PYROQUILON

The Uses of PYROQUILON

Pyroquilon is used for the control of blast (Pyricularia oryzae) in rice.

Definition

ChEBI: A pyrroloquinoline that is 1,2,5,6-tetrahydro-4H-pyrrolo[3,2,1-ij]quinoline in which the hydrogens at position 4 are replaced by an oxo group. A fungicide used to control rice blast, it is not approved wof use within the Eur pean Union.

Metabolic pathway

The fate of pyroquilon in rice and rats has been reported. Given the metabolic stability of cyclic amides, there are few options, other than hydroxylation, open for the metabolism of the compound. Its biotransformation involves initial hydroxylation at three sites in the molecule, followed by ring-opening, dehydration and further oxidation affording a somewhat complex picture. A study in rats revealed most of these metabolites but with some further metabolic degradation. The usual differences in conjugation were seen with mainly glucoside formation in plants and glucuronide and sulfate formation in animals.

Metabolism

Animals: Rapidly metabolized and eliminated via urine and feces. Residues in tissues were generally low, and there was no evidence for accumulation or retention of pyroquilon or its metabolites. Plants: Major metabolites in rice grain were 3,4-dihydro-4-hydroxy-2- oxoquinoline-8-acetic acid and two other acetic acid derivatives. Soil/Environment: DT₅₀ (silty soil) 2, (sandy loam) 18 w. Kd 1.3–42 μg/g soil, little to moderately mobile. Photolysis in water, DT₅₀ 10 d.

Degradation

Pyroquilon is stable to hydrolysis over a very wide pH range. It is degraded under conditions of aqueous photolysis with a DT₅₀ of 10 days (PM). Details are not available.

Toxicity evaluation

Mammalian toxicology. Oral: Acute oral LD₅₀ for rats 321, mice 581 mg/kg. Skin and eye: Acute percutaneous LD₅₀ for rats >3100 mg/kg. Not a skin irritant, minimal eye irritant (rabbits). Not a skin sensitiser (guinea pigs). Inhalation LC50 (4 h) for rats >5.1 mg/l air. NOEL: (2 yr) for rats 22.5, mice 1.5 mg/kg b.w. daily; (1 yr) for dogs 60.5 mg/kg b.w. daily. ADI: 0.015mg/kg b.w. Other: Not teratogenic, not mutagenic, not oncogenic. Toxicity class: WHO (a.i.) II; EPA (formulation) II RC risk R22. Ecotoxicology. Birds: LC50 (8 d) for Japanese quail 794, chickens 431 mg/kg. LC50 (8 d) for Japanese quail >10000 mg/kg. Fish LC50 (96 h) for catfish 21, rainbow trout 13, perch 20, guppy 30 mg/l. Bees: Practically nontoxic to honeybees; LD₅₀ (oral) > 20, (contact) > 1000 mg/bee. Daphnia LC50 (48 h) > 60 mg/L. Algae: No effect on Scenedemus acutus.