H-His-OEt · 2 HCl

H-His-OEt · 2 HCl is the dihydrochloride salt of histidine ethyl ester, featuring an L-histidine-derived stereocenter at the amino acid backbone with an ethyl ester at the C-terminus and a protonated primary amine masked as a hydrochloride. The imidazole side chain remains chemically addressable for coordination chemistry, acid/base-controlled reactivity, and selective functional group transformations, while the ester and salt form influence solubility and peptide-coupling compatibility. Salt formation with two equivalents of HCl stabilizes the amino functionality under handling and can modulate nucleophilicity during derivatization steps. As a chiral amino acid ester hydrochloride, H-His-OEt · 2 HCl functions as a practical intermediate for protected amino acid synthesis, peptide building block preparation, and downstream conversion to amide-linked histidine derivatives.

1. Peptide Coupling Chemistry

H-His-OEt · 2 HCl supports peptide synthesis workflows where histidine must be introduced as a C-terminal or side-chain-functionalizable residue precursor. The ethyl ester provides a handle for controlled activation and subsequent conversion to amide linkages, while the imidazole side chain enables orthogonal protection strategies to manage side-chain reactivity during coupling. Hydrochloride salt formation helps maintain the amino group in a defined protonation state, which can be advantageous for consistent coupling behavior in protected amino acid derivative preparation. Histidine ethyl ester hydrochloride can be transformed into appropriately protected histidine building blocks for solid-phase or solution-phase assembly of peptides and peptide fragments.

2. Side-Chain Functionalization

H-His-OEt · 2 HCl is suitable for chemical biology and synthetic organic chemistry applications that exploit the imidazole functionality for selective derivatization. The imidazole ring can participate in nucleophilic substitution, metal coordination, and pH-responsive chemistry, enabling construction of histidine-containing conjugates and imidazole-modified analogs. The amino acid ester format allows downstream conversion to amides or other linkages after side-chain modification, supporting sequential synthesis strategies where side-chain chemistry and backbone coupling are decoupled. Dihydrochloride salt handling can improve process robustness for intermediate isolation and can facilitate controlled reactivity during derivatization toward functionalized amino acid derivatives.

3. Chiral Amino Acid Intermediate

H-His-OEt · 2 HCl serves as a chiral amino acid intermediate for manufacturing routes that require L-histidine stereochemical fidelity before further protection and activation. The combination of a defined stereocenter, a C-terminal ester, and a side-chain imidazole allows conversion into N-protected histidine derivatives, C-terminal activated forms, or peptide-ready building blocks with stereochemical retention. Hydrochloride salt formation can be used to manage solubility and handling properties during intermediate preparation, including transitions from ester to protected acid or activated ester/acid chloride equivalents. The resulting histidine derivatives can then feed into fine chemical synthesis and peptide science pipelines requiring stereochemically consistent amino acid inputs.

4. Pharmaceutical Intermediate Preparation

H-His-OEt · 2 HCl can be applied in the preparation of histidine-containing intermediates used in medicinal chemistry and process development contexts. The amino acid ester and imidazole side chain enable construction of amide-linked fragments, peptidomimetic scaffolds, and constrained analogs where histidine provides coordination motifs or pH-dependent behavior. Hydrochloride salt form supports controlled intermediate handling prior to conversion into protected amino acid derivatives compatible with coupling chemistry used in drug-like molecule synthesis. Downstream transformations can include ester-to-acid conversion and N-protection/deprotection sequences that align with industrial-scale intermediate manufacturing practices.

5. Analytical Reference Standards

H-His-OEt · 2 HCl is suitable for analytical research applications where histidine ester forms and their salt states are needed as reference materials or derivatization substrates. The presence of an imidazole side chain and an esterified carboxyl group provides characteristic chemical behavior for chromatographic separation, mass spectrometric detection, and derivatization-based quantification of histidine-containing species. Hydrochloride salt composition can influence retention and ionization characteristics, making the compound relevant for method development targeting amino acid ester hydrochlorides and histidine-containing intermediates. Use in analytical standard development supports accurate tracking of histidine incorporation, ester/amide conversion, and impurity profiling during peptide building block preparation and related synthetic steps.

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