Bicyclopyrone

Bicyclopyrone is a selective herbicide developed for the control of broadleaf weeds and perennial grasses in crops such as corn, wheat, barley, and sugarcane. It acts pre- and post-emergence.

Common name (ISO): Bicyclopyrone

Synonyms: BIR (internal development code), SYN 425

Gross formula: C19H20F3NO5

Number CAS: 352010-68-5

Chemical class: triketone, belonging to the subclass of 4-hydroxyphenylpyruvate dioxygenase (HPPD) inhibitors, classified in Group F2 by the HRAC (Herbicide Resistance Action Committee).

Development history: Its development dates back to the 1970s, with roots in the discovery of natural HPPD inhibitors. In 1977, scientists at Stauffer Chemical observed that few weeds grew under the plant. Callistemon citrinus (bottle plant), due to leptospermone, a natural compound that causes bleaching symptoms in weeds. This led to a 1980 patent on natural triketones.

Regardless, in 1982, researchers at Stauffer accidentally synthesized a triketone (compound 4) during studies of acetyl-CoA carboxylase inhibitors, which directed efforts towards the optimization of benzocyclohexanediones, with the first herbicide patent in this class filed in 1983. In the 1980s, companies such as Ciba-Geigy, ICI and Stauffer explored heterocyclic nicotinoic analogs.

A key breakthrough occurred in the early 2000s, following work by Okada et al., who generated trifluoromethyl 2,4-disubstituted nicotinoic acid derivatives, leading to the first nicotinoic HPPD inhibitor in 2000 (patent WO 2000/015615). Optimization focused on corn selectivity by introducing metabolic weak points into the molecule. The compound with the 2-methoxy-ethoxymethyl substituent (initially SYN 425) was selected for development, receiving the ISO name bicyclopyrone in 2009.

Mode of action: Bicyclopyrone inhibits the enzyme 4-hydroxyphenylpyruvate dioxygenase (HPPD), essential in the biosynthetic pathway of carotenoids and tocopherols. This disrupts chlorophyll's protection against photodegradation, leading to chlorophyll destruction, plant bleaching, and subsequent necrosis. It is selective for crops such as corn, which rapidly metabolize the compound into inactive forms, while weeds are more sensitive. It shares a mode of action with mesotrione, isoxaflutole, and topramezone (Group 27/WSSA or F2/HRAC).

Patent numbers: WO 2000/015615, WO 2005/105717, WO 2013/180309 and others.