L-cysteine methyl ester hydrochloride is a cysteine-derived amino acid ester featuring a thiol-bearing side chain and a methyl ester at the carboxyl terminus, with the amino group present as a hydrochloride salt. The molecule contains a free sulfhydryl (-SH) functionality on the side chain and an esterified carboxyl group, while the hydrochloride counterion is associated with the protonated amino group, influencing solubility and handling during chemical synthesis. As an amino acid ester intermediate, it is used in peptide and thiofunctional derivative synthesis and in chemical labeling workflows where cysteine's thiol provides a reactive handle for controlled conjugation or further derivatization.
CAT No: CP00648
L-cysteine methyl ester hydrochloride contains the L-cysteine backbone with a methyl ester at the carboxyl terminus and a protonated amino group as the hydrochloride salt, while retaining a thiol side chain that can be selectively functionalized under controlled conditions. The stereogenic center of the L-configuration aligns the amino acid geometry for stereospecific peptide coupling and downstream chiral retention. The ester functionality supports conversion to activated carboxyl derivatives or peptide-ready forms, whereas the thiol provides a reactive handle for thioether formation, disulfide chemistry, and thioester or thioamide related transformations. Salt formation improves handling of the amino ester intermediate and can influence coupling conditions, making the compound a practical chiral amino acid ester for synthetic and biochemical workflows.
1. Protected Amino Ester Chemistry
L-cysteine methyl ester hydrochloride is used in protected amino acid synthesis workflows where controlled manipulation of the amino and thiol functionalities is required. The methyl ester enables staged conversion to peptide coupling partners, while the hydrochloride form supports reliable formation of N-protected derivatives using standard amine protection strategies. The free thiol can be managed through thiol-protecting-group approaches that preserve stereochemical integrity during ester activation and peptide bond formation. Downstream, the resulting N- and side-chain-protected cysteine methyl esters serve as peptide building blocks and chiral intermediates for generating cysteine-containing sequences and functionalized analogs.
2. Peptide Synthesis
L-cysteine methyl ester hydrochloride is applied in peptide synthesis as a cysteine-derived chiral building block precursor for assembling peptide fragments that require thiol-bearing residues. The combination of an amino ester and an L-configured stereocenter supports stereospecific incorporation into peptide chains after conversion to an appropriate activated carboxyl form and N-protected amino functionality. The thiol side chain enables formation of disulfide-linked motifs or selective thioether substitutions, which is compatible with orthogonal protection/deprotection schemes commonly used to control cysteine reactivity during multi-step couplings. The compound therefore supports preparation of cysteine-containing peptides, peptide fragments for ligation chemistry, and peptidomimetic scaffolds where side-chain sulfur chemistry defines the final structure.
3. Side-Chain Functionalization
L-cysteine methyl ester hydrochloride is suitable for side-chain functionalization strategies in chemical biology and synthetic organic chemistry that leverage thiol reactivity. The thiol group can undergo controlled derivatization to form thioethers, mixed disulfides, or other sulfur-containing linkages, while the methyl ester and amino functionality can be transformed into amide or carboxyl-activated derivatives for conjugation-ready intermediates. The L-stereochemistry allows construction of chiral thio-functional amino acid derivatives that retain the spatial orientation relevant to recognition in peptide-like systems. The resulting sulfur-functional intermediates can be carried into downstream synthesis of labeled probes, reactive handles for biomolecule modification, and cysteine analogs used to probe structure-function relationships.
4. Bioconjugation Chemistry
L-cysteine methyl ester hydrochloride is employed in bioconjugation and biomolecule labeling workflows where thiol chemistry provides a direct route to attachment points. The amino acid ester form can be converted into amide or activated carboxyl derivatives that integrate into linker architectures, while the thiol enables coupling to electrophilic conjugation reagents or formation of disulfide-based reversible linkages. The hydrochloride salt form can facilitate handling and consistent derivatization of the amino functionality prior to conjugation steps, supporting reproducible intermediate preparation. Downstream applications include generation of cysteine-based linkers for protein labeling, preparation of thiol-reactive small molecules for chemical biology studies, and synthesis of conjugation reagents used in biomolecular assay development.
5. Process Chemistry Intermediate
L-cysteine methyl ester hydrochloride functions as a chiral amino acid ester intermediate in process chemistry and fine chemical synthesis where sulfur-containing building blocks are required at scale. The methyl ester provides a controllable carboxyl equivalent for conversion into activated intermediates, while the L-configuration supports stereochemically defined downstream products. Thiol-bearing intermediates can be managed through protection and controlled deprotonation strategies to reduce side reactions during manufacturing-oriented sequences, including formation of N-protected cysteine derivatives and subsequent peptide-ready forms. The compound's structure therefore supports industrial intermediate preparation for cysteine-containing pharmaceuticals research reagents, peptide manufacturing supply chains, and specialty chemical production routes that require reliable access to chiral sulfur-functional amino acid derivatives.
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