H-Cys(Bzl)-OBzl · p-tosylate

H-Cys(Bzl)-OBzl · p-tosylate is a cysteine-derived, benzyl-protected amino acid ester salt in which the thiol is masked as a benzyl thioether (Cys(Bzl)) and the carboxyl group is present as a benzyl ester (OBzl), with the overall material converted to a p-tosylate counterion form. The molecule retains a stereogenic center at the cysteine alpha-carbon, enabling stereochemically defined peptide coupling when incorporated as a chiral building block. The benzylic ester and thioether functionalities are stable under many coupling conditions yet can be selectively transformed through hydrogenolysis or nucleophilic substitution strategies, while the tosylate counterion supports practical handling of the amino acid ester. This combination of protected amine-free cysteine functionality and removable benzyl-based protecting groups makes the compound suitable as a downstream intermediate for peptide synthesis, side-chain functionalization, and sulfur-containing motif construction.

1. Peptide Synthesis

H-Cys(Bzl)-OBzl · p-tosylate supports peptide building block preparation in solid-phase or solution-phase workflows by providing a chiral cysteine ester precursor whose benzyl-protected thiol can be carried through amide bond formation without uncontrolled side reactions. The benzyl ester (OBzl) can be converted to an activated carboxyl equivalent under peptide coupling conditions or used after ester transformation to enable N-to-C linkage chemistry while maintaining the thioether-protected sulfur. The defined stereochemistry at the alpha-carbon helps preserve stereochemical integrity during sequential couplings and minimizes racemization risk relative to less protected intermediates. Downstream deprotection and thiol unmasking can be applied after assembly to generate cysteine residues for native disulfide formation or for selective conjugation handles in peptide analogs.

2. Side-Chain Functionalization

H-Cys(Bzl)-OBzl · p-tosylate is suited for sulfur chemistry and side-chain derivatization strategies that require controlled access to cysteine-like reactivity. The Cys(Bzl) thioether and OBzl benzyl ester protect the sulfur and carboxyl groups during manipulations, enabling sequential functional group transformations such as thiol release, electrophile trapping after deprotection, or conversion into activated sulfur intermediates for thioether/thiol-based modifications. The tosylate counterion form can facilitate handling during intermediate preparation steps that involve salt formation or phase-transfer-compatible operations. Resulting derivatives can serve as intermediates for thiol-containing peptidomimetics, thioether scaffolds, and sulfur-functional probes used in chemical biology and materials-oriented conjugation chemistries.

3. Chiral Amino Acid Intermediate

H-Cys(Bzl)-OBzl · p-tosylate functions as a stereochemically defined chiral amino acid intermediate for asymmetric synthesis planning and protected amino acid chemistry where cysteine stereocontrol is required. The alpha-chiral center and the benzyl-based protecting groups provide a stable, isolable form that can be carried through multistep sequences before final functional group unmasking. The benzyl ester and benzyl thioether can be selected for compatibility with common peptide coupling reagents and for orthogonal deprotection timing relative to other protecting groups present on partner amino acids. Downstream use includes preparation of cysteine-containing fragments for library synthesis, stereodefined SAR studies, and chiral route development in fine chemical manufacturing.

4. Bioconjugation Chemistry

H-Cys(Bzl)-OBzl · p-tosylate can be applied to bioconjugation reagent and conjugate precursor development where cysteine-like sulfur functionality is introduced with controlled protection and later activation. The protected thiol state (benzyl thioether) supports manufacturing and storage stability during synthesis of conjugation-ready building blocks, while subsequent deprotection can generate a reactive thiol for maleimide coupling, disulfide exchange, or selective thioether formation depending on the chosen conjugation chemistry. The benzyl ester can be transformed into carboxylate or activated acid forms to enable attachment to targeting ligands, linkers, or polymer backbones. Resulting cysteine-derived conjugation intermediates can be used in labeling workflows, affinity probe construction, and modular scaffold generation for biochemical research.

5. Pharmaceutical Intermediate Preparation

H-Cys(Bzl)-OBzl · p-tosylate is relevant to pharmaceutical intermediate preparation for sulfur-containing peptidomimetic fragments and for the controlled incorporation of cysteine analogs into larger synthetic sequences. The protected amino acid ester form allows integration into fragment assembly strategies where side-chain sulfur must remain masked during coupling and purification, reducing undesired oxidation or electrophile side reactions. The tosylate counterion supports practical intermediate handling and can align with process chemistry needs for isolable salt forms in multistep manufacturing. Downstream transformation of the benzyl-protected groups enables conversion into carboxylic acid or thiol-bearing intermediates that can be further elaborated toward drug-like scaffolds, including cyclic thioether motifs and cysteine-derived linkers used in medicinal chemistry programs.

6. Process Chemistry Intermediate

H-Cys(Bzl)-OBzl · p-tosylate serves as a process chemistry intermediate for industrial-scale synthesis of protected cysteine derivatives and peptide-manufacturing feedstocks. The benzyl ester and benzyl thioether protecting groups provide chemical stability under many coupling and purification operations, supporting reproducible handling and consistent impurity profiles during scale-up. The chiral, stereodefined nature of the cysteine backbone helps maintain stereochemical requirements for downstream peptide analog construction and minimizes the need for extensive stereochemical correction steps. Deprotection-ready functionality supports batch-to-batch conversion into activated acids, thiol-reactive species, or sulfur-containing building blocks, aligning with fine chemical synthesis and specialty chemical production where protected amino acid intermediates are integrated into controlled manufacturing routes.

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