Fmoc-D-Cys-OH*H2O

Fmoc-D-Cys-OH·H2O is a chiral, N-(9H-fluoren-9-ylmethoxycarbonyl) protected cysteine monohydrate that combines an Fmoc-protected amino group with a free carboxylic acid and a thiol-bearing side chain in the D configuration. The molecule's stereogenic center at the α-carbon and the thiol functionality enable stereochemically defined peptide coupling while supporting thiol-directed derivatization, including oxidation-state control and selective protection/deprotection workflows. The presence of the carboxylic acid supports standard peptide bond formation chemistry, while the Fmoc carbamate is compatible with base-labile deprotection commonly used in solid-phase peptide synthesis. The monohydrate form can influence handling and reproducibility in synthetic and analytical contexts, making it a practical chiral amino acid building block and intermediate for downstream sulfur-functionalized peptide analogs and conjugates.

1. Peptide Synthesis

Fmoc-D-Cys-OH·H2O is applied in peptide synthesis workflows where Fmoc protection and a free carboxyl group support incorporation as a cysteine residue building block. The D-stereochemistry at the α-carbon allows construction of stereodefined peptide sequences for mapping epimerization effects, controlling conformational preferences, and preparing D-cysteine-containing analogs. The thiol side chain can be managed through orthogonal protection strategies or in situ oxidation/reduction control to enable disulfide formation or thiol-specific conjugation after coupling. The resulting peptide products can be used as reference standards, mechanistic probes, or scaffold materials in peptide science and synthetic methodology development.

2. Side-Chain Functionalization

Fmoc-D-Cys-OH·H2O is suitable for side-chain functionalization programs that exploit the cysteine thiol as a reactive handle for sulfur chemistry. The molecule's thiol can be converted into thioether, disulfide, sulfenamide-type motifs, or activated intermediates for subsequent coupling to electrophiles, while the Fmoc group provides a protected amine that remains stable during many derivatization steps until deprotection is required. The free carboxylic acid and defined stereochemistry help maintain compatibility with downstream peptide coupling or fragment assembly, enabling controlled introduction of sulfur-containing functionalities into larger constructs. Downstream derivatives can serve as intermediates for bioconjugation reagents, redox-responsive linkers, and peptidomimetic building blocks.

3. Bioconjugation Chemistry

Fmoc-D-Cys-OH·H2O is utilized in bioconjugation chemistry to generate cysteine-based conjugation motifs that rely on thiol reactivity and stereochemical control. The protected amino group and carboxylic acid facilitate sequential synthesis of peptide conjugates or linker-bearing fragments, while the D-cysteine configuration can be used to tune stability against proteolysis and to control stereochemical outcomes in conjugate libraries. Thiol-directed conjugation can be performed after appropriate protection management, enabling attachment to maleimide-bearing surfaces, activated esters, or other electrophilic partners under conditions that preserve the peptide backbone. The resulting conjugates can function as chemical biology tools, labeling reagents, or platform intermediates for constructing sulfur-linked biomolecule derivatives.

4. Protected Amino Acid Chemistry

Fmoc-D-Cys-OH·H2O is applied as a protected amino acid derivative for protected amino acid synthesis and orthogonal protection planning in peptide building block preparation. The Fmoc carbamate provides a base-labile N-protection strategy that supports iterative coupling/deprotection cycles, while the free carboxylic acid aligns with common peptide coupling reagents and solid-phase assembly logic. The thiol side chain introduces a second reactive site that can be selectively managed through thiol protection choices, oxidation state control, or orthogonal protecting groups to prevent side reactions during chain elongation. The compound's defined D stereochemistry and functional group arrangement make it a practical chiral intermediate for constructing D-amino acid-containing peptides and for producing sulfur-functionalized peptide fragments used in research and fine chemical synthesis.

5. Chiral Building Block Development

Fmoc-D-Cys-OH·H2O is employed in chiral synthesis programs where a D-configured amino acid intermediate is required for stereochemically defined sulfur-containing products. The α-chiral center and thiol side chain enable preparation of enantiomerically specified intermediates for structure-activity relationship studies, stereochemical mapping, and epimerization-sensitive peptide analog design. The Fmoc-protected amine supports controlled incorporation into peptide sequences, while the carboxylic acid enables conversion into activated derivatives for fragment coupling or intermediate assembly. Downstream chiral products include D-cysteine-containing peptidomimetics, redox-active linkers, and stereodefined standards for analytical method development in amino acid and peptide chemistry.

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