Pyrethrates

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. 

Chrysanthemum dicarboxylic acid or pyrethric acid may exist in eight stereoisomers, owing to the trans or cis configuration on the side chain of the double bond as well as that of the cyclopropane. The natural acid has been shown to be the trans-trans acid. As in the case of the chrysanthemum monocarboxylic acid, the naturally occurring configuration is more insecticidally active than the racemic form or any of the three isomers synthesized. 

Figure 4. Infrared spectrum of methyl-transrpyrethrate Prepared from pyrethric acid isolated from hydrolysis mixture of pyrethrum concentrate. Pure ester isolated by gas chromatography...

METHYL CHRYSANTHEMATE DIMETHYL PYRETHRATE mixture contribute to the total monocarboxylic and dicarboxylic acids found. 

Many semi-synthetic esters, e.g. bioresmethrin, permethrin, and phenothrin, have been produced and these have increased toxicity towards insects and also extended lifetimes. All such esters retain a high proportion of the natural chrysanthemic acid or pyrethric acid structure. 

Pyrethrum refers to the oleoresin extracted from the dried flowers of Tanacetum cinerariaefolium (Asteraceae) and is the source of the pyrethrins, chrysanthemates and pyrethrates. Among the natural pyrethrins, those incorporating the alcohol pyrethrolone, namely pyrethrins 1 and II (Fig. 9), are the most abundant and account for most of the insecticidal activity. The pyrethrins are recommended for control of a wide range of insects and mites on fruit, vegetables, field crops, ornamentals, glasshouse crops and house plants, as well as in public health, stored products, animal houses and on domestic and farm animals. Pyrethrins are sold in a wide variety of formulations, under many different trade names by a large number of different manufacturers. 

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 ... 

ENT 7,543 PYRETHRIN PYRETHROLONE CHRYSANTHEMUM DICARBOXLIC ACID METHYL ESTER PYRETHROLONE ESTER of CHRYSANTHEMUMDICARBOXYLIC ACID MONOMETHYL ESTER (-f)-PYRETHRONYL (+)-PYRETHRATE PYRETRIN II... 

D1 (+)-fra/7s-Chrysanthemic acid D2 (+)-frans-Pyrethric acid D3 (1S,2S)-Fragranol D4Junionone... 

Environmental residues of pyrethroids and pyrethr-ins are degraded by hydrolysis, and pyrethrins by photolysis, and so do not accumulate in most ecosystems. The main environmental hazard associated with pyrethroid use is contamination of freshwater by acute run-off after use as an agricultural pesticide or ectoparisitide near to water, which can lead to death of aquatic invertebrates or fish (which have very limited pyrethroid detoxification capacity). 

Ueda, K.. and Matsui. M., Studies on chrysantemic acid. Part 20. Synthesis of four geometrical isomers of ( )-pyrethric acid. Agric. Biol. Chem., 34, 1119, 1970. 

Fitzsimmons and Fraser-Ried have converted the protected glycoside 289 into ( + )-(290) and (- )-pyrethric acid. The route is long, and the introduction of the cyclopropane in 289, using methyl diethylphosphonopropionate [(EtO)2POCHMeCOOMe] occurred in only 50% yield, but both optical isomers were made from the same intermediate. 

Researches on chrysanthemic acid and its derivatives are usually oriented to synthesising esters of trans-chrysanthemic acid, many of which are naturally occurring (and are, therefore, presumably biodegradable) insecticides. The synthesis of pyrethric acid or its mono-ester (65) from chrysanthemic acid has been carried out in two laboratories. Ueda and Matsui prepared all four... 

Pyrethric acid (18) and from this, by optical resolution, the pure (-l-)-isomer, forming the acid component of pyrethrin II (10), cinerin II (12) and jasmolin II (14), was prepared by Matsui and Yamada (1963) by the oxidation of ( )-chrysanthemic acid. 

The Chrysanthemum Extract comprise of a mixture oiester e.g., chrysanthemic and pyrethric acids alcohols e.g., cinerolone and pyrethrolone. As the esters are usually more prone to get hydrolyzed and oxidized, hence it must be stored in sealed light-proof containers in a cool place. 

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