Exploring the antiviral activity of flavonoids from Strychnos variabilis leaves against SARS-CoV-2

Strychnos variabilis De Wild. is a small deciduous tree that is primarily distributed in and around Brazzaville and Kinshasa, located on both sides of the Congo River in Africa [1]. While the leaves have only trace amounts of indoline alkaloids (retuline series) [2] [3], our laboratory isolated numerous rare flavonoids, including flavonol glycosides, from the leaves over three decades ago [4] [5] [6]. Flavonoids are known for their antiviral activity, especially when in glycosidic form, which increases their solubility and effectiveness compared to their non- glycosidic forms [7] [8]. Therefore, our present study aims to investigate the potential antiviral activity of S. variabilis leaves against SARS-CoV-2. Our findings revealed that the total extract of S. variabilis exhibits significant antiviral activity with an IC50 range of 12.5 to 6.25 µg/mL. Moreover, we tested two flavonoids, variabilosides C and D [5], which demonstrated even greater potency with an IC50 range of 6.9 to 3.5 µM.

We suggest that the flavonoids present in S. variabilis leaves could provide a promising pathway for the development of a new herbal substrate used as an adjunctive therapeutic in the treatment of coronavirus disease. Further investigation into the pharmacological properties of these flavonoids is thus warranted to fully explore their potential as therapeutic agents against SARS-CoV-2.