Discovery of oxochromanyl–naphthoquinone hybrids as a new chemotype of selective Enterovirus A71 inhibitors

Viruses are relentless invaders, and among the most troublesome are those that cause hand, foot, and mouth disease. While this illness often seems mild in children, a specific strain known as Enterovirus A71 can trigger severe complications in the brain and nervous system, leading to paralysis or even death. For decades, scientists have searched for a medicine that can stop this virus without harming the human body, but no effective treatment has yet reached the clinic. Existing vaccines offer some protection, yet they are not available everywhere and may not work against every new version of the virus. This leaves a critical gap in global health: a need for a new kind of drug that can specifically target this virus while ignoring the rest of the biological world.

To fill this gap, a team of researchers in Italy turned to nature's own chemical toolbox. They looked at two distinct families of compounds that have shown promise in fighting infections: naphthoquinones, which are found in plants and have a long history of antimicrobial use, and chromones, a group of oxygen-rich structures often found in flavonoids. The scientists wondered if they could fuse the best features of both into a single, rigid molecular structure. By joining these two shapes together, they hoped to create a new type of molecule that would act as a precise key, fitting into the machinery of the virus to stop it in its tracks.

The researchers set out to build a small library of these new hybrid molecules. Using a chemical process that links the two parent structures together, they created sixteen different variations. Each variation was slightly different, with various atoms or groups attached to the core framework, allowing the team to test how these small changes affected the molecule's ability to fight the virus. They then put these new compounds to the test in the laboratory, exposing them to Enterovirus A71 and several other RNA viruses, including the one that causes respiratory syncytial virus and the virus responsible for COVID-19.

The results were strikingly specific. Almost all of the new compounds were harmless to human cells, showing no signs of toxicity even at high concentrations. More importantly, they displayed a powerful ability to stop the Enterovirus A71 from multiplying, while having little to no effect on the other viruses they tested. This high level of selectivity is exactly what doctors need in an antiviral drug: a substance that attacks the enemy without hurting the host. One compound in particular stood out as the most effective. It was able to reduce the amount of virus in a sample by a factor of one hundred when used at a very low concentration, and it remained safe for human cells at concentrations one thousand times higher. This wide margin between the dose that works and the dose that harms suggests a strong potential for safety.

To understand how these molecules work, the scientists performed a series of experiments to see exactly when and how they interfered with the virus. They first checked if the compounds could kill the virus particles directly, like a disinfectant. The tests showed that simply mixing the drug with the virus did not stop it; the virus remained infectious. This ruled out the idea that the drug acts as a surface cleaner. Instead, when the researchers added the drug at different times during the infection process, they found that it only worked if present right at the very beginning. Once the virus had already entered the cell and started its work, the drug lost its power. This timing suggests that the new molecules interfere with the earliest steps of the viral life cycle, perhaps blocking the virus from entering the cell or preventing it from releasing its genetic instructions, but they do not destroy the virus particle itself.

The study also revealed that the ability to stop the virus was not limited to just one perfect shape. Many of the different variations the team created, despite having different chemical groups attached to them, retained the ability to fight the virus. This indicates that the core structure itself is the active ingredient, providing a solid foundation for future drug development. The researchers found that the position of certain atoms on the molecule mattered; moving a single atom from one spot to another could turn a powerful drug into an inactive one, or vice versa. This sensitivity to structure gives scientists a clear map for refining the molecule further.

Ultimately, this work introduces a completely new class of chemical structures that can selectively disable Enterovirus A71. It does not claim to have a finished cure, but it offers a promising new path forward. By proving that this specific hybrid framework can stop the virus with high precision and low toxicity, the researchers have provided a fresh starting point for medicinal chemists. The most effective compound identified in the study, with its ability to suppress viral production significantly while remaining safe for cells, serves as a lead candidate for further study. As the search for treatments for severe viral infections continues, these oxochromanyl–naphthoquinone hybrids represent a tangible step toward a future where effective antiviral therapies are available for those who need them most.