Discovery of diversified cassane diterpenoids as potent antibacterial agents from Caesaplinia pulcherrima and their mechanisms

BACKGROUND Natural products play a significant role in the development of novel bactericide candidates. Caesalpinia pulcherrima, a traditional medicine, had anti‐inflammatory, antimicrobial, and antifeedant activities, therefore the previous bioassay results of C. pulcherrima implied that its main active ingredients may have potential to be used as botanical bactericides. RESULTS Bio‐guided isolation of C. pulcherrima was conducted to obtain 11 novel cassane diterpenoids (capulchemins A–K) and 10 known sesquiterpenes. Their structures were established by extensive spectroscopic methods and single‐crystal X‐ray diffraction analyses. Capulchemins A–F possess a rare aromatic C ring, while capulchemin K with a 15,16‐degradative carbon skeleton represents a rare group of cassane diterpenes. Capulchemin A exhibited remarkable antibacterial activity against four phytopathogenic bacteria, particularly against Pseudomonas syringae pv. actinidae and Bacillus cereus, with minimal inhibitory concentration values of 3.13 μM. Meanwhile, capulchemin A showed significant control effect on kiwifruit canker in vivo. Further investigation of its mechanism of antibacterial activity revealed that compound 1 was closely related to destroy cell membrane to cause cell death. Additionally, some of those cassane diterpenoids showed potential antifeedant against Mythimna separate walker and Plutella xylostella. Consequently, capulchemin A could have the potential to be used as a template for the development for new eco‐friendly NP‐based bactericides. CONCLUSION These data contribute to a better understanding of the antibacterial activity of cassane diterpenes. Cassane diterpenes have been discovered to be leading to broad application prospects in the development as novel botanical bactericides. © 2023 Society of Chemical Industry. Eleven novel cassane diterpenes were isolated from Caesalpinia pulcherrima. Most cassane diterpenes exhibited inhibitory effects on four phytopathogenic bacteria and their mechanisms were demonstrated. Their antifeedant activities against two insects were tested.