Page 21 - Volume 3, Issue 2, July 2010
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© Benaki Phytopathological Institute
Mosquito oviposition aggregation pheromone
51
lustrated by the synthesis of the oviposition
pheromone of the mosquito
Cx. quinquefas-
ciatus
(Trost and Rhee, 2002). A catalytic sys-
tem composed of CpRu[(p-CH
3
O
6
H
4
)
3
P]
2
Cl
and excess (
p
-CH
3
O-C
6
H
4
)
3
P directs the reac-
tion toward the oxidative cyclization to form
δ
-lactones in good yields (Figure 32).
2.9. Syntheses of racemic or diastereoi-
someric mixtures
Ochiai
et al.
(1985) synthesized the
eryth-
ro
-6-acetoxy-5-hexadecanolide starting from
(
E
)-hexadec-5-enal
99
(Figure 33). Oxidation
of aldehyde
99
with sodium chlorite, epoxida-
tion by treatment with
m
-chloroperbenzoic
acid, lactonization of the resulting oxirane by
heating in toluene-cyclohexane at reflux for
1 day and finally acetylation afforded a mix-
ture of (5
R
,6
S
)- and (5
S
,6
R
)-6-acetoxy-5-hexa-
decanolide
(4 steps, 40% yield)
.
From the seeds of the summer cypress
plant,
Kochia scoparia
, (5
R
,6
S
)-isomer was ef-
ficiently synthesized, in admixture with the
inactive (5
S
,6
R
)-isomer (Olagbemiro
et al
.,
1999). The intermediate (5
R
,6
S
)-6-hydroxy-
5-hexadecanolide,
106
, was prepared with
three different approaches from glycer-
ides of (
Z
)-5-hexadecenoic acid,
100
(Figure
34).
In the final step an acetylation gave the
enantiomerically enriched 6-acetoxyhexa-
decanolide,
1a
(Routes A, B and C 8, 12 and
16.5% yield respectively)
.
A diastereoisomeric mixture of the ovi-
position pheromone was synthesized via a
simple (five steps), efficient and high yield-
ing procedure (Figure 35) (Michaelakis
et al.
,
2005).
Oxidation,
cis
-dihydroxylation of the 9:1
mixture of
cis
and
trans
double bonds and
consequent lactonization led to the forma-
tion of the
erythro
and
threo
isomers re-
spectively. Thus, a mixture of the four ste-
reoisomers of 6-acetoxy-5-hexadecanolide
(
1a-d
) containing 45% of the natural ovipo-
sition aggregation pheromone [(–)-(5
R
,6
S
)],
45% of its enantiomer [(+)-(5
S
,6
R
)] and 10%
of the respective
threo
enantiomeric pair
[(–)-(5
S
,6
S
) and (+)-(5
R
,6
R
)] was prepared
(5
steps, 45% yield)
.
3. Conclusion
Pheromone synthesis is important to obtain
sufficient quantities in order to be used for
the determination of their absolute config-
uration as well as for the biological studies,
both in laboratory and field conditions (Mori
and Tashiro, 2004).
The simple chemical structure of the cur-
rent oviposition aggregation pheromone
(only two asymmetric centres) and the fact
that the management of mosquitoes is im-
portant for reducing their impacts on pub-
lic health provoked many research groups
to synthesize or/and bioassay it.
Figure 32
Figure 33
