1.    Introduction

The genus Trichilia is known to be the largest genus belonging to the family Meliaceae, consisting of over 90 species known to be extensively dispersed throughout the tropical and subtropical regions [1]. Trichilia monadelpha (Thonn.) J. J. de Wilde, locally called Otanduro (Twi) or Tenuba (Nzema), meaning hatred medicine, is a medium-sized tree that grows 12-20 m high and propagates itself well in lowland high forests and evergreen semi-deciduous secondary jungles, often near river banks [2]. Ethnomedicinally, T. monadelpha has been used in traditional medicine in the treatment of numerous ailments in the human body. The stem bark of T. monadelpha has traditionally been used in the treatment of a number of central nervous system (CNS) conditions, such as depression, epilepsy, psychosis, pain, and inflammation [3]. The bark decoction is also used as an analgesic and anthelminthic and is also drunk to pacify cough [4]. Reports have also shown that T. monadelpha possesses pharmacological properties, including anti-trypanosomal, antiplasmodial [5], antidepressant [6], anti-inflammatory, antitumor and antioxidant properties [7, 8].

Phytochemical analysis of T. monadelpha bark revealed the presence of an array of plant constituents, such as saponins, tannins, alkaloids, cardiac glycosides, anthraquinones, reducing sugars, flavonoids, coumarin, triterpenoids and steroidal compounds, which are known to possess biological properties that could contribute to its traditional therapeutic value [8, 9]. Monadelphin A and B, which are lemonioid derivatives, and trichins A and B, which are sesquiterpene derivatives, were isolated from the leaves and stem extracts of T. monadelpha [10]. The isolated compounds were also reported to be strongly cytotoxic against mouse lymphoma [10].

Trichilia prieuriana A. Juss. (Meliaceae) is an evergreen shrub or tree with a dense, hemispherical crown that can grow up to 30 m tall and sometimes to a height of 40 m. It is commonly found in rainforests and savanna woodlands [11]. The ethnomedicinal usage of T. prieuriana Juss. includes the treatment of malaria, trypanosomiasis, syphilis, pneumonia and colds. Additionally, the treatment of various bacterial infections with water decoctions and infusions from T. prieuriana has been in use for many years [12]. Pagna et al. [13] isolated 22 compounds from hydroethanol extracts of T. prieuriana which include: 2β,3β,4β-trihydroxypregnan-16-one, prieurianin, flindissone, deoxyflindissone, and picraquassin E, among others. The isolated compounds were reported to exhibit noticeable antibacterial capability [13]. Additionally, two new triterpenoids, namely, 12-acetyloxy-β-oxotirucalla-7,24-dien-21,23-oxide and 29-hydroxy-piperone, were previously reported from the leaves of T. prieuriana [14]. In addition, Kuglerova et al. [15] reported that ethanol extracts of T. prieriana displayed promising antimicrobial properties against strains of gram-positive bacteria. However, despite the wide ethno-medical usage of the plant, there is little information on the chemical composition of the essential oil of T. monadelpha and T. prieuriana. Therefore, the current study aimed to investigate the chemical compositions of the essential oils from T. monadelpha and T. prieuriana.

2.    Materials and methods

2.1 Sample collection

T. monadelpha and T. prieuriana leaves were collected from farmland in Egbeda Village, Ibadan Oyo State, Nigeria, in May 2022. The plant samples were authenticated at the Herbarium section of Forestry Research Institute of Nigeria (FRIN), Ibadan Nigeria, where voucher specimens FHI: 113153 and FHI: 113142 were deposited for T. monadelpha and T. prieuriana, respectively.

2.2 Sample preparation and hydrodistillation

The collected fresh leaves of T. monadelpha and T. prieuriana were air dried under the shade and pulverized with a blender to increase the surface area.  500 grams of each pulverized sample of T. monadelpha and T. prieuriana was subjected to hydrodistillation for 4 h using an all-glass modified Clevenger-type apparatus according to the British pharmacopeia [16]. The essential oils of T. monadelpha and T. prieuriana obtained from the hydrodistillation were stored in a labeled sealed glass bottle with a screw lid cover and kept in a refrigerator. Oil yield was calculated on a dry weight basis.

2.3 Gas chromatographic–mass spectral analysis

The chemical composition of essential oils from T. monadelpha and T. prieuriana was determined using gas chromatography–mass spectrometry (GC–MS). This was achieved on a Shimadzu GCMS-QP2010 Ultra operated in the electron impact (EI) mode (electron energy = 70 eV), scan range = 40–400 atomic mass units, with a scan rate of 3.0 scans per s, with GC–MS solution software. The GC column was a ZB-5 fused silica capillary column (30 m length ×0.25 mm inner diameter) with a 5% phenyl-polymethylsiloxane stationary phase and a film thickness of 0.25 µm. Helium gas was used as a carrier gas with a column head pressure of 552 kPa at a flow rate of 1.37 mL/min. The injector temperature was 250 °C, and the ion source temperature was 200 °C. The oven temperature of 50 °C was initially programmed for the GC and gradually increased at 2 °C/min to 260 °C. The sample (5% w/v) was dissolved in dichloromethane, and 0.1 µL of the solution was injected using a split injection technique (30:1). Each constituent of the essential oils was identified by injection of pure samples and by comparison of the retention index values, through calibration using a series of n-alkanes, in addition to MS fragmentation comparisons with those found in the databases [17-20]. 

