Fluorinated molecules are central to modern drug discovery and crop protection because fluorine can substantially alter a compound’s biological, chemical and physical properties. Introducing the element can improve metabolic stability, change acidity, influence how a medicine binds to its target or modify the way a material behaves. Despite these advantages, the chemical installation of fluorine often depends on hazardous reagents. One of the most widely used examples is DAST, or diethylaminosulfur trifluoride, a powerful fluorinating agent that is toxic, thermally unstable and operationally demanding in large-scale manufacturing.

The Oxford researchers, led by Professor Véronique Gouverneur of the University’s Department of Chemistry, revisited a reaction first developed more than a century ago: the Appel reaction. Traditionally, the Appel reaction converts alcohols into alkyl halides by activating the alcohol with a phosphonium reagent and then allowing a halide ion to replace the oxygen-containing group. Chlorides, bromides and iodides can generally be produced efficiently in this way. Fluoride, however, has resisted the same strategy because it reacts with the phosphorus reagent to form a stable, unproductive compound rather than fluorinating the alcohol.

The problematic species is known as PPh₃F₂, or difluorotriphenylphosphorane. Its formation effectively traps fluoride before the ion can attack the activated alcohol. In chemical terms, the reaction pathway is diverted into a thermodynamic dead end. This explains why the classic Appel process, although broadly useful for other halides, has not provided a practical general method for converting alcohols into alkyl fluorides using a simple inorganic fluoride salt.

Oxford’s solution is a newly designed neopentoxyphosphonium salt. The reagent changes the behavior of the phosphorus-containing reaction system, preventing the formation of the unwanted PPh₃F₂ side product. In the presence of potassium fluoride, the salt generates a reactive intermediate that can activate the alcohol substrate. The resulting activated species is then attacked by fluoride, replacing the alcohol-derived group and forming the carbon–fluorine bond. The approach is catalytic in key components, meaning that the researchers can reduce the amount of material required while retaining high reactivity.

Potassium fluoride is particularly attractive because it is inexpensive, widely available and considerably easier to handle than many specialized fluorinating reagents. The Oxford team demonstrated the method across more than 80 substrates, producing a broad collection of fluorinated molecules with yields reaching 98 percent. The compounds included cyclic and heterocyclic structures as well as alkyl fluorides related to biologically relevant molecular frameworks. Such breadth is critical: a reaction that works only with one simple alcohol would have limited practical value, whereas a method compatible with diverse molecular architectures could become a valuable tool for medicinal and synthetic chemistry.

The researchers also achieved a more demanding feat: the preparation of enantioenriched fluorochemicals from racemic alcohols. Enantiomers are molecules that possess the same atoms and bonds but differ in three-dimensional arrangement, like left and right hands. Because biological targets are themselves chiral, the distinction can determine whether a compound is therapeutically useful, inactive or toxic. Conventional fluorination strategies often require an enantiomerically enriched starting material. The new reaction can instead use a readily available racemic alcohol and generate products with useful stereochemical enrichment, potentially simplifying the preparation of chiral fluorinated building blocks.

The sustainability implications extend beyond the reaction itself. The process does not depend on hydrogen fluoride, or HF, the hazardous fluorine source used throughout much of industrial fluorine chemistry. The fluoride-containing materials needed to prepare the new reagent can be made from fluorspar, an abundant mineral. In earlier work published in Nature in 2024, Gouverneur’s team demonstrated that fluorspar could be converted into fluorochemicals through low-temperature activation in water, offering a potential alternative to supply chains built around concentrated HF.

The Oxford researchers further report that both the catalyst and the phosphine oxide by-product can be recovered and recycled. This reduces waste and introduces elements of circular chemistry into a transformation traditionally associated with difficult-to-manage reagents and by-products. By combining a common fluoride salt, a recyclable reaction system and a broader source of fluorine derived from fluorspar, the strategy could help move fluorination toward safer and more resource-efficient manufacturing. The study, published in Science, suggests that a reaction once considered unsuitable for fluoride may now provide a practical route to valuable fluorinated medicines, crop-protection compounds and advanced materials.

Subject of Research: A potassium fluoride-based catalytic method for converting alcohols into fluorinated compounds.

Article Title: Catalytic Appel fluorination of alcohols with potassium fluoride

News Publication Date: 30 July 2026

Web References: University of Oxford: Véronique Gouverneur; Fluorspar to fluorochemicals upon low-temperature activation in water

References: Science, DOI: 10.1126/science.aec6298

Image Credits: Anirban Mondal

Keywords

Potassium fluoride, Appel fluorination, alcohols, alkyl fluorides, fluorine chemistry, catalytic chemistry, sustainable chemistry, circular chemistry, medicinal chemistry, University of Oxford

PFAS compounds have gained notoriety due to their persistence in the environment, resistance to degradation, and potential links to various health issues. Fluorine, a key atom in many PFAS molecules, contributes characteristic stability by forming robust carbon-fluorine bonds, which also finds utility in medicinal chemistry. In pharmaceuticals, incorporation of fluorine atoms can enhance drug bioavailability, metabolic stability, and molecular targeting, making fluorinated drugs an important class of therapeutics. Yet, the label of “forever chemicals” engenders concern about possible latent toxicities, especially as regulatory bodies start to categorize certain essential medicines as PFAS-containing.

