4-Fluoro-DL-Phenylalanine is a fluorinated, non-proteinogenic amino acid derivative in which a phenylalanine side chain bears a fluorine substituent at the 4-position of the aromatic ring, and the molecule contains both an amino group and a carboxyl group. The "DL" designation indicates a racemic mixture at the alpha stereocenter, while the aromatic ring provides a hydrophobic side chain whose electronic character is modified by the para-fluoro substituent, affecting how the amino acid can participate in peptide bond formation and in analytical differentiation from unlabeled phenylalanine analogues. This compound is used in peptide synthesis and chemical biology workflows to introduce a defined fluorinated aromatic residue for structure-activity studies, fluorine-directed NMR or mass spectrometric analysis, and the preparation of more complex fluorinated amino acid and peptide derivatives.
CAT No: CP14603
CAS No:51-65-0
Synonyms/Alias:4-FLUORO-DL-PHENYLALANINE;4-Fluorophenylalanine;51-65-0;p-fluorophenylalanine;2-amino-3-(4-fluorophenyl)propanoicacid;DL-p-Fluorophenylalanine;Alnasid;p-Fluoro-dl-phenylalanine;dl-4-Fluorophenylalanine;h-dl-phe(4-f)-oh;D,L-Fluorophenylalanine;D,L-p-Fluorophenylalanine;Phenylalanine,4-fluoro-;dl-4-f-phe-oh;DL-3-(4-Fluorophenyl)alanine;h-p-fluoro-dl-phe-oh;dl-(4-Fluorophenyl)alanine;DL-Phenylalanine,4-fluoro-;4-Fluoro-dl-para-phenylalanine;CCRIS4819;Alanine,3-(p-fluorophenyl)-;3-(4-fluorophenyl)-dl-alanine;XWHHYOYVRVGJJY-UHFFFAOYSA-N;4-Fluoro-DL-.beta.-phenylalanine;EINECS200-113-7
4-Fluoro-DL-Phenylalanine is a fluorinated phenylalanine analog provided as a DL mixture, combining the amino acid backbone with a para-fluoro substituent on the aromatic ring. This structural feature makes it a widely used building block for medicinal chemistry and peptide/peptidomimetic design where aryl fluorination is leveraged for electronic tuning and for introducing a spectroscopically and analytically distinctive motif. As an unprotected amino acid, it is typically handled as a defined chiral mixture for downstream synthesis, analytical method development, and reference material preparation.
1. Peptidomimetic Building Block
4-Fluoro-DL-Phenylalanine is commonly used in the synthesis of peptidomimetics and fluorinated peptide analogs where incorporation of a para-fluoro phenylalanine unit helps define aromatic electronics and provides a stable handle for structural characterization. Medicinal chemistry groups use this amino acid to prepare analog series for structure-activity relationship studies, often selecting the DL form when the goal is to generate material for comparative chemistry rather than stereochemically resolved analogs. In custom peptide and small-molecule development workflows, the fluorinated aromatic side chain supports straightforward downstream derivatization into amide-containing scaffolds and enables LC-MS and NMR confirmation using the fluorine-containing aromatic signature.
2. Medicinal Chemistry SAR Studies
4-Fluoro-DL-Phenylalanine serves as a practical fluorinated amino acid building block for medicinal chemistry programs that explore how aromatic fluorination influences physicochemical properties and binding-site interactions in peptide-derived or amino-acid-derived chemotypes. Research groups frequently employ it to construct fluorinated intermediates and amide-linked fragments for SAR campaigns, using the para-fluoro substitution to introduce a chemically distinctive substituent that can be tracked across synthesis and analytical characterization. Because the product is supplied as a DL mixture, it is often selected for early-stage analog generation where rapid access to fluorinated material is prioritized before committing to stereopure follow-up synthesis.
3. Pharmaceutical Intermediate Development
4-Fluoro-DL-Phenylalanine is used as a defined starting amino acid for downstream preparation of fluorinated pharmaceutical intermediates, including aryl-fluorinated fragments that feed into larger heterocycle, amide, and side-chain-functionalized scaffolds. Industrial and contract research organizations rely on this reagent when they need a reproducible fluorinated aromatic motif in a controlled amino acid-derived format, enabling consistent intermediate profiling and batch-to-batch comparability. The para-fluoro group also supports efficient analytical verification during intermediate release and process development, particularly when monitoring by LC-MS and fluorine-aware NMR workflows.
4. Analytical Reference Material
4-Fluoro-DL-Phenylalanine is also used to prepare analytical standards for method development and routine characterization of fluorinated amino acid derivatives in LC-MS-based workflows. Analytical chemistry teams use the compound as a reference to confirm identity and retention behavior of fluorinated phenylalanine-containing species, including intermediates and partially protected derivatives generated during synthesis. The presence of fluorine provides a useful orthogonal confirmation dimension for structural checks, and the DL composition can be advantageous when the analytical goal is to match total (racemic) signal patterns rather than resolve enantiomers.
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