Proherbicide

Proherbicides. Thio- and dithiocarbamates probably require metabolic activation prior to exerting their herbicidal effects. Sulfoxide metabolites of the -alkyl thiocarbamates are generally more potent herbicides than the parent compounds ( -5). The herbicidal action of these sulfoxides probably results from their carbamylating action for thiols, although the specific target site or receptor is not defined (23, 24). It is conceivable that the -chloroallyl thiocarbamate herbicides may act in the same way, since their sulfoxides are also potent carbamylating agents... 

As an alternative, diallate might be a proherbicide and 2-chloroacrolein the ultimate herbicide released on decomposition of diallate sulfoxide (8). 

The 1-Chloroalkyl carbonate (II), obtained through the reaction of 1-chioroalkyi chloroformate with glycerol carbonate was used for the preparation of a proherbicide derived from Acifluorfen (Ref. 77) [See scheme 67],... 

It is not known if m-tyrosine can be converted to l-DOPA by a cell-free extract of a species susceptible to m-tyrosine. If so, would the process be highly efficient in vivol Synthetic proherbicides, such as diclofop-methyl [11], that are inactive at the molecular target site are much more effective when applied to intact plants than the active molecule to which they are converted in vivo. This is due to superior cuticular and cellular uptake of the proherbicide. Some potent natural phytotoxins from microbial origin, such as hydantocidin and 2,5-anhydro-D-glucitol, are protoxins [170-171]. 

Metabolism of the proherbicide (i.e., a non-phytotoxic chemical that requires metabolic conversion to yield an active herbicide) FE, is an example of how Phase 1 and II metabolism, and use of a safener imparts selectivity between crop and weed species (Figure 1). FE is used to control many graminaceous weed species such as Avena fatua, Echinochloa crus-galli, Digitaria ischaemum, and Setaria glauca (40) in wheat which is moderately tolerant to this proherbicide. The primary basis for the selectivity of FE in grasses is due to differences in metabolism (40-42). FE is rapidly hydrolyzed to the herbicide fenoxaprop (F) in wheat, and in all the previously mentioned graminaceous weeds (4J). In wheat. 

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