INTRODUCTION:

Eucalyptus belong to the family Myrtaceae, it is a very diverse genus of flowering trees. There are more than 700 species of Eucalyptus, mostly native to the Australia. Only 15 species occur outside Australia, and only 9 do not occur in Australia. In India, over 100 species of Eucalyptus have been so far tried but only a few have been employed for large scale plantation and forestation works. Many species of genus Eucalyptus is main source of eucalyptus oil, which has wide application, as a pharmaceutical, antiseptic, repellent, flavoring, fragrance and industrial uses^{1, 2}.

Eucalyptus tereticornis Smith (syn. E. insignis Naudin, E. populifolia Desf., E. subulata A. Cunn. ex Schauer, E. umbellata (Gaertn.) Domin, and Leptospermum umbellatum Gaertn.) extensively grown in various states of India.It was first planted in India around 1790 by Tippu Sultan, the ruler of Mysore, on Nandi hills near Bangalore (Karnataka State) in the southand called as Mysore gum.^1-3 It is a valuable quick growing species grown on large scale for afforestation programs throughout the country for its use as a raw material for pulp wood industry. An examination of some other older plantation in Mysore i.e. so-called Eucalyptus hybrid (also called Mysore hybrid) is pure E. tereticornis (say up to 99 % pure).³ Porf. L.D. Taylor felt pretty confident that the “Mysore hybrid” as generally planted is mostly E. tereticornis. There is a possibility that about 1% population may contain hybrid genetically combination with E. propinqua which had been grown at Nandi hills in proximity with E. tereticornis.^1-4 E. tereticornis has a strong, hard and durable heartwood, with a density of about 1100 kg m⁻³. It is used for construction in heavy engineering, such as for railway sleepers.^4,5

The leaves of E. tereticornis have been used for the treatment of influenza and diarrhea in china. The boiling water extract of the leaves of this plant exhibited strong antibacterial activity against staphylococcus aureus and Streptococcus pneumonia.^1,6 The leaves extract act as natural larvicidal agent against malaria vector Anopheles sephensi.¹ The plant is also used in traditional medicine to control diabetes. The eucalyptol oil produced by the leaf of E. tereticornis has wide range of application as antiseptic, insect repellent, flavoring and fragrance. The oil and its constituents, α- and β-pinene, show accelerative properties on rat gastrointestinal transit.^1,7 The oil also exhibited antifungal, antibacterial, antioxidant and myorelaxtant properties.^8-10

Habitat and Distribution

Species of Eucalyptus are cultivated throughout the tropics and subtropics including the Americas, Europe, Africa, the Mediterranean Basin, the Middle East, China and the Indian Subcontinent.¹ E. tereticornis is native to Australia and extensively grown all the places of India. It was first introduced in Mysore from Australia.

Native: Australia, Papua New Guinea

Exotic: Argentina, Bangladesh, Brazil, Cambodia, Colombia, Congo, Cote d'Ivoire, Ethiopia, Fiji, Ghana, Greece, India, Indonesia, Israel, Kenya, Madagascar, Malaysia, Mozambique, Nigeria, Pakistan, Philippines, Sierra Leone, Solomon Islands, South Africa, Tanzania, Turkey, Uruguay, Vietnam, Zambia, Zimbabwe

Taxonomical Classification of E. tereticornis Smith

Kingdom	Plantae
Phylum	Tacheophyta
Class	Magnoliopsida
Order	Myrtales
Family	Myrtaceae
Genus	Eucalyptus
Species	E. tereticornis

Eucalyptus tereticornis

Habit

E. tereticornis is tree upto 50 m height. In generalization it is a single-stemmed "forest trees" and have a crown forming, a minor proportion of the whole tree height, bark smooth white or grey, shedding in large plates or flakes. Juvenile leaves disjunct, broad-lanceolate to ovate, glossy green. Adult leaves disjunct, narrow-lanceolate or lanceolate, 10–20 cm long, 1–3 cm wide, green, dull, concolorous. Fruit a capsule, ovoid or top shaped, with raised disc and prominent rim, opening with 4-5 raised valves curving inward; seeds many, tiny, shiny, dark brown to black.^1,11

Phytochemicals Analyses

Different species of Eucalyptus have been chemically investigated for various acyl phloroglucinol derivatives, triterpenoids, tannins, flavonoids, flavonone, flavones, flavans, flavanol glycosides, stilbene derivatives, long chain fatty acids, other phenolic compounds, inositol derivatives and others,¹² besides some non-volatile organic constituents, the leaves of Eucalyptus species is a good source of essential oil (eucalyptus oil).²

