Synthesis of the sex pheromone of the citrus mealybug, Pseudococcus cryptus

Article abstract of DOI:10.1271/bbb.67.2627

The sex pheromone of the citrus mealybug (Pseudococcus cryptus), [(1R,3R)-3-isopropenyl-2,2-dimethylcyclobutyl]methyl 3-methyl-3-butenoate, was synthesized from (+)-α-pinene in five operational steps in a 43% overall yield. The synthetic pheromone was identical with the natural pheromone in ¹H-NMR and mass spectroscopic properties, and showed almost the same pheromonal activity as the natural pheromone.

Full text of DOI:10.1271/bbb.67.2627

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Synthesis of the Sex Pheromone of the Citrus
Mealybug, Pseudococcus cryptus
Takashi NAKAHATAa, Noriaki ITAGAKIa, Tomonori ARAIb, Hajime SUGIEc & Shigefumi
KUWAHARAa
a Laboratory of Applied Bioorganic Chemistry, Division of Life Science, Graduate School
of Agricultural Science, Tohoku University1-1 Tsutsumidori-Amamiyamachi, Aoba-ku,
Sendai 981-8555, Japan
b Department of Citrus Research, National Institute of Fruit Tree ScienceKuchinotsu,
Nagasaki 859-2501, Japan
c National Institute of Agro-Environmental Sciences3-1-3 Kannondai, Tsukuba, Ibaraki
305-8604, Japan
Published online: 22 May 2014.
To cite this article: Takashi NAKAHATA, Noriaki ITAGAKI, Tomonori ARAI, Hajime SUGIE & Shigefumi KUWAHARA
(2003) Synthesis of the Sex Pheromone of the Citrus Mealybug, Pseudococcus cryptus , Bioscience, Biotechnology, and
Biochemistry, 67:12, 2627-2631, DOI: 10.1271/bbb.67.2627
To link to this article: http://dx.doi.org/10.1271/bbb.67.2627
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Biosci. Biotechnol. Biochem., 67 (12), 2627–2631, 2003
Synthesis of the Sex Pheromone of the Citrus Mealybug, Pseudococcus cryptus
3
Takashi NAKAHATA,1 Noriaki ITAGAKI,1 Tomonori ARAI,2 Hajime SUGIE
and Shigefumi KUWAHARA
,
1,
†
1Laboratory of Applied Bioorganic Chemistry, Division of Life Science, Graduate School of Agricultural
Science, Tohoku University, 1-1 Tsutsumidori-Amamiyamachi, Aoba-ku, Sendai 981-8555, Japan
2Department of Citrus Research, National Institute of Fruit Tree Science, Kuchinotsu,
Nagasaki 859-2501, Japan
3National Institute of Agro-Environmental Sciences, 3-1-3 Kannondai, Tsukuba, Ibaraki 305-8604, Japan
Received July 16, 2003; Accepted August 13, 2003
The sex pheromone of the citrus mealybug
Pseudococcus cryptus), [(1 ,3 )-3-isopropenyl-2,2-
dimethylcyclobutyl]methyl 3-methyl-3-butenoate, was
synthesized from ( )- -pinene in ˆve operational steps
tion of the male adult insects, which would eventual-
ly lead to the prediction of the most appropriate
timing for insecticides to be sprayed.2,3) We have
recently succeeded in isolating the sex pheromone,
the structure of which was deduced without assigning
the absolute stereochemistry to be 1 as shown in
(
R R
＋
a
in a 43
z
overall yield. The synthetic pheromone was
1
identical with the natural pheromone in H-NMR and
mass spectroscopic properties, and showed almost the
same pheromonal activity as the natural pheromone.
1
Scheme 1 from analyses of its MS and H-NMR
data.4) To conˆrm the structure, including its abso-
lute conˆguration, and to provide a su‹cient amount
of the pheromone for ˆeld monitoring tests, we set
about the synthesis of 1. Although the absolute
stereochemistry of the pheromone had not been
determined, we postulated it to be that shown in 1
by analogy with that of 5a, the sex pheromone of a
closely-related mealybug (Planococcus citri ).5) Since
its structural elucidation, the sex pheromone of P.
citri (5a) has been synthesized by several groups,6)
most of them employing acetylation of the corre-
sponding alcoholic precursor (5c) as the ˆnal step of
Key words: Pseudococcus
cryptus
;
pheromone;
terpenoid
The citrus mealybug, Pseudococcus cryptus
Hempel (Homoptera: Pseudococcidae), is one of the
most notorious pests for the production of citrus
fruits in Japan. EŠective control of this insect
requires predicting the emergence season of its ˆrst or
second instar nymphs, during which this mealybug is
most susceptible to insecticides.1) Many attempts
have therefore been made to isolate its sex phero-
mone that could be used for monitoring the popula-
＋
synthesis and ( )-
a-pinene (2) as the common start-
ing material. In the previous syntheses of 5a, one of
＝
Scheme 1. Reagents: a) Pb(OAc)4, Benzene (75
PPTS, THF; d) Ac2O, Then aq. NaOH (88
z
z
, 3a:3b 95:5); b) O3, MeOH, Then NaBH4, and Finally K2CO3 (72
z); c) HC(OMe)3,
from 4); e) 6, DCC, DMAP, CH2Cl2 (91 ).
z
†
To whom correspondence should be addressed. TelWFax: 81-22-717-8783; E-mail: skuwahar biochem.tohoku.ac.jp
＋ ＠

