INSECTICIDE PROPERTIES OF AN EXTRACT OF SEXTONIA RUBRA, AND THE CONSTITUENTS THEREOF

Abstract

The invention relates to the use of an extract of Sextonia rubra or the constituents thereof, rubrenolide and/or rubry-nolide, as an insecticide agent against mosquitoes, especially as a larvicide agent.

Claims

1. The use of a composition comprising a crude extract of Sextonia rubra, rubrynolide and/or rubrenolide as an agent that is insecticidal with respect to a mosquito strain.

2. The use as claimed in claim 1, wherein the insecticidal agent is a larvicidal agent.

3. The use as claimed in claim 1, wherein the mosquito strain is chosen from the Culicidae family.

4. The use as claimed in claim 3, wherein the mosquito strain is of the Aedes genus.

5. The use as claimed in claim 4, wherein the mosquito strain is the Aedes aegypti species.

6. The use as claimed in claim 1, wherein the crude extract of Sextonia rubra is an ethyl acetate extract.

7. A larvicidal treatment process, said process comprising applying an effective amount of a composition comprising a crude extract of Sextonia rubra, rubrynolide, and/or rubrenolide to a breeding place of larvae.

8. The process as claimed in claim 7, wherein the application is carried out by spraying.

9. The process of claim 7, wherein the larvae is mosquito larvae chosen from the Culicidae family.

10. The process of claim 9, wherein the mosquito strain is of the Aedes genus.

11. The process of claim 10, wherein the mosquito strain is of Aedes aegypti species.

12. The process of claim 7, wherein the composition comprises an ethyl acetate extract of Sextonia rubra.

Description

DESCRIPTION OF THE INVENTION

[0016] The inventors have now demonstrated, entirely unexpectedly, novel products extracted from the Sextonia rubra wood species, that are insecticidal, in particular larvicidal, with respect to the Culicidae forming a family of insects commonly called mosquitoes, more particularly with respect to the Aedes genus, preferentially with respect to the Aedes aegypti species.

[0017] Thus, the ethyl acetate extract of Sextonia rubra and also the two constituents thereof (rubrenolide and rubrynolide) taken independently have demonstrated in the laboratory an excellent larvicidal activity with respect to the Aedes aegypti mosquito, with in particular an LD50 (median lethal dose) of 3.15 pg/ml at 24 h on the PAEA laboratory strain, and LD50s of 0.6 and 3.8 μg/ml for rubrenolide and rubrynolide, respectively, under this same strain.

[0018] There are many advantages with regard to the production and use of these novel agents that are insecticidal with respect to the mosquito: efficacy, renewable, better biodegradability in general, better CO.sub.2 balance, no bioaccumulation in the food chain, no persistence in the environment and a very acceptable cost/performance ratio. In addition, these natural products do not cause excessive forestry exploitation since they can be prepared from forestry exploitation waste that is currently not exploited. A subject of the present invention is thus the use of a composition comprising an extract of Sextonia rubra or a constituent thereof (rubrenolide and/or rubrynolide) as an agent that is insecticidal with respect to the Culicidae (or mosquitoes), in particular as an agent that is larvicidal, more particularly with respect to mosquitoes of the Aedes genus, preferentially with respect to the Aedes aegypti species.

[0019] For the purposes of the present invention, the expression “agent that is insecticidal/larvicidal with respect to a mosquito strain” is intended to mean a compound which results in the death of the mosquito larvae placed in the presence of this compound, for example in the context of an in-cup trial carried out according to the protocol recommended by the WHO (Guidelines for Laboratory and Field Testing of Mosquito Larvicides, WHO/CDS/WHOPES/GCDPP/2005.13, 2005) [12], and for which, according to the WHO criteria for validating the tests, the mortality in the control batches is less than 20%.

[0020] According to one particular embodiment of the invention, for the purposes of the present invention, the term “extract of Sextonia rubra” is intended to mean a crude extract of Sextonia rubra or an extract comprising at least one constituent thereof, namely rubrynolide and/or rubrenolide, which can be used as an insecticidal agent in the context of the present invention.

