Cinnamomum glaucescens (Nees) Hand.-Mazz is an evergreen tree where the buds are enclosed in overlapping scales. The leaves are about 7 - 10 cm long placed on stalks which is about 1 - 2 cm long. The inflorescences are covered with brown hairs. The fruits are 3 cm long [1] [2] . The major compounds present in the fruit oil of C. glaucescens [3] were 1,8-cineole (13%) and methyl cinnamate (14%), while 1,8-cineole (56%) and α-terpineol (10%) were found in the pericarp oil. In another report, methyl (E)-cinnamate (40.5%) and 1,8-cineole (24.5%) were also identified in the fruit oil of C. glaucescens [4] . 1,8-Cineole (43.6%) and elemicin (92.9%) were described in the fruit [5] and leaf [6] oils respectively. The nematicidal, termiticidal, mosquito larvicidal [4] , insecticidal, antifungal, antiaflatoxin, antioxidant [5] and antibacterial [7] activities of essential oils of C. glaucescens have been reported.

Cinnamomum verum J.S. Presl is an evergreen tree that grows up to 18 m tall. The fruits are black when ripe and surrounded by the enlarged perianth at the base [1] . The various ethanol extracts of C. verum were reported to possessed high analgesic [8] , antifungal [9] [10] [11] [12] , anti-tuberculosis [13] , antioxidant [8] [14] [15] and antihyperglycaemic [16] properties. 2-Methoxycinnamaldehyde, a component of C. verum was described as a potential anticancer agent [17] [18] . The chemical constituents characterized from the methanolic extracts [9] of C. verum were trans-cinnamaldehyde (20.28%), (E)-3-(2-methoxyphenyl)-2-propenoic acid (40.41%) and 4-vinyl benzoic acid (10.54%).

Various authors have described different main compounds (chemotypes) of essential oils of C. verum. These include eugenol type [19] [20] [21] [22] , safrole type [23] , cinnamaldehyde and isomers type [21] [23] - [29] , (E)-cinnamaldehyde/ eugenol/linalool type [30] , cinnamyl acetate type [31] and benzyl benzoate type [32] . The essential oils of C. verum were reported to displayed antibacterial [24] [33] [34] [35] [36] , nematicidal [31] , antifungal, anti-elastase and anti-keratinase [37] and anti-rot [38] activities. Cinnamaldehyde, one of major compounds of C. verum oil exhibited antibacterial [25] and anthelmintic [39] properties. The biofungicides action [27] and the efficacy of C. verum essential oil as an acaricidal agent against Rhipicephalus microplus larvae was reported [32] . The oil had a protective effect on experimental Streptococcosis iniae infection in tilapia [29] . Moreover, the oil showed mosquito knock-down and adulticidal activities against Culex quinquefasciatus [40] .

In the present paper, the results of our studied on the phytochemicals in the essential oils of Vietnamese species of C. verum and C. glaucescens were reported. Previously, the phytochemical constituents of some other plants have been characterized and reported [41] .

The percentage yields of essentials oils obtained from the extraction processes were 0.42% (v/w, C. glaucescens) and 0.45% (v/w, C. verum). The colours of the essential oils were determined as light yellow. The compounds that were identified in the samples could be seen in Table 1 with detailed analysis of their retention indices and percentage compositions. Monoterpene hydrocarbons (25.9%) and oxygenated monoterpenes (64.3%) were determined as the dominant class of compounds of C. glaucescens oil. the main constituents of the oil were geraniol

^aCompounds order of elution from HP-5MS column; RI (cal.) Calculated retention indices of each compounds on HP-5MS column; RI (Lit.) Literature retention indices; -not identified.

