Deep-Sea Fungus Achieves Catalyst-Free CO2 Conversion in Water

A fungus recovered from deep-sea sediments in the northern South China Sea has yielded a finding that challenges textbook assumptions about carbon dioxide fixation. Researchers at the South China Sea Institute of Oceanology, Chinese Academy of Sciences, in collaboration with Hainan Normal University, have demonstrated that a five-membered cyclic carbonate structure in the natural product cytosporin can form spontaneously from CO2 and an epoxide precursor under conditions milder than anything previously reported for this class of reaction: room temperature, atmospheric pressure, neutral aqueous solution, and no catalyst of any kind.

The work, led by Yan Yan of the South China Sea Institute and Wan-Shan Li of Hainan Normal University, was published online in the Journal of the American Chemical Society on September 1, 2026.

A missing step in the assembly line

The discovery emerged not from a deliberate search for new CO2 chemistry but from an attempt to complete the biosynthetic map of cytosporin, a meroterpenoid produced by the marine fungus Eutypella sp. F0219. The organism was originally isolated from deep-sea sediments in the northern South China Sea. The research team had identified a roughly 46.8-kilobase gene cluster containing 15 genes responsible for producing cytosporin's molecular skeleton, and they could account for nearly every enzymatic transformation along the pathway. But one step remained stubbornly unexplained: the formation of the five-membered cyclic carbonate ring.

Wan-Shan Li likened the situation to an automobile factory where every component has been manufactured and every workstation identified, yet the machine that installs the tires is nowhere to be found, while the finished cars roll off the line with tires perfectly in place. The gene cluster contained no enzyme that could catalyze carbonate formation. The team eventually determined that none was needed.

How the reaction works

Under near-neutral conditions, bicarbonate ions in aqueous solution attack a C5 epoxide on the cytosporin precursor, opening the three-membered ring and generating a carbonate ester intermediate. A nearby C6 hydroxyl group then launches an intramolecular nucleophilic attack on the carbonyl carbon, and subsequent dehydration closes the five-membered ring. The entire process proceeds without enzymatic catalysis.

The reaction is sharply pH-dependent. At pH 6.0 to 6.5, no coupling occurs. At pH 7.0 and above, the reaction becomes significant. Above pH 7.5, competing hydrolysis dominates, and the product shifts from cyclic carbonate to an open-chain hydrolysis product. Isotope-labeling experiments confirmed that both oxygen atoms in the newly formed carbonate ring originate from bicarbonate, not from water or the epoxide itself.

The measured rate constant is approximately 0.15 M⁻¹·h⁻¹ at room temperature, with first-order dependence on both the substrate and bicarbonate concentrations. The reaction is not universal: bicyclic and tricyclic derivatives bearing a fused tetrahydropyran ring react, while monocyclic analogues do not, indicating that the specific polycyclic scaffold provides the conformational strain or geometry needed to drive the coupling.

Contrast with industrial CO2 chemistry

The industrial synthesis of cyclic carbonates from CO2 and epoxides is well established, but it has always required aggressive conditions. Typical processes use temperatures of 100 to 200 degrees Celsius, CO2 pressures of 1 to 5 megapascals, transition-metal catalysts such as cobalt, zinc, or chromium complexes, and organic solvents. Recent efforts in green chemistry have explored ionic liquids, deep eutectic solvents, and photo- or electrocatalytic routes, but all still require either external energy input, specialized reagents, or both.

The fungus accomplishes the same transformation in pure water at ambient conditions with no catalyst, no solvent beyond water, and 100 percent atom economy, meaning every atom from the starting materials ends up in the product with no byproducts. There is no precedent for a fully non-enzymatic, catalyst-free CO2-epoxide coupling forming a five-membered cyclic carbonate in the existing chemical literature.

Not a carbon-capture technology, yet

The discovery is a fundamental science result, not a deployable technology. The rate constant is modest, the substrate scope is narrow, and the reaction requires a specific polycyclic epoxide scaffold that is not trivially available. Scaling this to an industrial carbon-capture-and-utilization process would require engineering substrate analogues with broader availability, improving reaction kinetics, and integrating the chemistry into a continuous-flow system. These are engineering questions that the current study does not address.

What the finding does provide is a proof of concept that nature has found a route to a transformation chemists have always assumed required brute force, and a structural blueprint for designing synthetic CO2 acceptor molecules that could function under similarly mild conditions. Cyclic carbonates are valuable intermediates for lithium-ion battery electrolytes, polycarbonate plastics, and pharmaceutical synthesis, so a greener production route would have broad industrial relevance.

Analysis

The significance of this work lies less in the immediate practicality of the reaction than in the conceptual boundary it redefines. For decades, the assumption in both organic chemistry and chemical engineering has been that CO2, a thermodynamically stable and kinetically inert molecule, can only be coaxed into forming carbon-oxygen bonds under energetic conditions or with the assistance of a catalyst that activates the CO2 molecule. The fungus Eutypella sp. F0219 achieves the coupling through a different strategy: it pre-organizes the epoxide substrate into a strained polycyclic scaffold where the ring-opening reaction becomes thermodynamically favorable even at ambient temperature, and it performs the reaction in water, where bicarbonate serves as the CO2 source.

This is not the first time that biosynthetic pathways have revealed chemistry that would be difficult to replicate with conventional synthetic methods. But it is among the first demonstrations of a fully non-enzymatic step within a natural product pathway that directly engages CO2 as a reactant. Whether chemists can translate the structural principles underlying this reaction into a practical synthetic methodology remains an open question, and one that the authors themselves frame as a future direction rather than a solved problem.