Chemical diversity of abietane diterpenoids from Nepeta stewartiana Diels and their anti-bacterial and antifeedant effects.

Terpenoids exhibit a broad range of biological activities, such as antibacterial and antifeedant activities, along with a wealth of practical uses in various fields. This phytochemical study of Nepeta stewartiana Diels has led to the isolation of twelve undescribed diterpenoids (1-12) of the abietane family, along with seven known ones (13-19). The structures of these chemicals were elucidated with comprehensive spectroscopic analyses, including NMR, HR-ESI-MS, ECD, UV, and IR. Moreover, the absolute configuration of compound 1 was confirmed using single-crystal X-ray diffraction. The anti-bacterial and anti-feedant properties against four strains of bacteria, were found in three undescribed abietane diterpenoids, 1, 4, and 6, and two known compounds, 13 and 15. Antibacterial activity assay results showed that these compounds exerted varying degrees of inhibitory effects against Staphylococcus aureus and Bacillus subtilis, with IC50 values ranging from 37.29 to 516.32 μg/mL. Compound 4 also demonstrated inhibitory activity against Streptococcus pyogenes, with an IC50 value of 281.55 ± 64.49 μg/mL. Furthermore, these compounds demonstrated potent antifeedant activity against Spodoptera litura larvae, with compound 4 being the most obvious with an EC50 value of 12.81 ± 3.27 μg/cm2. The observed results suggest that N. stewartiana is rich in abietane diterpenoids, several of which have potential application value due to their significant anti-bacterial and antifeedant effects.