H-2-Mercapto-His-OH

H-2-Mercapto-His-OH is a histidine-based amino acid derivative featuring an imidazole side chain bearing a thiol at the 2-position, together with the free α-amino and α-carboxylic acid functional groups. The molecule is inherently chiral at the α-carbon, and its stereochemical integrity is typically preserved when used as a defined chiral amino acid intermediate for peptide construction. The imidazole ring and thiol group present complementary acid-base and nucleophilic reactivity, enabling thiol-metal coordination, disulfide formation, thioether formation, and selective derivatization strategies under controlled conditions. As a chemically functionalized histidine analog, H-2-Mercapto-His-OH can serve as a side-chain-modified building block for generating sulfur-containing peptide motifs and for downstream synthetic elaboration into protected or activated derivatives suited to coupling chemistry.

1. Peptide Synthesis

H-2-Mercapto-His-OH is applied in peptide synthesis workflows where a sulfur-functionalized histidine residue is required for thioether, disulfide, or metal-binding peptide architectures. The free α-amino and carboxylic acid groups enable conversion into N-protected amino acid derivatives and activated C-terminal forms compatible with amide bond formation, while the 2-thiol and imidazole side chain can be managed through orthogonal protection and selective deprotection. Thiol reactivity supports post-coupling transformations such as disulfide exchange or thioalkylation to install redox-active or coordination-capable motifs within peptides. Incorporation of the chiral sulfur-bearing histidine analog into peptide sequences can be used to generate defined structural variants for peptide science and synthetic methodology development.

2. Chemical Biology

H-2-Mercapto-His-OH is used in chemical biology research to introduce a thiol-bearing histidine side chain that participates in nucleophilic trapping, metal coordination, and redox-responsive conjugation chemistry. The imidazole functionality provides pH-dependent protonation behavior that can influence binding interactions and local microenvironment effects in biomolecular assays, while the thiol group enables selective labeling or crosslinking to electrophiles and activated linkers. Derivatization to thio-reactive intermediates can support preparation of probes that mimic histidine-sulfur motifs found in enzyme active sites or metal-binding domains. Downstream use can include generation of peptide-based chemical tools and controlled conjugation reagents for studying biomolecular recognition and side-chain reactivity.

3. Bioconjugation Chemistry

H-2-Mercapto-His-OH is suitable for bioconjugation chemistry where thiol-mediated coupling is required to attach amino acid-derived handles to proteins, peptides, or surfaces. The side-chain thiol can be converted into protected forms for stable storage during synthesis, then reactivated for conjugation to maleimide, haloacetamide, or other electrophilic partners under thiol-compatible conditions. The imidazole ring can contribute to conjugate stability and can influence conjugation microenvironment through reversible protonation, which may be relevant for linker design and post-conjugation behavior. The resulting conjugates can function as defined bioconjugation standards, linker-bearing reagents, or intermediate scaffolds for constructing larger biomolecular assemblies in applied biochemical research.

4. Protein Engineering

H-2-Mercapto-His-OH is applied in protein engineering and protein design programs that require incorporation of a sulfur-functionalized histidine analog to tune metal binding, redox behavior, or local coordination geometry. The chiral α-amino acid framework supports preparation of residue-specific building blocks for peptide or protein fragment synthesis, while the imidazole-thiol combination provides a side-chain motif capable of coordinating transition metals or forming disulfide-linked structures. Protection-group strategies for the thiol and imidazole can be used to control chemoselectivity during fragment assembly and to enable staged introduction of the reactive sulfur functionality. Downstream utility includes generating protein variants or protein-mimetic constructs for studying structure-function relationships in engineered biomolecular systems.

5. Process Chemistry Intermediate

H-2-Mercapto-His-OH is used as a process chemistry intermediate for manufacturing sulfur-containing amino acid derivatives and peptide building blocks at scale. The presence of both α-amino and α-carboxylic acid groups supports conversion into N-protected amino acid derivatives and activated intermediates for coupling, while the thiol functionality can be managed through robust protecting-group strategies to minimize oxidation and side reactions. The imidazole ring provides a handle for controlled functional group transformations, enabling downstream synthesis of thioether, disulfide, or metal-coordinating derivatives used in fine chemical production. Preparation of this chiral amino acid analog as a defined intermediate supports reproducible peptide coupling chemistry and consistent downstream derivatization in industrial amino acid and peptide-manufacturing pipelines.

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