Several GC and GC-MS methods have been used for quantification and identification of essential oils from the leaves of E. tereticornis. Singh et al.(2009)characterized presences of 42 and 47 constituents from the fresh and decaying leaves of E. tereticornis by GC and GC-MS analyses.¹³ Zhang et al. (2010) investigated and characterized lignins from E. tereticornis by high performance anion exchange chromatography (HPAEC) followed by acid hydrolysis for sugar composition of the contaminating carbohydrates and catechin characterized by quantitative ³¹P NMR as well as two-dimensional heteronuclear single-quantum coherence (¹³C-¹H) NMR.¹⁴ Barry et al. identified eight tannins including the gallotannins tri-O-galloyl-ß-D-glucose, tetra-O-galloyl-ß-D-glucose, penta-O-galloyl-ß-D-glucose, ellagitannins pedunculagin, tellimagrandin I, casuarinin, casuarictin and tellimagrandin II as well as three phenolic gallic acid, ellagic acid catechin in Eucalyptus species by using HPLC-PDA with ESI-MS.¹⁵ Further Maurya and Srivastava (2012) developed HPLC-UV method for the determination and quantification of two triterpenoids ursolic acid and ursolic acid lactone in the leaves of E. tereticornis.¹⁶

Essential Oil

The leaves of E. tereticornis yielded yellow colored oil (1.21 % v/w) by hydrodistillation.¹⁰ Singh et al. (2009) investigated hydro-distilled essential oil of fresh and decaying leaves of E. tereticornis. The oil was analyzed GC and GC-MS which resulted identification of total 42 and 47 constituents in fresh and decaying leaves, respectively. The major constituents of the fresh leaf oil were α-pinene (28.53%) and 1,8-cineole (19.48%), where as in the decaying leaf oil were β-citronellal (14.15%), (-)-isopulegol (13.35%), and (þ)- β-citronellol (10.73%).¹³Kuar et al. (2011) investigated leaves oil of E. tereticornis through GC/GC-MS analyses, which revealed that the oil, in general, was monoterpenoid in nature with 37 constituents. Among these, α- pinene was the major component (~30%) followed by 1,8-cineole (~22%).¹⁰

Acyl phloroglucinol derivatives

This is one of the most important groups of biologically active constituents characterized in different Eucalyptus species during the last few years. About 50 compounds having distinct biological activities have been reported so far from many Eucalyptus species. Chemically they can discuss under the following three different categories.

(A) Monomeric acyl phloroglucinols

(B) Dimeric acyl phloroglucinol

Acyl phloroglucinol-terpene adduct are presumed to be derived biogenetically by adduct formation of substituted acyl phloroglucinol aldehyde chromophore and some monoterpenes or sesquiterpenes. The two acyl phloroglucinol derivatives named euglobal T1 (1) and euglobal II c (2) were isolated and characterized from the leaves of E. tereticornis.¹⁷

Triterpenoids

Triterpenes are secondary plant metabolites wide spread in fruit peel, leaves and stem bark. In particular, the lupane-, oleanane-, and ursane triterpenes display various pharmacological effects while being devoid of prominent toxicity. The first report about on the presence of triterpenoids in Eucalyptus was the characterized of cycloartenol and cyloeucalemol.¹⁸

Ursolic acid (3) was characterized in nine different Eucalyptus species by Dayal (1982).¹⁹ Further Theagarajan et al. (1993) was reported betulinic acid (4) in the bark of E. tereticornis hybrid.²⁰ Dayal (1987) again investigated the leaves of E. tereticornis hybrid and reported some other triterpenoids named 2-α-hydroxy ursolic acid (5) and ursolic acid lactone (6).²¹ Some novel triterpene ester tereticornate A (7) and B (8) and betulonic acid (9) were reported in leaves of E. tereticornis by Hongcheng et al. (1993).⁷

Flavonoids

A large number of flavonoids compounds have been isolated and characterized. They are grouped according to their chemical characteristics viz. flavanone, flavones, flavan and their glycoside.

