Isoprothiolane

The Uses of Isoprothiolane

Isoprothiolane is a dithiolane pesticide. Isoprothiolane is commonly used in agriculture as a fungicide to control planthoppers and blast disease in rice plants.

The Uses of Isoprothiolane

Isoprothiolane is a fungicide that is used to control rice blast (Pyriculuriu aryzae), rice stem rot and Fusarium leaf spot on rice. It also reduces the plant-hopper population on rice.

Definition

ChEBI: Isoprothiolane is a malonate ester that is diisopropyl malonate in which the two methylene hydrogens at position 2 are replaced by a 1,3-dithiolan-2-ylidene group. An insecticide and fungicide used to control a range of diseases including Pyricularia oryzae, Helminthosporium sigmoideum and Fusarium nivale. It has a role as an insecticide, an environmental contaminant, a phospholipid biosynthesis inhibitor and an antifungal agrochemical. It is a malonate ester, a member of dithiolanes and an isopropyl ester. It is functionally related to a malonic acid. It derives from a hydride of a 1,3-dithiolane.

Hazard

Moderately toxic by ingestion.

Metabolic pathway

Isoprothiolane is easily oxidized by rat liver 9000 g supernatant to produce its racemic sulfoxide in this process, NADPH is an effective cofactor but NADH is not. The liver microsomes, however, preferentially form its (?+)-isomer in an enantiomeric excess of 38-43%. The sulfoxidation of isoprothiolane by rice plants proceeds too slowly to determine the metabolites. Both isoprothiolane (+?)- and (-)- sulfoxides undergo rapid racemization by rat cytosol (105 000 g supernatant) or rice plants, accompanied with reduction to isoprothiolane.

Degradation

Half-lives of isoprothiolane in river water were greater than 50 days (Hayakawa et. al., 1992). The compound is decomposed slowly in deionised water under UV light or sunlight. In rice paddy water, photodegradation was greatly accelerated by the presence of natural organic constituents (Chou and Eto, 1980; Eto et al., 1979). Isoprothiolane was placed on a silica gel TLC plate and irradiated at 10 cm distance with a 10 W lamp emitting mainly at 254 nm. Isoprothiolane photodegraded rapidly (half-life about 3 hours). Five products were detected. Proposed pathways of photodegradation are shown in Scheme 1 and involved cleavage of the dithiolane ring, ester hydrolysis, decarboxylation and the formation of dimeric heterocyclic compounds. The identities of oxalic acid (2), dithiolanylidenemalonic acid (3), dithiolanylideneacetic acid (4), 2,4- bis[bis(isopropoxycarbonyl)methylene]-1,3-dithietane (5), 3,5-bis[bis(isopropoxycarbonyl) methylene]-1,2,4-trithiolane (6) and elemental sulfur were confirmed. Isoprothiolane degraded more rapidly on sand than on a glass plate (Chou and Eto, 1980).