A widely used antiviral drug could be made through a radically different chemical route—one that turns carbon dioxide and phosphite into foscarnet using electricity and a specially engineered bismuth catalyst. In a study published in Nature Catalysis, researchers report an electrosynthetic process that couples two relatively simple inorganic feedstocks to produce foscarnet, a phosphorus-containing medicine used particularly against difficult viral infections. The approach addresses a long-standing challenge in foscarnet manufacturing: conventional synthesis is chemically demanding, while direct incorporation of carbon dioxide into the drug has proved difficult to control. The new system uses bismuth modified with an ionic liquid, abbreviated IL@Bi, to make the carbon dioxide-phosphite coupling sufficiently productive. Under the reported conditions, the catalyst reached a Faradaic efficiency of 37.5 percent for foscarnet, a current density of 224.2 milliamperes per square centimetre and a production rate of 1,555.6 micromoles per square centimetre per hour. That output was ten times higher than the rate obtained with unmodified bismuth, suggesting that the ionic-liquid coating does more than simply alter the electrode surface: it changes the reaction pathway itself.
Foscarnet is an antiviral drug with an unusual chemical structure and an important clinical role. Unlike many medicines that must be converted inside cells into an active form, foscarnet directly interferes with viral DNA polymerases and reverse transcriptases, enzymes that viruses need to copy their genetic material. Its phosphate-like structure enables it to interact with the catalytic machinery of these enzymes, helping block the extension of newly synthesized viral DNA. The drug is especially valuable in situations involving viral infections that have become resistant to other treatments, including certain cytomegalovirus and herpesvirus infections. Yet the same phosphorus-rich chemistry that gives foscarnet its biological activity also complicates its preparation. Producing the molecule requires precise control over carbon–phosphorus and oxygen-rich functional groups, and conventional routes can involve multiple steps, carefully selected reagents and waste-generating transformations. The possibility of building foscarnet electrochemically from carbon dioxide and phosphite is therefore significant not simply because it uses a different reactor, but because it proposes a more direct way to assemble a medically valuable compound from abundant, relatively inexpensive starting materials.
Carbon dioxide is chemically stable, which is one reason it accumulates in the atmosphere and another reason it is difficult to use as a raw material. To convert CO₂ into a useful organic or inorganic product, chemists must first activate it by adding electrons, often creating a highly reactive intermediate known as the carbon dioxide radical anion, CO₂·⁻. This species has an unpaired electron and can participate in bond-forming reactions that ordinary carbon dioxide cannot. Electrochemistry offers a way to generate such intermediates at an electrode, using electrical current rather than a separate chemical reducing agent. But the radical anion is also fleeting and can follow many competing pathways, including reactions that return it to carbon dioxide or convert it into unwanted products such as carbon monoxide, formate or oxalate. The central problem is thus not merely making CO₂·⁻, but producing it at the right rate and bringing it into contact with the correct reaction partner before it disappears. In this study, that partner is a phosphite-derived radical species, written as PO₃·²⁻, whose encounter with activated carbon dioxide leads toward the phosphorus-containing framework of foscarnet.
The researchers addressed the problem by modifying bismuth with an ionic liquid. Bismuth is already known as a useful electrocatalyst for carbon dioxide reduction because it can promote selective transformations while avoiding some of the hydrogen evolution and hydrocarbon-forming reactions associated with other electrode materials. On its own, however, bismuth did not produce foscarnet at the same rate. The ionic liquid changes the microscopic environment around the catalyst and the dissolved reactants. Ionic liquids are salts that remain liquid at relatively low temperatures, and their charged, highly tunable structures can influence solvent organization, ion transport, adsorption and electron-transfer reactions. According to the mechanistic analysis, the ionic liquid in IL@Bi participates in radical-mediated electron transfer, enhancing the generation of CO₂·⁻ in the electrolyte rather than leaving the electrode to carry out the entire activation process directly. This distinction matters because the reaction is controlled not only by the electrode’s composition, but also by what happens in the thin liquid layer surrounding it. By creating a more favorable interfacial environment, IL@Bi increases the supply of activated carbon dioxide available for the next bond-forming step.
