H-D-Cys(Fm)-OH is a protected, deuterated cysteine derivative featuring an N-terminal deuterium (H-D) and a cysteine side chain bearing an S-alkyl protecting group denoted as Fm (Fm = formyl-type thio protection), with the amino acid framework containing both an amino group and a carboxylic acid. The molecule retains the characteristic cysteine β-thiol functionality in masked form, while the free carboxyl group (-COOH) and the protected sulfur substituent together define its chemoselective behavior toward peptide coupling and side-chain deprotection steps. H-D-Cys(Fm)-OH is used as a building block for preparing cysteine-containing peptides and peptide-related intermediates, where the protected thiol helps control undesired thioether formation or disulfide scrambling during synthetic sequences and supports downstream access to cysteine chemistry after deprotection.
H-D-Cys(Fm)-OH is a chiral amino acid derivative corresponding to D-cysteine bearing an S-protected thiol as the formylmethyl (Fm) thioether, with a free carboxylic acid and an N-terminal deuterium label at the amino nitrogen. The molecule retains the cysteine backbone stereochemistry at the α-carbon while masking the highly nucleophilic, oxidation-prone side-chain thiol, thereby improving stability during peptide coupling and intermediate handling. The Fm thioether protecting group can be removed under conditions that regenerate the reactive thiol for subsequent disulfide formation, thioether exchange, or conjugation chemistry. The presence of the carboxylic acid enables direct participation in amide bond construction and downstream derivatization routes relevant to peptide science, chiral synthesis, and isotope-aware biochemical studies.
1. Protected Amino Acid Chemistry
H-D-Cys(Fm)-OH serves as a protected amino acid input for protected amino acid synthesis and peptide building block preparation, where the Fm-protected side-chain sulfur controls chemoselectivity during coupling. The free carboxylic acid and N-deuterated amino functionality support standard peptide coupling workflows, while the D-configuration provides stereochemical fidelity for D-cysteine-containing sequences and stereodefined analogs. The Fm group suppresses thiol oxidation and side reactions during activation and coupling, enabling cleaner conversion to amide-linked intermediates. Deprotection can regenerate the thiol for subsequent functional group transformations, including disulfide bridge construction or selective thioalkylation, supporting iterative amino acid chemistry and downstream scaffold elaboration.
2. Peptide Synthesis
H-D-Cys(Fm)-OH is suitable for peptide synthesis where cysteine residues require controlled thiol handling to maintain sequence integrity and minimize disulfide scrambling. The cysteine side-chain sulfur, masked as the Fm thioether, remains protected through activation of the α-carboxyl group and formation of peptide bonds, while the D-stereocenter allows access to D-cysteine peptides used in peptide engineering and stereochemical probes. N-deuteration can be leveraged in mechanistic studies or analytical tracking, since isotopic labeling may shift mass signatures for LC-MS monitoring of coupling and deprotection steps. Regenerated thiols after Fm removal can be incorporated into disulfide-containing peptides, thioether-stabilized analogs, or site-selective conjugation handles, linking protected amino acid chemistry to practical peptide construction.
3. Chemical Biology Labeling
H-D-Cys(Fm)-OH can be applied in chemical biology research and biomolecular labeling strategies that require cysteine-selective functionalization with controlled timing of thiol availability. The Fm protecting group provides a stable sulfur handle that can be converted to a reactive thiol under deprotection conditions, enabling conjugation to electrophilic probes, affinity tags, or crosslinking reagents while limiting premature oxidation. The D-cysteine stereochemistry can be used to tune recognition properties of cysteine-containing motifs in protein or peptide contexts, supporting structure-function investigations that depend on stereodefined side chains. The N-deuterium label supports isotope-aware analytical workflows, facilitating tracking of incorporation and monitoring of labeling efficiency through mass-based readouts.
4. Bioconjugation Intermediates
H-D-Cys(Fm)-OH functions as a cysteine-derived intermediate for bioconjugation chemistry where thiol reactivity must be controlled to achieve site-specific attachment. The protected thiol prevents undesired side reactions during intermediate preparation and storage, while the free carboxylic acid and amino group can be used to build amide-linked linkers or to generate activated derivatives for coupling to biomolecule scaffolds. The D-configuration enables access to stereochemically defined conjugates that may alter stability or processing relative to L-cysteine analogs. Downstream transformation of the regenerated thiol supports formation of disulfides, thioethers, or thiol-reactive adducts, making the compound relevant to manufacturing of labeled peptides, assay reagents, and research-grade conjugate libraries.
5. Pharmaceutical Manufacturing Intermediates
H-D-Cys(Fm)-OH is suitable for pharmaceutical manufacturing and fine chemical synthesis routes that involve cysteine-containing intermediates requiring robust protection strategies for thiol-bearing building blocks. The Fm group provides operational stability during peptide-like coupling chemistry and intermediate handling, aligning with process needs to limit oxidation, polymerization, and side-product formation from free thiols. The free carboxylic acid supports conversion to activated species for amide formation, enabling controlled incorporation into larger synthetic sequences that may be used for peptide therapeutics, diagnostics, or formulation-adjacent research materials. N-deuteration can also be leveraged in process development and analytical qualification contexts where isotopic signatures help verify identity and monitor transformations across synthetic steps, supporting reliable downstream intermediate generation.
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