[0021] Said sustainable Amazonian wood extracts are obtained from forestry exploitation waste using any appropriate solvent and method, including solvent extraction methods, or new extraction technologies (CO.sub.2, supercritical, microwave, ultrasound, etc.). The extraction process is not critical, and can be selected by those skilled in the art according to the desired concentration of extractables and to the type of larvicidal product expected. Preferably, the sustainable Amazonian wood extracts are obtained by means of a solvent extraction process, preferentially using a polar solvent. For the purposes of the present invention, the term “polar solvent” is intended to mean a solvent which has a dipole moment other than zero, and in particular greater than 1.5. For example, the polar solvent is a protic solvent such as water or an alcohol (methanol, ethanol, etc.) or a mixture thereof, for example an aqueous-alcoholic mixture, or an aprotic solvent such as an ester (ethyl acetate, etc.).

[0022] For example, the extraction method used is maceration in a polar solvent (water; alcohol, for example methanol, ethanol; aqueous-alcoholic mixture; ester, for example ethyl acetate, etc.), for 12 to 72 hours, preferably for 24 hours, at a temperature from 22 to 27° C., preferably at ambient temperature (25° C.). To do this, a volume of 2 to 5 liters of solvent, preferably of approximately 3 liters of solvent is used for 300 to 1000 g of wood shavings, preferably for approximately 800 g of wood shavings.

[0023] According to one particular embodiment of the invention, the extract of Sextonia is an ethyl acetate extract.

[0024] A subject of the present invention is also a larvicidal treatment process, said process comprising the application of an effective amount of a composition comprising an extract of Sextonia rubra, rubrynolide and/or rubrenolide to breeding places where the larvae are left.

[0025] For the purposes of the present invention, the term “effective amount” is intended to mean a dose resulting in 100% mortality of the larvae studied, in order to prevent any development of resistance phenomena.

[0026] For example, the minimum concentration corresponding to an effective amount is thus 18 μg/ml (ppm) for the extract of Sextonia rubra in order to obtain 100% mortality at 24 h. With regard to rubrenolide, this value is 2 μg/ml at 24 h. With regard to rubrynolide, this value is 17 μg/ml at 24 h.

[0027] According to one particular embodiment of the process of the invention, the application is carried out by spraying. For example, the extract of Sextonia rubra, rubrynolide and/or rubrenolide is (are) dissolved in ethanol and then diluted in water until the desired concentration is obtained, and then these aqueous-alcoholic preparations are subsequently sprayed on to breeding places where the larvae are left.

[0028] It will be possible for other advantages to further emerge to those skilled in the art on reading the examples below.

EXAMPLES

Example 1

Preparation of Crude Extracts of Sextonia Rubra, from which the Constituents Thereof Are Extracted

[0029] Ethyl Acetate Extract

[0030] An ethyl acetate extract of Sextonia rubra was obtained according to the procedure previously described in Rodrigues et al. (2010, mentioned above) [6] by maceration, in the solvent, of wood previously dried at ambient temperature and milled.

[0031] To do this, the Sextonia rubra wood powder (200 g) was placed in an Erlenmeyer flask and extracted (3×500 ml of ethyl acetate) with stirring, at ambient temperature for 48 h. After each extraction, the solution was filtered, the solutions resulting from the various extractions were combined, and the solvent was evaporated off under reduced pressure at a temperature of 30° C. The yield obtained for the extract was 4.2%.

[0032] The extract (3.6 g) was then purified according to a method previously described in Rodrigues et al. (2010, mentioned above) [6], by chromatography with an open column of silica using ethyl acetate (600 ml) as eluent and then methanol (rinsing). The eluate obtained with the ethyl acetate was then evaporated (3.0 g of beige residue obtained), and triturated with hexane. The insoluble fraction was then recovered by filtration and dried under vacuum (316.6 mg). This fraction contains a mixture of rubrenolide and rubrynolide. The separation of the two constituents was then carried out according to the procedure described in Thijs and Zwanenburg (Tetrahedron, 60: 5237-5252, 2004) [9]. The mixture was dissolved in 6.5 ml of absolute ethanol. A silver nitrate solution (1 g in 15 ml of ethanol) was then added. The whole mixture was left to precipitate for 4 h. The precipitate (containing the rubrynolide to be purified) was then recovered by filtration and dried under vacuum. The filtrate was evaporated under reduced pressure so as to give the rubrenolide to be purified. The precipitate containing the rubrynolide was dissolved in 5 ml of sodium cyanide (NaCN) solution and the mixture was extracted with 10 ml of diethyl ether. The organic phase was dried with magnesium sulfate (Mg.sub.2SO.sub.4) and filtered, and the solvent was evaporated off under reduced pressure. The pure rubrynolide was thus obtained (21.6 mg). The dry residue obtained from the filtrate was taken up in 80 ml of MilliQ water and extracted with 80 ml of diethyl ether. The organic phase containing a yellow precipitate was recovered, filtered and, once clear, dried over magnesium sulfate before again being filtered. After the solvent had been evaporated off, 106.8 mg of pure rubrenolide were obtained.

