allowing downstream deprotection and functionalization only after the desired sequence assembly is complete.
2. Cysteine-Containing Segment Building
Boc-Cys(Bzl)-ONp serves as a practical cysteine residue unit for constructing peptide intermediates where the sulfur must be protected as a benzyl thioether until the final stages of synthesis. Peptide chemists use this reagent to prepare intermediates for longer chain assembly, including thioether-stabilized sequences that later undergo controlled conversion to free thiol or other cysteine-derived functionalities under orthogonal conditions. The activated ONp ester form supports efficient incorporation of the cysteine residue during segment condensation, which is particularly valuable for libraries and iterative synthesis plans where reproducible coupling of protected amino acid units is required.
3. Pharmaceutical Intermediate Development
Boc-Cys(Bzl)-ONp is also used in the development of peptide-based pharmaceutical intermediates, where cysteine residues often need to be introduced under protection to maintain chemoselectivity during multi-step synthesis. Process and development chemists select Boc-protected, thioether-protected cysteine ONp esters to manage reactive functional groups during intermediate preparation, enabling later deprotection steps to be scheduled alongside purification and analytical checkpoints. This reagent format is frequently integrated into scalable peptide intermediate routes for generating defined cysteine-containing intermediates used in subsequent downstream transformations toward final peptide candidates or advanced conjugation-ready precursors.
4. Peptide Library Synthesis
Boc-Cys(Bzl)-ONp is employed in peptide library construction when a cysteine-containing motif must be introduced repeatedly with consistent protection patterns and coupling behavior across many analogs. Researchers performing structure-activity relationship studies often require a standardized, cysteine-compatible building block that minimizes variability arising from side-chain reactivity during synthesis. The combination of Boc at the amino terminus, Bzl protection on sulfur, and the ONp activated ester at the carboxyl terminus supports robust incorporation of the cysteine residue while keeping the side chain protected until library members are ready for final deprotection or further derivatization.
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