H-D-Cys-OH · HCl · H2O is a hydrochloride hydrate salt of the free amino acid derivative D-cysteine, featuring a thiol-bearing side chain (-CH2-SH) attached to the α-amino and α-carboxyl groups. As a salt form, it is present with chloride counterions and includes water of hydration, while the amino and carboxyl functionalities remain available for aqueous chemistry and can participate in acid-base equilibria; the stereochemistry is specified by the D-configuration in the product name. This labeled salt form is used as a chemically defined cysteine source for peptide and amino acid synthesis workflows, thiol-containing conjugation or derivatization studies, and analytical or method development contexts where a stable, weighable cysteine precursor is required.
H-D-Cys-OH · HCl · H2O is the hydrochloride monohydrate salt of D-cysteine, featuring a chiral β-carbon bearing an amino group and a thiol side chain, with the carboxylic acid present as a protonated salt under typical handling conditions. The D stereochemistry at the amino acid backbone enables stereochemically defined incorporation into peptides and stereopure cysteine analogs, while the thiol functionality can participate in nucleophilic substitution, disulfide exchange, and selective redox manipulations when appropriately protected. Salt formation with HCl and hydration influence solubility and handling, supporting reproducible coupling and downstream transformations in peptide synthesis and chemical biology workflows. The compound functions as a foundational amino acid intermediate for protected cysteine derivatives, thioether and disulfide-containing scaffold construction, and analytical or synthetic standards requiring defined stereochemistry and sulfur reactivity.
1. Peptide Synthesis
H-D-Cys-OH · HCl · H2O supports peptide building workflows through its amino and carboxyl functionalities, enabling amide bond formation after conversion to a suitable protected cysteine building block. The thiol side chain requires protection or controlled activation to prevent side reactions during peptide coupling, so the salt form can be used upstream to prepare S-protected derivatives that remain stable under common coupling conditions. D stereochemistry at the α-carbon allows construction of D-cysteine-containing peptides for stereochemical mapping, backbone constraint studies, and peptide analog generation. Downstream, the cysteine residue can be carried through to disulfide formation, thiol deprotection, or thiol-based conjugation steps to generate defined peptide architectures.
2. Side-Chain Functionalization
H-D-Cys-OH · HCl · H2O is directly relevant to side-chain derivatization strategies that exploit the thiol nucleophile and its redox behavior. The free thiol can be converted into thioether linkages, activated for conjugation chemistry, or used to generate disulfide-containing intermediates after appropriate protection and controlled oxidation. The carboxylic acid and amino group provide additional handles for orthogonal protection schemes, enabling selective transformation of the sulfur functionality without compromising the backbone. Resulting derivatives can serve as intermediates for thiol-reactive probes, linker units for biomolecule conjugation, and stereochemically defined cysteine analogs used in synthetic organic chemistry and materials precursor synthesis.
3. Chemical Biology Labeling
H-D-Cys-OH · HCl · H2O can be employed in chemical biology research where defined D-amino acid stereochemistry and thiol reactivity are needed for labeling and molecular recognition studies. The thiol side chain enables formation of thioether or disulfide-linked conjugates with electrophilic labeling reagents, while the amino acid backbone supports incorporation into peptides, peptidomimetics, or linker fragments. Salt and hydration can improve reproducible handling during derivatization steps that require consistent thiol availability and controlled pH conditions. Downstream use includes generation of D-cysteine-containing probes, affinity reagents, and standards for monitoring conjugation outcomes in biochemical assay development.
4. Protected Amino Acid Chemistry
H-D-Cys-OH · HCl · H2O serves as a practical starting material for protected D-cysteine derivatives used in protected amino acid synthesis and peptide coupling compatibility design. The presence of both an amino group and a carboxylic acid supports orthogonal protection planning, while the thiol typically requires S-protection to suppress oxidation and side reactions during activation and coupling. D stereochemistry is retained through protection and deprotection sequences, supporting stereopure intermediate preparation for unnatural amino acid incorporation and stereochemical control in peptide science. Prepared protected derivatives can then be used as reliable chiral building blocks for C-terminal and N-terminal peptide assembly, enabling consistent downstream formation of thioether, disulfide, or free-thiol residues as dictated by the target structure.
5. Analytical Research Standards
H-D-Cys-OH · HCl · H2O is suitable for analytical research where stereochemically defined cysteine standards are required to calibrate chromatographic separation, mass spectrometric identification, or derivatization-based quantitation. The defined D configuration at the α-carbon helps distinguish enantiomeric cysteine species in method development and quality control of peptide hydrolysates or thiol-containing samples. The thiol functionality supports derivatization workflows that convert sulfur into detectable derivatives, while the salt form can improve reproducibility of sample preparation and storage stability. Downstream, the compound can be used to generate reference materials for method validation, impurity profiling of cysteine-containing intermediates, and verification of stereochemical integrity in synthetic peptide and biochemical chemistry pipelines.
6. Pharmaceutical Intermediate Preparation
H-D-Cys-OH · HCl · H2O aligns with pharmaceutical intermediate preparation where cysteine-derived fragments are used to build thiofunctional motifs, linker units, or stereochemically defined amino acid components. The amino acid backbone enables conversion into activated forms for amide coupling, while the thiol side chain can be transformed into thioether or disulfide motifs that are common in medicinal chemistry scaffolds and peptide-like drug candidates. D stereochemistry can be leveraged to tune metabolic stability and stereochemical profiles of peptide fragments during synthetic route design, with protection strategies ensuring compatibility with multi-step synthesis. Resulting intermediates can feed into fine chemical production workflows, supporting downstream assembly of cysteine-containing analogs and process-ready building blocks for applied drug discovery chemistry.
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