Pyrethrins Pyrethrin

Pyrethroids consist of pyrethrum and its synthetic pyrethrum analogs called synthetic pyrethroids. Pyrethrum is a solvent extract of dried flowers of Chrysanthemum cinerariaefo-lium. The active ingredients of pyrethrum are called pyrethrins. Pyrethrins consist of four esters, namely, pyrethrins I and II and cinerins I and II, which comprise the combination of two different alcohols (pyrethrolone and cinerolone) and two different acids (chrysan-themic acid and pyrethric acid), as follows ... 

As mentioned earlier, pyrethrum is an extract from chrysanthemum flowers which contains a mixture of natural compounds including pyrethrins. Pyrethrin powder has been used for many years as an insecticide in domestic applications. Com-poimds having similar structures and properties have now been synthesized as pyrethroids which are cheaper than natural pyr-ethrums and more potent. They are even more effective in treating sea lice infestations on solomon and other sea water flsh. 

CAS 8003-34-7 EINECS/ELINCS 232-919-8 Synonyms Chyrsanthemum cinerareaefolium Insect powder Pyrethrin Pyrethrins ... 

Ecuador into the U.S. The active principals are pyrethrins I and II, cinerins I and II, and jasmolin I and II, collectively known as pyrethrins. Pyrethrins are used extensively in stock sprays, pet sprays, household sprays, aerosols, and food protection in warehouses. Pyrethrins are stable for long periods in water-based aerosols, in which modern emulsifiers are used. Dermatitis from natural pyrethrins usually occurs on parts of the body exposed to the spray. The substance is a moderately potent allergic sensitizer. Crossreactions occur among pyrethrum, chrysanthemum, shasta daisy, and ragweed oleo resin [31, 32]. Asthma and urticaria have also been reported as reactions to natural pyrethrin [33, 34]. In 1972, Mitchell et al. found that a sesquiterpene lactone, pyrethrosin, was the chief allergen in pyrethrin [35]. Contact dermatitis due to pyrethrum is usually mild, but bullous reactions have been reported [36]. In Denmark, positive patch-test reactions to pyrethrum were obtained in 1-2% of dermatitis patients [37]. 

Pyrethrum is comprised of the dried flowers of Chrysanthemum cinerariaefolium containing not less than 1% pyrethrins. Pyrethrin esters constitute a powerful degradable contact insecticide. They have a low order of systemic toxicity to man and produce no harmful residues on food crops. The flowers and extracts for pyrethrum are imported from Kenya and... 

Pyrethrins are a group of closely related, naturally occurring compounds that are the active insecticidal ingredient of pyrethmm and have been used for centuries. Pyrethmm, which has been used as a pesticide in commercial applications since the early nineteenth century, is extracted from the flowers of Chrysanthemum cinerariaefolium and Chrysanthemum cineum [1]. Most of the insecticides derived from plants traditionally have been considered safe for use on animals, and pyrethmm is an example of such material. There are six active insecticidal compounds that comprise the natural pyrethrins pyrethrin 1 and 11, cinerin 1 and 11, and... 

The six pyrethrins, Pyrethrin I, Jasmohn I, Cinerin I, Pyrethrin II, Jas-molin II, and Cinerin II were found to be present in the leaf extract of the Chrysanthemum cinerariaefolium seedlings. Pyrethrins are thought to act as defense mechanisms that prevent insects from feeding on the plant [27]. The pyrethrins repel insects and also paralyze flying insects, thereby exhibiting a knock-down effect. The active components occur to a small extent in all parts of the plant, but especially in the flower heads [28]. 

Piperonyl butoxide [51-03-6] is 5-[2-(2-butoxyethoxy)ethoxy]methyl-6-propyl-l,3-benzodioxole (11) d 1.04—1.07, vp 0.13 kPa at 25°C). The rat oral LD qS are 7500, 6150 mg/kg. Piperonyl butoxide is the synergist commonly used with natural pyrethrins in aerosol sprays. 

Pyrethroids from Chiysanthemic Acid. The unsaturated side chains of the aHethrolone alcohol moieties of the natural pyrethrins are readily epoxidized by microsomal oxidases and converted to diols, thus detoxifying the insecticides. Esterification of chrysanthemic acid (9), R = CH3, with substituted ben2yl alcohols produces usehil insecticides barthrin [70-43-9J, 2-chloro-3,4-methylenedioxyben2yl (+)-i7j ,/n7 j -chrysanthemate, and dimethrin [70-38-2] 2,4-dimethylben2yl (+)-i7j ,/n7 j -chrysanthemate. These have alimited spectmm of insecticidal activity but are of very low mammalian toxicity, ie, rat oralLD s >20,000 mg/kg. 

