Volatiles from the Rare Australian Desert Plant Prostanthera centralis B.J.Conn (Lamiaceae): Chemical Composition and Antimicrobial Activity

Timothy Collins,Graham Jones,Nicholas Sadgrove

doi:10.3390/agriculture4040308

Abstract

Hydrodistilled essential oils and dichloromethane (DCM) extracted volatiles were taken from cultivated specimens of Prostanthera centralis, endemic to central Australia. All volatiles were chemically characterised by Gas Chromatography-Mass Spectroscopy (GC-MS) with the use of authentic standards, followed by Nuclear Magnetic Resonance (NMR) Spectroscopy. The antimicrobial activity of the essential oils was measured against a range of Gram-negative and Gram-positive bacterial species using a micro-titre plate broth dilution assay. Twenty-two compounds were identified as components of the sweet smelling aromatic essential oil and DCM extracts, both showing a relatively high abundance of prostantherol. The volatiles extracted using DCM, differed only in the relative abundance of the major components and the lack of ledol and squamulosone. This study constitutes the first time ledol and squamulosone have been identified in a Prostanthera species. Antimicrobial assays showed moderate to high inhibitory activity against some Gram-positive bacteria and the yeast Candida albicans.

Highlights

The genus Prostanthera (Lamiaceae) comprises approximately 100 species endemic to Australia [1].Prostanthera centralis B.J.Conn is a shrub, 0.3–1 m in height, restricted to the Central Ranges bioregion, growing in gravelly sands and quartzite scree [2]
Components of essential oils produced from Prostanthera species included 1,8-cineole, maaliol and prostantherol [3,8], all of which have antimicrobial activity [8] while some of these components have anti-inflammatory and antinociceptive effects [9,10]
Additional volatiles, together with those observed in the essential oil, were identified in the dichloromethane (DCM) extracted concrete (Table 1)

Summary

Introduction

The genus Prostanthera (Lamiaceae) comprises approximately 100 species endemic to Australia [1].Prostanthera centralis B.J.Conn is a shrub, 0.3–1 m in height, restricted to the Central Ranges bioregion, growing in gravelly sands and quartzite scree [2]. The most recent study of Prostanthera, which did not include P. centralis, helped to resolve many but not all of the phylogenetic relationships in the genus using nuclear and chloroplast sequence analysis [11]. In concert with these molecular studies, it has been shown that a chemotaxonomic approach, using chemical variability of essential oils, has the potential to contribute to the collective understanding of species limits and phylogenetic relationships in Prostanthera and other species [12,13]

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