H-Thr(PO3H2)-OH

H-Thr(PO3H2)-OH is a threonine-derived amino acid bearing a side-chain phosphonic acid group, presented as the free amino acid with an N-terminal hydrogen and a carboxylic acid. The molecule contains a chiral threonine backbone with stereogenic substitution at the β-carbon, alongside a strongly acidic phosphonate (PO3H2) that can exist in mono- or dianionic forms depending on pH and can participate in metal coordination. The combination of an amino acid framework (amino and carboxylate) with a phosphonic acid functionality yields a polar, hydrogen-bonding-rich intermediate whose reactivity profile supports salt formation, controlled deprotonation, and subsequent derivatization. The structure is well suited as a chemically defined phosphothreonine analog for peptide and biochemical research workflows where phosphate mimicry and phosphate-stability considerations are central.

1. Peptide Phosphomimicry

H-Thr(PO3H2)-OH supports peptide synthesis and peptide analog construction in chemical biology by providing a phosphonic acid side chain that can mimic phosphorylated threonine while maintaining a stable P-C linkage. The amino acid backbone enables standard coupling chemistry at the α-amino and α-carboxylate positions, while the PO3H2 group can be protected as a temporary phosphonate derivative to prevent undesired side reactions during peptide assembly. The stereogenic threonine center allows stereochemically defined incorporation into sequences used for phosphorylation-site mapping, substrate recognition studies, and kinase-related SAR investigations. Downstream, deprotection and controlled ionization can generate defined phosphomimetic residues for studying recognition motifs and for producing peptide conjugates with phosphate-like charge distribution.

2. Protein Engineering Studies

H-Thr(PO3H2)-OH functions as a chiral phosphothreonine analog for protein engineering and enzyme-substrate interaction studies where a phosphate group surrogate is required. The phosphonic acid moiety can coordinate divalent cations and engage in electrostatic and hydrogen-bonding interactions that resemble phosphate-mediated recognition, while the amino acid framework preserves the spatial relationship between the β-substituent and the backbone. Protected amino acid strategies can be applied to incorporate the residue into longer polypeptides or peptide scaffolds, enabling controlled evaluation of how stereochemistry and charge density influence binding or catalytic turnover. The resulting phosphomimetic constructs can be used to generate chemically defined variants for mechanistic studies and for refining molecular models of phosphorylation-dependent recognition.

3. Enzyme Inhibitor Design

H-Thr(PO3H2)-OH can be employed in small-molecule and peptidomimetic inhibitor design programs that target enzymes with phosphate-binding pockets. The PO3H2 functionality provides a strongly acidic, tetrahedral phosphate mimic that can engage in specific interactions with catalytic residues or metal ions, while the threonine stereochemistry helps maintain a defined three-dimensional presentation of the side-chain functionality. Derivatization can convert the free phosphonic acid into protected intermediates suitable for fragment coupling, scaffold elaboration, or incorporation into constrained peptidomimetics. Downstream synthetic utility includes preparing analog libraries for structure-activity relationship studies and generating chemically stable phosphate surrogates for mechanistic interrogation of phospho-recognition motifs.

4. Protected Amino Acid Synthesis

H-Thr(PO3H2)-OH serves as a direct starting material for protected amino acid derivative preparation, including routes that protect the phosphonic acid to enable orthogonal chemistry during synthesis. The free amino group and carboxylic acid allow conversion into N-protected and/or activated forms for peptide building block preparation, while the phosphonate can be masked to suppress acid-catalyzed side reactions and to improve coupling compatibility. Stereochemically defined threonine ensures that downstream intermediates retain the chiral information necessary for stereoselective peptide coupling and for consistent structure-function outcomes. The resulting protected amino acid derivatives are suitable for fine chemical synthesis workflows that require controlled deprotection sequences and predictable reactivity at the α-amino/α-carboxyl positions.

5. Analytical Phosphothreonine Standards

H-Thr(PO3H2)-OH is suitable for analytical research and method development requiring defined phosphothreonine-like reference material. The presence of both carboxylic acid and phosphonic acid enables reproducible ionization behavior and characteristic charge states that can support mass spectrometric detection, chromatographic retention tuning, and calibration of analytical assays for phosphate-containing analytes. The chiral threonine backbone provides stereochemically defined standards that can help distinguish isomeric or stereoisomeric species in workflows involving phospho-mimetic labeling or derivatization. Downstream applications include preparing labeled or derivatized analogs for trace analysis, monitoring synthetic intermediates, and verifying identity of peptide constructs containing phosphonate-mimicking residues.

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