2,3-Pentanedione exhibits no inhibitory activity against several key human enzymes. Studies have shown that it has no inhibitory activity against human intestinal carboxylesterase 2, human liver carboxylesterase 1, rabbit liver carboxylesterase, human acetylcholinesterase, and human butyrylcholinesterase, with inhibition constants (Ki values) exceeding 100,000.0 nM for all assays. This suggests that the compound does not significantly interact with these esterase and cholinesterase targets. The compound's primary biological target appears to be the respiratory system, as inhalation of 2,3-Pentanedione is thought to be the cause of severe respiratory disease in humans, including occlusive bronchitis. The compound also serves as a solvent in various applications.

In vitro studies of 2,3-Pentanedione have focused primarily on its enzyme inhibition profile and flavor properties. The compound has been tested against human intestinal carboxylesterase 2, human liver carboxylesterase 1, rabbit liver carboxylesterase, human acetylcholinesterase, and human butyrylcholinesterase, showing no inhibitory activity with Ki values exceeding 100,000.0 nM. As a flavoring agent, the compound's sensory properties have been characterized through taste and aroma evaluation studies. Its role as a solvent has been examined in various chemical applications. Research has also investigated its presence in e-cigarette products and its potential respiratory effects. These in vitro findings provide foundational data for understanding the compound's biological interactions and safety profile.

In vivo studies of 2,3-Pentanedione have been conducted to evaluate its toxicity and respiratory effects. The National Toxicology Program (NTP) has conducted toxicity studies of 2,3-Pentanedione administered by inhalation to Wistar Han rats and B6C3F1/N mice. Inhalation of 2,3-Pentanedione is thought to be the cause of severe respiratory disease in humans, including occlusive bronchitis. These findings highlight the compound's potential for causing respiratory toxicity upon inhalation exposure. The compound's widespread use as a flavoring agent in food and e-cigarettes has prompted regulatory concern regarding its safety. Further in vivo studies are needed to fully characterize its dose-response relationships and mechanisms of respiratory toxicity.

In vitro enzyme inhibition assays for 2,3-Pentanedione typically involve testing its activity against various esterases and cholinesterases. Enzyme activity is measured spectrophotometrically by monitoring the hydrolysis of chromogenic or fluorogenic substrates in the presence of varying concentrations of the compound. For human intestinal carboxylesterase 2, human liver carboxylesterase 1, rabbit liver carboxylesterase, human acetylcholinesterase, and human butyrylcholinesterase, Ki values are determined from inhibition curves. The compound shows no significant inhibition with Ki values exceeding 100,000.0 nM for all assays. For flavor analysis, sensory evaluation panels are employed to characterize the compound's taste and aroma properties. All assays are performed with appropriate controls and standardized protocols to ensure reproducibility of results.

In vitro cell-based assays for 2,3-Pentanedione have focused primarily on its effects on respiratory cells given its association with respiratory disease. Bronchial epithelial cells or lung fibroblast cell lines are cultured and exposed to varying concentrations of the compound to assess cytotoxicity and inflammatory responses. Cell viability is measured using MTT or similar colorimetric assays. Inflammatory cytokine production (e.g., IL-6, IL-8, TNF-α) is quantified by ELISA. Oxidative stress markers such as reactive oxygen species levels are measured using fluorescent probes. The compound's effects on cell proliferation, apoptosis, and barrier function may also be evaluated. All experiments are performed in triplicate with appropriate controls (vehicle control, positive control with known respiratory toxicant) to ensure statistical reliability.

In vivo animal experiments for 2,3-Pentanedione have been conducted by the National Toxicology Program. Wistar Han rats and B6C3F1/N mice are administered the compound by inhalation at various concentrations. Animals are exposed for specified durations (typically 6 hours/day, 5 days/week) over several weeks or months. Parameters assessed include body weight, food consumption, clinical observations, and mortality. At study termination, respiratory tissues (lungs, trachea, bronchi) are collected for histopathological examination. Bronchoalveolar lavage fluid is analyzed for inflammatory cells and protein content. Hematological and clinical chemistry parameters are measured. Control groups exposed to filtered air are included for comparison. All procedures must comply with institutional animal care and use committee guidelines.

Metabolism / Metabolites
We have developed a system for exposing cultured human bronchial/tracheal epithelial cells (NHBE) to spice vapors. NHBEs were exposed to diacetyl or 2,3-pentanedione vapors (25 or ≥ 60 ppm) for 6 hours… Analysis of the basolateral medium showed that NHBEs metabolized diacetyl and 2,3-pentanedione to acetoin and 2-hydroxy-3-pentanedione, respectively.

