IngredientsN-Acetyl-L-phenylalanine is also known by several synonyms including Acetyl-L-phenylalanine, Acetylphenylalanine, L-N-Acetylphenylalanine, N-Acetylphenylalanine, N-Acetyl-l-phenalanine, NSC 45699, and N-acetyl-3-phenyl-L-alanine. In IUPAC nomenclature, the compound is formally named (2S)-2-(acetylamino)-3-phenylpropanoic acid, with the CAS Registry Number 2018-61-3 for the L-enantiomer. The D-enantiomer (N-acetyl-D-phenylalanine) carries CAS number 10172-89-1. According to ChEBI, N-acetyl-L-phenylalanine is the N-acetyl derivative of L-phenylalanine and is an acetyl analog of that amino acid.
The molecular formula for both enantiomers is C₁₁H₁₃NO₃ with a molecular weight of 207.23 g/mol. The compound appears as a white solid at standard conditions. Its crystal structure is characterized by a two-dimensional infinite network of intermolecular N–H···O and O–H···O hydrogen bonds.
N-Acetyl phenylalanine belongs to the broader chemical family of N-acylated aromatic amino acids. Within the fatty acid amide family of lipids, it belongs to the class of N-acyl amino acids (NA-AAs), and more specifically to a sub-class called the N-acyl aromatic amino acids (NA-ArAAs). The parent compound, L-phenylalanine, is an essential aromatic amino acid; N-acetylation at the alpha-amino group produces N-acetyl-L-phenylalanine while retaining the chiral (S)-center.
The compound exists in two enantiomeric forms. N-acetyl-D-phenylalanine is the enantiomer of N-acetyl-L-phenylalanine. In chemical and pharmaceutical research, N-acetyl-L-phenylalanine is widely used as a reactant to synthesize methyl or ethyl esters of N-acetyl-L-phenylalanine, which are employed as versatile building blocks in peptide synthesis. N-acetylphenylalanine is a derivative of phenylalanine produced through various chemical reactions, including interesterification and enzymatic kinetic resolution, often utilized in medicinal and pharmaceutical chemistry. In terms of physical handling, N-acetyl-L-phenylalanine is recrystallized from water, 20% MeOH/H₂O, or CHCl₃, and stored at 4°C.
According to ChEBI, N-acetyl-D-phenylalanine is a N-acyl-D-phenylalanine, a N-acetyl-D-amino acid, and a N-acetylphenylalanine. In the yeast context, N-acetyl-D-phenylalanine is a metabolite found in or produced by Saccharomyces cerevisiae.
N-Acetyl-L-phenylalanine is an endogenous metabolite in mammals, arising as a product of phenylalanine metabolism. The enzyme phenylalanine N-acetyltransferase (EC 2.3.1.53) catalyzes a chemical reaction in which the two substrates are acetyl-CoA and L-phenylalanine, yielding CoA and N-acetyl-L-phenylalanine as products. This enzyme belongs to the family of transferases — specifically, acyltransferases transferring groups other than aminoacyl groups — and its systematic name is acetyl-CoA:L-phenylalanine N-acetyltransferase, also called acetyl-CoA–L-phenylalanine alpha-N-acetyltransferase. It participates in phenylalanine metabolism.
The enzymatic synthesis was characterized early in prokaryotes. Cell-free extracts of Escherichia coli K12 catalyze the synthesis of N-acetyl-L-phenylalanine from acetyl-CoA and L-phenylalanine via an acetyl-CoA–L-phenylalanine α-N-acetyltransferase purified 160-fold from cell-free extracts; the enzyme has a pH optimum of 8 and catalyzes the acetylation of L-phenylalanine, with other L-amino acids such as histidine and alanine acetylated at slower rates.
In mammals, the compound is present in trace amounts under normal physiological conditions but the short-chain N-acyl aromatic amino acids are likely involved in the detoxification of high cellular levels of short-chain organic acids and/or aromatic amino acids because of a metabolic defect; one example is the presence of N-acetyl-L-phenylalanine in the blood and urine of people suffering from phenylketonuria.
