Ecdysone

Cholesterol or other sterols available from the diet or gut microflora are converted to the active hormone 20-hydroxyecdysone ([3-ecdysone or ecdys-terone) through several oxidative steps involving CYP enzymes. The last step is oxidation of a-ecdysone to (J-ecdysone, which can occur in many tissues, such as in the organ called the fat body. 

Secretion of ecdysone starts the many biochemical processes that are necessary for the molting. The cells in the epidermis are stimulated to produce a new cuticle, and when ready, the insect will creep out of its old skin. The molecular mechanism of ecdysone has been studied in some detail. The molecular target of ecdysone and other ecdysteroids consists of at least two proteins, the ecdysteroid receptor (EcR) and ultraspiracle (USP). Both EcR and USP are members of the steroid hormone receptor superfamily with characteristic ligand-binding domains. An EcR-USP-ecdysteroid complex is formed, which activates several genes that code for transcription factors, i.e., proteins that activate or repress the activity of other genes, and the appropriate amounts of proteases and other enzymes necessary to degrade old structures and rebuild new ones are formed in a time-controlled sequence. 

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The stereocontroUed syntheses of steroid side chains for ecdysone, cmstecdysone, brassinoHde, withanoHde, and vitamin D have been reviewed (185). Also, other manuscripts, including reviews on the partial synthesis of steroids (186), steroid dmgs (187—189), biologically active steroids (190), heterocychc steroids (191), vitamin D (192), novel oxidations of steroids (193), and template-directed functionali2ation of steroids (194), have been pubhshed. 

Insects, crustaceans, platehelminthes, nematodes and annelids use homoses-quiterpenoid epoxides (juvenile hormones) and ecdysteroids (ecdysone, 20-... 

The A -6-ketone functionality in polyhydroxy cholestanes is common to all the insect moulting hormones of the ecdysone type. Therefore, there has recently been considerable interest in the introduction of A -double bonds into 6-ketones. The different approaches that follow illustrate the utility of isomerization, rearrangement, and blocking groups. 

Caterpillars and other moulting insects excrete the hormone a-ecdysone which at moulting time becomes hydroxylated to 20-hydroxyecdysone (20-E), which in turn triggers the moulting process enabling the insect to shed its exoskeleton and resume feeding. Rohm and Hass have developed a novel insecticide, tebufenozide (Formula 9.5) which mimics 20-E, binding to the same site. The consequence of this is that the insect stops... 

Members of the family Amaranthaceae are known to produce ecdysteroids such as 8-ecdysone (19) and inocosterone (20). From petroleum ether extracts of Amaranthus splnosus Linn. Behari and Andhiwal (21) obtained 8-sitosterol (4), stigmasterol (3), campesterol and cholesterol. From the roots of the same species, Banerji (22) isolated two new saponins, a diglucoside and a triglucoside of o-spinasterol. More recently, Roy et al. (23)... 

Bryant Is that moulting controlled by an ecdysone-like hormone ... 

There have been no recent reports concerning ecdysone biosynthesis. For two reviews on this subject, see Goad [3] and Ikekawa [5]. 

Ecclesiastical wines, 26 301 Ecdysone receptor agonists, 14 345 ECHIP JMP 4.0.4, features compared to other software, 8 398t ECLP tube press, 11 373 Eco-check Product excellence, 24 189 Eco-efficiency analysis, 24 189, 190 Eco-Efficiency program, 9 457 Ecological and Toxicological Association of Dyestuffs and Organic Pigments Manufacturers (ETAD), 9 234, 238 19 452... 

Most of the more recently described allenic steroids bear an allene group at the 17-position, which was usually formed by an SN2 substitution [106] or reduction [86d] process of a suitable propargylic electrophile. Thus, reduction of the pro-pargylic ether 109 with lithium aluminum hydride followed by deprotection of the silyl ether resulted in the formation of the allenic steroid 110, which irreversibly inhibits the biosynthesis of the insect moulting hormone ecdysone (Scheme 18.35) [107]. 

Insect steroid metabolism has two biochemically distinctive components dealkylation of phytosterols to cholesterol and polyhydroxylation of cholesterol to ecdysone. We will focus on the first of these. Lacking the ability to synthesize sterols de novo, insects instead have evolved a dealkylation pathway to convert plant sterols to cholesterol(7-10). The dealkylation pathways are apparently absent in most other higher and lower organisms, which can convert mevalonate to squalene and thence into sterols( ). Specific insecticides are possible based on these biochemical differences. 

Ecdysone is the steroid hormone of the arthropods. It can be regarded as an early form of the steroid hormones. Steroid hormones with signaling functions also occur in plants. 

The most important steroid hormones in vertebrates are listed on p. 57. Calcitriol (vitamin D hormone) is also included in this group, although it has a modified steroid structure. The most important steroid hormone in invertebrates is ecdysone. 

Wang, S. et al.. Identification and determination of ecdysones and flavonoids in Serratula stran-gulata by micellar electrokinetic capillary chromatography, Planta Med., 68, 1029, 2002. 

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