H-Cit-betaNA · HBr

H-Cit-betaNA · HBr is a hydrobromide salt of an N-terminally protected citrulline derivative bearing a β-nitroaniline (βNA) substituent, featuring the characteristic amino acid framework with a side-chain urea functionality derived from citrulline. The compound's stereochemical integrity at the citrulline α-carbon supports stereodefined incorporation into peptide-like sequences, while the β-nitroaniline moiety introduces an aniline aromatic ring that can participate in electronic and conjugation-driven derivatization. The HBr salt form provides a protonated amine environment that can improve handling of the free base and influences downstream coupling and deprotection planning. The presence of both a ureido/amide-forming motif and an aromatic nitroaniline handle makes the molecule compatible with protected amino acid synthesis strategies and subsequent functional group transformations for building peptide conjugates and analytical probes.

1. Peptide Synthesis

H-Cit-betaNA · HBr supports peptide building-block workflows where citrulline-derived side-chain functionality can be preserved or selectively transformed during coupling chemistry. The protected amino acid derivative format, together with the α-amino and carboxyl functionalities inherent to the citrulline backbone, enables standard peptide coupling logic while the β-nitroaniline aromatic handle can remain as a spectroscopic or reactive tag depending on the protection scheme. The HBr salt state can be leveraged to manage amine protonation during activation and coupling planning, while the stereodefined α-center aids in producing consistent peptide stereochemistry. Downstream, citrulline-containing peptides and peptide analogs can be generated for structure-activity relationship studies and side-chain recognition investigations in biochemical research.

2. Chemical Biology Probes

H-Cit-betaNA · HBr can be applied in chemical biology research as a labeled amino acid or peptide component, where the β-nitroaniline aromatic motif serves as a functional reporter for monitoring binding environments or reaction progress. The citrulline urea/ureido character provides a polar, hydrogen-bonding-rich side chain that can participate in molecular recognition and can be carried into peptide conjugates or substrate mimics. The aniline nitro functionality enables downstream derivatization pathways such as reduction to an aniline or further electrophile-driven transformations, allowing probe tuning for fluorescence, affinity handles, or crosslinking strategies. The resulting labeled biomolecular constructs can be used to interrogate protein-ligand interactions, enzyme-substrate preferences, and amino acid recognition motifs in applied biochemical workflows.

3. Side-Chain Functionalization

H-Cit-betaNA · HBr is suitable for side-chain functionalization and tag installation strategies because it combines a citrulline-derived ureido motif with a β-nitroaniline aromatic handle on the same amino acid scaffold. The ureido functionality can be protected, converted, or incorporated into amide/urea-forming intermediates during synthetic sequence design, while the βNA aromatic nitro group can undergo controlled transformations to introduce amine-reactive or conjugation-ready functionalities. The stereogenic α-carbon enables stereochemically defined derivatives that can be carried into peptidomimetics and amino acid derivatization libraries. Downstream products may include modified amino acid building blocks, peptide analogs with altered electronic properties, and functional intermediates used for fine chemical synthesis and synthetic methodology development.

4. Protected Amino Acid Chemistry

H-Cit-betaNA · HBr can be employed in protected amino acid synthesis planning where salt formation and functional-group compatibility are central to reliable peptide coupling and deprotection sequences. The amino acid backbone provides the core nucleophilic and electrophilic sites used in peptide building-block preparation, while the citrulline side-chain functionality supports selective orthogonal protection strategies to control which functional group participates at each step. The β-nitroaniline substituent introduces a chemically addressable aromatic functionality that can be retained during coupling or selectively modified later to yield C-terminal or side-chain-modified derivatives. The compound therefore functions as a chiral amino acid intermediate for generating stereodefined protected amino acid derivatives and downstream peptide building blocks used in research-grade synthesis and applied manufacturing routes.

5. Analytical Research Standards

H-Cit-betaNA · HBr can serve as an analytical reference material in amino acid and peptide analysis workflows where the β-nitroaniline aromatic group provides a strong UV-active signature and a chemically transformable reporter. The citrulline backbone and stereodefined α-center help maintain structural fidelity when calibrating methods for peptide fragment analysis, derivatization studies, or monitoring of amino acid incorporation into larger constructs. The HBr salt form supports reproducible handling and can improve consistency in sample preparation for LC-based detection or derivatization-based quantification strategies. Downstream, the compound can be converted into related standards and internal calibration materials that support method development, impurity profiling, and structural confirmation in biochemical research and industrial chemical manufacturing contexts.

6. Pharmaceutical Intermediate Preparation

H-Cit-betaNA · HBr is applicable to pharmaceutical intermediate preparation and process chemistry intermediate design where citrulline-derived motifs and aromatic nitroaniline handles can be carried through multi-step syntheses. The amino acid framework supports conversion into activated intermediates for peptide-like scaffold construction, while the ureido side chain can be used to build polar pharmacophore elements or to generate constrained peptidomimetic structures. The βNA substituent provides a functional handle for later transformation into conjugation-ready or property-tunable derivatives, supporting route design for fine chemical synthesis. The resulting intermediates can feed into downstream combinatorial synthesis, SAR studies, and manufacturing-oriented generation of stereodefined amino acid derivatives used in applied chemical development pipelines.

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