Juvenile hormones examples

Stable in acidic, neutral and basic aqueous solutions Pale yellowish solid, faint characteristic odor Flash point 119°C (Pensky-Martens closed tester) Pyriproxyfen is an insect growth regulator which acts both as an ovacide and as an inhibitor of development (juvenile hormone mimic) against white flies, scale, and psylla. The specificity of pyriproxyfen, and its low mammalian toxicity, allow for some variation in application timing. For example, the lack of toxicity to bees allows pyriproxyfen to be applied during bloom on apple trees, and its low mammalian toxicity allows for a very short pre-harvest interval on citrus The residue definition is for pyriproxyfen alone... 

Particularly useful is the introduction of a sulphur atom as bridging element. One of the most classical examples, in which the sulphur atom introduces the necessary "rigidity" in order to ensure a complete acyclic diastereoselection of polyolefins, is the synthesis of the Cig-juvenile hormone [1] (Scheme 9.1). 

Caryophyllenes, as an example of two naturally occurring isomeric sesquiterpenes containing a medium-sized ring, in which the success of the total syntheses lies in the stereoselective control of a chiral centre, in a common synthetic key intermediate, which governs the configuration (JE or Z) of the double bonds present in each one of the two isomers. In this context, a brief reference to Cecropia Juvenile Hormone synthesis by the Syntex group, as well as to Johnson s cationic cyclisation of unsaturated polyolefins to fused polycyclic compounds, is made. 

For Instance, many terpene derivatives mimic insect hormone actioa Juvabione (15) is the classical example of a juvenile hormone (JH) mimic that prevents egg maturation in Pyrrhocoris bugs. Aromatic terpene ethers (16), methylene dloxyphenyl terpene ethers (17), and other farnesyl derivatives also have JH activity and the latter ones (18) also cause sterility in Pyrrhocoris. For the most part JH active terpenes are among the sesquiterpenes but several monoterpenes also have insect sterilizing effects (19. 20). The acyclic monoterpene cltral reduces the fertility of rats by causing follicular degeneration (21). 

A number of compounds important to animal physiology have been identified as isoprenoid compounds. Notable examples are vitamin A, retinal (Section 28-7), and squalene (Table 30-1). Also, terpene hydrocarbons and oxygenated terpenes have been isolated from insects and, like famesol, show hormonal and pheromonal activity. As one example, the juvenile hormone isolated from Cecropia silk moths has the structure shown in 3 ... 

Examples of applications of this strategy are given below, a) The unsymmetrical ketone juvabione, a molecule which possesses high juvenile hormone activity, has been synthesized from two readily-available alkenes (Equation B3.9). (The chiral centre present in the first alkene that reacts with thexylborane does not exert any control over which face of the... 

Conversion of a terminal alkyne to its alkynylsilane prevents loss of the relatively acidic terminal hydrogen (pKa of ethyne c. 25) during later synthetic steps. For example, the terminal hydrogen of propyne was masked whilst its propargylic anion was used in a synthesis of Cecropia juvenile hormone, a chemical which plays ail important role in insect development (Figure Si5.2). 

Fluoroketone analogues are also inhibitors of esterases. For example, the difluoro-ketone analogue 36 of sn-glycerol phospholipids is a potent competitive inhibitor of phospholipase A27 while the trifluoromethyl ketone 37 analogue of an insect juvenile hormone 38 is a potent and selective inhibitor of juvenile hormone esterase78. 

As an example, let s take a molecule known as juvenile hormone. It is a compound that prevents several species of insects from maturing and can be used as a means of controlling insect pests. Only very small amounts of the naturally occurring compound can be isolated, but it can instead be made in the lab... 

In the next examples, formaldehyde makes a primary alcohol from two deprotonated alkynes. The second reaction here (for which we have shown organolithium formation, reaction, and quench simply as a series of three consecutive reagents) forms one of the last steps of the synthesis of Cecropia juvenile hormone whose structure you met right at the beginning of the chapter. 

An example of increasing the efficiency by decreasing the flow rate is shown on a pellicular silica gel column in Figure 6-5a. (This figure was shown previously as Fig. 4-15.) This is the separation of a cis and trans isomer of synthetically prepared juvenile hormone mimics which are separated in the normal-phase mode. (Juvenile hormone mimics are used to stop or retard the maturation process of insects and, hopefully, control the insect population.) The presence of benzene is probably residue from the reaction solvent. At 2 mL/min the first peak corresponds to 5000 plates and the last peak corresponds to 2300 plates. By lowering the flow rate to 0.5 mL/min, there is a corresponding increase in efficiency in the separation. With the additional efficiency at the slower flow rate, it is possible to observe a small, additional shoulder (peak) under the first peak. However this was done at the expense of increased time (a factor of 4). 

The existence of a cytosolic epoxide hydrolase was first indicated by its ability to hydrolyze analogs of insect juvenile hormone not readily hydrolyzed by microsomal epoxide hydrolase. Subsequent studies demonstrated a unique cytosolic enzyme catalytically and structurally distinct from the microsomal enzyme. It appears probable that the cytosolic enzyme is peroxisomal in origin. Both enzymes are broadly nonspecific and have many substrates in common. It is clear, however, that many substrates hydrolyzed well by cytosolic epoxide hydrolase are hydrolyzed poorly by microsomal epoxide hydrolase and vice versa. For example, l-(4 -ethylphenoxy)-3,7-dimethy I -6,7-epoxy-//7//i,v-2-octene, a substituted geranyl epoxide insect juvenile hormone mimic, is hydrolyzed 10 times more rapidly by the cytosolic enzyme than by the microsomal one. In any series, such as the substituted styrene oxides, the trans configuration is hydrolyzed more rapidly by the cytosolic epoxide hydrolase than is the cis isomer. At the same time, it should remembered that in this and other series,... 

A good example of substrate specificity in enzyme action is the metabolism of juvenile hormone (JH) analogs by insects. In a series of experiments summarized in Table 9.7 to 9.10, the activity of esterases and microsomal monooxygenases from three dipterans against 12... 

Induction of carboxylesterases and epoxide hydroloases would also affect the toxicity of insecticides. For example, host plant induction of 1-naphthyl acetate esterase would decrease the toxicity of certain insecticides containing an ester linkage such as organo-phosphates, pyrethroids, and some juvenile hormone analogs and, possibly, carbamates. 

Knowledge and understanding of how hormones regulate cellular processes in mosquitoes may be of great importance for controlling their reproduction. Conceivably, new types of insecticides may be developed that interfere with hormonal regulation, as for example, does the juvenile hormone analog (methoprene). 

An instructive example of selective ozonolysis can be found in Corey s synthesis of the juvenile hormone 475 (Scheme 2.152). The main challenge in the preparation of 475 relates to the creation of a (Z)-configuration in the epoxide moiety. In the described synthesis this problem was solved by a... 

The central problem in the synthesis of acyclic polyunsaturated compounds (for example, many pheromones) is the construction of an aliphatic chain possessing double bonds of the required configuration in specified positions. The strategy of synthesis in this area could be based either at the identification of unsaturated synthons with double bonds in the needed configuration (as was done in the synthesis of the juvenile hormone, see Section 2.8), or the employment of stereoselective reactions in the process of chain construction, such as carbometallation of alkynes (see Section 2.3.3). 

The synthesis of Cjg juvenile hormone, the molecule that opened Chapter 20, is another example. The last steps of the synthesis are outlined in Figure 20.6. 

Although juvenile hormone itself is too unstable in light and too expensive to synthesize for use in controlling insect populations, related compounds, called juvenile hormone mimics, have been used effectively. The best known example is called methoprene, sold under such trade... 

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