Composition of Volatile Oils from Duranta repens Leaves and Fruits

Abstract

Duranta repens L. (syn: Duranta erecta L.; common name: golden dew drop or sky flower) belongs to the family Verbenaceae. D. repens is an evergreen shrub native to tropical America, and it is distributed in most tropical and subtropical regions [1]. The leaves have a very bitter taste. Folkloric claims indicate the use of the fruit as febrifuge and for the treatment of malaria and intestinal worms; the leaves are employed as a cure for abscesses and as insect repellant [2]. The plant has been shown to have some therapeutic activities, such as antithrombin, antioxidant, anticancer, antiviral, larvicidal, and antiplasmodial activities [1, 3–7]. There are some reports on the isolation of phytoconstituents of D. repens [1, 4, 5, 8, 9]. Literature search has proved that D. repens has not been previously studied for its essential oils. As an integral part of our systematic evaluation of the poorly studied aromatic Flora of Nigeria [10], we report the volatile constituents of D. repens leaves and fruits. The leaves and fruits of D. repens afforded 0.10% and 0.12% (v/w) of yellow aromatic oils, respectively. The essential oil composition of D. repens is presented in Table 1. Forty-seven (47) and forty-two (42) constituents were identified in the leaf and fruit oils, respectively. Twenty compounds were common to both oils; limonene and β-caryophyllene were among the most representative ones. The major components of the leaf volatile oil were limonene (11.6%), β-caryophyllene (7.5%), pentadecanal (6.7%), 1-octen-3-ol (5.1%), and α-humulene (5.0%). Carvacrol (16.5%), β-caryophyllene (10.1%), 1,10-di-epi-cubenol (10.1%), and n-hexadecane (7.0%) dominated the fruit oil. The percentage composition of classes of compounds in D. repens essential oils was indicated as such: monoterpenoids (26.3 and 36.9%), sesquiterpenoids (43.1 and 43.8%), phenylpropanoids (1.8 and 2.7%), and nonterpenoid derivatives (22.7 and 12.9%) for leaf and fruit, respectively. The leaves and fruits of D. repens were collected from mature plants cultivated in Uyo Local Government Area of Akwa Ibom State, Nigeria, in January 2017. A voucher specimen (UUH 3347) was deposited in the herbarium of the Department of Botany and Ecological Studies, University of Uyo. The essential oils were obtained by hydrodistillation (4 h) of the fresh plant parts using a Clevenger-type apparatus. The oils were dried over anhydrous sodium sulfate and stored in a refrigerator (4°C) after estimation of the percentage yield. GC analyses were carried out with an HP-5890 Series II instrument equipped with HP-WAX and HP-5 capillary columns (30 m × 0.25 mm, 0.25 μm film thickness); temperature program: 60°C for 10 min, ramp of 5°C/min up to 220°C; injector and detector temperatures 250°C; carrier gas helium (2 mL/min); detector dual FID; split ratio 1:30; injection of 0.5 μL (10% hexane solution). Component identification was carried out, for both columns, by comparing their retention times with those of pure authentic samples and by means of their linear retention index (LRI) relative to the series of n-hydrocarbons. GC-EI-MS analyses were performed with a Varian CP-3800 gas chromatograph, equipped with an HP-5 capillary column (30 m × 0.25 mm; coating thickness, 0.25 μm) and a Varian Saturn 2000 ion trap mass detector. Analytical conditions: injector and transfer line temperatures 220 and 240°C, respectively; oven temperature programmed from 60 to 240°C at 3°C/min; carrier gas helium at 1 mL/min; injection of 0.2 μL (10% hexane solution); split ratio 1:30. Constituent identification was based on comparison of retention times with those of authentic samples; this implied comparing their LRI with the series of n-hydrocarbons and using computer matching against commercial (NIST 2014 and Adams, 2007) and home-made library mass spectra (built up from pure substances and components of known oils and mass spectra literature data [11, 12].