Chemical Composition and Larvicidal Activity of the Essential Oils of Cordia leucomalloides and Cordia curassavica from the Northeast of Brazil

Os óleos essenciais das folhas de Cordia leucomalloides e Cordia curassavica foram obtidos por hidrodestilação e suas composições químicas determinadas por uma combinação de CGEM e CG-DIC. Como resultado, vinte e três componentes foram identificados em ambos os óleos, representando 98,6 e 91,2% da composição volátil. O óleo essencial de C. leucomalloides foi caracterizado por uma alta percentagem de sesquiterpenos (90,6%), sendo δ-cadineno (17,4%), (E)-cariofileno (15,7%), biciclogermacreno (12,5%) e germacreno D (11,2%) os majoritários. Por outro lado, o óleo de C. curassavica mostrou proporções similares de monoterpenos (47,3%) e sesquitepenos (43,9%), entre os quais α-pineno (20,5%), β-pineno (13,1%), (E)-cariofileno (12,4%) e biciclogermacreno (13,8%) foram os compostos predominantes. O potencial larvicida dos dois óleos foi avaliado contra larvas no terceiro estágio do mosquito Aedes aegypti. Os resultados mostraram que ambos os óleos apresentaram atividade biológica significativa, particularmente o óleo essencial de C. leucomalloides, o qual foi capaz de matar 98,7% das larvas numa concentração de 100 ppm.


Introduction
The pantropical genus Cordia, represented by shrubs and trees, is one of the major and most important genus of the family Boraginaceae. 15][6] Various phytochemical studies on Cordia species have been published, revealing a great number and diversity of secondary metabolites including triterpenes, 4 flavonoids, 7 sesquiterpenes, 8 saponins, 9 hydroquinones 3 and quinones. 10Nevertheless, there are few studies published about the chemical composition of the essential oils of those plants.To the best of our knowledge, only the chemical composition of the essential oils of C. curassavica (Jack.)(syn.: C. verbenacea D.C.), 1,11 C. nitida Vahl., 12 C. trichotoma Vell. 13and C. globosa (Jacq.)H.B.K. 14 have been described.The two later were recently subject of our studies, including their essential oils.
A literature survey revealed that the oil of C. leucomalloides has not been reported but C. curassavica has been the subject of several studies, probably due its etnobotanical value. 1,5,6,15C. curassavica is a medicinal plant with anti-inflammatory and antimicrobial properties.Indeed, artemetin, a flavonoid with anti-inflammatory activity 5 was isolated from the leaves and its essential oil has exhibited antimicrobial properties. 12In addition, naphthoquinones with antifungal and larvicidal activities have been isolated from the roots of this plant. 6As part of our research program on Cordia species native to Northeast of Brazil, [8][9][10]13,14,[16][17][18] the current paper describes the chemical composition of leaf oils of C. leucomalloides and C. curassavica, as well as their larvicidal effects against the mosquito Aedes aegypti, the vector of the yellow fewer and dengue.
Previous studies on leaf essential oil of C. curassavica, from the southeast region of Brazil, showed that the main compounds were α-pinene (29.7%) and (E)-caryophyllene (25.3%).Other terpenoids were also found in significant amounts including allo-aromadendrene (10.0%), αhumulene (4.6%), β-gurjunene (4.1%), spathulenol (2.8%) and bicyclogermacrene (2.7%). 6On the other hand, in the oil of C. curassavica from Panama, the most prominent constituent was β-terpinene (32.0%) followed by (E)caryophyllene (12.0%), camphene (9.0%), germacrene D (9.0%) and α-pinene (6.0%). 1 Despite the compositional differences detected in the three oils samples of C. curassavica from different geographic sites it is important to emphasize the presence of (E)-caryophyllene and α-pinene among the main constituents of both oils of Brazilian origin compared to the high content of β-terpinene solely for C. curassavica of Panamanian origin.α-Pinene, (E)-caryophyllene, β-elemene, α-humulene, bicyclogermacrene and δ-cadinene are common constituents for C. curassavica of any origin, while camphene is common just to C. curassavica oils from Panama and Northeastern Brazil.It is also important to point out that (E)-caryophyllene, germacrene D and bicyclogermacrene are the major  19,20 Taking in consideration the LC 50 of the mentioned oils and the almost two fold higher toxicity of the oil from C. leucomalloides, relative to C. curassavica, it can be stated that the oil from the former has potential to become a promising natural agent to threat the mosquito life cycle, thus helping in the prevention of dengue fever.