[0033] The ethyl acetate used for the extraction does not exhibit any toxicity, the only risks noted being eye irritation, drowsiness or dizziness. The use of this solvent thus makes it possible to obtain an extract under good safety conditions. Finally, the yields of the crude extract >4%, of the rubrynolide extract of 0.6% and of the rubrenolide extract (the most active molecule) of 2.9% that were obtained make this extraction process by maceration a process that is simple to carry out and efficient in terms of yield, thereby making it possible to favorably envision a switch to the industrial scale with regard to the production of the extract and of the compounds thereof.

[0034] Alcoholic Extracts

[0035] Alcoholic extracts of Sextonia rubra were obtained by maceration, in methanol or ethanol, of wood previously dried at ambient temperature and milled.

[0036] To do this, Sextonia rubra wood shavings (200 mg) were macerated in 5 ml of each of the solvents chosen, at ambient temperature. The mixture was then placed in an ultrasonic bath for 4×15 minutes, and then centrifuged and filtered in order to recover the solution. The solvent was evaporated off under reduced pressure at a temperature of 30° C.

[0037] The extraction yields obtained for the various solvents are the following: ethanol, 4.6%; methanol, 5.1%. An ethyl acetate extract was obtained under the same conditions and an extraction yield of 4.2% was obtained.

[0038] The relative composition of the extracts resuspended in methanol was then analyzed by high performance liquid chromatography (HPLC) using a column of C18 type and a water/acetonitrile gradient supplemented with 0.1% of formic acid for the elution. By comparison with standards, the rubrenolide and rubrynolide were identified by means of a light scattering detector (ELSD), and the respective areas of the corresponding peaks were measured. This analysis made it possible to demonstrate that the extracts are virtually exclusively composed of these two compounds. The relative proportions of each of the compounds in the various extracts obtained were thus calculated. The following results were obtained:

TABLE-US-00001 Relative proportions of the compounds (%) Extracts Rubrynolide Rubrenolide Ethanol 69 28 Methanol 64 32 Ethyl acetate 70 27

[0039] The relative proportions of rubrynolide and rubrenolide in the three extracts are equivalent. Insofar as it has previously been demonstrated that this activity is associated with these two compounds, these extracts should exhibit equivalent larvicidal activities.

[0040] It should be noted that, even though methanol makes it possible to obtain a yield >5%, which is slightly higher than the other two solvents, it presents a risk of toxicity by inhalation, by skin contact or in the event of ingestion which requires additional precautions during handling thereof in the laboratory.

[0041] On the other hand, just like ethyl acetate, the ethanol used for the extraction does not present any major toxicity problems during handling in the laboratory, the only risks noted being eye irritation and drowsiness. The use of these solvents thus makes it possible to obtain extracts under good safety conditions. Finally, the yields of the crude extracts >4% and the proportions of rubrynolide and rubrenolide that were obtained make this extraction process by maceration a process that is simple to carry out and efficient, thereby making it possible to favorably envision a switch to the industrial scale with regard to the production of the extracts and of the compounds thereof.

Example 2

Insecticidal Activity of the Ethyl Acetate Extract of Sextonia Rubra, and of the Constituents Thereof

[0042] The biological trials were carried out on larvae of Aedes aegypti mosquitoes of the PAEA laboratory strain sensitive to all insecticides. The protocol described hereinafter was adapted according to the WHO protocols.

[0043] This strain originating from French Polynesia has been maintained for about ten years at the insectarium of the Institut Pasteur of Guyana, in Cayenne. The mosquitoes were bred under natural conditions: temperature of 28° C.±2° C., humidity of 80%±20%, and daytime duration 12:12 h±20 min during the year. The Aedes aegypti eggs were kept dry on strips of blotting paper at the insectarium temperature. Hatching was carried out by placing these strips in water under a vacuum bell jar for at least 20 min. The larvae thus obtained were fed with yeast tablets. The larvae at growth stage 3-4 were then used for the extract and constituent activity tests. 100 larvae were transferred into plastic cups containing 99 ml of distilled water. Four cups per concentration (4×25 larvae) and at least 5 concentrations of each extract or constituent diluted in ethanol (crude extract of Sextonia rubra: 1, 2, 3, 4, 5, 7, 10, 25, 35, 50, 75, 100 μg/ml, rubrenolide: 0.1, 0.3, 0.5, 0.7, 1, 1.5, 2 μg/ml, rubrynolide: 0.1, 0.3, 0.5, 0.7, 1, 1.5, 4, 6, 8 μg/ml) were used to measure mortalities ranging from 0 to 100%. Each concentration of extract or of constituent (1 ml) was added to the cup. Controls were also carried out by adding 1 ml of ethanol to the cup. The mortality was evaluated at 24 h and 48 h after exposure of the larvae to the test product (crude extract, isolated constituent, ethanol).

