Description
Isoxaflutole is a 4-benzoyl isoxazole molecule and is used
as a pre- and early post-emergence herbicide for the control
of a wide range of important broadleaf and grass weeds in
maize (Zea mays), both in Europe and in North America.
It is also registered for use in sugarcane in Central and
South America (2–4). It causes characteristic bleaching of
newly developed tissues of susceptible species followed by
growth cessation and necrosis. Marketed as Balance for
corn (maize) in the United States, and Merlin for corn in
Europe; and in sugarcane, it mixes well with metolachlor,
acetochlor, dimethenamid, and atrazine to complete the
weed spectrum and to reduce the application rates of the
latter compounds (2). Isoxaflutole also controls triazineresistant
weeds in the field (4).
Definition
ChEBI:Isoxaflutole is a member of the class of isoxazoles that is 1,2-oxazole substituted by a 2-(methanesulfonyl)-4-(trifluoromethyl)benzoyl group and a cyclopropyl group at positions 4 and 5, respectively. It is a 4-hydroxyphenylpyruvate dioxygenase inhibitor which is used as a herbicide for weed control in maize and sugarcane. It has a role as an EC 1.13.11.27 (4-hydroxyphenylpyruvate dioxygenase) inhibitor, a proherbicide and an agrochemical. It is a member of cyclopropanes, a member of isoxazoles, an aromatic ketone, a member of (trifluoromethyl)benzenes and a sulfone.
Pharmacology
Isoxaflutole is readily taken up by roots and foliar
tissues and then rapidly degraded to a diketonitrile derivative
(2-cyclopropyl-3-(2-mesyl-4-trifluoromethylphenyl)-
3-oxo propanenitrile) , which is translocated
throughout the plant via xylem and phloem (2,3,6,8). It
is this metabolite that inhibits HPPD (7), thereby depleting
the plastoquinone pools in developing leaves. Plastoquinone
is a cofactor in the desaturation of phytoene, levels
of which increase in bleached leaves, concomitant with
decreases in colored carotenoids (6). Although bleaching
is the primary symptom associated with HPPD inhibition,
subsequent growth suppression and necrosis are also
believed to be a consequence (8).
Isoxaflutole also degrades to the diketonitrile derivative
in the soil (3,8). The half-life of isoxaflutole in soil
is dependent on soil type, pH, and moisture, ranging
from 12 hours to 3 days under laboratory conditions (8).
The physicochemical properties of isoxaflutole and of
diketonitrile play an important role in both soil and
herbicidal activity and selectivity (8).
