Fmoc-Cys(SO3H)-OH · disodium salt is an Fmoc-protected cysteine derivative bearing a sulfonic acid substituent on the side chain, classifying it as a modified, proteinogenic amino acid analogue used in peptide chemistry. The molecule contains an N-terminal fluorenylmethoxycarbonyl (Fmoc) protecting group, a free carboxyl group, and a side-chain sulfonate functionality (present as a disodium salt), with stereochemistry not specified in the product name. In synthesis and labeling workflows, the protected amino acid form supports stepwise incorporation into peptide intermediates while the sulfonate side chain provides a strongly polar, anionic handle for solubility modulation, salt formation, and further conjugation or analytical characterization.
Fmoc-Cys(SO3H)-OH · disodium salt is an Fmoc-protected cysteine derivative bearing a sulfonic acid side chain in the Cys thioether oxidation state, presented as the disodium salt to enhance water compatibility and ionic stability. The molecule contains a chiral cysteine backbone with an Fmoc carbamate at the amino terminus and a free carboxylic acid suitable for peptide coupling after activation. The side-chain sulfonate group is strongly acidic, highly polar, and resistant to many peptide-synthesis conditions, enabling reproducible charge-defined motifs in peptide building blocks. The combination of an orthogonally removable Fmoc group and a sulfonate functionality supports controlled peptide assembly, downstream ion-pairing or salt-formation strategies, and post-synthetic functional manipulation in aqueous or mixed solvents.
1. Peptide Synthesis
Fmoc-Cys(SO3H)-OH · disodium salt is used as a protected cysteine building block for solid-phase peptide synthesis and automated peptide assembly where a stable, negatively charged side chain is required. The Fmoc carbamate protects the α-amino group for iterative coupling cycles, while the free α-carboxyl group participates in standard peptide coupling chemistry to form amide bonds without disturbing the sulfonate. The sulfonate side chain can be retained through synthesis to provide a defined anionic handle that influences peptide solubility, conformation, and metal-ion interactions. The resulting peptides can serve as charge-tagged scaffolds, binding probes, and sequence variants for structure-function studies that depend on consistent side-chain ionization.
2. Chemical Biology
Fmoc-Cys(SO3H)-OH · disodium salt supports chemical biology workflows that require an amino acid-derived sulfonate for polar recognition and bioconjugation-ready peptide constructs. The sulfonate group functions as a stable, strongly ionizable moiety that can participate in electrostatic interactions and can be used to tune local charge density in peptide ligands. The Fmoc-protected backbone enables incorporation into longer peptide sequences, including probes designed for receptor mapping, pathway interrogation, or affinity screening where charge patterning is a key design variable. The disodium salt form facilitates handling in aqueous media, supporting downstream conjugation and analytical evaluation of peptide-based biomolecular probes.
3. Bioconjugation Chemistry
Fmoc-Cys(SO3H)-OH · disodium salt is applicable to bioconjugation strategies that rely on incorporating a sulfonate-bearing amino acid motif into peptide linkers and carrier fragments. The Fmoc group enables stepwise peptide assembly to position the sulfonate at a defined location relative to N- or C-terminal functional elements. The sulfonate can serve as a hydrophilic spacer, a charge-modulating element for solubility control, and a handle for forming salt bridges with cationic partners during conjugate formation. The resulting sulfonate-containing peptide intermediates can be used to generate conjugates for imaging, affinity capture, or materials-directed binding studies in biochemical research and applied chemical manufacturing of functional biomolecules.
4. Process Chemistry Intermediate
Fmoc-Cys(SO3H)-OH · disodium salt is suitable as a manufacturing intermediate for producing sulfonate-functional peptides and peptide analogs at scale, where salt-form control and robust functional-group tolerance matter. The disodium salt presentation improves aqueous processing behavior for downstream coupling and purification steps, while the Fmoc protection strategy provides a predictable deprotection handle during peptide production. The sulfonate side chain is chemically stable under many peptide-processing conditions, supporting consistent incorporation into product streams without side-chain degradation pathways associated with more labile groups. The compound's defined stereochemistry and protected amino/carboxyl functionality make it compatible with industrial peptide synthesis workflows and fine chemical production of charged amino acid derivatives.
5. Analytical Research Standards
Fmoc-Cys(SO3H)-OH · disodium salt can be employed to prepare analytical standards and calibration materials for peptide characterization where sulfonate-containing cysteine residues are targeted. The Fmoc-protected amino acid format allows controlled incorporation into short reference peptides, enabling method development for LC-MS, capillary electrophoresis, and ionization behavior studies of anionic peptide motifs. The strongly acidic sulfonate group and the disodium salt form can be leveraged to reproduce charge states and retention characteristics that are sensitive to side-chain ionization. The resulting reference peptides and intermediate fragments support reliable identification, quantification, and structural verification of sulfonate-bearing sequences in biochemical research and industrial quality control of peptide-based products.
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