Carbazate acaricides

The discovery, synthesis, structure-activity relationship and biology of this new class of carbazate acaricides and bifenazate is described in this chapter. 

Table 30.2.2 Definitions of general formula for carbazate acaricides (see Fig. 30.2.2).

Neurotoxic compounds have been traditionally the largest category of acaricides, with several representatives from the organophosphate, carbamate, and pyreth-roid classes. Several new pyrethroid compounds such as acrinathrin, lubrocythri-nate and halfenprox and an analog of the macrolide abamectin milbemectin were recently introduced as acaricides. A completely new acaricidal chemistry has been found with carbazate chemistry [1]. 

Serendipity in the traditional screening approaches is, up to now, one of the main resources for discovering acaricides with novel biochemical and physiological targets [2]. Based on the discovery that fungicidal phenylhydrazide compounds had some acaricidal activity, a synthesis program was initiated in Crompton Co. Research in 1990. From among several hundred carbazate derivatives synthesized and evaluated for acaricidal activity the methoxy-biphenyl-substituted carbazate (bifenazate. Fig. 30.2.1, Table 30.2.1) was selected for development [3]. 

After the discovery that ortho-biphenyl substituted hydrazide compounds [5] had acaricidal activity in the pesticide discovery screen (Table 30.2.3) several hundred - structurally diverse - biphenyl-substituted carbazate analogs were synthesized, and, in an optimization process using a bioassay with the two spotted spider mite (Tetranychus urticae Koch), isopropyl-2-(4-methoxy[l,l -biphenyl]-3-yl) hydrazine carboxylate (bifenazate) [3, 8] was identified as the most advantageous compound. 

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