(36.2%) and terpinen-4-ol (19.7%). α-Pinene (6.0%), sabinene (6.0%) and limonene (5.2%). Sesquiterpne compounds were present in amount < 1%. Except for α-terpineol, all other known compounds such as 1,8-cineole and methyl cinnamate [3] [5] , α-terpineol [3] , (E)-cinnamate [4] and elemicin [6] that were previously identified in the essential oil of C. glaucescens were not present in the present oil sample. On the other hand, the present oil sample contained large quantities of geraniol and terpinen-4-ol which were not identified in previously studied oil samples of C. glaucescens.

In the present study, sesquiterpene hydrocarbons (30.0%), oxygenated monoterpenes (29.5%), oxygenated sesquiterpenes (18.8%) and monoterpene hydrocarbons (12.5%) were the classes of compounds present in C. verum. The major constituents of the oil were mainly linalool (22.0%) and bicyclogermacrene (11.2%). Additionally, β-bisabolene (7.7%), caryophyllene oxide (5.6%) and g-cadinene (4.0%) were also present in the oil in significant amount.

A comparative analysis of the present oil of C. verum and previous studies [20] [21] [22] [24] [25] [26] [27] [28] [30] [31] [32] indicated great variations in their chemical compositions. Several of the compounds that were present in the previously investigated oil samples were not identified in the present oil sample and vice versa. For example, the present oil of C. verum contained lower quantity of eugenol and benzyl benzoate when compared with previous results [20] [21] [22] [32] . In addition, compounds such as (E)-cinnamaldehyde [21] [24] [25] [26] [27] [28] [30] and cinnamyl acetate [31] that were described previously as main compounds of C. veum oil, were not obtained in the oil sample. However, the amount of linalool in the present C. veum oil was in agreement with previously investigated oil sample [31] . A noteworthy observation is that bicyclogermacrene, a main compound in the present C. veum oil was not described to be a significant compound in previously investigated samples of C. verum oils.

Several reports describing the chemical compositions of essential oils from some Vietnamese species of Cinnamomum have been published. In summary, each of the essential oils possessed compounds that were different from the other oil samples. The main compounds in the essential oil of C. sericans [41] were spathulenol (14.5%) and caryophyllene oxide (9.3%), while ρ-cymene (15.6%), limonene (13.9%) and α-phellandrene (9.2%) were found C. durifolium [41] . However, bicyclogermacrene (33.9%) and β-caryophyllene (25.5%) make up the composition of C. magnificum [41] . The essential oil of C. iners [41] consisted mainly of β-caryophyllene (35.9%) and caryophyllene oxide (12.6%). The leaf oil of C. curvifolium contained high contents of benzyl cinnamate and benzyl benzoate [42] . Interestingly, a-selinene ((24.5%) and β-caryophyllene (23.0%) were the major volatiles of C. rigidifloim [42] .

From the chemotaxonomy point of view, C. verum in the present study contained linalool which was also found to be the dominant compound of essential oils of C. damhaensis and C. cambodianum from Vietnam [42] . However, the essential oils of most Cinnamomum species from Vietnam possessed low content of (E)-cinnamaldehyde [41] [42] when compared with other samples analyzed from other parts of the world.

The paper reported the compounds identified in the essential oils of C. verum and C. glaucescens grown in Vietnam. The significant compounds of C. glaucescens were geraniol and terpinen-4-ol whil, C. verum comprised of linalool and bicyclogermacrene. In addition, a comparative analysis of the composition of the essential oils was performed with results from other species reported from Vietnam as well as Cinnamomum plants grown in other parts of the world. More studied will be required in order to be able to delineate the various chemotypes of essential oils of Cinnamomum plants in various parts of the world.

Authors are grateful to Mrs. Musilimat Ogunwande for the typesetting of the manuscript.

Chinh, H.V., Luong, N.X., Thin, D.B., Dai, D.N., Hoi, T.M. and Ogunwande, I.A. (2017) Essential Oils Leaf of Cinnamomum glaucescens and Cinnamomum verum from Vietnam. American Journal of Plant Sciences, 8, 2712-2721. https://doi.org/10.4236/ajps.2017.811182