N-acetyl-L-phenylalanine appears in large amounts in the urine of patients with phenylketonuria, a human genetic disorder due to the lack of phenylalanine hydroxylase, the enzyme necessary to metabolize phenylalanine to tyrosine. Multiple metabolomic studies in PKU patients have documented this elevation. Gamma-glutamylphenylalanine and N-acetylphenylalanine were both found elevated in urine samples from PKU patients. In a 2026 pediatric metabolomics study, metabolites involved in phenylalanine metabolism showed significant correlations with plasma phenylalanine, such as N-acetyl-L-phenylalanine (correlation coefficient r = 0.77; p < 0.001; n = 82).
Increased excretion of N-acetyl-amino acids also occurs in other inborn errors of metabolism. In addition to the characteristic metabolites of these disorders, increased amounts of N-acetylleucine, N-acetylisoleucine, and N-acetylvaline were found in Maple Syrup Urine Disease urine; increased excretion of N-acetylphenylalanine occurred in PKU, and in tyrosinemia both the latter compound and increased N-acetyltyrosine excretion were observed. More broadly, increased urinary N-acetylphenylalanine has been detected in phenylketonuria, N-acetyltyrosine in hypertyrosinemia, N-acetyllysine in hyperlysinemia, N-acetylhistidine in histidinemia, and N-acetylcitrulline in citrullinemia.
N-acetyl-D-phenylalanine is a metabolite found in or produced by Saccharomyces cerevisiae (baker's yeast). Streptomyces bacteria have also been identified as producers of N-acetylated aromatic amino acid derivatives. N-acetyl-3,4-dihydroxy-L-phenylalanine has been identified as a bioactive metabolite produced by Streptomyces sp. 8812.
N-acetyl phenylalanine as an isolated or named chemical entity has no documented history of traditional or folk medicinal use in pre-modern herbal or ethnobotanical systems. This is consistent with its status as an endogenous metabolite identified only following the development of modern analytical biochemistry in the twentieth century. The parent compound, L-phenylalanine, has been widely studied in nutritional science and was employed in medicine beginning in the mid-twentieth century, but N-acetyl phenylalanine as a discrete supplement ingredient or therapeutic agent emerged primarily as a synthetic chemical of industrial and research interest.
N-acetyl-L-phenylalanine is a protected analogue of L-phenylalanine, an essential amino acid used for medical, feed, and nutritional applications such as in the preparation of aspartame. Its documented industrial use in aspartame synthesis relates to its function as a protected amino acid intermediate in peptide chemistry — aspartame is a dipeptide formed with an amide bond between an activated carboxyl group of one amino acid and the amino group of another; activation is necessary to increase the rate and yield of the condensation, and the desired pure peptide requires protection of all other functional groups not involved in the peptide bond formation, with protecting groups subsequently removed; aspartame can be prepared by reaction of N-protected-L-aspartic anhydride with L-phenylalanine methyl ester.
In the context of early dietary and nutritional research, N-acetylphenylalanine was recognized as a marker of phenylalanine overload as early as the 1960s. In these early studies, paper chromatography or ion exchange chromatography were used as the separation procedure to detect N-acetylated amino acids in urine specimens from metabolic disease patients.
N-acetyl-L-phenylalanine is classified as a principal acylamino acid and can be synthesized from L-phenylalanine and acetyl-CoA. As a protected amino acid, its acetyl group shields the alpha-amino nitrogen, altering the molecule's physical properties — particularly its amphipathic character — compared with free L-phenylalanine. This amphipathic nature has biological significance: the renal transtubular excretory mechanism may possibly operate in elimination of N-acetylphenylalanine, a hazardous amphipathic metabolite of phenylalanine, from plasma into urine in phenylketonuric patients.
