The Unique Role of Halogen Substituents in the Design of Modern Crop Protection Compounds

Abstract

The past 30 years have witnessed a period of significant expansion in the use of halogenated compounds in the field of agrochemical research and development. In the search for a so-called “optimal product” in modern crop protection in terms of efficacy, environmental safety, user friendliness, and economic viability, the substitution of active ingredients with halogen atoms or halogen-containing substituents is an important tool. A number of these recently developed agrochemical candidates containing halogensubstituents represent novel classes of chemical compounds with new modes of action (MoA). However, the introduction of such halogen atoms or substituents into a molecule can lead to either an increase or a decrease in biological efficacy, depending on the MoA, the physico-chemical properties, target interaction or metabolic susceptibility and transformation of the compound. Despite modern design concepts it is still difficult to predict the sites in a molecule at which halogen substitution will result in optimal desired effects. Nonetheless, the technical availability of active ingredients containing halogens or halogen-substituted substituents has been greatly improved by an increase in access to new intermediates. This review describes comprehensively the successful utilization of halogens and their unique role in the design of modern agrochemicals, exemplified by various commercial products from Bayer CropScience coming from different agochemical areas.