Acaricidal Potentials of Active Properties Isolated from Cynanchum paniculatum and Acaricidal Changes by Introducing Functional Radicals

This study evaluated the acaricidal activities of acetophenone and its derivatives for their potentials as natural acaricides using an impregnated fumigant bioassay against Dermatophagoides spp. and Tyrophagus putrescentiae . On the basis of the LD50 values against D. farinae, 3'-methoxyacetophenone (0.41 μg/cm(2)) was 89.9 times more toxic than DEET (36.87 μg/cm(2)), followed by 4'-methoxyacetophenone (0.52 μg/cm(2)), 2'-methoxyacetophenone (0.75 μg/cm(2)), 2'-hydroxy-5'-methoxyacetophenone (1.03 μg/cm(2)), 2'-hydroxy-4'-methoxyacetophenone (1.29 μg/cm(2)), acetophenone (1.48 μg/cm(2)), 2'-hydroxyacetophenone (1.74 μg/cm(2)), 2',5'-dimethoxyacetophenone (1.87 μg/cm(2)), 2',4'-dimethoxyacetophenone (2.10 μg/cm(2)), and benzyl benzoate (9.92 μg/cm(2)). In regard to structure-activity relationships between acaricidal activity and functional radicals (hydroxyl and methoxy groups) on the acetophenone skeleton, a monomethoxy group (2'-, 3'-, and 4'-methoxyacetone) on the acetophenone skeleton was more toxic than were the other groups (2',4'- and 2',5'-dimethoxyacetophenone, 2'- and 4'-hydroxyacetophenone, 2'-hydroxy-4'-methoxyacetophenone, 2'-hydroxy-5'-methoxyacetophenone, and 4'-hydroxy-3'-methoxyacetophenone). These results indicated that acaricidal activity against three mite species changed with the introduction of functional radicals (hydroxyl and methoxy groups) onto the acetophenone skeleton.