Propesticides

Abstract

For most pesticides, the chemically intact active ingredient of the marketed formulation is responsible for the biological activity at the molecular level. In some cases, however, the actual substance responsible for the desired effect is a chemically transformed product of the pesticide that was applied in the field. Such transformations are activation processes usually involving enzymes characteristic to the target organism, but the conversion can occur in the environment and by nonenzymatic processes. The expected biological activity is typically observable only in studies with whole organisms or in the field. The increase in selective toxicity for the target and nontarget organisms results from differential uptake, translocation, and metabolism of such pesticide precursors or propesticides. Selectivity, thus, increased safety, of neurotoxic insecticides can be achieved by incorporation of specific sulfur functionalities into the parent compound. Differential phytotoxicity of several classes of herbicides is based on selective oxidative and hydrolytic degradations in various plants. Hydrolysis and reduction are involved in the bioactivation of several profungicides. Bioactivation processes are also important for some organic and inorganic rodenticides. Although in many cases the propesticide nature of a compound was discovered during structure optimization and metabolism studies, there are several examples where incorporation of metabolically labile moieties into an insufficiently selective lead compound was crucial for commercial development.

Propesticides and their use as agrochemicals

“…For more than four decades, the selectivity of agrochemicals has been one of the significant topics of research and development . With increasing knowledge of the biochemistry and genetics of major pest insects, weeds and agricultural pathogens, the search for selectivity is an important part of pesticide development and can be achieved by appropriate structural modifications of the active ingredient . The benefits to be derived in overcoming development barriers and issues by propesticide concepts in crop protection have been known for more than a half century and can be demonstrated with examples coming from different areas of agrochemical research (Fig.…”

“…From the proinsecticide malathion (X = S; R = Et), the bioactive metabolite malaoxon (X = O; R = Et) is formed in significant amounts in situ only in insects via cytochrome P450 monooxygenase oxidative desulfuration (P = S into P = O) (Table ) …”

“…sunlight‐mediated reaction; see Section 2.1; activation type c) by oxidative desulfurisation into the insecticidally active carbodiimide derivative (Fig. ) …”

“…Physicochemical factors of the active ingredient such as differential uptake by and translocation within target and non‐target species can contribute to disparate biological activities. In order to improve the agrochemical profile of pesticides, the propesticide approach has been used in agrochemistery for quite a long time …”

The systemic effects of juvenoids on the red firebug Pyrrhocoris apterus and on the pea aphid Acyrthosiphon pisum with data on life table response

“…At present, the juvenogens, together with sulfenylated, sulfinylated and sulfonylated derivatives of fenoxycarb, are classified as projuvenoids and as members of the propesticide group generally 22, 23…”