Isolation, characterisation and synthesis of insecticidal natural products of the Myrtaceae family

New insecticidal natural products are required to find compounds with higher intrinsic activities to lower field application rates, and with novel modes of action to combat insect pest species which have developed resistance to current commercial insecticides. Using a taxonomic approach, studies on plants of the Myrtaceae family led to the isolation and characterisation of a range of insecticidal natural products 1 - 9 (figure 1). These compounds are all structurally related as they contain a tetramethylcyclohexenedione group, attached to either a terpene or a phloroglucinol moiety. Seven of the nine compounds (1 - 6, 9) are novel. For compounds 7 and 8, no synthesis had been previously reported. The compounds are active against a range of insect species, although in general they are less active than commercial natural products. Further tests show some of the compounds are potent antifeedants. Synthesis of seven of the nine natural products (1 - 5, 7, 8) by short, convergent, stereospecific and high yielding routes was achieved. The synthetic routes were devised to mimic the postulated biosynthesis of the compounds. Reaction of syncarpic acid, an aldehyde and pyrrollidine formed a Mannich base, which on elimination gave a key alkylidene intennediate. This key intermediate was reacted, with either terpenes in Diels-Alder reactions or with phloroglucinols in aromatic alkylation reactions, to synthesise seven of the natural products

The pyrethrins and related compounds. Part XXXVIII. Optimisation of insecticidal activity in 3-[(alkoxyimino)methyl]-4-fluorobenzyl esters

Optimisation of activity in 3-[(alkoxyimino)methylbenzyl] esters has been investigated by introducing an alpha-cyano group and a fluorine atom in position 4 of the benzylic moiety in conjunction with varying the length and nature of the side chain. Of the five side-chain variations investigated, the 3-methoxyiminomethyl was more effective than others. Introduction of fluorine in position 4 of the benzylic moiety generally increased activity, particularly against mustard beetles, as in previous instances. Surprisingly, the effect on insecticidal activity of introducing an alpha-CN group ranged from positive to negative depending upon the nature of the alkoxyimino substituent, an effect not observed previously. The most effective esters were derived from alpha-cyano-4-fluoro-3-[(methoxyimino)methyl]benzyl alcohol, which was synthesised from 2-{4-fluoro-3-[(hydroxyimino)methyl]phenyl}-1,3-dioxolane

The pyrethrins and related compounds. Part XLI. Structure-activity relationships in non-ester pyrethroids against resistant strains of housefly (Musca domestica L.)

A series of pyrethroids, related to NRDC 200 and etofenprox (MTI500) in which the central region is represented by a non-ester link, have been tested against one susceptible and two resistant strains (kdr and super-kdr) of houseflies (Musca domestica L.). A range of structural variations in the central region have been examined. Resistance factors mostly fell within narrow ranges for both resistant strains i.e. 10-50-fold resistance against kdr and 50-150-fold against super-kdr; thus no correlation of resistance with structural features was detectable for this region. Other changes examined were the substituent on the phenyl ring in the 'acid' component and the bridging group in the 'alcohol' component where small variations in response were observed. Examination of the effect of varying the 'alcohol' side chain was limited by lack of active analogues