Characterization and bioactivity of essential oils from novel chemotypes of 'Eremophila longifolia' (F. Muell) (Myoporaceae): a highly valued traditional Australian medicine

Abstract

Leaf specimens of 'Eremophila longifolia' were collected from western New South Wales, Australia. Essential oils were extracted using hydro-distillation. Characterizations using GC-MS and GC-FID were consistent with those reported in previous work, but demonstrated greater chemo-variability. Antimicrobial activity from disc diffusions and broth dilutions indicated that oils dominated by hydrocarbon monoterpenes and monoterpenols had moderate antimicrobial activity for both Gram-positive and Gram-negative bacteria, including 'Staphylococcus aureus' and 'S. epidermidis'. Oils dominated by ketones demonstrated less activity but showed substantially greater yields in wet-weight leaves. Bioautography revealed the most active constituents to be related to the most abundant - karahanaenone and menthone - but active constituents also included ᴅ-limonene, borneol, sabinene, terpinolene and α-terpineol. Antifungal capacity for 'Trichophyton interdigitalis', 'rubrum' and 'mentagrophytes' was determined using an agar transplant method. Results indicated very high activity from oils rich in borneol and also for oils that were distilled from leaves accidentally burnt or partially pyrolysed during hydro-distillation. This serendipitous observation may have relevance given the traditional manner of use in smoking ceremonies. Free radical scavenging was determined using the DPPH method in methanol and antioxidant capacity with the FRAP assay. Results indicated that oils dominated by monoterpenols had moderate ability, but became very high when the oils were partially pyrolysed.