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 D-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 hydrodistillation. 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.

A Contemporary Introduction to Essential Oils: Chemistry, Bioactivity and Prospects for Australian Agriculture

“…The essential oils dominated by the alcohols, fenchol (21) and borneol (18), demonstrated high antimicrobial activity against the yeast C. albicans, bacterial species, such as Staphylococcus aureus, S. epidermidis, and the human pathogenic fungal species Trichophyton rubrum, T. mentagrophytes and T. interdigitalis [62]. Similar activity was demonstrated by the fenchyl- (22) and bornyl acetate (20) oils against C. albicans and S. epidermidis [81].…”

“…Perhaps more problematic is the diffusion of components from one well to another, which has the capacity to create the appearance of synergistic or antagonistic interactions, which again reduces the reproducibility of the results. Whilst using parafilm to lock all volatiles into the 96-well plate has the advantage of slowing the evaporation of essential oils during the experiment [62], the disadvantage is that synergistic or antagonistic interactions can be enhanced. Thus, a more reliable method uses a sterile plastic sticky sheet to cover all wells individually [63].…”

“…Other well-known examples from the chemical groups described by Franchomme and Penoel (Table 2) include the phenol carvacrol (13) from oregano (Origanum vulgare L.: Lamiaceae), which has been potentially implicated in liver damage, along with a host of other phenols and more specifically, phenylpropanoids, such as the aforementioned carvacrol (13) and the potentially hepatotoxic safrole (14) and methyl eugenol (15), known to be available in high yields from various Australian Zieria (Rutaceae) species [79] and an unusual and rare chemotype of Eremophila longifolia F.Muell (Scrophulariaceae) [22,62], as mentioned previously.…”

“…Although the use of camphor (17) is treated with suspicion, after studies demonstrated potential convulsant activity and liver/central nervous system damage, the camphor (17) and α-pinene (2) rich chemotype of rosemary continues to be used as a liniment for muscle aches and pains [40]. Camphor (17) is the ketone of the alcohol borneol (18), which occurs abundantly in a specific essential oil chemotype of the Australian species E. longifolia that demonstrated moderate antimicrobial activity [62].…”

Plant‐derived medicinal entomochemicals: an integrated approach to biodiscovery in Australia

“…microtheca † Witchetty grubs (M, F); Lerps (Psyllidae) (F); Galls (Eriococcidae) (F) (Deegan et al 2010;Latz 2018) Colds, flu, internal pains, joint pain, skin sores, pruritus, headache (L, B); toothache, medicinal wash (B) (ACNT 1993;Peile and Bindon 1997;Bordulk et al 2012) Antibacterial, antifungal, antioxidant, insecticidal (L) (Ghaffar et al 2015;Maghsoodlou et al 2015;Nikbakht et al 2015;Siddique et al 2017Siddique et al , 2018 Saponins (B); terpenoid essential oils (e.g. 1,8cineole and α-pinene) (L, F) (ACNT 1993;Bignell et al 1997;Ghaffar et al 2015;Maghsoodlou et al 2015;Nikbakht et al 2015;Siddique et al 2017Siddique et al , 2018 Eucalyptus intertexta (Floater 1996;Walsh et al 2014) Sores, burns, cuts (G) (Bindon 1996) Antitumour activity (L, St) (Collins et al 1990 (ACNT 1993;Bindon 1996;Latz 2018) Antimicrobial, antioxidant (L, Sm, St); modulation of platelet activity (antiheadache) (L, F); cardioactive effects (L) (Pennacchio et al 1996;Rogers et al 2000;Hayhoe and Palombo 2011;Sadgrove et al 2011;Singab et al 2013; Terpenoid essential oils, iridoid glucoside (geniposidic acid), alkaloids, phenylpropanoids (L); genifuranal (Sm); phenolics (St) (Pennacchio et al 1996;Sadgrove et al 2011;Singab et al 2013; References are provided within each subheading. Note: the terms 'witchetty/edible grubs', 'lerp' and so forth may constitute many different species.…”