Insect molting

Figure 8.8 is an example of the use of solvent extraction to Isolate and concentrate the insect molting hormone eedysterone... 

Figure 6. Stereostructures of the Insect Molting Hormone, Ecdysterone, and a Plant Analog, Ponasterone A...

Dehydroxylation.1 Treatment of the photoecdysteroid muristerone (1) with ( ISi((H3)3 and Nal results in 14-desoxymuristerone (2). Unlike 14-desoxysteroids, which generally are less active than the 14a-hydroxy counterparts, 2 exhibits enhanced activity as an insect molting hormone. 

K. Nakanishi, Past and present studies with ponasterones, the first insect molting hormones from plants , Steroids, 1992, 57, 649-657. 

To date, interest in the ecdysteroids has focused primarily on their role in insect molting and metamorphosis and it is perhaps somewhat unfortunate that bioassays for ecdysteroid activity have been restricted almost exclusively to evaluating their effect on the molting process. It now appears probable that molting is just one of several important regulatory functions (e.g., embryogenesis, reproduction) performed by the ecdysteroids and that we are only just beginning to scratch the surface of an insect steroid system that is equally as complex as that in vertebrate species. 

The molting and other hormonal activities of the ecdysteroids are, of course, modulated by the titer of the insect juvenile hormone and the two materials typically function in close concert with one another in dictating insect molting and metamorphosis as well as in reproductive maturation (21). 

Figure 1. Stereostructures of the Insect molting hormone, ecdysterone and the phytoecdysone, ponasterone A.

Phytoecdysteroids, the well-known molting hormones are another important class of naturally occurring organic compounds isolated from Taxus species. Insect molt hormone activity associated with extracts of yew leaves has been reported by Takemoto et a/. (207). 

Table 8 lists phytoecdysteroids alongwith other common steroids isolated from the yew. These consist of a number of closely related active compounds (insect metamorphosis hormones) possessing insect molting activity. The most common of these phytoecdysteroids is ecdysterone (271). 

It is of interest that the structure of brassinolide resembles that of the insect molting hormone, ecdysone, which also is of plant origin. The structure of ecdysone is shown in Figure 1 and differs from the structure of brassinolide in that the orientation of the vicinal hydroxyl group at C-2 and C-3 is beta, the A/B junction is cis rather than trans as in the brassinolide structure and that ecdysone lacks the lactone oxygen in the B-ring. 

Physiological and Molecular Basis of Insect Molting Hormone Action... 

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