The Diversity of Volatile Compounds in Australia’s Semi-Desert Genus Eremophila (Scrophulariaceae)

Abstract

Australia’s endemic desert shrubs are commonly aromatic, with chemically diverse terpenes and phenylpropanoids in their headspace profiles. Species from the genus Eremophila (Scrophulariaceae ex. Myoporaceae) are the most common, with 215 recognised taxa and many more that have not yet been described, widely spread across the arid parts of the Australian continent. Over the years, our research team has collected multiple specimens as part of a survey to investigate the chemical diversity of the genus and create leads for further scientific enquiry. In the current study, the diversity of volatile compounds is studied using hydrodistilled essential oils and leaf solvent extracts from 30 taxa. Several rare terpenes and iridoids were detected in chemical profiles widely across the genus, and three previously undescribed sesquiterpenes were isolated and are assigned by 2D NMR—E-11(12)-dehydroisodendrolasin, Z-11-hydroxyisodendrolasin and 10-hydroxydihydro-α-humulene acetate. Multiple sampling from Eremophila longifolia, Eremophila arbuscular, Eremophila latrobei, Eremophila deserti, Eremophila sturtii, Eremophila oppositifolia and Eremophila alternifolia coneys that species in Eremophila are highly chemovariable. However, taxa are generally grouped according to the expression of (1) furanosesquiterpenes, (2) iridoids or oxides, (3) mixtures of 1 and 2, (4) phenylpropanoids, (5) non-furanoid terpenes, (6) mixtures of 4 and 5, and less commonly (7) mixtures of 1 and 5. Furthermore, GC–MS analysis of solvent-extracted leaves taken from cultivated specimens conveys that many heavier ‘volatiles’ with lower vapour pressure are not detected in hydrodistilled essential oils and have therefore been neglected in past chemical studies. Hence, our data reiterate that chemical studies of the genus Eremophila will continue to describe new metabolites and that taxon determination has limited predictive value for the chemical composition.

Advanced Chemophenetic Analysis of Essential Oil from Leaves of Piper gaudichaudianum Kunth (Piperaceae) Using a New Reduction-Oxidation Index to Explore Seasonal and Circadian Rhythms

“…In other species, the influence of biotic and abiotic factors on the composition of EOs is frequently reported in the literature [ 2 , 53 , 54 , 55 ]. Phenotypic plasticity has become a major challenge in the context of understanding correlators of chemistry to taxa [ 56 , 57 ]. Hence, tools/methodologies to evaluate and to interpret phenomena around phenoplasticity are still evolving [ 58 , 59 , 60 ].…”

Purely Australian Essential Oils Past and Present: Chemical Diversity, Authenticity, Bioactivity, and Commercial Value

“…Chinnock, which normally expresses a high yield of the iridoid methoxymyodesert-3-ene. However, the species is made up of several chemotypes, and one is the ngaione type [59], or types that include related furanosesquiterpenes. Because stock animals graze heavily on the species, E. deserti has been associated with animal fatalities, but the inconsistency in poisonings was a mystery until it was realized that toxicity was caused by a ngaione chemotype.…”

“…Because stock animals graze heavily on the species, E. deserti has been associated with animal fatalities, but the inconsistency in poisonings was a mystery until it was realized that toxicity was caused by a ngaione chemotype. The Australian desert genus Eremophila has several species that express furanosesquiterpenes like ngaione [59], and they should all be regarded as inedible.…”

Pharmacology of Natural Volatiles and Essential Oils in Food, Therapy, and Disease Prophylaxis

“…While hydrodistillation requires masses of leaves, energy input, time, and effort to produce essential oils, solvent extraction requires a small leaf and a small volume of solvent (DCM, Hexane). This method was used in a chemophenetic study of heterogeneous species aggregates in Eucalyptus ( Collins et al, 2018 ), Phebalium nottii ( Sadgrove N. J. et al, 2020 ) and Eremophila ( Sadgrove et al, 2021 ), and in the former two the leaf samples were taken from herbarium voucher specimens. In the case of Eucalyptus , the sesquiterpene diol cryptomeridiol does not survive hydrodistillation and eliminates a hydroxyl group to randomly produce three eudesmols, either alpha (α-), beta (β-), or gamma (γ-).…”

“…The semi-volatile coumarins were easily detected by GC-MS if the column temperature was raised to 280–300°C and held for 20 min ( Sadgrove N. J. et al, 2020 ). Species in Eremophila also express semi-volatiles that may have significance in taxonomic studies because of a reduced susceptibility to the effects of phenoplasticity ( Sadgrove et al, 2021 ). In this latter study it was realized that the effects of phenoplasticity from contemporary weather changes, such as droughts or excessive wet periods, are more dramatic in leaf material than in timber.…”