The proposed mechanism then brings the two radical intermediates together. Phosphite, a lower-oxidation-state phosphorus compound, can be converted under electrochemical conditions into the phosphite radical PO₃·²⁻. The ionic-liquid-modified surface helps facilitate an encounter between this species and CO₂·⁻, allowing the carbon component from carbon dioxide to become connected to the phosphorus-containing component. Subsequent electron-transfer and proton-transfer steps can then produce the oxygen-rich structure associated with foscarnet. The importance of the ionic liquid is therefore twofold: it promotes the formation of carbon dioxide radicals and helps organize or accelerate their reaction with phosphite radicals. This is a form of reaction control that operates through local molecular encounters. Instead of treating the electrolyte as an inert medium through which current merely flows, the study presents it as an active chemical participant in steering reactive intermediates toward the desired product. Such control is especially valuable in radical chemistry, where small changes in concentration, charge distribution or diffusion distance can determine whether a useful coupling occurs or the intermediates are lost to side reactions.
The performance figures provide a quantitative measure of the advance. Faradaic efficiency describes the fraction of electrical charge that is used to form the target product rather than driving competing reactions. A value of 37.5 percent means that more than one-third of the electrons passed through the electrochemical system contributed, on the reported basis, to foscarnet formation. The current density of 224.2 milliamperes per square centimetre indicates how much electrical current the electrode can sustain per unit area while operating in the process. High current density is important for practical electrochemical manufacturing because it can allow more product to be made from a smaller electrode, although efficiency, stability, separation and energy consumption must also be considered when judging industrial potential. The reported production rate—1,555.6 micromoles per square centimetre per hour—was ten times that achieved with unmodified bismuth. Together, these measurements show that the ionic-liquid modification substantially improves throughput, not merely the detectability of a previously inaccessible product. They also establish a benchmark for future work aimed at raising selectivity and converting more of the electrical input into foscarnet.
The study is part of a broader effort to transform carbon dioxide from an emissions problem into a feedstock for valuable chemicals. Electrochemical manufacturing can, in principle, be powered by renewable electricity and can replace some stoichiometric reducing or oxidizing reagents used in conventional synthesis. That does not automatically make every electrochemical process sustainable: the overall environmental profile depends on the source of electricity, the lifetime and manufacture of the catalyst, the identity and recovery of the electrolyte, solvent use, product purification and the fate of unreacted feedstocks. Ionic liquids can be advantageous because they have low volatility and tunable properties, but their production, recycling and possible environmental release also require assessment. Likewise, phosphite is a useful phosphorus source, yet the complete material and energy balance of the process will determine whether it offers a meaningful advantage at manufacturing scale. The new results nevertheless provide a compelling proof of concept: carbon dioxide can be incorporated into a clinically relevant phosphorus-containing molecule through a carefully engineered electrochemical radical-coupling pathway rather than being treated solely as an inert by-product.
The researchers’ findings could influence both pharmaceutical synthesis and catalyst design, but several steps remain before the method can be considered a replacement for established production routes. Long-duration operation will need to show that the IL@Bi catalyst retains its activity and that the ionic liquid does not leach, degrade or become contaminated by reaction products. The process must also be tested with respect to product isolation, purity, water and energy requirements, electrode fabrication and operation at larger scales. A laboratory current density and production rate are promising indicators, but scale-up can change mass transport, heat management and the distribution of reactive intermediates across the electrode. Further improvements in Faradaic efficiency could reduce electrical waste and simplify downstream purification. Even with those challenges, the work demonstrates a striking chemical possibility: a greenhouse gas and an inorganic phosphorus compound can be joined through electricity to make an important antiviral drug. By using an ionic liquid to mediate radical formation and pairing it with a bismuth catalyst, the researchers have shown how the boundaries between electrode, electrolyte and reactant can be deliberately blurred to create new routes to valuable medicines.
