Monoterpene indole N-oxide alkaloids from Tabernaemontana corymbosa and their antimicrobial activity

Tabernaemontana corymbosa is a traditional folk medicine. In our research, six monoterpene indole N-oxide alkaloids and their parent alkaloids were obtained from the stem bark of T. corymbosa, including seven new alkaloids (1-7) and five known alkaloids (8-12). Their structures and absolute configurations were elucidated by extensive spectroscopy, quantum chemical calculations, and DP4+ probability analyses. The antimicrobial activity of the obtained compounds was evaluated, among which alkaloids 4, 8, 12 showed significant antimicrobial activity against Staphylococcus aureus with an MIC value of 6.25 μg/mL, while alkaloids 11, 12 showed moderate antimicrobial activity against Bacillus subtilis with an MIC value of 25 μg/mL.