Volatiles of Acacia howittii F. Muell., The

Abstract

The volatiles obtained from the phyllodes of Acacia howittii have been analyzed by GC and GC/MS and found to contain 1-hexen-3-one (8-21%) and 1-octen-3-one (36-46%) as principal components. The major terpenes present in the oil were α-pinene (0.6-7%) and β-caryophyllene (2-5%). The yield of volatiles was less than 0.1%.

Key Word Index

Acacia howittii, Mimosaceae, phyllode volatiles, essential oil composition, 1-hexen-3-one, 1-octen-3-one.

Introduction

The genus Acacia sens, strict., which belongs to the Mimosaceae, contains well in excess of 1,000 described species. Most of these are Australian. It should be noted that other plants currendy included in Acacia sens. lat. will be transferred to other genera following a decision by the Nomenclature Section of the XVII International Botanical Congress in Vienna in July 2005. The interested reader is referred to The World Wide Wattle web site for more information about Acacia taxonomy (1).

Acacia howittii F. Muell. (Howitt s Wattle, Sticky Wattle) is a smaU shrub or tree growing to 9 m in height, with a graceful drooping habit and small, pleasant-smelling flower heads, making it a useful garden specimen. It occurs in a small area of eastern Victoria from die upper Macalister River area near Mt Howitt south to near Yarram and east to near Tabberabbera. In spite of its popularity as an ornamental shrub, it is, in fact, a species on the list of rare Australian species. Further details can be found in the monograph by Maslin et al. (2).

When the atmosphere is stdl, especiady between sunset and sunrise, a faint, but not unpleasant acrylate-like odor, can be perceived near the plant. This was especiady noticeable during a recent heatwave (45°C) in Sydney. The odor comes from the plant s viscid phyllodes (laterally compressed petioles) (3). The viscid material is produced by small glandular trichomes that are scattered over the phyllode surfaces (3). We have noticed that although die sticky phyllodes were not attacked by jawed insects such as beedes, our specimen carried an active and apparently healthy population of an unidentified sap-sucking homopteran.

Little work has been reported on the phyllode or leaf ods of die genus Acacia. A. spirobis subsp. solandri (Bendi.) Pedley (syn. A. spirobis Benth) produced an od in which the main components were the sesquiterpenes β- caryophyllene, viridiflorene and viridiflorol (4). Also reported in this paper is an unpublished work in which a lemon-scented oil, probably rich in citronellal being obtained from A. hilliana Maiden (I. Southwell, unpublished). AnotherAcacia widi sticky phyllodes, A. nuperrima ssp. cassitera Pedley, was found to exist in two chemical forms in which either the sesquiterpene etìier, kessane, (89%) or α-pinene (16%) were the major components (5, ,6). Acacia saligna (Labdl.) H. L.Wendl.has been reported to contain diirty-five components in its leaf oil, of which die major components were nonadecane, pentadecane, heptadecane, heptadecene and mediyl 14-mediylpentadecanoate (7).

Experimental

Plant material: Leaf material, of unknown provenance, was obtained from plants cultivated in R.J.G s garden at Wahroonga, New South Wales. A voucher sample (RJG894) has been deposited in the J.T. Waterhouse Herbarium, University of New South Wales.

Isolation of oils: The leaf oils were isolated by hydrodistillation with cohobation as previously outlined (8). Analyses of the oils were carried out by gas chromatography and combined gas chromatography-mass spectrometry. The od yields quoted below are weight/weight and based on fresh material.

Identification of Components: Analytical gas chromatography (GC) was carried out on a Shimadzu GC17 gas Chromatograph. A WCOT DB-Wax [60 m x 0.5 mm, film thickness 1 µm] was used, programmed from 50°-225°C at 3°C/min with He at 3.5 mL/min as carrier gas. GC integrations were performed on a SMAD electronic integrator without the use of correction factors. GC/MS was performed on bodi a VG Quattro mass spectrometer operating at 70 eV ionization energy; the column used was DB-Wax [60 m x 0.32 mm, film thickness 0.25 pm] programmed from 35°-220°C at 3°C/min, with He flowing at 35 cm/sec as carrier gas and a Shimadzu QP5000 instrument equipped with a DB-5 column [30 m x0.25 mm, film thickness 0.25 µm]. The column was programmed from 35°-250°C at 5°C/min, helium carrier gas flow rate was 30 cm/sec. Compounds were identified by their identical GC retention times to known compounds and by comparison of their mass spectra with either known compounds or published spectra (9-13). FuU lists of the components identified are given in Table I.

Results and Discussion

The volatiles obtained by steam distillation of the phyllodes and twiglets of A. howittii were obtained in poor yield (

The principal terpenoid components identified in die od were α-pinene (0.6-7%), limonene (1-2%), 1,8-cineole (1-3%), linalool (0.4-0.6%), β-caryophyllene (2-5%), (E,E)-α-farnesene (0.1-0.5%) and caryophyllene oxide (2-A%).