Leaf Essential Oils of the Australian Species of Acronychia (Rutaceae)

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

Abstract

The leaf oils of die 19 Australian members of the genus Acronychia have been investigated by GC and GC/MS. Oil yields were all in the range of 0.1-0.5%, with the exception of A. oblongifolia, which was 1.3-1.8%. Acronychia aberrans gave an oil which contained (Z)-ocimenone (40-55%) and (E)-ocimenone (23-28%) as principal components, while in A. acuminata the principal component was oc-pinene (33-64%). Acronychia acidula gave oils rich in either monoterpenes or sesquiterpenes, with δ-3-carene (32-40%) and terpinolene (13-46%) the principal components of the monoterpene chemotype and α-santalene (2-15%), aromadendrene (2-8%) andgermacrene B (0.6-18%) major components of the sesquiterpene chemotype. Spathulenol (37-52%) was the principal component of the leaf oil of A. acromjchioides and α-pinene (65%) that of A. baeuerlenii. The leaf oil of A. chooreechillum was dominated by α-pinene (45-66%) while that of A. crassipetala contained up to 40% monoterpenes, the remainder being sesquiterpenes. The oil from A. eungellensis contained mostly sesquiterpenes, though α-pinene (21-26%) was the single largest component. The oil of A. imperforata was sesquiterpenoid, with β-caryophyllene (13-20%) and bicyclogermacrene (21-26%) being the principal components. Acronychia laevis gave both mono- and sesquiterpenoid chemotypes, with elemol, α-pinene and bicyclogermacrene being the principal components of the various oils. Both A. wilcoxiana and A. littoralis gave oils in which β-caryophyllene, pregeijerene and geijerene were principal components. Acronychia octandra gave an oil rich in (Z)-β-ocimene (15-23%), (E)-β-ocimene (15-23%) and limonene (4-21%), while in A. oblongifolia the principal components were α-pinene (34-87%), limonene (0.1-26%) and terpinolene (0.1-29%). In A. parviflora the major components were β-caryophyllene (2-34%) and allo-aromadendrene (0.3-20%), while in A. pauciflora the principal components were α-pinene (14-45%) and β-caryophyllene (10-24%). Acronychia pubescens gave asesquiterpenicoil, with β-caryophyllene (15-39%) as the principal component, as did Acronychia sp. (Batavia Downs, J.R.Clarkson 8511) (3-21%). Acronychia suberosa gave an oil in which (Z)-ocimenone (20-23%), (E)-ocimenone (9-13%) and β-caryophyllene (4-10%) were the main constituents and A. vestita gave a variable oil in which α-pinene (40%) and β-caryophyllene (23.5%) or limonene (67-80%) were major components.

Key Word Index

Acronychia aberrans, Acronychia acuminata, Acronychia acidula, Acronychia acronychioides, Acronychia baeuerlenii, Acronychia chooreechillum, Acronychia crassipetala, Acronychia eungellensis, Acronychia imperforata, Acronychia laevis, Acronychia littoralis, Acronychia oblongifolia, Acronychia octandra, Acronychia parviflora, Acronychia pauciflora, Acronychia pubescens, Acronychia sp., Acronychia suberosa, Acronychia vestita, Acronychia wilcoxiana, Rutaceae, essential oil composition, elemol, (Z)-β-ocimene, (E)-β-ocimene, bicyclogermacrene, α-pinene, sabinene, spathulenol, (Z)-ocimenone, (E)-ocimenone, β-caryophyllene, allo-aromadendrene, aromadendrene, (E)-nerolidol, δ-3-carene, terpinolene, oc-santalene, germacrene B, caryophyllene oxide, geijerene, pregeijerene, limonene.

Introduction

The genus Acronychia J.R.Forst, et G.Forst, is comprised of shrubs and trees, with nearly 50 species known from India, China, Malesia, New Caledonia and eastern Australia (1-5). The greatest areas of species diversity are in New Guinea and eastern Australia. Species of Acronychia are usually readily distinguished by having opposite leaves, bisexual eight-staminate flowers, valvate petals and indehiscent, drupaceous fruits. The genus belongs to the Rutaceae subfamily Rutoideae and is allied to BoroneUaBaill.,Brombya F.MuelL, Euodia J.R.Forst, et G.Forst., Medicosma Hook.f., Melicope J.R.Forst, et G.Forst., Myrtopsis Engl. and Perryodendron T.G.Hartley (6). It is speculated that Acronychia may have evolved from a Melicope-type ancestor via seed dispersal specialization (6).

One species of Acronychia (A. octandra] is unusual in that its fruits are connate only at the base and semi-fleshy when diy, as opposed to the usual situation where the carpels are connate throughout and the fruit comprises a woody mesocarp covered by a fleshy exocarp. The condition found in A. octandra is thought to be primitive in the genus with a morphological progression in fruit type through to the species considered advanced (3).

In Australia, the genus is restricted to the eastern seaboard from Cape York in the north to Victoria in the south. Some f 9 Australian species are recognized, with the majority being centered in the "Wet Tropics" region of northeastern Queensland. All of the Australian species occur in rainforest communities and a few also occur as understorey elements in adjoining wetter open forests dominated by eucalypts.

All of the Australian species have quite fleshy, generally strongly astringent fruits, which are usually green, cream, pink or purple in color. Some species, e.g. A. acidula, are favored for the use of the fruit in preserves and experimental plantings for this "bushfood" industry have been undertaken on a small scale. The foliage of all the Australian species has noticeable oil-glands, and the leaves when crushed emit a generally strong aromatic citrusy scent.