Leaf Oils of the Genus Brombya (Rutaceae)

Journal of Essential Oil Research: JEOR, Sep/Oct 2004 by Brophy, Joseph J, Goldsack, Robert J, Forster, Paul I

Abstract

The leaf oils of the two species of Brombya were examined by GC and GC/MS. They were found to be dominated bysesquiterpene hydrocarbons. Bromhyaplatynemaguve an oil which was either dominated by germacrene D (1178%), [beta]-bisabolene (0.8-22%), bicyclogermacrene (14-22%) and kessane (1-17%) or by [beta]-bisabolene (19-53%), [gamma]-curcumene (26.7%), bicyclogermacrene (7.7%) and ar-curcumene (10.6%). The rare Brombya sp. (Gap Creek L.S. Smith 11116) produced a leaf oil dominated by [beta]-bisabolene (22.9%), ar-curcumene (14.6%) andcc-santalene(9.2%).

Key Word Index

Bromhya platijnema, Brombya sp., Rutaceae, essential oil composition, germacrene D, bicyclogermacrene, kessane, ar-curcumene, [gamma]-curcumene, [beta]-bisabolene.

Introduction

The genus Brombya F. Muell. is comprised of two species and is endemic to Australia in the wet tropics region of northeastern Queensland. It is thought to be most closely related to Medicosma. Hook. {.,Boronia Sm. and Euodia J. R. and G. Forst. (1). Both species of Brombya are shrubs or small trees that grow in the rainforest. Brombya platynema F. Muell. is widespread in the wet tropics and generally occurs at altitudes above 200 m in well-drained rainforest. The undescribed Brombya sp. (Gap Creek L.S. Smith 11116) is a veiy rare species known only from a restricted area south of Bloomfield where it occurs in swampy lowland rainforest below 200 m altitude.

There are only two reports in the literature on the chemistry of Brombya. A number of novel compounds, based on the naphthalene skeleton (the brombyns) and two cinnamic acid derivatives have been isolated from the bark of B. platynema (2,3), but no work has been reported on the unnamed species. Neither species have particularly aromatic foliage, and have never been examined for leaf essential oils.

We report here on the compositions of the leaf oils of the genus Brombya.

Experimental

Collection of plant material: Where possible leaves from two individual plants and a further collection from three different plants were obtained. B. platynema: PIF25126, Daintree N.P., Pinnacle Rock Track, QId, 16�23'S, 145�18'S; PIF16737, Djallon Creek, Palmerston N.P., QId, 17�35'S, 145�43[Epsilon]. Brombya sp. (Gap Creek L.S. Smith 11116): PIF15586, Cedar Bay N.P., QId, 15�48'S, 145�18[Epsilon]. Voucher samples are lodged at the Queensland Herbarium (BRI).

Oil isolation: The leaf oils were isolated by hydrodistillation for 8 h of fresh leaf (50-100 g) with cohobation as previously outlined (4). oil yields (on a fresh weight basis, w/w) are given with each species. Analyses of the oils were by gas chromatography and combined gas chromatography-mass spectrometry.

Identification of components: Analytical gas chromatography (GC) was carried out on a Shimadzu GC6 AMP gas chromatograph. Either a SCOT column (90 m x 0.5 mm) coated with FFAP or a WCOT DB-Wax (60 m x 0.5 mm, film thickness 1 �m) was used, both programmed from 50�0 -225�C at 3�C/min with helium at 3.5 mL/min as carrier gas. GC integrations were performed on a SMAD electronic integrator. GC/MS was performed on both 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 �m) programmed from 35�0 -220�C at 3�C/min, with helium at 35 cm/min as carrier gas and a Shimadzu QP5000 instrument equipped with a DB-5 column (30 m x 0.25 mm, film thickness 0.25 �m). The column was programmed from 35�-250�C at 5�C/min and helium carrier gas fiowrate was 30 cm/s. Compounds were identified by their identical GC retention times to known compounds and by comparison of their mass spectra with either those of known compounds or published spectra (5-9).

Results and Discussion

The leaf oils from both species of Brombya presented complex mixtures of sesquiterpenes with virtually no monoterpenes present. The oil yields were all less than 0.5% w/w based on fresh leaves.

Brombya platynema gave leaf oils which differed slightly between the two collection sites from which this species was obtained. The samples from Daintree N.P. (PIF25126) gave oils in which the principal components were germacrene D (11-78%), [beta]-bisabolene (0.8-22%), bicyclogerinacrene (14-22%) and kessane (1-17%). There were lesser amounts of [beta]-caryophyllene (3-6%), fnms-a-bergamotene (1-3%), [beta]-elemene (1-3%), [beta]-humulene (2-4%) and spathulenol (3-5%). The samples from Palmerston N.P. (PIF16737) about 140 km south of Daintree, gave leaf oils in which the principal compounds were [beta]-bisabolene (19-53%), [gamma]-curcumene (26.7%), bicyclogermacrene (7.7%), arcurcumene (10.6%), bgr;-elemene (2%) and spathulenol (2.2%). The oil yield, based on fresh leaves, was 0.1-0.4%. Representative analyses of oils from both locations are given in Table I.

Brombya sp. (GapCreekL.S. Smith 11116) gave aleafoil in which the principal components were [beta]-bisabolene (22.9%), ar-curcumene (14.6%), a-santalene (9.2%), [beta]-elemene (3.5%), [alpha]-cadinol (2.9%) 1,3,5-trimethoxybenzene (5.8%) and two unknown terpenoids of molecular weights 194 (A) and 236 (B). The oil yield, based on fresh leaves, was 0.1%. A representative analysis is given in Table I.