Composition of an Essential Oil from Agonis fragrans J.R. Wheeler et N.G. Marchant

Journal of Essential Oil Research: JEOR, Jul/Aug 2007 by Lowe, Robert F, Russell, Michael F, Southwell, Ian A, Robinson, Christopher J, Day, John

Abstract

The leaf essential oils of Agonis fragrans, isolated by steam distillation and solvent extraction, were analyzed by GC and GC/MS. The major components identified in five of the six samples investigated were 1,8-cineole (28%-34% and 12%-26%, respectively) and α-pinene (14%-28 % and 12%-18% respectively). The remaining sample was almost devoid of 1, 8-cineole (1% in oil and 0% in extract) with higher concentrations of α-pinene (22% and 39%), linalool (25% and 18%) and ( )-(1S, 5R)-myrtenol (20% and 12% respectively). The compositional variation within the species indicated that a breeding project could identify and use the best composition for commercial development.

Key Word Index

Agonis fragrans, Myrtaceae, Coarse Agonis, Coarse Tea Tree, essential oil composition, ethanolic extract, 1,8-cineole, ( )-(1S, 5R)-myrtenol, linalool, α-pinene, antimicrobial activity.

Introduction

The genus Agonis (Myrtaceae) (1), closely related to MeIaleuca andLeptospermum, is limited in natural occurrence to the south west of Western Australia. These woody shrubs or small trees are cultivated for their ornamental shrub and cutflower value. Agonis fragrans, previously recognized as Agonis sp. Coarse Tea Tree and as Agonis sp. Coarse Agonis, is a newly described (2), fine-leaved, lignotuberous shrub reaching 2.4m in height on acid peaty sand in seasonally waterlogged margins of broad valleys. This investigation reports the essential oil composition of another essential oil of commercial potential from the Australian flora.

Experimental

Plant Material: Agonis fragrans voucher specimens from each population were lodged with the Perth Herbarium in Western Australia. Six single plant extracts and six mixed plant, single provenance distilled oils were compared. Samples 6863 and 6864 (Voucher CJR 1332) were from Beardmore Road west of Walpole (34°49'S, 116°32?), 6870 and 6873 (Voucher CJR 1334) from Conspicuous Cliffs Road east of Walpole (35°01°S,116°52?), 6881 (Voucher CJR 1335) from Kernutt's Road north-east of Denmark (34°55'S, 117°24'E) and sample 6888 (Voucher CJR 1336) from Randall Road east of Denmark (34°58'S, 117°24?). oil samples are from bulk collections of either plantation trees or wild plants. Samples A and C were derived from different provenance plantationgrown bulk harvests located north-west of Harvey (33°02'S, 115°45?), sample B was from plantation grown harvest from "Buxton's Farm", Redmond West Road in Redmond (34°55'S, 117°30'E) and from seed originating from Redmond. SampleX was from wild trees in Beardmore Road (34°49'S, 116°32?), Y, from an isolated provenance of trees at the same location and Z from plants from Randall Road east of Denmark (34°58'S, 117°24?).

Oil Isolation: oil samples were obtained by hydrodistillation of bulk leaf with terminal stems in a Clevenger-type distillation apparatus. Micro-ethanolic extractions of the leaf were performed as previously described (3-5).

Oil Composition: Optical rotations were determined on an Optical Activity AA-5 series automatic polarimeter in ethanol. IR spectra were determined as liquid films on a Perkin Elmer 16PC FTIR. Volatile component identifications were performed on a Hewlett Packard 6890 series GC/MS fitted with an HP5-MS 29.5m ? 0.25mm, 0.25pm film thickness, FSOT column with He (36 cm/s) as carrier gas, injection port (split 1:50) at 25O0C, mass selective detector (HP 5973) at 25O0C (source) and 15O0C (quad) with transfer line 28O0C and ion source filament voltage of 70 eV. Retention indices were measured with respect to n-alkane standards on the HP5-MS column. Component identifications were made on the basis of mass spectral fragmentation, retention time comparison with authentic constituents and mass spectral and retention matching with commercial (NIST (6), Wiley (7), Adams (8)) and in-house libraries. Area percent concentrations of the components were determined by GC/FID on one of two gas chromatographs. For column compatibility with the GC/MS, the first choice was a Shimadzu GC-14B Chromatograph fitted with a HP5-MS 30m ? 0.25mm, 0.25pm film thickness, nonpolar FSOT column. Carrier gas was H2 (55cm/s), injection port temperature 20O0C with a 1:50 split, flame ionization detector set at 30O0C and temperature programming from 5O0C (5 min. ) to 25O0C at 10°C/min. Where quantitation could be improved, components were determined on a Hewlett Packard 6890 series GC with an Altech AT35 60m ? 0.25mm, 0.25um film thickness, mid polarity FSOT column. Carrier gas, injection port, detector and temperature program conditions were as perthe Shimadzu GC-14B. The identity of ( )-lS,5R-myrtenol was confirmed by separation from the oil by elution from an alumina column using 10% diethyl ether in hexane followed by comparison of GC/MS, GCRI, FTIR and [a]D data with those of authentic ( )-lS,5R-myrtenol.

Results and Discussion

Agonis fragrans is a source of an aromatic and medicinal commercial essential oil with no previously recorded investigations of essential oil chemistry. In this study, leaf-extract and oil components were identified by GC/M S by comparison with mass spectra and retention indices of authentic constituents (Table I). Major oil components in the 1,8-cineole variant were found to be a-pinene (14-28%), 1, 8-cineole (28-34%) and linalool (3-15%). Extract composition was similar to that of the distilled oils with the only major differences being caused by non steam-volatile constituents such as neophytodiene or steam labile constituents such as epi-cryptomeridiol and cryptomeridiol. In addition, the concentrations of steam labile cyclodecadienes (eg bicyclogermacrene, hedycaryol) were significantly higher in the extracts than in the oils.