---

The pharmacokinetic properties of 2,3-Pentanedione reflect its nature as a small volatile diketone compound. It has a molecular weight of 100.12 and is a yellow liquid at room temperature. The compound is volatile, allowing for rapid absorption through the respiratory tract following inhalation exposure. It is also absorbed through the gastrointestinal tract when ingested as a flavoring agent. The compound is distributed throughout the body and metabolized primarily in the liver. Its small size and lipophilic nature facilitate crossing of biological membranes. The compound is excreted through urine and exhaled air. The compound's widespread use as a flavoring agent indicates that it has been evaluated for absorption, distribution, metabolism, and excretion in the context of food safety assessments.

Toxicity Summary
Identification and Uses: 2,3-Pentanedione is a yellow liquid. It is used as a flavoring agent (butter flavoring), including in many e-cigarette brands. Human Exposure and Toxicity: Inhalation of butter flavoring by workers in the microwave popcorn industry may lead to "popcorn worker lung." Cultured human bronchial/tracheal epithelial cells (NHBEs) were exposed to diacetyl or 2,3-pentanedione vapor (25 or ≥ 60 ppm) for 6 hours, and their effects on short-circuit current and transepithelial resistance (Rt) were measured. Exposure to 25 ppm of both flavorings immediately reduced Na+ transport but did not affect Cl- transport or Na+,K+- pump activity. Concentrations of diacetyl and 2,3-pentanedione at 100–360 ppm have been reported to cause epithelial damage in vivo, while a concentration of 60 ppm has caused death of NHBEs within 0 hours of exposure. The results showed that lower concentrations of fragrance could transiently inhibit ion transport in airway epithelial cells compared to concentrations that caused changes in cell morphology in vivo or in vitro. Animal experiments: Rats were inhaled into air or different concentrations of 2,3-pentanedione (112, 241, 318, or 354 ppm) for 6 hours and sacrificed the following day. Rats inhaling 2,3-pentanedione developed necrotizing rhinitis, tracheitis, and bronchitis. To investigate delayed toxicity, other rats were inhaled at a concentration of 318 ppm (range: 317.9–318.9 ppm) of 2,3-pentanedione for 6 hours and sacrificed at 0–2 hours, 12–14 hours, or 18–20 hours post-exposure. Upper nasal respiratory tract epithelial damage involved apoptosis and necrosis and continued to progress within 12–14 hours post-exposure. Olfactory neuroepithelial damage includes the loss of olfactory neurons, in which the expression of the 2,3-pentanedione metabolic enzyme, dicarbonyl/L-xylitol reductase, is reduced relative to supporting cells. Activation of Caspase 3 is occasionally involved in the olfactory nerve bundles that form synapses in the olfactory bulb (OB). In another group of rats, after inhalation of 270 ppm 2,3-pentanedione for 6 hours and 41 minutes, real-time PCR detection revealed increased expression of IL-6 and nitric oxide synthase-2, and decreased expression of vascular endothelial growth factor A in the olfactory bulb, striatum, hippocampus, and cerebellum. Claudin-1 expression was increased in the olfactory bulb and striatum. In another experiment, male and female rats and mice were exposed to 0, 50, 100, or 200 ppm 2,3-pentanedione for 6 hours daily, 5 days a week, for up to 2 weeks. Bronchoalveolar lavage fluid (BALF) was collected after 1, 3, 5, and 10 exposures, and histopathological evaluation was performed after 12 exposures. In rat bronchoalveolar lavage fluid (BALF) exposed to 200 ppm for 5 and 10 days, the levels of MCP-1, MCP-3, CRP, FGF-9, fibrinogen, and OSM increased 2 to 9-fold. In mice, only fibrinogen levels increased after 5 days of exposure to 200 ppm. All mice and rats exposed to 200 ppm showed toxic effects on the respiratory epithelium. Notably, 2,3-pentanedione also caused intraluminal and intramural fibrotic airway lesions in rats. In a third experiment, rats exposed to 150 or 200 ppm of 2,3-pentanedione developed bronchofibrosis. In mice, concentrations up to 50% of 2,3-pentanedione did not show skin irritation. However, in mice, a concentration-dependent increase in lymphocyte proliferation was observed after exposure to 2,3-pentanedione.

