The sesquiterpenes-rich leaf essential oil of Ekebergia carpensis Sparrm. from South West Nigeria

Ekebergia capensis Sparrm. commonly known as the cape ash, is a medicinal tree of the family Meliaceae whose bark, leaves, and roots are widely employed for the treatment of fever, gastrointestinal disturbances and respiratory ailments. The present study investigated the volatile composition, enantiomeric distribution, and antimicrobial potential of the leaf essential oil of E. capensis collected from southwestern Nigeria. The essential oil, obtained by hydrodistillation, was analyzed using gas chromatography–mass spectrometry (GC–MS) and chiral GC-MS. A total of 56 phytochemical constituents were identified, revealing a sesquiterpene- rich oil. The dominant constituents were β-caryophyllene (47.51%), caryophyllene oxide (9.43%), δ-cadinene (7.92%), α-copaene (5.93%), and α-humulene (5.42%). Enantiomeric profiling showed distinct stereochemical patterns: α-copaene and β-caryophyllene occurred exclusively in the levorotatory form [(+)0:(–) >99%ee:], whereas β-bourbonene and δ-cadinene were entirely dextrorotatory [(+)>99%ee:(–)0]. The essential oil displayed broad-spectrum antimicrobial and antifungal activity, with minimum inhibitory concentrations (MICs) ranging from 156.3 to 1250 μg/mL. Notable activity was observed against Staphylococcus epidermidis and Streptococcus pyogenes (both 156.3 μg/mL), as well as Candida albicans (312.5 μg/mL). Pseudomonas aeruginosa (625 μg/ mL), Aspergillus niger (312.5 μg/mL), Microsporum canis (312.5 μg/mL), Serratia marcescens (625 μg/mL), and Trichophyton rubrum (312.5 μg/mL), showed moderate activity against the oil. Activity against S. aureus, Bacillus cereus, and A. fumigatus was comparatively weaker (MIC 1250 μg/mL). The strong antimicrobial potency may be attributed to its dominant sesquiterpene constituents, particularly β-caryophyllene and the enantiomerically pure β-bourbonene, fraction. This work on leaf essential oil supports its ethnomedicinal relevance and highlights its potential as a natural antimicrobial agent.