AUTHOR=Lai Yongji , Zhong Yu-Ting , Liang Yu , Chen Wei-Chen , Liao Qiuyan , Li Mu , Han Pan , Cai You-Sheng , Wang Fuqian 

TITLE=Identification of antibacterial constituents from Rhododendron simsii Planch with an activity-guided method

JOURNAL=Frontiers in Pharmacology

VOLUME=15

YEAR=2024

URL=https://www.frontiersin.org/journals/pharmacology/articles/10.3389/fphar.2024.1490335

DOI=10.3389/fphar.2024.1490335

ISSN=1663-9812

ABSTRACT=<p>Bacterial infections and antibiotic resistance pose significant public health challenges globally. Natural products serve as valuable sources for discovering antimicrobial agents. <italic>Rhododendron simsii</italic> Planch, a folk medicine, is traditionally used to treat various inflammatory diseases. In this study, we investigated the antibacterial metabolites derived from <italic>R. simsii</italic> Planch. Rhodosimsiin A (1), bearing a 1,5-<italic>seco</italic>-1,6 and 3,6-epoxy grayanane diterpene skeleton, representing a novel 5/6/7/6/5 pentacyclic ring system, and 3<italic>β</italic>,16<italic>α</italic>-dihydroxy-6<italic>β</italic>-ethoxy-14<italic>β</italic>-acetoxy-grayan-1(5)-ene-10-one (4), which represents the first example of the degradation of C-20 and carbonylation in C-10 diterpenoid, together with two new grayanane diterpenes (2−3), three new triterpenes (13−15), and known analogs (5−12, 16−30), were isolated from the leaves of <italic>R. simsii</italic> Planch by using the bioassay-guided method. Their structures were elucidated by comprehensive spectroscopic analyses, and absolute configurations were established by single-crystal X-ray diffraction and calculated ECD spectra. Compounds 14, 15, 18, 20, 27, 28, and 30 exhibited potent antibacterial activity with an MIC<sub>50</sub> of 1.4–24.3 <italic>μ</italic>g/mL against <italic>Staphylococcus aureus</italic>. The findings of this research indicate that secondary metabolites derived from <italic>R</italic>. <italic>simsii</italic> Planch are promising natural antimicrobial candidates.</p>