N-acetyl phenylalanine interacts with multiple amino acid transport systems, which constitutes one of its most studied biochemical activities. In human erythrocytes, system T accepts N-methyl- and N-acetyl-derivatives of tryptophan, and tryptophan uptake mediated by the TAT1 transporter is inhibited by N-methyl- and N-acetyl-derivatives of aromatic amino acids. In a cellular model using Xenopus laevis oocytes, N-acetyl-L-phenylalanine inhibits the uptake of L-tryptophan, showing varying degrees of inhibition (from 90% to 100%), indicating potential bioactivity related to tryptophan transport processes.
A cDNA isolated from rat small intestine by expression cloning encodes a novel Na⁺-independent transporter for aromatic amino acids; when expressed in Xenopus oocytes, the encoded protein designated as TAT1 (T-type amino acid transporter 1) exhibited Na⁺-independent and low-affinity transport of aromatic amino acids such as tryptophan, tyrosine, and phenylalanine (Km values approximately 5 mM), consistent with the properties of classical amino acid transport system T. N-acetyl derivatives of aromatic amino acids such as N-acetylphenylalanine interact with this system, potentially competing with natural substrates.
N-acetylphenylalanine is handled by the renal organic anion transport system. In rat studies, intravenously administered N-acetylphenylalanine undergoes renal peritubular transport via a probenecid-sensitive excretory system for organic anions. Specifically, probenecid, a potent inhibitor of the renal excretory system for organic anions such as hippuric acid, sharply decreased the rate of disappearance from the circulation, renal accumulation, and urinary secretion of intravenously administered N-acetylphenylalanine.
The fatty acid amide family is divided into different classes based on the conjugate amine; the N-acyl amino acids (NA-AAs) are another class within this family, and the N-acyl aromatic amino acids (NA-ArAAs) are a further sub-class of the NA-AAs. The NA-ArAAs could serve as biosynthetic intermediates in both mammalian and non-mammalian organisms. In this regard, N-acetyl-L-phenylalanine is a precursor in the synthesis of the glucosamine derivative NAPA (see Section 6 below), and also serves as a protected building block in the chemical synthesis of dipeptides and larger peptides.
The best-established scientific evidence for N-acetylphenylalanine pertains to its role as a disease biomarker rather than a therapeutic agent.
Phenylketonuria (PKU; OMIM #261600) is an inborn error of metabolism caused by pathogenic variants in the gene encoding the enzyme phenylalanine hydroxylase (PAH), which converts phenylalanine to tyrosine using the cofactor tetrahydrobiopterin; PAH deficiency leads to elevated phenylalanine levels in blood, urine, and brain, which if untreated result in variable intellectual disability, behavioral and psychiatric disturbances, motor dysfunction, and additional clinical features such as seizures and hypopigmentation of the skin.
A 2025 untargeted metabolomics study using HPLC-QTOF-MS analyzed urine from 36 adult patients with PKU and 34 healthy controls. This study applied untargeted metabolomics to analyze urine from 36 adult patients with PKU and 34 healthy controls, with biomarker analysis performed using MetaboAnalyst 6.0; a total of 73 significant metabolites were identified, and a Random Forest-based model demonstrated enhanced predictive performance when integrating 10 metabolites, supporting their potential utility as biomarkers for PKU. N-acetylphenylalanine was among the significantly elevated Phe-derived compounds in this cohort.
In a 2026 pediatric metabolomics study, urine phenylalanine showed higher levels in PKU subgroups compared to controls, and urine and plasma phenylalanine showed a strong positive correlation (r = 0.82; p < 0.001; n = 82); metabolites involved in phenylalanine metabolism showed significant correlations with plasma phenylalanine, such as N-acetyl-L-phenylalanine (r = 0.77; p < 0.001; n = 82).
Evidence strength: Strong — multiple cross-sectional metabolomics studies in human PKU patients consistently demonstrate elevated urinary N-acetylphenylalanine and its high correlation with phenylalanine burden. Its utility as a biomarker is well-supported.