[0044] The following mortality values (in μg/ml, ppm equivalent) were obtained:

TABLE-US-00002 At 24 h At 48 h Extract/Constituent LD50 (SE) LD90 (SE) LD50 (SE) LD90 (SE) Sextonia rubra 3.150 (0.018) 8.442 (0.029) 2.062 (0.018) 4.513 (0.022) Rubrenolide 0.605 (0.023) 2.110 (0.041) 0.300 (0.024) 0.788 (0.027) Rubrynolide 3.840 (0.018) 8.909 (0.031) 2.105 (0.023) 8.200 (0.043) Dichlorvos 0.039 (0.012) 0.064 (0.026) 0.029 (0.012) 0.049 (0.020) Spinosad 0.387 (0.025) 1.118 (0.065) 0.193 (0.020) 0.444 (0.028)

[0045] Negative control [ethanol at 1% by volume (1 ml of ethanol added to 99 ml of water)]: mean mortality on 100 larvae: at 24 h, mean 0.63% (SE 0.52%), at 48 h mean 1.75% (SE 1.11%).

[0046] The values obtained, in particular for rubrenolide, are in the same range as those obtained for spinosad (LD50 at 24 h of 0.6 μg/ml for rubrenolide compared with 0.4 μg/ml for spinosad).

[0047] In comparison, in Guyana, anti-larval control is based on treating the breeding places mechanically or chemically with a granulated formulation of Bacillus thuringiensis var. israeliensis or Bti (Vectobac®G). This product was not tested in the context of the present study, but experiments carried out at the Institut Pasteur of Guyana have demonstrated for this formulation LD50 values at 24 h of 0.11 μg/ml and LD95 values at 24 h of 0.22 μg/ml, on the PAEA strain.

[0048] It emerges from the present study that the ethyl acetate extract of Sextonia rubra exhibits larvicidal activity, in particular with respect to the larvae of the Aedes aegypti mosquito. Furthermore, rubrenolide derived from the ethyl acetate extract of Sextonia rubra wood results in mortalities on the larvae of the PAEA strain of the same order of magnitude or better than those obtained for products known for their larvicidal activity, such as spinosad or Bti used as anti-larval treatment in Guyana.

List of References

[0049] 1) Simmons et al., N. Engl. J. Med., 366: 1423-1432, 2012

[0050] 2) OMS (WHO), Dengue et dengue hemorragique [Dengue and hemorrhagic dengue], http://www.who.int/mediacentre/factsheets/fs117/fd, 2014

[0051] 3) Dusfour et al., Mem. Inst. Oswaldo Cruz, 106: 346-352, 2011

[0052] 4) Regnault-Roger et al., Biopesticides d'origine végétale [Biopesticides of plant origin], Paris: Tec & Doc Lavoisier, 2008

[0053] 5) Van der Weff, Novon, 7: 436-439, 1997

[0054] 6) Rodrigues, Analyse et valorisation bioinspirée des métabolites secondaires àl'origine de la durabilité naturelle des bois exploités de Guyana francaise [Analysis and biobased exploitation of secondary metabolites responsible for the natural durability of exploited wood from French Guyana], doctoral thesis, 2010

[0055] 7) Rodrigues et al., Pest. Manag. Sci., 67: 1420-1423, 2011

[0056] 8) Patent application FR 2959642

[0057] 9) Thijs and Zwanenburg, Tetrahedron, 60: 5237-5252, 2004

[0058] 10) Jansen and Beebe, Microbes Infect., 12(4): 272-279, 2010

[0059] 11) Fouque and Carincil, Bull. Soc. Pathol. Exot., 89(2): 115-119, 1996

[0060] 12) OMS (WHO), Guidelines for Laboratory and Field Testing of Mosquito Larvicides, WHO/CDS/VVHOPES/GCDPP/2005.13, 2005