---

Non-human toxicity values
Oral LD50 in rats: 3000 mg/kg

---

The toxicity profile of 2,3-Pentanedione has been extensively studied due to its widespread use as a flavoring agent and its presence in e-cigarettes. Inhalation of 2,3-Pentanedione is thought to be the cause of severe respiratory disease in humans, including occlusive bronchitis. The National Toxicology Program has conducted inhalation toxicity studies in rats and mice. The compound is classified as a respiratory toxicant with potential for causing severe lung damage upon repeated inhalation exposure. The compound's flavoring properties have led to regulatory review regarding its safety in food and e-cigarette products. Proper handling procedures including use of fume hoods and personal protective equipment are recommended to minimize exposure. The compound should be used with caution in laboratory settings.

[1]. Bronchial and bronchiolar fibrosis in rats exposed to 2,3-pentanedione vapors: implications for bronchiolitis obliterans in humans. Toxicol Pathol. 2012;40(3):448-465.

2,3-Pentanedione is an α-diketone formed by substituting pentane at the 2 and 3 positions with carbonyl groups. It is a flavoring agent. It is both an α-diketone and a methyl ketone. It is derived from the hydride of pentane. 2,3-Pentanedione has been reported in tobacco (Nicotiana tabacum), onions (Allium cepa), and several other organisms with relevant data. 2,3-Pentanedione is a metabolite found in or produced by the yeast Saccharomyces cerevisiae.

---

2,3-Pentanedione (CAS# 600-14-6) is also known as acetylpropionyl. It has the molecular formula C5H8O2 and a molecular weight of 100.12. The compound is a common constituent of synthetic flavorings used to impart butter, strawberry, caramel, fruit, rum, or cheese flavor in various food products. It is also released during the roasting of coffee beans and is found in wine and yogurt. The compound is used as a flavoring agent in many e-cigarette brands. Inhalation of 2,3-Pentanedione is thought to be the cause of severe respiratory disease in humans, including occlusive bronchitis. The compound shows no inhibitory activity against human carboxylesterases and cholinesterases. It also serves as a solvent in various applications. The compound is intended for research and flavoring applications.

C5H8O2

100.12

100.052

600-14-6

2,3-Pentanedione-d5; 352431-46-0

11747

Light yellow to green yellow liquid

1.0±0.1 g/cm3

108.0±0.0 °C at 760 mmHg

-52 °C ; -52 °C ; -61.6 °F

18.9±0.0 °C

26.4±0.2 mmHg at 25°C

1.395

-0.8

0

2

2

7

94.3

0

O=C(C(C([H])([H])[H])=O)C([H])([H])C([H])([H])[H]

TZMFJUDUGYTVRY-UHFFFAOYSA-N

InChI=1S/C5H8O2/c1-3-5(7)4(2)6/h3H2,1-2H3

pentane-2,3-dione

2,3-Pentanedione

2934.99.9001

Powder      -20°C    3 years

                     4°C     2 years

In solvent   -80°C    6 months

                  -20°C    1 month

Room temperature (This product is stable at ambient temperature for a few days during ordinary shipping and time spent in Customs)

DMSO: 100 mg/mL (998.80 mM)

Solubility in Formulation 1: ≥ 2.5 mg/mL (24.97 mM) (saturation unknown) in 10% DMSO + 40% PEG300 + 5% Tween80 + 45% Saline (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 25.0 mg/mL clear DMSO stock solution to 400 μL PEG300 and mix evenly; then add 50 μL Tween-80 to the above solution and mix evenly; then add 450 μL normal saline to adjust the volume to 1 mL.
Preparation of saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH₂ O to obtain a clear solution.

---

Solubility in Formulation 2: ≥ 2.5 mg/mL (24.97 mM) (saturation unknown) in 10% DMSO + 90% (20% SBE-β-CD in Saline) (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 25.0 mg/mL clear DMSO stock solution to 900 μL of 20% SBE-β-CD physiological saline solution and mix evenly.
Preparation of 20% SBE-β-CD in Saline (4°C，1 week): Dissolve 2 g SBE-β-CD in 10 mL saline to obtain a clear solution.

---

View More

Solubility in Formulation 3: ≥ 2.5 mg/mL (24.97 mM) (saturation unknown) in 10% DMSO + 90% Corn Oil (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 25.0 mg/mL clear DMSO stock solution to 900 μL of corn oil and mix evenly.

---

 (Please use freshly prepared in vivo formulations for optimal results.)