Analysis of essential oil of eaglewood tree (Aquilaria agallocha Roxb.) by gas chromatography mass spectrometry

Introduction

Agar, a valuable aromatic oleoresinous deposit found in the stems of Aquilaria agallocha Roxb. (syn. Acquilaria malaccensis Lamk., family: Thymelaeaceae) is available in Bangladesh, East India and other parts of South East Asia (Gibson, 1977). The present investigation includes essential oils and identification of fungal isolates from three samples of agar collected in the Sylhet region of Bangladesh. The eaglewood tree A. agallocha is a precious floral wealth of Indian subcontinents like Bangladesh (Anonymous., 1948). The resinous patches of fragrant wood of the plant known as 'agar' is used as incense in Egypt, Arabia and throughout the northeast part of Bangladesh where it can be found. The oil obtained from agar is described as a stimulant, cardiac tonic and carminative. It is also used in the cosmetic and pharmaceutical industries.

Agarwood (jinkoh in Japanese) is an oriental medicine for use as a sedative (Okugawa et al., 1993). Agar is considered to be a pathological product produced by fungal invasion of the host (Qi Shu-Yuan et al., 1992). Since 1938, few workers have been studying about agar formation and reported the agar zones to be associated with mold and decay fungi (Bose, 1938; Bhattacharyya et al., 1952; Jalaluddin, 1977; Venkataramanan et al., 1985; Beniwal, 1989; Tamuli et al., 2000ab; Mitra and Gogoi, 2001). Among different fungal species reported to be associated with agar zones, few could exhibit pathogenesis with the development of disease symptoms while others seem to be of saprophytic nature in different eco-geographical conditions. Studies on the oil of infected A. agallocha were made by various workers (Maheshwari et al., 1963; Varma et al., 1965; Paknikar and Naik, 1975; Thomas and Ozainne, 1976; Pant and Rastogi, 1980; Bhandari et al., 1982; Nagashima et al., 1983; Ishihara et al., 1991, 1993). Maheshwari et al. (1963) isolated three new sesquiterpenic furanoids of the selinane group from agarwood oil, obtained from the fungus infected plant and their structures and absolute configurations determined by degradative studies and physical measurements. Varma et al. (1965) examined that degradative studies and physical measurements supported by an unambiguous synthesis of the derived ketone have led to the assignment of a novel spiro-skeleton to agarospirol, a sesquiterpene alcohol isolated from the essential oil of infected agarwood. Paknikar and Naik (1975) reported that on hydrogenation of α-agarofuran and β-agarofuran the same dihydroagarofuran was obtained. Thomas and Ozainne (1976) reported some naturally occurring dihydroagarofuran and isodihydroagarofuran to unequivocally show that the dihydroagarofuran found was indeed dihydro-β-agarofuran and isodihydroagarofuran was isodihydro-β-agarofuran; two separate compounds. Pant and Rastogi (1980) and Bhandari et al. (1982) isolated a new sesquiterpene, agarol and a couinarinolignan, aquillochin, respectively, from the oil of agarwood. Nagashima et al. (1983) further characterized the presence of two more sesquiterpene alcohols, jinkohol II and jinkoh- eremol, from the Indonesia agar wood oil. Nakanishi et al. (1984) again reported that a benzene extract of an Indonesian sample of 'Jinkoh' agarwood was found to contain α-agarofuran, 10-epi-γ-eudesmol and oxo-agarospirol. Ishihara et al. (1991) characterized seven new sesquiterpenes based on the guaiane skeleton in a sample of agarwood oil. Five new eudesmane sesquiterpenes and three other compounds further characterized by Ishihara et al. (1993) in a sample of agarwood extract produced in the laboratory from A. agallocha of Vietnamese origin. Vesicular-arbuscular myccorhizal association in the tree species and changes in amino acid composition due to pathogenesis were also studied by Tamuli et al. (2002a, 2002b). Tamuli et al. (2005) investigate the difference in composition of oils obtained from healthy, naturally infected and artifically inoculated eaglewood using GC and GC-MS analyses. This investigation shows a marked difference in the oil compositions among the treatments with regards to their quality. Valerianol (3.0%) and tetradecanoic acid (7.1%) contents were recorded higher in the oils of naturally infected plants than in that of healthy ones (0.1 and 6.9% respectively). Pentedecanoic acid was totally absent in the oils of healthy plants, whereas it was found in a greater amount (6.8%) in the oil of naturally infected plants. In contrast dodecanoic acid (3.1%), pentedecanoic acid (6.2%), hexadecanoic acid (31.5%) and octadecanoic acid were found in the oils of healthy plants, while the oils obtained from naturally infected plants contained lower amounts of these components (2.3, 4.8, 20.0 and 1.0% respectively). The oils obtained from the inoculated plants showed almost similar distribution of the components with healthy plants. So far the qualitative study of the oils of healthy and wounds eaglewood has yet to be investigated. The present investigation was, therefore, undertaken to study the qualitative differences in the oils obtained from healthy, naturally infected and artificially screw wounds eaglewood. This paper reports the results obtained by GC-MS on A. agallocha oils.