Biology Reference
In-Depth Information
The first ecdysteroid isolated was ecdys-
one (25 mg) from pupae (500 kg) of the silk
worm
Bombyx mori
, using the
Calliphora
bioassay to direct the isolation (Butenandt
and Karlson, 1954). The poor yield, which
represents a purification factor of about 1:10
7
of the hormone, as well as the absence of
modern physical techniques, delayed the
structural elucidation of this compound
(Karlson, 1996). The full structural elucida-
tion of ecdysone (
1
) was achieved in 1965,
by a combination of chemical experiments
(Karlson
et al
., 1965) and X-ray analysis of
the crystals (Huber and Hoppe, 1965).
Since then many ecdysteroids have
been found in arthropods, such as
20-hydroxyecdysone (
2
), recognized as the
most important ecdysteroid in insects, as
well as ponasterone A (
3
), 2-deoxyecdysone
(
4
) and 25-deoxyecdysone (
5
), among others
(Fig. 11.1). The principal structural feature
of ecdysteroids, the 14a-hydroxy-7-en-6-
one chromophore, is derived from choles-
terol (
6
). For this reason, most of them have
C
27
cores.
There is, however, some diversity in
the number of carbons of ecdysteroids
depending on the alimentary habits of spe-
cies and their metabolic pathways. The
phytophagous insects include in their diets
C
28
and C
29
sterols such as b-sitosterol (
7
),
stigmasterol (
8
), campesterol (
9
) and fungal
ergosterol (
10
). In some insects, those phy-
tosterols can be metabolized to synthesize
cholesterol and then be used as a hormone
precursor to form C
27
ecdysteroids (Fig. 11.2).
They can dealkylate C
28
or C
29
phytosterols.
On the other hand, if the insects are not
OH
OH
OH
(a)
OH
OH
HO
HO
OH
OH
HO
HO
H
H
O
O
Ecdysone (
1
)
20-hydroxyecdysone (
2
)
OH
OH
OH
OH
HO
OH
OH
HO
HO
H
H
O
O
2-deoxyecdysone (
4
)
Ponasterone A (
3
)
OH
21
(b)
22
18
24
20
27
23
12
13
14
17
19
11
25
HO
16
26
15
1
9
OH
2
3
10
8
7
H
5
6
HO
4
HO
H
O
25-deoxyecdysone (
5
)
Cholesterol (
6
)
Fig. 11.1.
(a) Chemical structures of some of the most commonly occurring ecdysteroids in insects.
(b) Cholesterol, their chemical precursor.
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