Effects of structural differences on the antibacterial activity of biflavonoids from fruits of the Brazilian peppertree (Schinus terebinthifolius Raddi).

Flavonoids, synthesized by plants across all families and therefore found in a huge variety, possess a diverse range of pharmacological properties. Direct antibacterial and synergistic activities as well as the inhibition of several bacterial virulence factors are known. Besides the mode of action, it is important to understand the structure-activity relationship to identify key structural characteristics. This study aimed to identify biflavonoids with antibacterial activity from Schinus terebinthifolius Raddi fruits. The purified biflavonoids were characterized in terms of their antibacterial effects. We found that the activity of biflavonoids, including agathisflavone (AGF), amentoflavone (AMF), and tetrahydroamentoflavone (THAF), was dependent on their chemical configuration and degree of oxidation, with THAF showing the highest activity on planktonic cells. Additionally, biofilm formation and composition were strongly influenced by THAF. Even slight differences in the chemical structure have fundamental effects on the activity of isolated biflavonoids. This suggests a specific binding of these substances in bacteria and thus enables detailed investigations of the mode of action in the future.