Chemical Composition of the Essential Oil of Cnidoscolus quercifolius from Brazil

Published in Khimiya Prirodnykh Soedinenii, No. 5, September–October, 2020, pp. 798–800.

The Caatinga is a semi-arid biome exclusive to Brazil with considerable biodiversity and a biological heritage including 4880 species of flowering plants, 291 of which are endemic to the region [[1]]. Cnidoscolus quercifolius (syn. Cnidoscolus phyllacanthus) belongs to the family Euphorbiaceae and is found exclusively in the Caatinga. This typically xerophilic tree can reach a height of 12 meters. Its leaves are long, thick, and lanceolate, with jagged edges; stinging trichomes cover the branches, leaves, and fruit [[2]]. C. quercifolius is abundant in states of the northeastern region of the country and is known locally as favela, favela–de-cachorro, or faveleira [[3]].

The cataplasm under the outer bark and infusions made from the leaves are used in folk medicine due to their healing, analgesic, anti-inflammatory, antibiotic, and diuretic properties, as well as for the treatment of rashes and to remove warts [[4]]. Different parts of the plant are used to feed animals, and the seeds are used to make flour and to extract oil of high nutritional value [[6]].

The literature reveals several biologic activities for different parts of C. quercifolius. The seed oil of C. quercifolius showed high antioxidant activity [[8]], and the ethanolic extract of the leaves, roots, and root barks revealed anti-inflammatory [[5]] and antimicrobial activity [[9]]. The ethyl acetate fraction of the ethanolic extract demonstrated a strong cytotoxic effect against prostate and breast cancer cell lines [[10]], and aqueous extracts of C. quercifolius showed a hypoglycemic effect and no oral toxicity, revealing a new source of compounds for the control of diabetes [[11]].

Phytochemical studies of the species reveal the occurrence of amino acids, terpenoids [[12]], tetracyclic cyclobutene (neofavelanone) [[13]], tetracyclic cyclopropane (favelanone) [[14]], and tricyclic benzocycloheptene derivatives (deoxofaveline, faveline methyl ether, and faveline) [[15]].

To the best of our knowledge, C. quercifolius has not previously been investigated for the identification of the chemical constituents of its essential oils. This paper reports for the first time the chemical composition of essential oils from the leaves, flowers, and bark of C. quercifolius occurring in the Caatinga of Brazil.

The essential oils obtained through conventional hydrodistillation of fresh leaves, flowers, and bark of C. quercifolius had a light yellow color. The yield on a fresh weight basis was 0.01% for leaves, 0.03% for flowers, and 0.01% for bark. The oils were submitted to CG-MS for the determination of the constituents. Thirty-one, thirty, and eighteen compounds were identified in the essential oils from leaves, flowers, and bark, respectively, accounting for 97.3%, 98.5%, and 81.4% of the total oils (Table 1).

Composition of Essential Oil from Leaves, Flowers, and Barks of Cnidoscolus quercifolius, Yield (%) ± SD

a RI: Retention indices calculated from retention times in relation to those of a series of C8–C40n-alkanes on a DB-5 capillary column; RI: Retention index; MS: mass spectroscopy; CI: co-injection with authentic compounds. Method of identification: RI, MS and *RI, MS, CI.

Diterpene was the predominant class of compounds in the leaf (44.6%) and bark (72.5%) oils, whereas monoterpenes predominated in the flower oil (95.5%). The major constituents identified in the leaf oil were phytol (42.1%), α-terpineol (10.9%), and 11,12-dihydroxyvalencene (7.8%). The major constituents identified in the flower oil were γ-terpinene (20.5%) and β-pinene (9.6%). The diterpenes dehydroabietal (29.9%) and abietadiene (21.4%) were the major constituents identified in the bark oil. These results suggest the chemical variability among the essentials oils from different organs of C. quercifolius.

Fresh leaves, flowers, and bark of C. quercifolius were collected from the municipality of Patos in the state of Paraiba (Brazil) in the morning in September 2017 from an adult specimen in an area of the Caatinga under human pressure.

The plant was identified by botanist Dr. Maria de Fatima de Araujo Lucena of the Centro de Saude e Tecnologia Rural [Center for Health and Rural Technology] of the Universidade Federal de Campina Grande (UFCG). A voucher sample of the species was mounted and deposited in the herbarium of the UFCG Centro de Saude e Tecnologia Rural under No. 6786. The extraction of the essential oil through conventional hydrodistillation of the fresh leaves was performed as described previously by Moraes et al. (2012) [[16]]. The gas chromatography-mass spectrometry (GC-MS) (Clarus® 580 PerkinElmer, Shelton, CO, USA) analysis was carried out using a system with a mass-selective detector, mass spectrometer in EI 70 eV with a scan interval of 0.5 s and fragments from 40 to 550 Da. A nonpolar DB-5 fused silica capillary column (30 m × 0.25 mm × 0.25 μm) was used, with the oven temperature programmed from 60 to 240°C at a rate 3°C min–1. The injector and detector temperature was 260°C. Helium was used as the carrier gas at a flow rate of 1 mL min–1 in split mode (1:30), flow rate = 1 mL min–1. The injection volume was 0.5 μL of a diluted solution (1/100) of the oil in n-hexane. Identification of the components was based on GC-MS retention indices with reference to a homologous series of C8–C40 n-alkanes calculated using the Van den Dool and Kratz equation [[17]] and by computer matching against the mass spectral library of the GC-MS data system (NIST 11 and Wiley 11th) and co-injection with authentic standards, as well as other published mass spectra [[18]].