4-Chloro-L-Phenylalanine is a natural-proteinogenic amino acid derivative featuring an L-phenylalanine backbone with a chloro substituent at the para (4-) position of the aromatic side chain, classifying it as a halogenated phenylalanine analogue. The molecule contains a free α-amino group and a free α-carboxyl group alongside a benzyl-type aromatic side chain bearing the electron-withdrawing chloro substituent, with stereochemistry specified as L by the product name. It is used in peptide synthesis and structure-activity or labeling studies where incorporation of a para-chloro phenylalanine residue helps modulate aromatic interactions, provide a distinct chemical handle for analytical differentiation, or support the preparation of halogenated peptide and amino acid derivatives.
4-Chloro-L-Phenylalanine is a halogenated, proteinogenic amino acid building block featuring an L-phenylalanine backbone with a para-chloro substituent on the aromatic side chain. This structural motif makes it valuable for peptide and protein-related workflows where aryl halogenation supports downstream functionalization, analytical differentiation, and controlled incorporation of modified phenylalanine residues. In synthetic and chemical biology contexts, the chloro group provides a chemically distinct handle relative to unsubstituted phenylalanine while maintaining the stereochemical identity required for amino acid-based assembly.
1. Peptide Synthesis Building Block
4-Chloro-L-Phenylalanine is used by peptide chemistry groups to introduce a para-chloro substituted phenylalanine residue into custom peptides, including sequence-defined analogs for structure-activity relationship studies and mechanistic peptide probes. The amino acid's L-configuration aligns with standard peptide assembly workflows, enabling incorporation where a halogenated aromatic side chain is required for later derivatization or for tuning physicochemical properties such as hydrophobicity and aromatic electronics. Researchers commonly select this residue when they need a chemically distinguishable phenylalanine variant that remains consistent with peptide synthesis logic while providing a functional substituent for downstream chemistry.
2. Protein Engineering Residue Analog
4-Chloro-L-Phenylalanine supports protein engineering and protein chemistry programs that require site-specific introduction of a modified phenylalanine analog for studying residue-level effects in protein structure and function. In workflows that build or modify peptide segments used in protein constructs, the para-chloro aromatic group offers a distinct chemical signature compared with native phenylalanine, which can facilitate mapping, comparative studies, and orthogonal handling during downstream processing. This residue is particularly useful when the experimental design benefits from an aryl halogen that can be targeted selectively in later derivatization steps or used as a marker for analytical readouts in protein-related systems.
3. Medicinal Chemistry SAR Analog
4-Chloro-L-Phenylalanine is used in medicinal chemistry and peptidomimetic development to prepare halogenated amino acid fragments and peptide-like structures for structure-activity relationship (SAR) exploration. The para-chloro substituent provides a practical handle for generating analog series that differ by aromatic substitution pattern, supporting systematic evaluation of how aryl electronics and steric/halogen effects influence binding motifs or overall molecular behavior in lead optimization campaigns. Teams developing constrained or aromatic-rich scaffolds often choose this building block to maintain an amino acid stereochemical framework while enabling a targeted substitution pattern that is difficult to reproduce using unsubstituted phenylalanine.
4. Analytical Reference and Derivatization
4-Chloro-L-Phenylalanine is also applied as an analytical reference material and derivatization precursor in LC-MS and related analytical workflows where a halogenated phenylalanine species is needed for method development, calibration strategy, or comparative quantitation of modified amino acid content. The presence of the chloro substituent provides a distinct mass signature and chemical identity relative to standard phenylalanine, which can improve discrimination in complex samples such as peptide digests, protein hydrolysates, or synthetic mixture analyses. Analytical chemistry teams use this compound to validate detection performance for halogenated amino acid variants and to support downstream confirmation of incorporation or derivatization outcomes in peptide and protein studies.
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