H-Cys(Bzl)-OEt · HCl

H-Cys(Bzl)-OEt · HCl is a cysteine-derived amino acid ester presented as the hydrochloride salt, featuring a chiral α-amino acid framework with a side-chain thiol protected as a benzyl thioether and a carboxyl group masked as an ethyl ester. The benzyl (Bzl) thioether stabilizes the sulfur functionality during peptide coupling and other electrophile-rich transformations, while the ester form supports controlled reactivity and downstream conversion to amide or carboxylate derivatives. Salt formation with HCl improves handling of the amino component and can influence solubility in peptide-synthesis media. The combination of a protected thiol and an esterified carboxyl group makes the compound a practical chiral intermediate for cysteine incorporation and for sulfur-functional modifications after selective deprotection or functional group interconversion.

1. Peptide Synthesis

H-Cys(Bzl)-OEt · HCl is used in peptide building-block preparation where cysteine side-chain protection and ester activation are central to coupling compatibility. The benzyl-protected thioether preserves sulfur from undesired oxidation and side reactions during amide bond formation, while the ethyl ester enables conversion to activated carboxyl equivalents or controlled transformations toward peptide-ready derivatives. The hydrochloride salt form supports amino reactivity under standard peptide coupling conditions and can be integrated into workflows that require N-protection management and orthogonal deprotection planning. Downstream, the protected cysteine residue can be incorporated into linear peptides and later converted to free thiol or thiol-reactive motifs for disulfide formation, thioether elaboration, or site-specific conjugation.

2. Side-Chain Functionalization

H-Cys(Bzl)-OEt · HCl supports sulfur chemistry in molecular modification programs that rely on controlled unveiling of cysteine functionality. The benzyl thioether acts as a removable protecting group strategy for the thiol equivalent, enabling sequential synthesis where the sulfur is held inert during carbonyl chemistry and then transformed into thiol, thioester, sulfenamide, or other sulfur-bearing intermediates. The ethyl ester and amino group provide additional handles for stepwise derivatization, including conversion to amide-linked analogs or further functional group installation at the α-position. Resulting derivatives can serve as intermediates for thioether analogs, redox-active peptide fragments, and sulfur-functional probes used in biochemical research and chemical biology workflows.

3. Chiral Amino Acid Intermediate

H-Cys(Bzl)-OEt · HCl serves as a chiral amino acid intermediate for stereochemically defined syntheses where retention of the cysteine stereocenter is required. The α-amino acid backbone with the protected side-chain sulfur enables downstream transformations that preserve stereochemical integrity while allowing functional group interconversion at the ester and amine. The hydrochloride salt form can be leveraged to improve reproducibility in chiral intermediate handling, particularly in fine chemical synthesis sequences that require consistent salt formation and controlled deprotection timing. The resulting chiral building block can be routed into protected amino acid derivatives, peptide coupling partners, and stereodefined thio-functional molecules used for structure-activity relationship studies and synthetic methodology development.

4. Chemical Manufacturing Intermediates

H-Cys(Bzl)-OEt · HCl is applicable to industrial intermediate preparation where cysteine-protected forms are required for scalable peptide and sulfur-functional manufacturing routes. The benzyl thioether protection strategy is compatible with process conditions that involve carbonyl activation and amide bond construction, helping manage thiol oxidation risk and reducing impurity formation from sulfur reactivity. The ethyl ester functionality supports conversion to downstream carboxyl derivatives under controlled processing logic, enabling integration into batch or continuous fine chemical synthesis steps that generate peptide-grade intermediates. Industrially relevant downstream uses include preparation of cysteine-containing peptide fragments, protected sulfur building blocks, and intermediate streams for specialty chemical production that depend on reproducible sulfur protection and predictable deprotection behavior.

5. Chemical Biology Probes

H-Cys(Bzl)-OEt · HCl can be employed in chemical biology research to generate cysteine-derived probes and labeling reagents that require controlled thiol availability. The protected sulfur enables synthesis of thiol-bearing molecules without premature oxidation during conjugation-relevant steps, while the amino acid ester framework can be converted into amide-linked scaffolds or reactive derivatives for biomolecule targeting. The hydrochloride salt form supports handling in aqueous-compatible or mixed-solvent labeling workflows after appropriate conversion to the desired reactive form. Downstream derivatives derived from this intermediate can be used for site-specific tagging strategies, thiol-reactive conjugation chemistry, and preparation of cysteine-containing standards for analytical characterization of peptide and protein modifications.

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