Hongcheng et al. (1993) isolated flavonoids sideroxylin (10) and 8-demethylsideroxylin (11) in the leaves of E. tereticornis.⁷ Another constituent 7-Methoxy-aromadendrin (12) also isolated from E. tereticornis.¹²

Other miscellaneous compounds

In addition of above mentioned compounds several other non-volatile constituents belonging to different chemical classes have been characterized in Eucalyptus species like amino acid, fatty acids, phenolic aldehyde acid sterol and chromene derivatives. Wang et al. (1993) reported long chain phenolic (13) and undulatoside (14) and Verma et al. (2011) reported gallic acid (15) in the leaves of E. tereticornis.^12,22

(15)

Pharmacological Activity

Myorelaxant

Coelho-de-Souza et al. (2005) studied the effect of the oil on gunea-pig tracheal smooth muscle. The oil (10 - 1000 microg/mL) relaxed the tracheal basal tonus with EC (50) value of 125.3 [52.2 - 300.9] microg/mL. The oil produced significant myorelaxant effects on guinea-pig isolated trachea, an effect that seems to result from a complex interaction between its monoterpenoid constituents.¹¹

Larvicidal activity

Nathan (2007) tested essential oil of E tereticornis mature and immature mosquito vector Anopheles stephensi Liston (Diptera) under laboratory condition. The leaf extracts suppressed the pupal and adult activity of Anopheles stephensi and showed high bioactivity at high doses. The oil extracts exhibited strong larvicidal, pupicidal and adulticidal activity.²³

Antifungal activity

Kaur et al. (2011) studied antifungal activity of extracted essential oil from E. tereticornis. The essential oil (0.5, 1, 2.5, 5, and 10 ppm) was tested against the three test fungi viz. Fusarium oxysporum, Rhizoctonia solani and Heminthosporium oryzae by food poison technique. The oil exhibited a strong fungitoxicity against three tested phytopathogenic fungi viz; F. oxysporum, R. solani and H. oryzae, which was compared to commercially used fungicide mancozeb.¹⁰

Kaur et al. (2011) also evaluated the antioxidant activity of the oil (25-200 μg/ml) in terms of free radical scavenging (as DPPH activity), and H₂O₂ quenching. The oil obtained from E. tereticornis strongly transformed DPPH radical into its reduced form. It increased with increasing concentration of oil. Nevertheless, essential oil showed a lesser scavenging activity towards H₂O₂ (IC₅₀ 270.1 μg/ml). The essential oil has an IC₅₀ value of 146 and 270 μg/ml for DPPH and H₂O₂respectively. DPPH scavenging activity of oil was parallel to that of BHT (163 μg/ml) thereby indicating a strong antioxidant activity.¹⁰

Antihyperglycemic activity

Guillén et al. (2015) demonstrated antihyperglycemic activity through in-vitro assay, the ethyl acetate extract increase glucose uptake and inhibit their production in insulin-resistant C2C12 and HepG2 cells, respectively. Furthermore, in a nutritional model using diabetic mice, the administration of extract reduced fasting glycaemia, improved tolerance to glucose, and reduced resistance to insulin.²⁴

Antibacterial activity

Ammer et al. (2016) investigated antibacterial activity of methanolic extract of E. tereticornis for against the bacterial strain Escherichia coli through response surface methodology. The optimum conditions for maximum antibacterial activity (zones of inhibition, mm) were found out to be E. tereticornis extract i.e., Limonene, 3 µL; 1, 8-Cineole, 11 µL; Terpinen-4-ol, 15 µL; pH, 7.0 and temperature, 40 ^oC.⁹

CONCLUSION:

The extensive survey of literature revealed that the leaf of E. tereticornis is an important source many pharmacologically and medicinally important phytoconstituents, such as triterpenoids and essential oil (Eucalyptus oil), which have been used in aromatherapy. The oil has wide range application in flavour, fragrance and cosmetic industries. Various chromatographic methods have been reported by using HPLC, GC, GC-MS and anion exchange chromatography for the quality assessment of the plant and quantitative estimation of the phytochemical markers in respect of quality assessments. The leaf extract and oil have also been studied for their pharmacological activates like antihypergycemic, antibacterial antifungal, antioxidant larvicidal and myorelaxant property. Since presence of essential oil, triterpenoids and other constituents in the leaf of E. tereticornis, the leaves can be utilized for isolation of important non-volatile constituents like ursolic acid and betulinic acid after extraction of essential oil. The review makes an effort for the various phytochemical analyses, pharmacological properties and uses of E. tereticornis. Therefore, the information will be helpful for the scientists and researchers to essential oil analyses and its comparison and screening of compounds responsible for different bioactivities.

ACKNOWLEDGEMENTS:

Authors are thankful to Pharmacopoeia Commission for Indian Medicine and Homeopathy (PCIM&H), PLIM Campus, Ghaziabad for providing necessary facilities to write this review.

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Received on 12.08.2016 Modified on 14.09.2016

Asian J. Research Chem. 2016; 9(10):457-461.

DOI: 10.5958/0974-4150.2016.00068.7