Research into the transport biology of N-acetylphenylalanine has largely been conducted in cell-based and animal models. The central finding is inhibition of aromatic amino acid transport, particularly tryptophan uptake. Phenylalanine at concentrations similar to those found in phenylketonuric patients competitively inhibits tryptophan uptake with a Ki of the same order as the Km for tryptophan; this inhibition could be responsible for the depletion of serotonin found in phenylketonuria.
Studies on the T-type amino acid transporter (TAT1) in Xenopus oocytes showed that N-acetyl derivatives of aromatic amino acids potently inhibit tryptophan transport by the TAT1 transporter. Tryptophan uptake mediated by TAT1 is inhibited by N-methyl- and N-acetyl-derivatives of aromatic amino acids, whereas their methylesters have no effect on TAT1-mediated transport.
Evidence strength: Preliminary — evidence derives from in vitro cell models (oocyte expression systems, erythrocytes) and animal studies; no clinical human interventional studies directly measuring the effects of N-acetylphenylalanine on tryptophan transport or serotonin levels in humans have been identified in the peer-reviewed literature.
The most actively investigated therapeutic application of N-acetyl-L-phenylalanine is as a chemical precursor and structural component of NAPA (2-(N-acetyl)-L-phenylalanylamido-2-deoxy-β-D-glucose), a glucosamine derivative synthesized by coupling N-acetyl-L-phenylalanine with glucosamine.
The synthesis and selection of NAPA, among glucosamine derivatives, was related to its higher bioavailability compared with glucosamine at the intracellular level, due to the hydrophobic character imparted by the aromatic ring of phenylalanine. NAPA has been extensively studied in cell and animal models of osteoarthritis.
In vitro evidence (cell-based): The aim of one study was to determine the effects of glucosamine and its 2-(N-Acetyl)-L-phenylalanylamido-2-deoxy-β-D-glucose (NAPA) derivative on IKK kinases and, consequently, on NF-κB activation in human chondrocytes; the human chondrosarcoma cell line HTB-94 and human primary chondrocytes were stimulated with tumor necrosis factor-α after pre-treatment with glucosamine or NAPA. This study suggests that glucosamine and NAPA interfere with activation of NF-κB and AP-1 transcription factors, which are responsible for the expression of genes involved in diverse biological processes such as cell growth and death, inflammatory and stress responses.
Both gene and protein expression analysis indicated the ability of NAPA to counteract key cartilage catabolic enzymes (ADAMTS-5) and effectors (MCP-1); molecular analysis showed the ability of NAPA to reduce IKKα nuclear translocation and H3Ser10 phosphorylation, thus inhibiting IKKα transactivation of NF-κB signalling, a pivotal step in the NF-κB-dependent gene expression of some of its targets.
The ability of the N-acetyl phenylalanine glucosamine derivative (NAPA) to increase anabolism and reduce catabolism via inhibition of IKKα kinase has been previously observed in vitro and in vivo; osteoarthritis remains the most prevalent degenerative joint disease and still lacks a true disease-modifying therapy.
In a co-culture model using primary chondrocytes and synoviocytes, both gene and protein expression analysis indicated the ability of NAPA to counteract key cartilage catabolic enzymes (ADAMTS-5) and effectors (MCP-1); molecular analysis showed NAPA's ability to reduce IKKα nuclear translocation and H3Ser10 phosphorylation, inhibiting IKKα transactivation of NF-κB signalling.
In a biochemical and computational study of IKKα, NAPA was studied on human primary chondrocytes from patients with osteoarthritis. The study combined molecular docking, molecular dynamics simulation, and cell-based experiments to characterize how NAPA interacts with IKKα at the molecular level.
In vivo evidence (animal model): One pilot study analyzed the effects of glucosamine and its N-acetyl-phenylalanine derivative (NAPA) in a vitamin A model of osteoarthritis in rabbits. In the in vivo study, both glucosamine and NAPA were very effective in reducing cartilage changes induced in rabbit knee by intra-articular injection of vitamin A.
