Cartap

A few of the properties of cartap, nicotine, and the neonicotinoids are taken from The Pesticide Manual (Tomlin, 2000) and are given in Table 6.2 together with some other insecticides. 

The neonicotinoids have very low fish toxicity, are not adsorbed through mammalian skin, and are not irritating or allergenic in the tests carried out so far. The pyrethroids (and DDT group) have a negative temperature correlation these insecticides are more active in warm weather. 

Cartap is also an important insecticide acting at the nicotinic acetylcholine receptor site. It causes insects to stop feeding, is systemic, and has a low mammalian toxicity. It should therefore be a perfect insecticide. Cartap is not toxic per se, but is biologically converted to the cholinergic agonist nereistoxin, described later. 

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In searching for other proinsecticides of nereistoxin it must be kept in mind that the compound must possess labile groups bonded to the thiolsulfur atoms so that nereistoxin may be formed readily. Cartap and bensultap represent two types of compounds which may be transformed into nereistoxin by two different processes. A plausible mechanism for cartap is split of the S-C(O) bond by attack of a nucleophile, e.g. water, on the carbonyl carbon atoms, generating the 2-dimethylaminopropanedithiol which is then oxidized to nereistoxin. 

A recently introduced insecticide from the nitromethylene group, imidacloprid (Figure 3.6), has been shown to work in exactly the same way as nicotine and cartap but is of more interest commercially because... 

The tobacco alkaloid nicotine (96) (B-67MI10702) is insecticidal by virtue of its action on the acetylcholine receptor. It was used widely as an aphicide, especially as a fumigant. Another natural product thought to act on the same receptor is the 1,2-dithiolane nereistoxin (97) (B-72MI10703), isolated from the marine annelid Lumbriconereis heteropoda. The active form has been shown to be the ring opened dithiol (98), and the protected form of it, cartap (99), is sold as a rice insecticide. The 1,2,3-trithiane thiocyclam (100) (72SAP7007824) is also active, presumably because of metabolic conversion to (98). 

Carbosulfan carbamate, benzofuran Carboxin oxathiin, amide Cartap thiocarbamate CDAA see Allidochlor CJiinomethionat dithiin, heterocyclic nitrogen, quinoxaline... 

Dichloro propyl benzoate penconazole 1.3 Dichloro propyl dimethylamine cartap... 

The powerful action of some natural products on the central nervous system may suggest their potential value in insect control. If their mammalian toxicity can be reduced by structural modification they may be useful insecticides. Cartap, a rice insecticide, is a bisthiocarbamate. Its structure was based on that of the natural product, nereistoxln, a neurotoxin isolated from shellfish, and it is likely that an in vivo metabolic conversion of cartap to nereistoxln or related compound is responsible for its activity (11). 

The members of this class of insecticides are all analogs of nereistoxin, a natural toxin of the marine worm Lumbriconcrcis heteropoda. This class includes thiocyclam, cartap, and bensultap. 

Cartap hydrochloride is a broad-spectrum insecticide used for control of coleopterous, lepidopterous, and sucking insects, especially Colorado potato beetles, diamondback moths, rice stem borers, and thrips on rice and vegetables. Its oral LD30 in rats is 345 mg/kg. 

The nereistoxin analogs (cartap hydrochloride, bensultap, and thiocyclam) are all proinsecticides that must be activated in vivo to become nereistoxin (see Chapter 4, subsection 4.2.12.8 for nereistoxin structure). Nereistoxin acts as an antagonist of the acetylcholine receptor. Unlike with nicotine, insects treated with nereistoxin are rapidly immobilized without convulsive symptoms, possibly because nereistoxin does not induce depolarization (Corbett et al., 1984). 

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