Analysis of the Leaf Oil of Araucaria cunninghamii Sweet. Grown In Nigeria

Journal of Essential Oil Research: JEOR, Jul/Aug 2005 by Olawore, Nureni O, Ogunwande, Isiaka A

Abstract

The yield and chemical composition of the oil obtained by hydrodistillation of the leaves of Araucaria cunninghamii Sweet., grown in the southwest region of Nigeria are reported. The analyses were made by GC and GC/MS. The oil was found to contain α-pinene (14.8%), terpinen-4-ol (14.7%), shyobunol (8.9%) and spathulenol (8.8%) as major constituents.

Key Word Index

Araucaria cunninghamii, Araucariaceae, essential oil composition, α-pinene, terpinen-4-ol, shyobunol.

Introduction

Araucaria cunninghamii Sweet., (family Araucariaceae) is an evergreen coniferous tree that grows in the southern hemisphere. It occurs in South America, Australia, New Guinea, New Caledonia, New Hebrides and Norfolk Island, under tropical, sub-tropical and temperate climates (1). Today, the tree has been introduced into other parts of the world. It is commonly known as colonial pine, hoop pine, Richmond river pine and white pine. The juvenile leaves are spirally arranged, usually lanceolate ortriangular, 0.66-0.75 in (1.68-1.90 cm) long, straight, spreading, sharp pointed, green or glacious with entire margin. Those of older trees are crowded and overlapping.

The flavonoid derivatives of this species have been previously studied. These included 4"'-7-di-O-methyl agathisflavone, 7-O-methyl agathisflavone, 4'-4"'-7-7"-tetra-O-methyl amentofl avone, 4'-7-di-O-methyl amentoflavone, 7"-O-methyl amentoflavone, 4'-4'"-7-7"-tetra-O-methyl cupressuflavone, 4'-7-7"-tri-O-methyl cupressuflavone and 7-7"-di-O-methyl cupressuflavone (2). The presence of a carbohydrate, L-acofriose (3) and an alkaloid (4) have been identified in the plant. The oil of A. cunninghamii has not been previously reported in the literature. In the present work, we study the chemical composition of the leaf oil of A. cunninghamii grown in Nigeria.

Experimental

Plant materials: The leaves of A. cunninghamii were collected from a location at the Forestry Research Institute of Nigeria (FRIN), Ibadan, Nigeria, in May 2000. TK. Odewo of the Herbarium headquarters, FRIN, Ibadan, authenticated the plant. Voucher specimens were deposited at the Forest Herbarium of FRIN, Ibadan, Nigeria.

oil isolation: The dried leaves of the plant were hydrodistilled for 3 h in a Clevenger-type apparatus according to the British Pharmacopoeia specifications (5). The resulting oils were collected, preserved in a sealed tube and stored under refrigeration until analyses.

Gas chromatography: GC analyses were performed on an Orion Micromat 412 double focusing chromatography system fitted with two capillary columns coated with CP-SiI 5 and CP-SiI 19 (fused silica, 25 m x 0.25 mm, 0.15 µm film thickness) and flame ionization detector (FID). The volume injected was 0.2 µL, and the spilt ratio was 1:30. Oven temperature was programmed from 50°-230°C at 3°C/min using hydrogen as carrier gas. Injection and detector temperatures were maintained at 200°C and 250°C, respectively. Quantitative data were obtained by electronic integration of peak areas without the use of correction factors.

Gas chromatography/mass spectrometry analysis: A Hewlett-Packard HP 589OA GC was interfaced with a VG Analytical 70-25Os double-focusing mass spectrometer. Helium was used as the carrier gas. The MS operating conditions were: ionization voltage 70 eV, ion source 230°C. The GC was fitted with a 25 m x 0.25 mm, fused capillary silica column coated with CP-SiI 5,0.15 µm film thickness. The GC operating parameters were identical with those of the GC analysis.

Retention indices for all the compounds were determined according to the Kovats method relative to the n-alkanes series (6). The identification of the compounds was done by comparison of retention indices (6,7) and by matching their fragmentation patterns in mass spectra with those of published mass spectra data (8) and with data in the library built up from those of authentic reference substances.

Results and Discussion

The percentage yield of the colorless oil obtained from the hydrodistillation of the leaves of A. cunninghamii was 1.35%. The detected constituents in the leaf oil are shown in Table I, together with their peak percentage (w/w) and classification based on functional groups. The components are listed in order of their elution on the CP-SiI 5 capillary-coated column.

Fifty components, which made up 93.0% of the total composition of the oil, were identified. The oil contained 31 hydrocarbons (39.4%), 9 alcohols (39.6%), 4 ketones (6.6%), 4 oxides (6.1%) and 1 aldehyde (0.8%). As shown in Table I, α-pinene (14.8%), terpinen-4-ol (14.7%), shyobunol (8.9%) and spathulenol (8.8%) were the major constituents.

The analyses above showed that about 86% of the volatile component originated from isoprene metabolites. The contribution of the oxygenated terpenes to the total oil composition is high (52.3%). It has been widely accepted that the oxygenated terpenes give a more relevant contribution to fragrance. Hence the nine alcohols, along with other aldehyes, ketones and oxides may be responsible for the characteristic odor of the plant.