H-D-Cys(tBu)-OH · HCl

H-D-Cys(tBu)-OH · HCl is the hydrochloride salt of the D-enantiomer of cysteine bearing a tert-butyl-protected thiol, presented as a free carboxylic acid. The molecule contains a stereogenic center at the alpha carbon (D-configuration), a protected side-chain sulfur in the form of a thioether-like tBu thio-protecting group, and an acid functional group suitable for activation and coupling. The salt form improves handling of the amino acid while maintaining compatibility with standard peptide synthesis conditions that rely on carboxyl activation and amine protection/deprotection logic. The tBu-thiol protection strategy enables controlled chemoselective transformations of the sulfur functionality during peptide assembly, fragment elaboration, and downstream thiol-based conjugation chemistry.

1. Peptide Synthesis

H-D-Cys(tBu)-OH · HCl supports peptide building block preparation where cysteine side-chain protection is required to prevent premature thiol reactivity during coupling. The D-configured alpha-amino acid backbone enables incorporation of D-cysteine residues into peptides, supporting stereochemical control for peptidomimetic scaffolds and stability-focused sequence design. The carboxylic acid can be converted into activated derivatives compatible with amide bond formation, while the tert-butyl thiol protection can be maintained through iterative coupling cycles and then removed under conditions selected for sulfur unmasking. The resulting D-cysteine-containing peptides can be further processed for disulfide formation, thioether linkage construction, or site-specific functionalization, aligning amino acid chemistry with peptide science workflows.

2. Side-Chain Functionalization

H-D-Cys(tBu)-OH · HCl is suitable for side-chain functionalization strategies that target cysteine sulfur chemistry after controlled deprotection. The protected thiol group (tBu-protected) enables storage and handling without uncontrolled oxidation or side reactions, while the D-stereocenter can be used to tune stereochemical recognition in synthetic constructs. Thiol unmasking can generate a reactive sulfur nucleophile for alkylation, acylation, or conjugation to electrophiles bearing handles for downstream labeling or crosslinking. The amino acid-based intermediate nature of H-D-Cys(tBu)-OH · HCl also supports conversion into derivatives that serve as functional fragments in broader synthetic organic chemistry and chemical biology programs.

3. Bioconjugation Chemistry

H-D-Cys(tBu)-OH · HCl can be applied in bioconjugation workflows where cysteine-derived thiol functionality is required for site-selective coupling to biomolecules. The compound's carboxyl group and protected amine/acid framework can be leveraged to build conjugation-ready linkers that incorporate D-cysteine residues, supporting stereochemically defined attachment points in protein labeling or peptide-based probes. The tert-butyl thiol protection strategy helps manage chemoselectivity by minimizing thiol oxidation during linker synthesis and purification, while the D-configuration can be used to influence binding orientation and stability of the conjugated product. Downstream derivatives prepared from this amino acid can be employed for constructing thioether or disulfide-linked biomolecule conjugates and for generating controlled chemical reporters for analytical and biochemical investigations.

4. Peptidomimetics And SAR Studies

H-D-Cys(tBu)-OH · HCl is relevant to peptidomimetic construction and structure-activity relationship studies that require incorporation of stereochemically defined D-cysteine residues. The D-amino acid backbone and protected sulfur allow assembly of analogs where side-chain chemistry is introduced at a controlled stage, supporting consistent handling of thiol-containing motifs during synthesis. The carboxylic acid functionality enables conversion into coupling partners for fragment assembly, while the tBu thiol protection supports selective deprotection to generate reactive intermediates for sulfur-based modifications. D-cysteine-containing peptidomimetics derived from this intermediate can be used to probe how stereochemistry and sulfur substitution patterns impact molecular recognition, conformational preferences, and functional group presentation in SAR-oriented molecular design.

5. Pharmaceutical Intermediate Preparation

H-D-Cys(tBu)-OH · HCl fits pharmaceutical intermediate preparation pipelines that require protected cysteine building blocks for downstream synthesis of sulfur-functional drug-like molecules. The hydrochloride salt form supports controlled handling of the amino acid during industrial fine chemical synthesis, while the D-configuration provides a stereochemical handle for manufacturing routes that target specific stereoisomeric outcomes. The tert-butyl thiol protection strategy enables the sulfur functionality to remain masked during early stages of coupling, protecting against oxidation and side reactions that can complicate scale-up. The resulting intermediates can be carried forward into peptide-like fragments, thioether/disulfide motifs, or sulfur-containing linker units, supporting process chemistry needs for reproducible intermediate generation and subsequent functional group unveiling.

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