Limonoids With Antimicrobial Activity From <i>Phellodendron chinense</i> Schneid

Phellodendron chinense Schneid, a traditional Chinese medicinal herb, has been widely utilized in the treatment of various diseases. In an effort to discover new bioactive compounds, the present study conducted a systematic isolation of chemical constituents from this medical plant, which led to the isolation of a new limonoid named pheldronone (1) and six known limonoids (2-7). The planar structure of the new compound was identified by extensive spectroscopic analyses. DP4+ method was employed to assign the relative configurations of 1 as 20R*,21R*,22R*, and 23S* with a possibility of 99.99%, which validated the nuclear magnetic resonance-derived stereochemical assignments. The absolute configuration was determined by electronic circular dichroism data. The antimicrobial activities of all isolates were tested using a 2-fold dilution method. Compound 3 exhibited antimicrobial activity against Plectosphaerella cucumerina with a minimum inhibitory concentration (MIC) of 4.00 µg/mL. Compounds 3 and 4 exhibited antimicrobial activity against Alternaria panax with MIC values of 4.00 and 8.00 µg/mL respectively. Compound 4 also exhibited antimicrobial activity against Fusarium solani with a MIC value of 2.00 µg/mL, which was comparable to Nystatin. The present study provides a scientific basis for the application of the antibacterial activity of P. chinense.