Comparative Study Of Insectici Dal Activity Among Terpinen-4-Ol Optical Isomers And Racemate

Terpinen-4-ol, monoterpene, was an important component in many essential oils. It was widely applied in treatment of dermatoses for its broad spectrum of antibacterial activity. In decade years, terpinen-4-ol was found to be toxic against many pests. Terpinen-4-ol gains two optical isomers, viz., (+)-terpinen-4-ol, isolated from Sabina vulgaris Ant and Origanum majorana oil et al, and (-)-terpinen-4-ol, extracted from Eucalyptus dives and Zanthoxylum rhetsa oil et al.Bioactivity of many natural compounds is related with their absolute configuration. However, there is no report about the relationship between bioactivity of terpinen-4-ol and its spatial configuration. With the purpose of comparing the insecticidal activity of terpinen-4-ol optical isomers and providing theoretical foundation for utilization of efficient isomer, we evaluated insecticidal activity of terpinen-4-ol optical isomers and racemate. Fumigation toxicity, knock-down toxicity and effects on Na+, K+, ATPase of terpinen4-ol optical isomers and racemate were tested against Aedes albopictus, Culex pipiens pallens, Mythimna separata and Musca domestic a.Results are as follows:(1) Terpinen-4-ol optical isomers and racemate exhibited fumigation activity against four kinds of insects. Racemate was more toxic than (+)-terpinen-4-ol and (-)-terpinen-4-ol against two kinds of mosquitoes and housefly, while (+)-terpinen-4-ol and (-)-terpinen-4-ol showed differences in fumigation activity against different insects. Terpinen-4-ol optical isomers and racemate exhibited no remarkably difference in fumigation activity against M. separata. Median lethal concentrations (LC50) of racemate were 1.05 μL/L against A. albopictus,1.53 μL/L against C. pipiens pallens,7.49 μL/L against M. separata and 2.50 μL/L against M. domestica, respectively.(2) Terpinen-4-ol optical isomers and racemate exhibited knock-down activity against four kinds of insects. Racemate was more toxic than (+)-terpinen-4-ol and (-)-terpinen-4-ol against two kinds of mosquitoes and housefly, while (+)-terpinen-4-ol and (-)-terpinen-4-ol showed no significant differences. Terpinen-4-ol optical isomers and racemate exhibited no remarkably difference in knock-down activity against M. separata. Median knock-down times (KT50) of racemate were 6.4 min against A. albopictus,9.1 min against C. pipiens pallens,16.3 min against M. separata and 12.6 min against M. domestica, respectively.(3) Terpinen-4-ol racemate and optical isomers inhibited Na+, K+, ATPase significantly in vivo against four kinds of insects. For the same insect, the inhibition was enhanced with symptom of poisoning exacerbating. However, (-)-terpinen-4-ol performed the most significant inhibition efficacy in paralysis stage with inhibition ratio of 78.93% against A. albopictus,72.96% against C. pipiens pallens,75.60% against M. separata and 35.76% against M. domestica, respectively.(4) Terpinen-4-ol racemate and optical isomers exhibited inhibitory activity against Na+, K+, ATPase in vitro with dose-dependent property. And racemate was remarkably superior to (+)-terpinen-4-ol and (-)-terpinen-4-ol, while (+)-terpinen-4-ol and (-)-terpinen-4-ol exhibited no remarkably difference.In conclusion, terpinen-4-ol racemate was more toxic than monomers, while optical isomers showed no difference in insecticidal activity. Terpinen-4-ol might target on Na+, K+, ATPase and its absolute configuration made no sense to Na+, K+, ATPase. Thus mixture of optical isomers should be considered when develop terpinen-4-ol into insecticide.