Description
Imazapic is a selective pre- and post-emergent herbicide. It has a high aqueous solubility, is volatile and, based on its chemical properties, is moderately mobile and may leach to groundwater. It may be persistent in soil systems but usually degrades quickly in aquatic systems via photolysis. It has a low mammalian toxicity and has a high potential for bioaccumulation. It has a low level of toxicity to birds but is more toxic to aquatic life and honeybees.
Uses
Imazapic is registered throughout the world for use
in peanuts, rangeland, sugarcane, and imidazolinoneresistant
canola (12). A nonionic surfactant or oil adjuvant
is required for maximum activity.
Uses
Imazapic can be used in analytical and biological studies of residue analysis and determination of imidazolinone herbicides in sunflower and soil by GC-MS.
Definition
ChEBI: 5-methyl-2-[4-methyl-5-oxo-4-(propan-2-yl)-4,5-dihydro-1H-imidazol-2-yl]pyridine-3-carboxylic acid is a pyridinemonocarboxylic acid that is 5-methylpyridine-3-carboxylic acid which is substituted at position 2 by a 4,5-dihydro-imidazol-2-yl group, which in turn is substituted at positions 4, 4, and 5 by isopropyl, methyl, and oxo groups, respectively. It is a pyridinemonocarboxylic acid, an imidazolone, a member of imidazolines and a member of methylpyridines.
Production Methods
Imazapic is synthesised through a multi-step chemical process involving the construction of its imidazolinone core and pyridinecarboxylic acid side chain. The production typically begins with the formation of the imidazolinone ring, which is achieved by cyclising precursors such as methyl isobutyrate and urea derivatives under controlled conditions. This intermediate is then coupled with a methyl-substituted pyridine compound through a condensation or acylation reaction to yield the final active ingredient.
Mechanism of action
Selective, systemic, contact and residual activity, inhibiting the production of amino acids necessary for cell division and growth. Inhibits plant amino acid synthesis - acetohydroxyacid synthase AHAS.
Pharmacology
Imazapic kills plants by inhibiting acetolactate synthase
(ALS) (I50 = 1 μM), which is the first common enzyme in
the biosynthesis of the branched chain amino acids, valine,
leucine, and isoleucine. Imazapic is rapidly absorbed
through the leaves of plants. Once it enters the plant,
imazapic translocates to the growing points and growth
ceases within 1 day after herbicide application followed by
chlorosis and then necrosis of the growing points. Total
plant death will occur within 2 to 3 weeks after treatment.
Environmental Fate
Imazapic is weakly to moderately adsorbed on sandy loam
and silt loam soils. The Freundlich adsorption coefficient
ranges from 0.17 to 2.99, (12). Because imazapic is a weak
acid and exists in different ionic states, soil pH has an effect
on soil binding properties. The anionic form predominates
at soil pH as low as 5.5, and this form binds weakly to soil. The neutral or molecular form is important at
soil pH from 4 to 6.5. This form binds to soil organic
matter and clay. The cationic form is important at pH
less than 4. Because the soil is a heterogeneous mixture of acid and base chemical groups, there may be sites within
a particular soil that are 2 to 3 pH units higher or lower
than the average pH. The cationic form will bind tightly to
the lower pH components. Because of these interactions,
small decreases in pH below 6 will result in large increases
in binding. The half-life of imazapic in the soil is 106 d.
Imazapic remains in the top 30 cm of the soil with low
leaching potential. The degradation route of imazapic in
the soil has not been determined.
Metabolism
Plant Metabolism. The selectivity of imazapic is due to
differential rates and routes of metabolism in tolerant
crops versus susceptible weeds(10). Imazapic
has excellent selectivity in peanuts, but is not selective in
soybeans. The difference in the tolerance of these two
legumes is due to the different routes of metabolism
of imazapic in the two crops. The primary metabolite
in soybeans is an imidazopyrrolo-pyridine derivative,
whereas in peanuts, the primary metabolite is the
glucose conjugate of hydroxy-imazapic. Although the
imidazopyrrolo-pyridine derivative formed in soybean is
immobile and is not an inhibitor of acetolactate synthase,
the rate of degradation of imazapic in soybeans is not rapid
enough for selectivity (10). In imidazolinone-resistant
crops, the primary mechanism of selectivity is due to
an altered acetolactate synthase that is not inhibited by
the imazapic (11).
Animal Metabolism (12). Metabolism studies in the rat
showed that imazapic is rapidly excreted in the urine.
There was no accumulation of imazapic or any of its
derivatives in the liver, kidney, muscle, fat, or blood.
Toxicity evaluation
Imazapic has shown no mutagenic or genotoxic activity in
the Ames assay, mammalian cell gene mutation assay, in
vitro chromosome aberration assay, in vitro unscheduled
DNA synthesis (URS) assay, or the in vivo dominant lethal
assay inmale rats. The acute toxicity and effects on wildlife
and soil microflora of imazapic are shown in Table 6. This
herbicide also has a low potential for bioaccumulation
in fish.
