Essential oil composition of 'Eremophila longifolia' (F. Muell) (Myoporaceae): evidence for new chemovarieties

Abstract

'Eremophila longifolia' is a woody shrub, endemic to arid and semi-arid regions of Australia, where it is employed in traditional indigenous medicine to treat a wide variety of conditions. An early report examining 'E. longifolia' leaf essential oil composition had indicated high levels of the hepatotoxic and carcinogenic phenylpropanoid safrole, and as a result, authors have urged caution in the use of traditional preparations derived from this species. The present study was initiated after noting significant variations in morphology and odor profiles of wild 'E. longifolia' specimens in the state of New South Wales, (NSW) Australia. Leaves from several specimens were collected across a range of biogeographic regions in NSW. Essential oils were obtained by hydrodistillation and analysed using GCMS and NMR spectroscopy. Thirty-five compounds were identified with comparison of retention data and mass spectra with that of published values. Considerable variation was found among specimens in essential oil yield and composition, resulting in identification of three distinct types (here designated A, B and C). Type A specimens produced oils at relatively high yields (3.1% - 5.7 %) with major constituents isomenthone (61.1% - 86.7%), menthone (8.8% - 22.6%) and α-terpineol (8.4% - 11.0%). Type B specimens produced oils of relatively moderate yield (0.5% - 1.9% g/g) with major constituents karahanaenone (81.0% - 82.2%) and α -terpineol (4.1% - 11.7%). One specimen (designated type C) produced essential oil at relatively low yield (0.4% g/g fresh leaves) with major constituents identified as borneol (31.7%), fenchol (19.7%) and limonene (9.9%). No phenylpropanoids, including safrole, were detected in any of the specimens examined here. The relatively uncommon monoterpenoid karahanaenone is valued as a precursor in the fragrance industry and to the best of our knowledge the leaves of type B specimens described here represent the richest known natural source of this compound.