Insecticidal activity of menthol derivatives against mosquitoes.
BACKGROUND
The insecticidal activity of essential oil of Mentha piperita L. emend. Huds. against local mosquitoes as disease vectors was recognized and found to be due to the presence of menthol, which is the major aroma compound of the oil. The minor compounds of the oil, i.e. menthone, beta-caryophyllene, menthyl acetate, limonene, alpha-pinene and pulegone, showed either less or no activity against the mosquitoes tested. L-Menthol derivatives were synthesized and their knockdown effect and mortality were evaluated against local mosquitoes of Culex quinquefasciatus Say, Aedes aegypti L. and Anopheles tessellatus Theobald as disease vectors. This is the first report of mosquitocidal activity of menthol and its derivatives against Cx. quinquefasciatus, Ae. aegypti and An. tessellatus.


RESULTS
Derivative synthesis followed by structure-activity relationship studies identified several derivatives, i.e. menthyl chloroacetate, menthyl dichloroacetate, menthyl cinnamate, menthone glyceryl acetal, thymol, alpha-terpineol and mugetanol, with enhanced mosquitocidal activity against Cx. quinquefasciatus, Ae. aegypti and An. tessellatus relative to the parent compound L-menthone.


CONCLUSIONS
In ester derivatives of L-menthol the optimum activity is dependent on the size and shape of the ester group and the presence of chlorine atoms in the ester group. In structurally related derivatives of L-menthol the optimum activity is dependent on the aromaticity, the degree of unsaturation, the position of the hydroxy group and the type of functional group.
Samarasekera
Radhika
R
Natural Products Development Group, Industrial Technology Institute (Successor to CISIR), 363, Bauddhaloka Mawatha, Colombo 7, Sri Lanka. radhika@iti.lk
Weerasinghe
Indira S
IS
Hemalal
Kd Patrick
KP
D000818:Animals; D001681:Biological Assay; D002849:Chromatography, Gas / Q000379:methods; D009033:Culicidae / Q000187:drug effects*; D007303:Insect Vectors / Q000187:drug effects*; D007306:Insecticides / Q000737:chemistry / Q000633:toxicity*; D007928:Lethal Dose 50; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D036142:Mentha piperita / Q000737:chemistry*; D008610:Menthol / Q000031:analogs & derivatives* / Q000737:chemistry; D009822:Oils, Volatile / Q000633:toxicity*; D013329:Structure-Activity Relationship
D007306:Insecticides; D009822:Oils, Volatile; D008610:Menthol