Juvenile hormones chiral

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. 

It is worth noting that in this synthesis of Cecropia juvenile hormone a strategy which is the reverse of the one developed by W.S. Johnson [8] for the synthesis of steroids and other fused polycyclic systems bearing cyclohexane rings is used. This method involves a non-enzymatic cyclisation of a polyunsaturated intermediate with the appropriate stereochemistry (all-trans) (Scheme 13.3.6). Such cyclisation occurs with a really amazing stereoselectivity and several new chiral centres with the correct stereochemistry are created in one single step ... 

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... 

Although the past three years have witnessed many ingenious syntheses of the two insect juvenile hormones, the preparation of the naturally-occurring dextrorotatory Cl8 hormone (cis-epoxide) has only recently been achieved. Indeed, in two independent studies, both enantiomeric pairs of the cis- and trans-epoxides. have been prepared and it has been firmly established that the two chiral centres have the 10R,11S configurations in the naturally-occurring material. Findlay et al. have now published full details of their previously announced synthesis of the two juvenile hormones and other double-bond isomers. In an earlier synthesis of the C18 hormone, Corey et al. used the dienol (30 R = Et) as a key intermediate and now they have described two new stereospecific routes to this compound (Scheme 2). In the first synthesis the lactone (27) was converted into the hydroxy-olefin (28) by hydrolysis, esterification, tosylation, and lithium... 

In addition to pheromones (vide infra), we were interested in juvenile hormones (JHs), and synthesized ( )-juvabione [12] and (-t-)-juvabione [13-14]. JH mimics were later found to be useful as practical insect growth regulators (IGRs). We synthesized ( )-JH I [15], (-i-)-JH I [16] and unnatural (-)-JH I [17]. The naturally occurring (-i-)-JH I was 1.2 x lO times more active than (-)-JH I. Chirality plays an important role at JH receptor sites. 

I learned three things by synthesizing these bioactive natural products related to pesticides. Perhaps every pesticide chemist is familiar with the following points. First of all, natural products are often too complicated and fragile to be used as practical pesticides. Nevertheless, they can be the prototypes or lead compounds of new pesticides as in the cases of pyrethroids and juvenile hormones. Secondly, chirality plays a key role in the binding of these bioactive molecules at the active site. Thirdly, bioactivity observed in vitro or in vivo in lab tests may not always be reproduced in the field. 

Brassinosteroids, Brevicomin, Chirality, Enantioselective Synthesis, Gibberellins, Glycinoeclepin A, Juvenile Hormones, Minamata Disease, Pheromones, Phytoalexins, Strigolactones... 

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