Evidence strength: Preliminary/preclinical — research into NAPA as a disease-modifying OA drug has been conducted exclusively in vitro (human cell lines and primary chondrocytes) and in a rabbit animal model. No published randomized controlled trials in human subjects have been identified at the time of writing. The in vitro mechanism data are consistent across multiple independent studies, lending biochemical plausibility, but clinical translation has not yet been established.
N-acetyl-L-phenylalanine has demonstrated antiviral activity against SARS-CoV-2, inhibiting cytotoxicity in Caco-2 and VERO-6 cells at a concentration of 10 µM with inhibition rates of 20.55% and 0.1% respectively after 48 hours; additionally, N-acetyl-L-phenylalanine has demonstrated 13.69% inhibition of the SARS-CoV-2 3CL-Pro protease at 20 µM, suggesting its role in interfering with the virus's replication process.
Evidence strength: Very preliminary — these data are from in vitro cell assays only, with modest inhibition rates. No animal or human studies have been reported. This area of research requires considerable further investigation before any conclusions can be drawn.
N-acetyl-L-phenylalanine shows inhibitory activity towards the human HDAC6 enzyme with 4.6% inhibition using a commercial peptide substrate, indicating its potential as an HDAC6 inhibitor.
Evidence strength: Very preliminary — percentage inhibition values reported are very small and derived from biochemical assays only. No cell-based, animal, or human studies have been conducted to evaluate this activity.
Via its derivative NAPA, N-acetyl-L-phenylalanine has been studied in the context of osteoarthritis, cartilage biology, and joint inflammation. The molecule targets the NF-κB inflammatory signaling pathway within chondrocytes — cells responsible for maintaining articular cartilage integrity. Several in vitro studies have underlined the positive effects of glucosamine, an essential compound of most cartilage proteoglycans; it inhibits NF-κB and AP-1 activation, IL-6, iNOS, COX-2, and PGE2 release, MMPs and collagenase activity, while stimulating aggrecan synthesis. NAPA was developed with the aim of improving on glucosamine's limitations.
Regarding extracellular matrix effects, one study investigated the effects of glucosamine and its peptidyl-derivative NAPA on extracellular matrix synthesis in human primary chondrocytes; dose-dependent effects of glucosamine and NAPA on glycosaminoglycan, collagen type II, and small leucine-rich proteoglycans were examined by incubating human primary chondrocytes, cultured in micromasses (3D), with various amounts of each molecule. The lowest concentration at which glucosamine and NAPA were able to affect extracellular matrix synthesis was 1 mM.
N-acetyl-L-phenylalanine can be used in kidney research owing to its defined behavior in renal tubular transport systems. The compound is cleared primarily by the kidney via peritubular organic anion transport. In rats, intravenously administered N-acetylphenylalanine was rapidly extracted from the circulation predominantly by the kidney and excreted into urine; plasma clearance of the injected ligand was markedly decreased by bilateral nephrectomy but not by bilateral ureter ligation. These findings make N-acetylphenylalanine a research tool for studying organic anion transport physiology.
N-acetylphenylalanine's interference with aromatic amino acid transport has implications for neurotransmitter synthesis, as the blood-brain barrier transport of tryptophan (the precursor of serotonin), tyrosine (the precursor of dopamine and norepinephrine), and phenylalanine itself are all mediated by shared large neutral amino acid transporters. Competitive inhibition at these transporters — which can involve N-acetylated aromatic amino acid derivatives — could theoretically affect neurotransmitter precursor availability. However, no direct human evidence exists linking N-acetylphenylalanine supplementation to neurological endpoints.
Acetylphenylalanine is a product of the enzyme phenylalanine N-acetyltransferase in the pathway of phenylalanine metabolism. Its elevation serves as a metabolic indicator of impaired phenylalanine catabolism and is used in metabolomics-based monitoring of PKU patients.
N-acetyl-L-phenylalanine is a protected analogue of L-phenylalanine used for medical, feed, and nutritional applications such as in the preparation of aspartame. In aspartame manufacture, the N-acetyl group serves as a temporary protecting group during the coupling of phenylalanine with aspartate. Once the peptide bond is formed, the protecting group can be selectively removed. This use is industrial and not related to direct consumption of N-acetyl phenylalanine as a supplement.
