Michael Elliott

PRESENT STATUS AND FUTURE PROSPECTS FOR SYNTHETIC PYRETHROIDS

The potential number of insecticidally active variations of compounds with a discernible relationship to pyrethrin I is continually increasing as new acid, alcohol, and other components, many of them asymmetric, are discovered. Knowledge of how structure affects activity for important practical uses (activity against pest species, acaricidal activity, selectivity between pests and beneficial species, persistence on crops and in the environment, rapidity of action, antifeedant or repellent properties, toxicity to mammals, birds and fish, etc.) is being rapidly accumulated. Although strictly such information can only be obtained by direct testing of many related compounds, broad conclusions about the physical properties that influence the behaviour of pyrethroids in the environment can be predicted from their structures. As with applications of such procedures to other groups of pesticides, most results are precise only within an order of magnitude but these nevertheless provide a basis for valuable generalisations. The prospects for developing pyrethroids with properties especially appropriate for particular insect control applications are therefore encouraging, and the scope of pyrethroids may become comparable with those of the longer established groups of insecticides.

Recent Structure-Activity Correlations in Synthetic Pyrethroids

Abstract The potencies of synthetic pyrethroid esters, some of the most powerful lipophilic insecticides known, are very sensitive to the structure and chirality of the acidic and alcoholic components. Active compounds include esters of 5-benzyl-3-furylmethyl and 3-phenoxybenzyl alcohols with 3-(2,2-dimethyl- or 2,2-di-halovinyl)-dimethylcyclopropanecarboxylic or α-arylisovaleric acids. The influence on biological activity of isosteric replacements at four sites in these molecules is examined: (i) replacement of the 2,2-dimethyl group in the cyclopropanes by a dimethylene group and the analogous comparison of cyclopropyl with isopropyl in the isovalerate series (ii) stepwise replacement of the methyl groups of the isobutenyl side chain by chlorines (iii) variation of the link between the ring and the side chain in the alcoholic component (iv) replacement of either α-H in 3-phenoxybenzyl esters by a cyano group.

Roman Mieczyslaw Sawicki. 20 April 1930-22 July 1990

Roman Sawicki was renowned for his research on the origins of resistance to insecticides in insects, and for the strategies he developed to prevent such resistance. Earlier, in one of his first projects, he had developed definitive bioassays comparing the activities of the constituents of natural pyrethrum, thereby contributing significantly to the development at Rothamsted of a new class of insecticides, the synthetic pyrethroids.