Chemistry of the Australian Gymnosperms Part VIII. The Leaf Oil of Prumnopitys ladei (Podocarpaceae)

Journal of Essential Oil Research: JEOR, Mar/Apr 2006 by Brophy, Joseph J, Goldsack, Robert J, Forster, Paul I

Abstract

The leaf oil of Prumnopitys ladei, which was analyzed by a combination of GC and GC/MS, was found to contain significant amounts of mono-, sesqui- and diterpenes, with α-pinene (15-25%), β-caryophyllene (12-16%), rimuene (3-27%) and kaurene (5-29%) being the principal components.

Key Word Index

Prumnopitys ladei, Podocarpaceae, essential oil composition, α-pinene, β-caryophyllene, rimuene, kaurene.

Introduction

The genus Prumnopitys Phil. (Podocarpaceae) comprises nine species and occurs in Australia, New Caledonia, New Zealand and South America. On the basis of rbcL chloroplast gene data, Prumnopitys was considered by Conran et al. (1) to be most closely allied to Sundacarpus (Buchholz et N.E. Gray) Page, and more distantly related to Halocarpus Quinn, Lagarostrobos Quinn and Manoao Molloy. Their analyses and conclusions contrast markedly with those of Kelch (2) using 18S rDNA data, where Prumnopitys was most closely allied to Halocarpus, Lagarostrobos, Lepidothamnus Philippi, Manoao, Parasitaxus de Laubenf., Phyllocladus Mirbel. and Sundacarpus. Both of these studies have used only small parts of the genome, and it is likely that the final word on the phylogeny of Podocarpaceae is yet to be written.

Prumnopitys has a single species, P. ladei (F.M. Bailey) de Laubenf. (brown pine, Mt. Spurgeon black pine) (3), endemic to Australia. P. ladei is a large tree, growing up to 30 m in height. It is a geographically restricted species, endemic to northeastern Queensland, where it is found in the vicinity of Black Mountain, Mt. Lewis and Mt. Spurgeon, northeast of Cairns. It grows in upland rainforests (complex notophyll vineforest) on granite-derived soils at elevations of 1000-1200 m. The leaves are small, usually 12-16 mm long and 2.5-4 mm wide. Despite the eventual large size of P. ladei, this species has proven amenable and popular to pot culture, being tolerant of low light conditions. P. ladei yields timber that is useful for building applications (4).

Little chemistry has been reported on members of this genus and none previously on Prumnopitys ladei. Only two species, P. taxifolia (D. Don) de Laub. (syn. Podocarpus spicatus) and P. ferruginea, have had their leaf oils examined and, in both cases, mixtures of mono-, sesqui- and diterpenes were found (5-7 and references quoted therein).

Experimental

Leaves were obtained from 5 trees, including two bulk collections of three trees each. All P.I. Forster (PIF) vouchers are deposited at the Queensland Herbarium (BRI). PIF19214: State Forest 143, South Mary Logging Area, 16° 31'S, 145° 15'E; PIF22894: Daintree National Park, NW of Black Mountain, 16° 23'S, 145° 11'E; RG735: cultivated, at Wahroonga, NSW, purchased from Belltrees Nursery, Durai, NSW.

Isolation of oils: The leaf oils were isolated by hydrodistillation with cohobation as previously outlined in (8). Analyses of the oils were carried out by gas chromatography and combined gas chromatography/mass spectrometry. The oil yield was 0.07% w/w, 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 an 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 µm] programmed from 35°-220°C at 3°C/min, with He at 35 cm/s as carrier gas) and a Shimadzu QP5000 instrument (equipped with a DB-5 column [30 in x 0.25 mm, film thickness 0.25 µm]). The column was programmed from 35°-250°C at 5°C/min; He carrier gas flow rate 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 known compounds or published spectra (9-13).

Results and Discussion

The leaf oil of P. ladei contained a mixture of mono-, sesquiand diterpenes in approximately equal amounts. The principal monoterpene was CC-pinene (15-25%), with limonene (1-3%), verbenone (0.6-3%) and p-cymene (0.4-0.7%) as the next most abundant components. The principal sesquiterpenes found in the oil were β-caryophyllene (12-16%), caryophyllene oxide (1-8%), spathulenol (2-4%) and α-humulene (2-3%). Other sesquiterpenes were present in amounts of less than 2%. The major diterpenes found in the oil were rimuene (3-27%, the majority greater than 25%) andkaurene (5-29%), with beyerene (0.2-2%) and 13-isopimaradiene (0.7-2%) being the next most abundant members. A complete list of the components identified in a typical leafs oil is given in Table I.

Also present with the volatile leaf oil was a substance that manifesteditself as a white amorphous, possibly polymeric, solid in the cooler parts of the distillation apparatus. This material was insoluble in all common laboratory solvents. The solid gave an ir spectrum with absorbances at 1745, 1650, 1199 and 1063 cm^sup -1^, which leads to the supposition that it was a polymeric ester. A similar insoluble polymer has been reported by Clark et al. from the steam distillation of the leaves of P. ferruginea (3), and this phenomenon had been commented on almost 50 years previously (4). It may well be that this type of compound is characteristic of the genus Prumnopitys.