In laboratory and pharmaceutical chemistry, N-acetyl-L-phenylalanine is widely used as a reactant to synthesize methyl or ethyl esters of N-acetyl-L-phenylalanine, which are employed as versatile building blocks in peptide synthesis. A 2023 study at Sapienza University of Rome examined racemization challenges encountered during this synthetic process: a thorough study on the amidation conditions of N-acetyl-L-phenylalanine using TBTU and various bases was reported for the synthesis of 2-(N-acetyl)-L-phenylalanylamido-2-deoxy-D-glucose (NAPA), described as a promising drug for the treatment of joint diseases. The possibility of reducing racemization using pyridine as a base was evidenced.
N-acetyl phenylalanine as an isolated supplement ingredient is not a subject of established clinical dosage guidelines from any government health body (NIH ODS, EMA, EFSA, or WHO) reviewed at the time of writing. The following dosage-related information derives solely from the research literature:
No human clinical trials establishing therapeutic oral dosages of N-acetyl phenylalanine as a supplement have been identified in the peer-reviewed literature. Supplement preparations (capsules, powders) are commercially available but no dosage recommendations are supported by clinical evidence.
The designation of N-acetylphenylalanine as a "hazardous amphipathic metabolite" in the scientific literature pertains specifically to its pathological accumulation in PKU patients. The renal transtubular excretory mechanism may possibly operate in the elimination of N-acetylphenylalanine, described as a hazardous amphipathic metabolite of phenylalanine, from plasma into urine in phenylketonuric patients. This toxicological characterization relates to the excess metabolite context in an enzyme-deficient patient population and does not directly establish risk of administration in healthy individuals. Individuals with PKU carry particular risk from any intervention that further loads the phenylalanine/N-acetylphenylalanine pathway.
N-acetylphenylalanine undergoes renal peritubular transport via a probenecid-sensitive excretory system for organic anions. This means that substances which inhibit organic anion transporters — including the uricosuric drug probenecid, certain NSAIDs, and other organic acids — could theoretically reduce renal clearance of N-acetylphenylalanine, leading to its accumulation. Among the significantly elevated metabolites following probenecid treatment in humans, 21 subpathways were enriched, including subpathways traditionally associated with OAT-mediated transport (Primary Bile Acid Metabolism, Phenylalanine Metabolism, Tyrosine Metabolism, Tryptophan Metabolism, etc.).
In the rat model, in vivo and in vitro analysis revealed that N-acetyl-¹⁴C(ul)-phenylalanine bound to plasma albumin. Plasma albumin binding is relevant for potential displacement interactions with other albumin-bound drugs or metabolites, though no clinical studies have characterized this interaction in human subjects.
Because N-acetylphenylalanine and related N-acetyl aromatic amino acid derivatives inhibit TAT1-mediated transport of tryptophan, in human erythrocytes, system T accepts N-methyl- and N-acetyl-derivatives of tryptophan and aromatic amino acids, competitive inhibition with free tryptophan at shared transporters represents a theoretical concern. This is particularly relevant if large amounts are ingested alongside dietary protein. However, this interaction has been characterized only in cellular transport models, not in human pharmacokinetic or pharmacodynamic studies.
No formal toxicology studies (NOAEL, LD50 in mammals, chronic exposure studies) specific to N-acetyl-L-phenylalanine used as a dietary supplement in humans have been identified in government regulatory databases (FDA, EMA, EFSA, or WHO) or the peer-reviewed clinical literature at the time of writing. Its classification in commercial reagent databases is explicitly "for research use only — not for human use." Products are chemical reagents for research use only and are not intended for human use. No approved drug applications or authorized novel food status for N-acetyl phenylalanine as a standalone supplement ingredient have been identified in EMA, EFSA, or FDA records.
Health conditions that N-acetyl phenylalanine may help support.
Body systems that N-acetyl phenylalanine may help support.
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