H-Cys(tBu)-OH · HCl

H-Cys(tBu)-OH · HCl is a cysteine-derived amino acid hydrochloride in which the thiol side chain is protected as a tert-butyl thioether (Cys(tBu)), while the amino acid framework retains a free carboxylic acid and an amino group present as its hydrochloride salt. The stereogenic center of cysteine is preserved, enabling stereochemically defined peptide and conjugation chemistry. The tert-butyl thioether functions as a robust sulfur-protecting group that can be cleaved under acidic or thiol-releasing conditions to regenerate the reactive cysteine thiol for subsequent coupling, ligation, or labeling. The salt form improves handling of the amino acid intermediate and supports consistent reactivity in protected amino acid synthesis and downstream transformations.

1. Protected Amino Acids

H-Cys(tBu)-OH · HCl is used in protected amino acid synthesis workflows where cysteine thiol chemoselectivity is required during peptide building block preparation. The carboxylic acid and salt-protected amino functionality support standard peptide coupling strategies, while the tBu thioether protects the sulfur from premature oxidation and side reactions. Deprotection can be scheduled to occur after chain assembly, enabling controlled exposure of the thiol for late-stage functionalization. Downstream, the regenerated cysteine residue can be incorporated into peptides, used to generate thioether or disulfide-containing analogs, or serve as a defined intermediate for sulfur-functional chemical libraries.

2. Peptide Synthesis

H-Cys(tBu)-OH · HCl is suitable for peptide synthesis programs that require cysteine-containing sequences with controlled side-chain reactivity. The amino acid ester/acid functionality and stereodefined backbone allow incorporation into peptide coupling chemistry while the tert-butyl thioether prevents thiol participation during amide bond formation. Orthogonal protection behavior supports strategies where the thiol is revealed selectively after N-/C-terminal assembly, supporting disulfide formation, thioether installation, or site-specific conjugation. Resulting peptide products can be used as research-grade substrates for biochemical assays, as reference standards for analytical characterization, or as precursors to peptidomimetics bearing sulfur-based functional handles.

3. Bioconjugation Chemistry

H-Cys(tBu)-OH · HCl is applied in chemical biology and bioconjugation contexts that depend on cysteine thiol chemistry for controlled attachment of biomolecule conjugates. The protected sulfur group enables handling and coupling steps without uncontrolled thiol oxidation, while the amino acid scaffold supports incorporation into peptide linkers and functional domains. Scheduled deprotection can generate a thiol suitable for conjugation to electrophiles, affinity tags, or crosslinkers, enabling formation of thioether or disulfide-linked constructs. The stereochemical integrity of the cysteine residue supports reproducible linker geometry in downstream conjugate synthesis and in structure-defined biomolecule modification studies.

4. Peptidomimetics And Linkers

H-Cys(tBu)-OH · HCl serves as a chiral sulfur-containing building block for peptidomimetic construction and linker design in synthetic organic chemistry. The protected thiol can be converted into alternative sulfur functionalities after assembly, including thioether derivatives or disulfide motifs that influence conformational stability and binding-site presentation. The free carboxylic acid and amine as hydrochloride support transformation into activated intermediates for fragment coupling, enabling incorporation into non-natural scaffolds or constrained peptide analogs. Downstream utility includes generation of sulfur-functional fragments for SAR studies, reference compounds for method development, and modular intermediates for combinatorial synthesis of peptide-like molecules.

5. Process Chemistry Intermediate

H-Cys(tBu)-OH · HCl is used as a manufacturing-oriented intermediate in fine chemical synthesis where cysteine thiol protection is required to manage reactivity and impurity formation. The tert-butyl thioether protection strategy supports robust handling through aqueous and organic processing steps that would otherwise promote thiol oxidation, while the hydrochloride salt form can improve reproducibility in feed preparation and isolation. The compound's defined stereochemistry and functional group set facilitate scale-compatible conversion into protected amino acid derivatives and activated coupling forms for peptide-grade supply chains. Downstream, the material can be employed to prepare cysteine-containing intermediates for pharmaceutical intermediate preparation, specialty chemical production, and industrial peptide manufacturing routes that require controlled sulfur deprotection timing.

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