Plant material
The leaves of C. leucomalloides (No. 34725) and C. curassavica (No. 34715) were harvested during the flowering stages in January 2005, from Crato County, Ceará, Brazil.Voucher specimens have been deposited at the Herbário Prisco Bezerra (EAC) of the Departamento de Biologia, Universidade Federal do Ceará.

Extraction of the essential oils
The fresh leaves of C. leucomalloides (780 g) were subjected to hydrodistillation in a Clevenger-type apparatus for 2:00 hours to afford 0.07% of a pale yellow oil: [α] 2 D 0 -16° (c = 0.05, CHCl 3 ), η 25 1.6705.The same procedure were applied to fresh leaves of C. curassavica (900 g) to yield 0.13% of also a pale yellow oil: [α] 2 D 0 -30° (c = 0.05, CHCl 3 ); η 25 1.6633.The yields (m/m) were calculated based on the fresh weight of the plant materials.The isolated oils, after drying over anhydrous sodium sulfate and filtered were stored in sealed glass vials and maintained under refrigeration before analysis.

Chemical analysis
GC-FID.The quantitative analysis was performed on a Shimadzu GC-17A gas chromatograph equipped with a flame ionization detector using a non-polar DB-5 fused silica capillary column (30 m × 0.25 mm i.d., 0.25 μm film thickness).Hydrogen was used as carrier gas at a flow rate of 1 mL min -1 and 30 psi inlet pressure; split ratio 1:30; the column temperature was programmed from 35 ºC to 180 ºC at a rate of 4 ºC min -1 , then heated at a rate of 17 ºC min -1 to 280 ºC and held isothermal for 10 min; both injector temperature and detector temperature were 250 ºC.
GC-MS.The analysis was carried out on a Hewlett-Packard Model 5971 GC/MS using a non-polar DB-5 fused silica capillary column (30 m × 0.25 mm i.d., 0.25 mm film thickness); carrier gas helium, flow rate 1 mL min -1 and with split mode.The injector temperature and detector temperature were 250 ºC and 200 ºC, respectively.The column temperature was programmed from 35 °C to 180 ºC at 4 ºC min -1 and then 180 °C to 250 ºC at 10 ºC min -1 .Mass spectra were recorded from 30 -450 m/z.Individual components were identified by matching their 70 eV mass spectra with those of the spectrometer data base using the Wiley L-built library and two other computer libraries MS searches using retention indices as a preselection routine, 21,22 well as by visual comparison of the fragmentation pattern with those reported in the literature. 23,24rvicidal bioassay Portions of essential oils (5 to 500 ppm) dissolved in H 2 O:DMSO (98.5:1.5) were placed in a beaker (50 mL).50 instar III larvae of A. aegypti were delivered to each beaker.After 24 hours, at room temperature, the number of dead larvae was counted and the lethal percentage calculated.A control using DMSO and water was carried out in parallel.For each sample, three independent experiments were run.The bioassays were performed at Laboratório de Entomologia, Núcleo de Endemias da Secretaria de Saúde do Estado do Ceará, Brazil.
At the concentrations of 500 and 250 ppm there was 100% larvae mortality for both oils.At 100 ppm the observed mortality was 98.7±0.9 and 50.7±2.0,while at 50 ppm the figures were 9.3±1.2 and 16.0±2.0,for C. leucomalloides and C. curassavica, respectively.This made possible the calculation of the LC 50 as 63.1±0.5 and 97.7±1.0, for C. leucomalloides and C. curassavica, respectively.

Table 1 .
Volatile compounds identified in the leaf essential oils of C. common for oils from C. leucomalloides and C. curassavica from Northeast of Brazil, but δ-cadinene for C. leucomalloides and αand β-pinene for C. curassavica can distinguish them.The leaf oils from both investigated Cordia species exhibited significant activity against the third-instar of A. aegypti larvae, showing LC 50 of approximately 63.1 ppm for C. leucomalloides and of approximately 97.7 ppm for C. curassavica.The same order of LC 50 have been observed previously for the essential oils from Lippia sidoides (63 ppm), Cymbopogon citratus (69 ppm), Ocimum americanum (67 ppm) and O. gratissimum (60 ppm) all considered of high interest for the control of A. aegypti.
a Constituents listed in order of elution on DB-5 column.bKI = kovats retention index according to n-alkanes.components