Shedding light on an active principle from the aerial parts of Echinacea purpurea against SARS-CoV-2 in vitro

Echinacea purpurea has traditionally been used to prevent and treat influenza and other viral respiratory infections. During the SARS-CoV-2 pandemic, a mixture of aqueous-alcoholic extracts prepared from the aerial parts and roots of E. purpurea, used in commercial products, was shown to inhibit viral infection in vitro against coronaviruses. Since the compounds responsible for these effects remain unknown, this study aimed to identify antiviral compounds in a pretreatment assay setup. Therefore, fractionation was combined with bioactivity and analytical profiling data. The hydroalcoholic extract of dried E. purpurea aerial parts demonstrated an antiviral effect against SARS-CoV-2 in an in vitro virus pretreatment assay. Subsequent fractionation by liquid–liquid extraction and washing from silica gel using solvent mixtures of rising polarity yielded twelve fractions, of which two showed a protective effect. Due to the integrated approach, combining in vitro bioactivity screening with untargeted metabolite profiling, pheophorbide A was identified as an effective compound in E. purpurea aerial parts extract, without the need for isolation. Although pheophorbide A is already known as an antiviral compound, this is the first study linking the activity of E. purpurea to the content of this chlorophyll break-down product. • Pheophorbide A was identified as one effective compound in Echinacea purpurea extracts. • The active fractions demonstrated up to 85% protection against SARS-CoV-2. • Combined bioactivity and metabolite profiling enabled discovery without isolation.