A-Cyano-3-phenoxybenzyl alcohol

Synthetic pyrethroids now account for at least 30% of the world insecticide market and are rapidly replacing other agricultural chemicals for control of insect pests. Fenvalerate is one of the more widely used synthetic pyrethroid insecticides. It is derived from a combination of a-cyano-3-phenoxybenzyl alcohol and a-isopropyl phenylacetate ester. Technical fenvalerate is a mixture of four optical isomers, each occurring in equal amounts but with different efficacies against insect pests. Fenvalerate does not usually persist in the environment for >10 weeks, and it does not accumulate readily in the biosphere. Time for 50% loss (Tb 1/2) in fenvalerate-exposed amphibians, birds, and mammals was 6 to 14 h for reptiles, terrestrial insects, aquatic snails, and fish it was >14 h to <2 days and for various species of crop plants, it was 2 to 28 days. Fenvalerate degradation in water is due primarily to photoactivity, and in soils to microbial activity. Half-time persistence in nonbiological materials is variable, but may range up to 6 days in freshwater, 34 days in seawater, 6 weeks in estuarine sediments, and 9 weeks in soils. 

In general, these authorities agree that pyrethroids containing both a halogenated acid esterified with the a-cyano-3-phenoxybenzyl alcohol — such as fenvalerate, deltamethrin, and cyper-... 

Efficient biochemical processes were developed for the preparation of the two optically active pyrethroid insecticides by a combination of enzyme-catalyzed reactions and chemical transformations. These are based on the findings that a lipase from Arthrobacter species hydrolyzes the acetates of the two important secondary alcohols of synthetic pyrethroids with high enantioselectivity and reaction rate. The two alcohols are 4-hydroxy-3-methy1-2-(2 -propynyl)-2-cyclopentenone (HMPC) and a-cyano-3-phenoxybenzyl alcohol (CPBA). The enzyme gave optically pure (R)-HMPC or (S)-CPBA and the unhydrolyzed esters of their respective antipodes. 

The pyrethroids and DDT are by far the most important insecticides in this category. According to their modes of action, they are sometimes classified into two types. Type 1 includes DDT, its analogues, and pyrethroids without a cyano group, whereas type 2 compounds include the pyrethroids with an a-cyano-3-phenoxybenzyl alcohol. In mammals, they give slightly different symptoms by poisoning. Type 1 causes whole-body tremors, whereas type 2 causes salivation and choreoathetosis. Insects also show different symptoms, but not so distinct. 

A. Chemical structure of fenvalerate denoting two asymmetric carbon atoms ( ) the 2C position of the acid moiety, and the aC position of the a-cyano-3-phenoxybenzyl alcohol moiety. These two chiral centers, at the 2C and aC positions, yield a mixture of four stereoisomers, in approximately equal amounts, but with greatly different biological properties. 

CPBA is an alcohol moiety of highly potent synthetic pyrethroids such as fenvalerate ( a-cyano-3-phenoxybenzyl 2-(4-chloropheny1)-3-methyl-butyrate) or cyphenothrin (a-cyano-3-phenoxybenzyl chrysanthmate). 

Fenvalerate[(RS)-a-cyano-3-phenoxybenzyl (RS)-2-(4-chlorophenyl)iaovalerate] consists of four optical isomers due to the presence of two chiral carbons in the acid and alcohol moieties. Of the four isomers, one specific isomer ([2R,CXS]) was preferentially metabolized in mammals including rats and mice to a cholesterol ester which was formed by condensation of the acid moity with cholesterol. This conjugate does not seem to be produced via three known endogenous biosynthesis routes of cholesterol esters, but via transesterification mediated by microsomal... 

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