Fmoc-L-cysteic acid · disodium salt is an Fmoc-protected, naturally occurring amino acid derivative featuring the L-cysteic acid backbone bearing a side-chain sulfonic acid group, classifying it as a polar, strongly anionic amino acid. The molecule contains an Fmoc carbamate on the amino group and a free carboxylate functionality that, together with the sulfonate side chain, is present as a disodium salt, with stereochemistry indicated as L by the product name. In peptide chemistry and chemical biology, this protected, salt-form amino acid is used as a building block for stepwise peptide synthesis and for preparing sulfonate-containing peptide or conjugate analogues that provide defined negative charge and handle for aqueous-phase characterization.
CAT No: CP26993
CAS No:320384-09-6
Synonyms/Alias:Fmoc-Cya-OH · disodium salt
Fmoc-L-cysteic acid · disodium salt is an Fmoc-protected L-cysteic acid derivative in which the amino acid side chain is oxidized to a sulfonic acid group, and the carboxylate is present as a disodium salt. The molecule combines an Fmoc carbamate at the α-amino position with strongly polar, anionic functional groups (carboxylate and sulfonate), producing high water affinity and salt-stabilized handling during synthesis. The stereogenic center at the α-carbon is fixed in the L-configuration, supporting stereochemically defined incorporation into peptide sequences. The sulfonate and carboxylate functionalities enable salt-state control, ion-exchange behavior, and robust coupling-compatible chemistry after appropriate protection or activation strategies.
1. Peptide Synthesis
Fmoc-L-cysteic acid · disodium salt is applied in solid-phase peptide synthesis where the Fmoc group enables stepwise N-terminal protection and deprotection cycles. The α-amino Fmoc carbamate and the L-stereocenter support stereodefined peptide coupling, while the side-chain sulfonate and carboxylate provide a charged, hydrophilic residue that can be incorporated into peptide building blocks for aqueous peptide scaffolds. The anionic sulfonic acid functionality can be carried through coupling as a stable, non-oxidizable group, supporting downstream peptide analog construction without relying on thiol oxidation chemistry. The resulting cysteic-acid-containing peptides can serve as charged mimics for post-translationally modified motifs and as defined reference standards in peptide chemistry workflows.
2. Chemical Biology
Fmoc-L-cysteic acid · disodium salt is used in chemical biology for constructing ionizable peptide probes and for mapping electrostatic contributions in biomolecular recognition. The sulfonate side chain and carboxylate group create a persistent negative charge pattern that can be used to tune binding interactions in molecular recognition studies while maintaining the α-amino acid backbone geometry. Fmoc protection allows incorporation into longer peptides or peptide fragments used in affinity ligands, receptor-binding studies, or membrane-interaction assays where charged residues influence partitioning. The disodium salt form supports reproducible ion-state behavior in labeling and screening formats that depend on defined anionic functional group density.
3. Bioconjugation Chemistry
Fmoc-L-cysteic acid · disodium salt is suitable for bioconjugation workflows that require a stable, highly polar handle for conjugate formation and solubility control. The Fmoc-protected amine enables controlled release of the free amine under standard deprotection conditions, allowing the cysteic-acid residue to be introduced into peptide linkers that connect to biomolecules via amide-forming or coupling chemistries. The sulfonate group can function as a non-reactive, charge-bearing element that improves conjugate water compatibility and can reduce aggregation during conjugation and purification. The resulting cysteic-acid-containing conjugates can be used as defined linker architectures in biomolecule modification and analytical reference materials.
4. Side-Chain Functionalization
Fmoc-L-cysteic acid · disodium salt supports amino acid derivatization strategies centered on the sulfonate-bearing side chain and its controlled ionization state. The sulfonic acid functionality can be exploited for downstream transformations that target salt-state management, ion-exchange materials, or conversion to alternative sulfonyl derivatives when compatible with the Fmoc-protected amino group. The presence of both carboxylate and sulfonate groups enables selective functional group manipulation after orthogonal protection choices, supporting synthesis of multifunctional amino acid intermediates. The chiral, L-configured backbone allows incorporation of the modified side-chain architecture into peptide analogs and synthetic organic intermediates where charge distribution is a structural determinant.
5. Pharmaceutical Manufacturing
Fmoc-L-cysteic acid · disodium salt is relevant to pharmaceutical manufacturing and process chemistry as a protected amino acid intermediate for producing charged peptide fragments used in drug substance or drug product manufacturing pipelines. The Fmoc group provides a standardized N-protection handle compatible with automated peptide assembly, while the stable sulfonate functionality reduces susceptibility to oxidation-state drift compared with thiol-based cysteine derivatives. The disodium salt form can be used to manage solubility and handling during scale-up of peptide building block preparation and intermediate purification steps. The resulting cysteic-acid-containing intermediates can be carried into downstream peptide coupling, fragment assembly, and analytical characterization stages that require defined stereochemistry and reproducible anionic functionality.
6. Analytical Research
Fmoc-L-cysteic acid · disodium salt is utilized in analytical research as a reference-building block for method development and characterization of charged peptide species. The combination of a defined L-configuration and persistent sulfonate/carboxylate charge enables reproducible retention and fragmentation behavior in chromatographic and mass spectrometric analyses of peptide libraries. Fmoc protection supports standardized incorporation into peptides used as calibrants or internal standards, helping evaluate ionization efficiency and separation performance for highly polar residues. The compound's salt-state characteristics facilitate controlled sample preparation for analytical workflows that distinguish peptide variants by charge and polarity, supporting robust amino acid and peptide method validation.
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