The recently published study in PLOS ONE represents an extensive evaluation of real-world adverse drug reactions associated with fluorinated medicines in the United Kingdom. Utilizing data spanning five years (2019 to 2024) from the UK Medicines and Healthcare products Regulatory Agency (MHRA) Yellow Card reporting system, researchers meticulously compared the ADR frequencies of thirteen fluorinated pharmaceutical agents with six structurally analogous drugs lacking fluorine content. The goal was to discern whether the fluorine content correlated with a heightened incidence or differing profile of ADRs.

Analytical results demonstrated no statistically significant association between the presence or quantity of fluorine atoms within these pharmaceuticals and the rates of reported adverse drug events. Among the drugs evaluated, lansoprazole—a proton pump inhibitor extensively prescribed for acid-related gastrointestinal disorders—showed a particularly low rate of ADRs at just 14.1 reactions per one million prescriptions dispensed. This observation underscores the tolerability of widely used fluorinated drugs despite their PFAS classification.

Dr. Alan Jones, corresponding author and pharmacology expert at the University of Birmingham, emphasized the importance of these findings within the context of ongoing PFAS discourse. He explained that although PFAS compounds are ubiquitous in consumer goods and environmental matrices, their risk profile when embedded within the molecular framework of essential medications does not appear to elevate adverse reaction risk. The study reassures both healthcare professionals and patients that fluorine-containing medicines maintain safety profiles consistent with non-fluorinated analogues.

The research explored the complexity of adverse reaction types, recognizing that certain ADRs have been previously linked with PFAS exposure in environmental or occupational settings. However, when comparing fluorinated versus non-fluorinated drugs, the pattern and nature of ADRs largely aligned more closely with each drug’s pharmacological mechanism of action rather than fluorine content. This distinction highlights that observed adverse effects are likely attributable to intrinsic drug activity rather than chemical fluorination per se.

Interestingly, among the thirteen fluorinated medications studied, drugs such as sitagliptin, an antidiabetic agent, and flecainide, an antiarrhythmic, contain relatively high fluorine atom counts but did not correspond to higher incidences of ADRs. This observation further dissociates fluorine moiety abundance from clinical safety concerns, reinforcing the notion that medicinal fluorination, when structurally and pharmaceutically tailored, does not inherently confer toxicity risks typical of environmental PFAS.

While the study provides robust evidence, the authors acknowledge inherent limitations primarily rooted in the voluntary and self-reported nature of the Yellow Card surveillance system. Underreporting or incomplete adverse event documentation could potentially underestimate actual ADR frequencies. Despite this, the extensive dataset covering millions of prescriptions renders these conclusions highly informative for regulators and pharmacovigilance bodies.

Beyond immediate regulatory implications, this research encourages a nuanced understanding of fluorination’s dual role. On one hand, fluorine introduces chemical inertness and environmental stability, which can be problematic in environmental pollutants. On the other, in the medicinal chemistry domain, carbon-fluorine bonds enhance drug efficacy, metabolic resistance, and target specificity, contributing substantially to therapeutic success and patient outcomes.

The findings also prompt reconsideration of blanket categorization of pharmaceuticals containing fluorine within the PFAS umbrella. While vigilance concerning environmental and systemic PFAS exposure remains paramount, essential medicines incorporating fluorine atoms may warrant distinct classification reflective of their clinical safety and benefit profiles. Such stratification could prevent unnecessary alarm among patients and healthcare providers while maintaining robust safety monitoring.

Moreover, this study exemplifies the powerful integration of pharmacovigilance data with chemical informatics to address emergent questions in drug safety. By leveraging real-world evidence and comparative structural analysis, researchers established a comprehensive framework to evaluate chemical features vis-à-vis clinical outcomes. This approach may serve as a model for future assessments of drug safety in the context of evolving environmental toxicology concerns.

In conclusion, the University of Birmingham-led investigation provides a reassuring narrative that medicinal fluorination, although chemically related to PFAS substances, does not drive an escalation in adverse drug reactions within clinical populations. This insight alleviates some of the scientific and public apprehension about the health impacts of fluorine-containing pharmaceuticals and highlights the continuing importance of evidence-based pharmacovigilance in an era of complex chemical safety challenges.

Subject of Research: Safety profiles and adverse drug reaction analysis of fluorinated pharmaceuticals in relation to PFAS exposure concerns.

Article Title: Observational suspected Adverse Drug Reaction Profiles of Fluoro-Pharmaceuticals and potential mimicry of Per- and polyfluoroalkyl Substances (PFAS) in the United Kingdom

News Publication Date: 2-Sep-2025

Web References: 10.1371/journal.pone.0331286

Keywords

Medicinal chemistry, Pharmacology, Drug interactions, Chemical structure