Chemical Structure and Physical Properties

3-Chloro-L-phenylalanine (SKU: C117067) is a halogenated aromatic amino acid derived from L-phenylalanine by substitution of a hydrogen atom at the meta (3-) position of the benzene ring with a chlorine atom. Its molecular formula is C₉H₁₀ClNO₂, with a molecular weight of 199.63 g/mol. The compound retains the L (S) stereoconfiguration at the alpha-carbon characteristic of naturally occurring amino acids, making it a stereospecific probe in biochemical assays.

Like other phenylalanine analogues, 3-Chloro-L-phenylalanine exists as a zwitterion at physiological pH, with the amino group protonated and the carboxylate deprotonated. The introduction of the electron-withdrawing chloro substituent at the meta position modifies the electronic character of the aromatic ring, subtly altering the compound's acidity (pKa values), lipophilicity (logP), and hydrogen-bonding capacity relative to the parent amino acid. These electronic and steric effects underpin its distinct interactions with enzymes, receptors, and synthetic coupling reagents.

The compound typically appears as a white to off-white crystalline powder. It is soluble in dilute aqueous acid or base and in polar organic solvents such as DMSO, but shows limited solubility in nonpolar solvents. Researchers should confirm specific physicochemical data against the certificate of analysis provided with each lot.

Research Applications and Biological Relevance

3-Chloro-L-phenylalanine serves multiple roles across biochemical and pharmacological research. Its most prominent application is as a building block in the solid-phase peptide synthesis (SPPS) of modified peptides incorporating halogenated residues. The meta-chloro substituent can confer improved metabolic stability, altered receptor binding selectivity, and enhanced membrane permeability compared with unmodified phenylalanine, properties exploited in medicinal chemistry programs aimed at optimizing peptide-based drug candidates.

In enzymology, halogenated phenylalanine derivatives including the 3-chloro isomer are employed as substrate analogues to interrogate the active-site geometry and substrate specificity of aromatic amino acid-metabolizing enzymes such as phenylalanine hydroxylase, aromatic amino acid decarboxylase, and aminotransferases. By comparing turnover rates and binding affinities with the natural substrate, researchers can map the electronic and steric tolerance of the enzyme active site.

A historically significant application of chlorophenylalanine analogues relates to the inhibition of tryptophan hydroxylase (TPH), the rate-limiting enzyme in serotonin biosynthesis. Para-chlorophenylalanine (PCPA) is a well-established TPH inhibitor used to produce serotonin-depleted animal models; the 3-chloro (meta) isomer provides a structurally related tool to compare positional effects on TPH inhibition and selectivity, thereby contributing to neuroscience research on serotonergic neurotransmission. Researchers should note that pharmacological activity data specific to the meta isomer should be verified against primary literature before experimental design.

Additionally, 3-Chloro-L-phenylalanine can be used as a chiral reference standard or internal standard in analytical method development, including HPLC and LC-MS/MS assays for amino acid quantification in biological matrices.

Handling, Storage, and Solubility Recommendations

Proper handling and storage of 3-Chloro-L-phenylalanine are essential to maintain compound integrity and ensure reproducible experimental results. The compound should be stored in a cool, dry place away from light, moisture, and incompatible materials such as strong oxidizers. A storage temperature of 2–8 °C or room temperature in a desiccated environment is typical for solid amino acid derivatives; consult the product label and certificate of analysis for lot-specific recommendations.

For solution preparation, 3-Chloro-L-phenylalanine is most readily dissolved in dilute hydrochloric acid (e.g., 0.1 M HCl) or dilute sodium hydroxide solution, exploiting the zwitterionic equilibrium to achieve millimolar to low-molar concentrations. Dissolution in DMSO is an alternative for applications requiring an organic solvent vehicle; stock solutions in DMSO should be aliquoted and stored at −20 °C to minimize freeze-thaw degradation. Aqueous solutions should be prepared freshly or stored frozen and protected from light to prevent racemization or oxidative degradation.

Standard laboratory safety precautions apply: wear appropriate personal protective equipment including gloves, eye protection, and a laboratory coat. Avoid generating dust during weighing. Consult the Safety Data Sheet (SDS) for complete hazard information, first-aid measures, and disposal guidance before use.

Analytical Characterization and Quality Considerations

When incorporating 3-Chloro-L-phenylalanine into sensitive experiments, researchers should verify compound identity, purity, and stereochemical integrity prior to use. Key analytical techniques include:

• High-Performance Liquid Chromatography (HPLC): Reverse-phase HPLC with UV detection at 210–220 nm (amide bond / peptide backbone absorption region) or at 265–270 nm (aromatic absorption of the chlorophenyl ring) provides purity assessment. Chiral HPLC or derivatization with chiral reagents confirms enantiomeric excess (ee) and L-configuration.
• Nuclear Magnetic Resonance (NMR) Spectroscopy: ¹H and ¹³C NMR spectra confirm structural identity and the meta-substitution pattern of the chlorine on the phenyl ring. Characteristic signals include the aromatic protons in the 7.1–7.5 ppm region and the alpha-CH signal near 3.8–4.0 ppm.
• Mass Spectrometry (MS): ESI-MS or LC-MS confirms the molecular ion at m/z 200.04 [M+H]⁺ and the characteristic isotope pattern (approximately 3:1 ratio of M:M+2) diagnostic of a mono-chlorinated compound.
• Optical Rotation: Measurement of specific optical rotation in an appropriate solvent (e.g., water or dilute HCl) confirms stereochemical purity and L-configuration relative to literature values.

Aladdin Scientific provides a certificate of analysis with each product lot specifying identity, purity, and other quality parameters. Researchers are encouraged to request and review this documentation before use in critical assays.