Insecticidal, Antifungal and Herbicidal Activities

The trans-chrysanthemic acid 88 is an essential component of naturally occurring pyrethrin esters which are present in the flower of Chrysanthenum cinera-riaefolium and has a defense function in these plants [122]. Very effective as an antifeedant for herbivores, it presents a broad spectrum as an insect repellent. 

Synthetic derivatives such as the (S)-bioallethrin 89 or bioresmethrin 90 are known for their high insecticidal activity with low mammalian toxicity, Eq. (33, 34) [123]. 

Various structural modifications particularly involving the chrysanthemic acid moiety led to compounds with enhanced stability and insecticidal activity for a wide range of insect pests. It has been reported that plant growth was also stimulated by the photostable insecticidal biopermethrin 91, Eq. (34) [123cj. 

The highest insecticidal activity was reached with the deltamethrin 92, by introduction of a benzylic cyano group and of a dibromovinyl substituent with the czs configuration,Eq. (35) [123cj. 

The mechanism of insecticidal action has been attributed to blocking of the sodium channel in target cell membranes and consequent blocking of ion transport [124]. Following these observations a considerable effort was developed for the preparation of synthetic pyrethroids as commercial insecticides. 

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