Secondary metabolites from <i>n</i> -hexane fraction of the stem bark of <i>strombosia grandifolia</i> hook.f. ex benth (olacaceae) and their antibacterial activity

Abstract

Chemical and biological studies of the <i>n</i>-hexane fraction of the stem bark extract of <i>Strombosia grandifolia</i> led to the isolation and characterisation of one undescribed lup-20(29)-ene derivative named, grandifolione (<b>1</b>), alongside with nine known compounds <b>2-10</b>. These compounds were isolated from this species for the first time. Their structures were elucidated based on NMR and MS spectroscopic data as well as by comparison with existing data of the literature. The antibacterial activity of the crude extract (CH₂Cl₂/MeOH 1:1), the <i>n</i>-hexane fraction and some of the isolated compounds were evaluated against ten bacterial strains including gram positive (<i>Staphylococcus aureus</i>) and gram negative (<i>Acinetobacter baumannii</i>, <i>Pseudomonas aeruginosa</i>, <i>Escherichia coli</i>, <i>Shigella flexneri</i>, <i>Klebsiella pneumoniae</i> and <i>Salmonella typhimirium</i>). The crude extract (CH₂Cl₂/MeOH 1:1) exhibited moderate activity against <i>S. aureus (</i>ATCC12600 and ATCC700698), <i>P. aeruginosa</i> HM801 and <i>S. typhimirium</i> with MIC values of 125, 125, 250 and 500 µg/mL respectively. The <i>n</i>-hexane fraction exhibited moderate activity against <i>P. aeruginosa</i> NR-48982 and <i>S. aureus</i> NR-46003 with MIC values of 250 µg/mL for both. Sub-fraction F3 exhibited significant activity against <i>S. aureus (</i>ATCC12600 and ATCC700698) and <i>P. aeruginosa</i> HM801 with MIC values of 62.5 µg/mL. Lupeol (<b>3</b>) demonstrated moderate activity against <i>A. baumannii</i> NR-41897, <i>S. aureus</i> ATCC12600, ATCC700698 and NR-46003 with MIC values of 25, 15.6, 31.2 and 25 µg/mL respectively.