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Abstract

The chemical composition of the leaf oil of Cinnamomum pubescens Kochummen was examined by GC with authentic samples on two columns of different polarity, GC/MS and retention indices. Oils hydrodistilled from samples collected from two different sites at different periods were found to possess minor compositional differences but considerable variation in the levels of some components. The oils were rich in benzyl benzoate (46.1-47.1%) and β-phellandrene (14.9-16.4%). The samples could be differentiated from each other in which one sample contained a significantly higher concentration of benzyl salicylate and relatively lower concentrations of pinenes and (E)-methyl cinnamate.

Key Word Index

Cinnamomum pubescens, Lauraceae, essential oil composition, benzyl benzoate, β-phellandrene.

Introduction

Cinnamomum pubescens Kochummen (family: Lauraceae) is a small tree up to 7 m tall. It is endemic to Peninsular Malaysia and is rare, found in the montane forests of Pahang at about 1500 m (1). The leaves are opposite to alternate, trinerved, with a 1-2 cm long velvety hairy stalk. The blade is leathery, drying greenish yellow, lanceolate, apex pointed, base cuneate, finely pubescent on the undersurface, midrib and secondary nerves flattened to sunken on the upper surface, raised on lower surface (1-2). As with all Cinnamomum species, the whole parts of the tree are aromatic and are used in traditional medicine as medang but this species has not been used commercially (3).

There are 21 species of Cinnamomum on the Malaysian peninsula (1). The chemical composition of the oils of 14 of these species has been reported by us, including those of C. pubescens (4-10). The oils were found to contain mainly 1,8-cineole, safrole, eugenol, linalool, camphor, terpinen-4-ol, (E)-methyl cinnamate, methyl eugenol, benzyl benzoate or cinnamaldehyde as major components (4-10). The leaf oil of C. pubescens collected from Jengka, Pahang was found to contain terpinen-4-ol (37.2%) and linalool (27.4%) as the major components (4). In this paper, we report on the chemical constituents of the leaf oils of C. pubescens obtained from two different sites in Cameron Highlands, Pahang, at different periods.

Experimental

Plant materials: The fresh leaves of C. pubescens were collected from two different locations in Cameron Highlands, Pahang, Malaysia. Sample 1: June 2002, Gunung Jasar, altitude 1500 m. Sample 2: June 1999, Gunung Berembun, altitude 1570 m. Voucher specimens were deposited at the Herbarium of the Forest Research Institute Malaysia, Kepong.

Oil isolation: The plant materials were subjected to water distillation in a Clevenger-type apparatus for 8 h. The oily layers obtained were separated and dried over anhydrous magnesium sulfate. The yields were averaged over three experiments and calculated based on dry weight of the plant materials.

Analysis of the oils: The oils were analyzed on a Shimadzu GC 14A chromatograph equipped with a FID detector using a DB-5 capillary column (25 m x 0.25 mm, 0.25 µm film thickness). The operation parameters were: nitrogen as carrier gas at 50 cm/s, injector and detector temperatures were maintained at 250°C. The column was programmed initially at 75°C for 10 min, then 3°C/min to 210°C and held for 1 min. The oils were also examined using a DB-1 stationary phase column (25 m x 0.25 mm, 0.25 µm film thickness) programmed from 60°C for 10 min, then 3°C/min to 180°C and held for 10 min. Peak areas and retention times were measured by electronic integration. The relative amounts of individual components are based on peak areas obtained, without FID response factor correction. Temperature program linear retention indices of the compounds were also determined relative to n-alkanes (11).

The oils were also analyzed by GC/MS with a Hewlett-Packard GC-MSD 5890 series 2 mass spectrometer (70 eV direct inlet) on a BPX5 column (30 m x 0.25 mm, 0.25 µm film thickness) initially at 75°C for 10 min, then 3°C/min to 210°C and held for 1 min with helium as carrier gas. The constituents were identified by comparison of their retention indices with literature values and their mass spectral data with those from the Wiley mass spectral database, and in some cases by co-chromatography on the different columns with authentic samples (12-14).

Results and Discussion

Water distillation of the leaves of C. pubescens gave the following yields (on a dry weight basis): Sample 1 (100g-5.0%) and Sample 2 (100g - 5.7%). The list of constituents identified in the leaf oils is shown in order of elution on a DB-5 type columnin Table I. Examination of the data in Table I revealed that the oils were very similar to each other, although there were some qualitative and quantitative differences between them. The chromatogram of Sample 1 indicated the presence of at least 35 components, of which 30 components were identified (99.6% of the oil), while 37 out of 42 compounds indicated in the chromatogram of Sample 2 were determined (97.9% of the oil) (Table I).

As with the essential oils of many Cinnamomum species, viz. C. mollissimum, C. iners, C. impressicostatum, C. microphyllum and C. rhyncophyllum, the leaf oil of C. pubescens was also a natural source of benzyl benzoate which constituted 46.1-47.1% of the oils studied (4,8,9). Other constituent that was present in significant amounts in both samples was β-phellandrene (14.9-16.9%). Sample 1 could be differentiated from Sample 2 by containing a significantly higher concentration of benzyl salicylate while the latter contained relatively higher concentrations of pinenes and (E)-methyl cinnamate (Table I).

A comparison between the chemical composition of the leaf oils of C. pubescens in this study (Table I) and those previously reported by us (4) reveals that they are discernably different. Terpinen-4-ol and linalool, which were the major constituents of the leaf oil of C. pubescens collected from Jengka, Pahang, were only present as minor components in the samples studied (4). The differences may be due to ontogenetic variations or the existence of intraspecific chemical differences (chemical races) within this species.

Acknowledgements

This work was supported by IRPA grant no. 09-02-02-0052-EA148.

References

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11. E. Kovats, Gas chromatographic characterization of organic substances in the retention index system. Chapter 7. In: Advances in Chromatography. Edits., J.C. Giddings and R.A. Keller, Vol. 1, pp 229-249, Marcel Dekker, New York (1965).

12. R.P. Adams, Identification of Essential Oil Components by Gas Chromatography/Quadrupole Mass Spectroscopy. Allured Publishing Corporation, IL (2001).

13. F.W. McLafferty and D.B. Staufer, The Wiley NBS Registry of Mass Spectral Data. Vol. II, John Wiley and Sons, New York (1989).

14. N.W. Davies, Gas chromatographic retention indices of monoterpenes and sesquiterpenes on methyl silicons and Carbowax 20M phases. J. Chromatogr., 503, 1-24 (1990).

Ibrahim bin Jantan,* Mira Febrina Yalvema, Bukhori Abu Bakarand Kartiniwati Muhammad

Department of Pharmacy, Universiti Kebangsaan Malaysia, Jalan Raja Mucla Abdul Aziz, 50300 Kuala Lumpur, Malaysia

Norsiha Ayop and Abu Said Ahmad

Forest Research Institute Malaysia, Kepong, 52109 Kuala Lumpur, Malaysia

* Address for correspondence

Received: December 2002

Accepted: February 2003

1041-2905/05/0005-0513$6.00/0-© 2005 Allured Publishing Corp.

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