Boscalid

Inhibition of succinate dehydrogenase, the complex II in the mitochondrial respiration chain, has been known as a fungicidal mechanism of action since the first examples were marketed in the 1960s. The first compound in this class was carboxin, which had a narrow spectrum of useful biological activity, mainly on basidiomycetes and was used as a seed treatment. Many companies made analogues with the aim of expanding the range of fungal species controlled and boscalid was one of the first compounds successful in doing so. == Synthesis ==

The following three step synthesis of boscalid was disclosed in patents filed by BASF in 1995. : The aminobiphenyl required for reaction with the acid chloride of 2-chloronicotinic acid is prepared in two steps. The first is a palladium-catalysed Suzuki reaction with 2-chloro-1-nitrobenzene and 4-chloro-phenylboronic acid, followed by hydrogenation of the nitro group. As the final is product used nearly worldwide at the multi-tonne scale, considerable efforts have been made to improve yields. == Mechanism of action ==

Succinate dehydrogenase inhibitors (SDHI) of this type act by binding at the quinone reduction site of the enzyme complex, preventing ubiquinone from doing so. As a consequence, the tricarboxylic acid cycle and electron transport chain cannot function. == Usage ==

Boscalid has fungicidal effects against a wide range of crop pests. These include Alternaria species, grey mold (Botrytis cinerea), white mold (Sclerotinia sclerotiorum), and powdery mildew (Uncinula necator). As a result, it is used in the production of fruits, soybeans and vegetables. Global sales in 2014 were estimated at $390 million. The compound lacks full control of important cereal crop diseases, especially Zymoseptoria tritici. == Human safety ==

Boscalid has low acute toxicity: == Environmental effects ==

The compound is very persistent in field conditions and its environmental fate and consequent ecotoxicology have been reviewed. == Resistance management ==

Fungal populations have the ability to develop resistance to SDHI inhibitors. This potential can be mitigated by careful management. Reports of individual pest species becoming resistant The risks of resistance developing can be reduced by using a mixture of two or more fungicides which each have activity on relevant pests but with unrelated mechanisms of action. FRAC assigns fungicides into classes so as to facilitate this. ==Brands==

Boscalid is the ISO common name for the active ingredient which is formulated into the branded product sold to end-users. It was also known as nicobifen. Endura and Emerald are the brand names first used by BASF's formulations but the compound has subsequently been sold under a range of product names. == References ==