3.    Results

3.1 Trichilia monadelpha

The GC–MS analysis of essential oil from T. monadelpha revealed 43 compounds representing 99.1% of the total constituents of the oil. The constituents displayed were sesquiterpene hydrocarbons (60.3%), oxygenated sesquiterpenoids (31.1%), oxygenated monoterpenoids (1.7%) and   nonterpenoids (6.0%). The major components identified were (E)-β-caryophyllene (26.2%), caryophyllene oxide (18.2%), δ-cadinene (8.5%), α-copaene (5.1%) and α-humulene (4.7%). Compounds present in a significant amount included humulene epoxide II (2.4%), geranyl acetone (2.22%), allo-aromadendrene  (2.14%), β-selinene (2.2%) and selin-11-en-4α-ol (2.0%). Table 1 displays the constituents of the leaf essential oil of T. monadelpha while Fig. 1 and 2 displayed the structure of the major components and the chromatogram of T. monadelpha oils respectively.

Table 1. The chemical constituents of T. monadelpha leaf essential oil

Figure 1. Major components of essential oils from T. monaldepha,

Figure 2: Gas chromatogram of T. monadelpha oil on a ZB-5 column (30 m ×0.25 mm) with helium carrier,

3.2 Trichilia prieuriana

The hydrodistillation of T. prieuriana yielded a pale-yellow essential oil, which was made up of sesquiterpene hydrocarbons (68.9%) and oxygenated sesquiterpenoids (15.5%). The major components in the essential oil were α-santalene (44.4%), caryophyllene oxide (11.1%), trans-α-bergamotene (8.4%) and 6-methyl-α-ionone (5.4%). Compounds found to be significantly present were β-Santalene (2.8%), β-bisabolene (2.6%), α-humulene (2.0%), epi-β-santalene (1.6%), trans-β-bergamotene (1.6%), γ- himachalene (1.4%) and humulene epoxide II (1.3%). Table 2 displays the constituents of the leaf essential oil of T. prieuriana while Fig. 3 and 4 displayed the structure of the major components and the chromatogram of T. prieuriana oils respectively

Table 2: Chemical constituents of T. prieuriana leaf essential oil

Fig. 3: Major components of essential oils from T. prieuriana

Fig. 4: Gas chromatogram of T. prieuriana oil on a ZB-5 column (30 m ×0.25 mm) with helium carrier

4.    Discussion

Few literature reports have described the chemical compositions of essential oils from the genus Trichilia. Odeja and Onocha [21] reported 15 compounds from the leaf essential oil of T. monadelpha, with β-caryophyllene (35.41%) as the most abundant component. The report also revealed that the essential oils of T. monadelpha possess antioxidant and antimicrobial potentials. The report is similar to the current finding with β-caryophyllene (26.2%) as the most abundant constituent of T. monadelpha. However, the current findings reported 43 compounds from the essential oils of T. monadelpha against the 15 reported in the literature [21]. Additionally, caryophyllene oxide (18.2%), δ-cadinene (8.5%), α-copaene (5.1%) and α-humulene (4.7%), which were part of the major compounds in the current report, were absent from previous findings [21]. These variations in the compositions of the oils might be due to several factors, including geographical origin, genetic differences, part of the plant used, method of extraction, age/stage of maturity, and season of harvest [22-23].

Furthermore, α-Santalene (44.4%) was the most abundant compound in the oil of T. peruriana, while the other major components included β-bisabolene (2.6%), α-humulene (2.0%), epi-β-Santalene (1.6%), trans-β- bergamotene (1.6%), and γ-himachalene (1.4%). This is in contrast to the composition of T. monaldepha, with β-caryophyllene (26.2%) as the most abundant compound together with the other major compounds δ-cadinene (8.5%) and α-copaene (5.1%). However, caryophyllene oxide and α-humulene were present in both oils. Ewansiha et al [22] reported factors that might be responsible for variations in the components of essential oils. Meanwhile, some of the identified components of essential oils from T. monadelpha and T. peruriana were reported to have diverse pharmacological activities. Analgesic and anti-inflammatory activities of caryophyllene oxide have been reported [24] while β-caryophyllene exhibits antimicrobial, antioxidant, anesthetic, anti-inflammatory and anticancer activities [25-29]. The anti-inflammatory property of humulene was also reported [30]. Moreover, santalol, which has santalene as a precursor, displays antidepressant, Alzheimer's, and antipsychotic potentials [31-32]. The presence of these bioactive volatile constituents in the oils of T. monadelpha and T. prieuriana are likely responsible for their usefulness in folklore medicine.

5.    Conclusions

The essential oil of T. monadelpha and T. prieuriana contain bioactive compounds with diverse pharmacological activities, indicating their potential as sources of future lead drugs that may be useful in combating various diseases and health challenges. However, further studies need to be performed on the essential oils of T. monadelpha and T. prieuriana to establish their biological potential.

Authors’ contributions

Designed of the research, A.O. and M.O.; Executed the research, A.O., O.O., A.A., S.B., M.O. and W.S.; Analyses the data and interpreted the results, A.O., O.O., A.A., S.B., M.O. and W.S.; Wrote the first draft of the manuscript writing, A.O., O.O. and S.B. 

Acknowledgements

The authors acknowledge Dr. Niyi Odewo of the Herbarium section, Forestry Research Institute of Nigeria (FRIN), Ibadan Nigeria for his technical assistance.

Funding

Authors did not receive any fund to execute the study.

Conflicts of interest

Authors declared no conflicts of interest

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