Ecdysones biosynthesis

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

To date, the definitive conversion of cholesterol to a-ecdysone by these glands in vitro has not yet been reported, and without such evidence neither the detailed study of ecdysone biosynthesis nor its inhibition by chemicals as potential pesticides can be expected to progress rapidly. 

Obviously, ecdysone or analogues that have similar or antagonistic modes of action could disturb the normal development of the insects and so can be used as insecticides. Inhibitors or inducers of the ecdysone biosynthesis may also be developed as insecticides. 

Many endogenous ecdysteroids which can be considered as the intermediates of ecdysone biosynthesis were isolated from the ovaries of L. migratoria by Hoffmann and Horn [204]. From the results of the bioconversion of labelled precursors, the following sequence in the biosynthetic pathway of ecdysteroids in vitellogenic ovaries of the insect was proposed conversion of cholesterol to 3)3-hydroxy-5)8-cholest-7-en-6-one followed by 14a-hydroxylation to 3/S,14-dihydroxy-5/6-cholest-7-en-6-one (112) hydroxylation at C-25 and C-22 (in this order) to 2-deoxyecdysone (114) hydroxylation at C-2 to ecdysone (107). 

Figure 12. Ecdysone Biosynthesis Inhibitor of Crustaceans (Adapted from ref. 42).

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]. 

The biosynthesis of insect moulting hormones has been reviewed.340 Labelled MVA and cholesterol were incorporated (0.5 and 1%, respectively) into inoko-sterone and /3-ecdysone (110) by seedlings and homogenates of Achyranthes... 

Arthropod Sterols.—The absence of sterol biosynthesis has been observed in further examples from the class ArachnidaT The conversion of /5-sitosterol back to cholesterol was demonstrated in bees and in locusts/ where it was shown that fucosterol, but not 24-methylenecholesterol, was probably a precursor of desmosterol and cholesterol. Some interconversions of pregnane, andros-tane, and oestrane steroids have been examined in the cricket.The stages in the oxidation of the side-chain of ecdysone hormones have been studied in several species. In Calliphora, the sequence of oxidation seems to be hydroxylation at C-25, C-22,and C-20 i.e. (115)— (116)— (117)— (118). The last step, conversion... 

The biosynthesis of ecdysteroids in filarial worms has been studied [75]. It has been shown that D. immitis and Brugia pahangi can not synthesize ecdysteroids from cholesterol. Further, no evidence was available to support the conversion of ecdysone (14) to 20-hydroxyecdysone (15). Not withstanding the fact that the basic studies regarding endocrinology of female worms are still not elaborate, interference of ecdysteroid biosynthesis and function in female helminths may provide... 

Our laboratory is concerned with targeting potential insecticides that disrupt normal development and metamorphosis in insects. Juvenile hormones (JHs), acting in concert with the steroid hormone ecdysone, are believed to control the timing of the larval-larval molts, larval-pupal and pupal-adult transformations of the insects. It has been demonstrated that the events leading to pupation are initiated by reduction of the JH titer in the hemolymph. In addition to a cessation of biosynthesis, this reduction in JH titer is controlled by degradative metabolism (16,17). Hydrolysis of the epoxide and ester functionalities present in active JH are two routes of degradation and subsequent inactivation of JH (18). The primary route of JH metabolism in the hemolymph of last stadium lepidopterous larvae is ester hydrolysis, and it is catalyzed by the enzyme juvenile hormone esterase (JHE). JHE has been shown to... 

The important insect hormone a-ecdysone (121) and related steroids are also present in plants (Section 9). Their biosynthesis from cholesterol probably proceeds via the A -diene to the triolone (119). The side chain is then hydroxylated to the (22/ )-hydroxy steroid (120), a-ecdysone (121), and ) -ecdysone (122) (crustecdysone). Finally, breakdown of )8-ecdysone gave... 

The biosynthesis and metabolism of the insect moulting hormone, ecdysone have been the subject of recent reviews [184-186]. Ecdysone (107) was first isolated in a crystalline form from the silkworm, Bombyx mori, by Butenandt and Karlson in 1954, and the structure was determined in 1965. Soon after, the second moulting hormone was isolated and the structure was elucidated as 20-hydroxyecdysone (108). Ibe same hormone was also isolated from the sea-water crayfish, Jasus lalandei by Horn in 1966. Many ecdysone analogues were isolated from arthropods and certain... 

TBW larvae characterized by rapid feeding cessation and absence of tarry frass (as seen with the IDDs), with the cuticle not impaired. This unique phenotype was not similar to that produced by juvenile hormone agonists, ecdysone agonists or the chitin biosynthesis disruptor classes represented by the BPUs. 

Rees, Studies on insect moulting hormones Biosynthesis of ecdysone, ecdysterone, and 5 3-hydroxyecdysterone in Polypodium vulgare. Phytochemistry, 9, 1247-1252 (1970). 

Ikekawa, N., Sterol metabolism in insects and biosynthesis of ecdysone in the silkworm, Experientia, 39, 466-472 (1983). 

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