H-Homoarg-OH

H-Homoarg-OH is a homoarginine amino acid (side-chain guanidinium) presented in the free amino acid form, bearing a primary amino group and a carboxylic acid at the α-position alongside a longer methylene-extended guanidine side chain relative to arginine. The stereochemical element is the α-chiral center, typically handled as the L-configuration in amino acid chemistry to maintain compatibility with peptide coupling and stereospecific recognition. The guanidinium functionality is strongly basic and can engage in salt formation, hydrogen-bonding networks, and ionic interactions, while the carboxylic acid and amino group support standard amide-forming peptide chemistry. As a reactive, unprotected building block, H-Homoarg-OH functions as a chemically defined intermediate for protected amino acid synthesis, guanidinium-containing peptide construction, and downstream functional transformations that preserve the side-chain cationic character.

1. Peptide Synthesis

H-Homoarg-OH is applied in peptide synthesis workflows where a guanidinium-bearing amino acid is required at a specific position within a peptide sequence. The α-amino and α-carboxyl groups enable peptide coupling after appropriate protection strategies, while the homoarginine side-chain guanidine can be protected as a guanidinium-stabilized derivative to control reactivity during amide bond formation. The extended side chain length influences backbone/side-chain packing and can be used to tune intramolecular salt bridges and hydrogen-bonding patterns in peptide analogs. Homoarginine-containing peptides prepared from this amino acid can serve as substrates, standards, or structural probes in peptide science and chemical biology.

2. Amino Acid Derivatization

H-Homoarg-OH is suitable for amino acid derivatization and functional group interconversion where the guanidinium group is targeted for controlled modification while maintaining the α-amino acid scaffold. The free carboxylic acid can be converted into activated esters or coupling-ready derivatives, and the amino group can be selectively protected to enable stepwise synthesis of N-protected homoarginine intermediates. The strongly basic guanidine can be engaged in salt formation, ion-pairing studies, and conversion into protected guanidinium forms that withstand peptide coupling conditions. Resulting derivatives can be used as chiral building blocks, peptide coupling reagents, or intermediates for generating cationic pharmacophore mimics in synthetic organic chemistry.

3. Chemical Biology Probes

H-Homoarg-OH is used in chemical biology research to create cationic amino acid analogs and peptide fragments that participate in electrostatic and hydrogen-bonding recognition events. The guanidinium side chain supports strong interactions with anionic residues and nucleic acid phosphates, enabling design of molecular probes for binding studies, uptake investigations, or receptor-interaction mapping in vitro. The α-amino acid framework allows incorporation into peptides or constrained scaffolds, supporting controlled stereochemical presentation of the guanidinium group. Derivatives derived from H-Homoarg-OH can be formatted as peptide building blocks for probe synthesis and as defined standards for studying guanidinium-mediated molecular recognition.

4. Protein Engineering Substitutions

H-Homoarg-OH is relevant to protein engineering and protein-analogue construction where homoarginine substitution is used to probe how side-chain length and guanidinium positioning affect structure and interaction networks. The homoarginine side chain, longer than arginine by one methylene, can be introduced into peptide segments that model protein microenvironments, allowing systematic variation of salt-bridge geometry and hydrogen-bonding distance. Protection and deprotection strategies for the α-amino and guanidinium groups support incorporation into peptide fragments that are later assembled into larger constructs. Downstream use includes generating defined protein-region mimics for binding characterization, interaction mapping, and mechanistic studies of cationic residue effects.

5. Pharmaceutical Intermediate Preparation

H-Homoarg-OH is employed as a precursor for pharmaceutical intermediate preparation in synthetic routes that require a protected homoarginine unit or a guanidinium-containing chiral intermediate. The presence of both α-amino and α-carboxyl functionalities supports conversion into N-protected and C-activated forms, enabling controlled peptide coupling or fragment assembly in fine chemical synthesis. The guanidinium group can be transformed into protected forms compatible with multi-step synthesis, supporting downstream incorporation into peptidomimetic scaffolds and cationic drug-like motifs. Resulting intermediates can feed into manufacturing-oriented synthesis of guanidinium-rich compounds, including peptide-like inhibitors, receptor ligands, and other amino acid-derived chemical entities.

6. Analytical Standards And Method Development

H-Homoarg-OH is suitable for analytical research and method development where defined homoarginine material is needed for calibration, identity confirmation, or monitoring of derivatization steps. The free amino acid form provides a consistent reference for chromatographic and mass spectrometric workflows, especially when assessing guanidinium-containing analytes and their ionization behavior. The guanidinium functionality enables predictable salt-state formation and can be used to validate sample preparation strategies that involve protection, activation, or conversion to peptide-compatible derivatives. Homoarginine-based standards derived from H-Homoarg-OH can support quality control of amino acid intermediates and verification of synthetic incorporation in peptide-building-block programs.

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