Sesamex [51-14-9] (Sesoxane) (30) is a synergist oflow toxicity, acute oral LD q (rat) = 2000 2270 mg/kg, for pyrethrins and allethrin. 6,7-Dihydroxy 4-methylcoumarin has been offered as an antioxidant for phenoHcs and polymers, and as an anthelmintic. 2,4,5-Trihydroxybutyrophenone has been available as an antioxidant and light stabilizer for polyolefins, waxes, and foods. Isoflavones, eg (31), have been patented as components of antioxidant compositions for foods and cosmetics (qv) (97). 

Many other compounds are presendy in use a 1993 database search showed 27 active ingredients in 212 products registered by the U.S. EPA for human use as repellents or feeding depressants, including octyl bicycloheptene dicarboxamide (A/-2-ethylhexylbicyclo[2.2.1]-5-hepten-2,3-dicarboxamide), dipropyl isocinchomeronate (2,5-pyridine dicarboxyhc acid, dipropyl ester), dimethyl phthalate, oil of citroneUa, cedarwood oil, pyrethrins, and pine tar oil (2). Repellent—toxicant or biting depressant systems are available which are reasonably comfortable for the user and can protect completely against a number of pests for an extended period of time (2). 

Another problem Hes in the overlap of repeUent—toxicant definition, in that many toxicants are known to have repeUent effects (43). Pyrethrins are... 

Pyrethrins are a group of naturally occurring insecticidal substances found in the flowers of various plants of the chrysanthemum family. The following is the structure of a typical pyrethrin, cinerin I (exclusive of stereochemistry) ... 

Alkyl phenols (HOC6H4CH2—), pyrethrin II (MW = 372) See benzoin isopropyl ether (MW = 254)... 

A review of the chemistry and biochemistry of pyre-thrum is presented based mainly on work done subsequent to 1945. The greatest advances in the chemistry of pyrethrum have occurred since the disclosure of the heterogeneity of pyrethroids. On the biological side, the most recent work has been made possible by the use of chromatographic column separation and gas chromatography separation of the four active components of pyrethrins. 

The great advance in the field of instrumentation, coupled with the discovery of the heterogeneity of the pyrethrolone radical, has advanced the knowledge of pyrethrum chemistry considerably beyond that known in 1945. LaForge and Barthel (24,25) have shown the structure of the active ingredients of pyrethrum, known collectively as pyrethrins, to be esters as represented by the structure shown in Table I. 

Recently a new constituent of pyrethrum extract was described by Godin et al. (9) jasmolin II, the cir-pent-2-enylrethronyl ester of pyrethric acid. Jasmolin II differs from pyrethrin II in that the terminal double bond of the alcoholic side chain is saturated. This constituent forms about 3% of the total pyrethrins. Jasmolin II is less toxic to the insects tested than a similar concentration of pyrethrins. The pyrethrum extract was 16 to 17 times as toxic as jasmolin II to Aedes aegypti and Fhaedon cochlearia adults, less than 17 times... 

Pyrethrins are esters and therefore may be discussed in terms of the chrysanthemumic or pyrethric moiety and the keto alcohol moiety. 

Godin et al. (10), working on the effect of insecticidal activity of pyrethrum flowers from fresh and dried flowers, showed that extracts from fresh flowers had little or no greater effect on pyrethroid content and insecticidal activity than extracts from dried flowers with drying temperatures up to 80 °C. However, some of all the pyrethrin was lost at 120°C. The principal loss was in pyrethin I and not pyrethin II. 

Pyrethrolone and cinerolone make up the keto alcohol moiety of the pyrethrins. Both of these keto alcohols have one asymmetric carbon at the 4-position and a double bond in the side chain which is capable of cis-trans isomerism in the 2-position. It is possible, therefore, to have four stereoisomers for each keto alcohol. Katsuda et al. (22) show that only the ( + ) form occurs in the natural esters. Elliott (8) has shown recently, by a new procedure developed to obtain pure ( + ) pyrethrolone, that the hitherto unidentified prye-throlone C is in reality pyrethrolone contaminated with thermally isomerized material. (+) Pyrethrolone forms a crystalline monohydrate from which the pure alcohol is obtained. The natural configurations of the keto alcohols in the esters are insecticidally more active, as is the case with the acid moiety. 

They indicated that this method might be advantageous for the partial separation of pyrethrins I and II on an industrial scale, thus tailoring pyrethrin extracts for specific uses depending upon the insect to be controlled. 

Sawicki et al. (33) prepared by reconstitution pure samples of pyrethrins I and II and cinerins I and II and compared the toxicity of these esters with the regular pyrethrum extract on houseflies 5 to 6 days old. 

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