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Title: Toxicity of thiophenes from echinops transiliensis (Asteraceae) against aedes aegypti (Diptera: Culicidae) larvae

Author
item NAKANO, HIROSHI - National Agricultural Research Organization - Japan (NARO)
item ALI, ABBAS - University Of Mississippi
item REHMAN, JUNAID - University Of Mississippi
item MAMONOV, LEONID - Almaty
item Cantrell, Charles
item KHAN, IKHLAS - University Of Mississippi

Submitted to: Chemistry and Biodiversity
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/7/2013
Publication Date: 7/14/2014
Citation: Nakano, H., Ali, A., Rehman, J., Mamonov, L., Cantrell, C.L., Khan, I.A. 2014. Toxicity of thiophenes from echinops transiliensis (Asteraceae) against aedes aegypti (Diptera: Culicidae) larvae. Chemistry and Biodiversity. 11(7):1001-1009.

Interpretive Summary: Mosquitoes transmit pathogens that cause serious human diseases including malaria, Japanese encephalitis, yellow fever, dengue and filariasis. Insecticides from various chemical groups are the basic tools used for management of mosquito populations. Due to continuous use of insecticides, mosquitoes have developed resistance against these chemicals and vector population management has become difficult. Natural product-based products have gained special importance as potential new pesticides. In our continuing study of the thiophenes from Echinops species, we isolated six known thiophene compounds from Echinops transiliensis. This paper describes the isolation and structure elucidation of these compounds and structure-activity relationships of thiophene compounds as larvicides against Aedes aegypti. These data indicated that Ae. aegypti larvicidal activity of thiophenes increase with increase in the number of thiophene rings and the most important active site in the structure of thiophenes could be the tetrahydrothiophene moiety. In bithiophenes, Ae. aegypti larvicidal activity increased with increasing the number of acetoxy groups attached to C-3' or C-4' indicating that acetoxy groups may play important role in the larvicidal activity.

Technical Abstract: Six known thiophenes, 5-(3,4-diacetoxybut-1-ynyl)-2,2'-bithiophene (3), 2-(penta-1,3-diynyl)-5-(3,4-diacetoxybut-1-ynyl)thiophene (4), 5-(4-acetoxy-3-hydroxybut-1-ynyl)-2,2'-bithiophene (5), 2-(penta-1,3-diynyl)-5-(4-acetoxy-3-hydroxybut-1-ynyl)thiophene (6), 2-(penta-1,3-diynyl)-5-(3-acetoxy-4-hydroxybut-1-ynyl)thiophene (7), and 5-(3,4-dihydroxybut-1-ynyl)-2,2'-bithiophene (8) were isolated from the roots of Echinops transiliensis. The structures of compounds 3-8 were elucidated on the basis of spectroscopic analyses. This is the first report on the presence of compounds 3-8 in E. transiliensis. Structure-activity relationships of compounds 3-8 and previously isolated 1, 2, and 9 were evaluated for their larvicidal activity against Aedes aegypti larvae. Compound 1 belongs to the class of compounds designated as trithiophene, compounds 3, 5, and 8 belong to the class designated as bithiophenes, and compounds 2, 4, 6, 7, and 9 belong to the class designated as monothiophenes. Structural differences among compounds 3, 5, and 8 consist of differing functional groups attached to C-3' and C-4'. Acetoxy groups are attached to C-3' and C-4' of compound 3. Hydroxy and acetoxy groups are attached to C-3' and C-4', respectively, of compound 5. Hydroxy groups are attached to C-3' and C-4' of compound 8. Compound 1 showed the highest activity (LC50, 0.61 g/mL) among compounds 1-9, followed by compounds 3 (LC50, 4.22 g/mL), 5 (LC50, 7.45 g/mL), 8 (LC50, 9.89 g/mL), 9 (LC50, 12.45 g/mL), 2 (LC50, 14.71 g/mL), 4 (LC50, 17.95 g/mL), 6 (LC50, 18.55 g/mL), and 7 (LC50, 19.97 g/mL). These data indicated that Ae. aegypti larvicidal activity of thiophenes increase with increase in the number of thiophene rings and the most important active site in the structure of thiophenes could be the tetrahydrothiophene moiety. In bithiophenes, Ae. aegypti larvicidal activity increased with increasing the number of acetoxy groups attached to C-3' or C-4' indicating that acetoxy groups may play important role in the larvicidal activity. Also, Ae. aegypti larvicidal activity of thiophene had a significant negative correlation with LogP (r = -0.726*).