2628
T. NAKAHATA et al.
1
the ten carbon atoms of 2 was eliminated without
the H-NMR spectrum of the mixture. Although the
mixture gave virtually a single spot on a silica gel
TLC plate, repeated silica gel column chro-
matography of the mixture enabled the isolation of
5a and 5b, and their spectroscopic characteriza-
tion.12,13) Acetate 5a is considered to have been
formed from alcoholic intermediate 7a upon treat-
ment with acetic anhydride, and formate 5b from the
orthoester derivative of 7a (i.e., 7b), although no
attempt was made to isolate the intermediates. The
mixture containing 5a and 5b was treated with an
aqueous NaOH solution in tetrahdrofuran to eŠect
the hydrolysis of both 5a and 5b to give 5c, whose 1H-
NMR spectrum matched that reported in the litera-
ture.12) In a large-scale experiment, the two-step
sequence starting from the mixture of 7a and 7b was
carried out in a one-pot operation, furnishing 5c in
being incorporated into 5c, except for the synthesis
5)
by Bierl-Leonhardt et al
.
We describe here a new
synthesis of 5c which utilizes all the carbon atoms
contained in 2, and its conversion into the target
pheromone (1). This present synthesis eventually led
to conˆrmation of the (1R,3R) absolute stereoche-
mistry of the pheromone reported in our previous
paper.4)
Results and Discussion
＋
Our synthesis began with the oxidation of ( )-
a
-
pinene (2) into 3a with lead tetraacetate. According
to Whitham's procedure,7) lead tetraacetate was
added over a period of 20 min to a solution of 2 in
dry benzene at 60–65
stirred for 50–60 min at the same temperature.
However, the only product obtained was trans
9C, the resulting mixture being
an 88
z
overall yield from 4. Finally, esteriˆcation of
-
5c with 3-methyl-3-butenoic acid 6, which was
obtained by the Jones oxidation of 3-methyl-3-buten-
1-ol, in the presence of 1,3-dicyclohexylcabodiimide
and 4-(dimethylamino)pyridine (DMAP) aŠorded 1
verbenyl acetate (3b),8) the allylic rearrangement
product of 3a, this also having been obtained by
Criegee with the same oxidation method apart from
the workup procedure.9) This rearrangement had
been reported to be facilitated by the action of acetic
acid or lead(IV) oxide, the former being a by-product
of this oxidation reaction and the latter being a
product generated during aqueous workup of this
reaction mixture.7,10) The addition of sodium acetate
or sodium bicarbonate to the reaction mixture in an
attempt to suppress the acidity of the reaction
medium gave the same result, giving only 3b instead
of desired 3a. After several unsuccessful attempts, we
ˆnally succeeded in obtaining an inseparable ca. 95:5
in a 91
z
yield. It is worth mentioning that the use of
a catalytic amount of DMAP (ca. 0.1 equivalent) was
essential for preventing the migration of the double
bond of the acid moiety to the conjugated position,
because the migration occurred when 1 equivalent of
DMAP was employed, giving a 12:1 mixture of the
desired ester and the thermodynamically more stable
migration product. The 1H-NMR and mass spectra of
synthetic 1 were identical with those of the natural
pheromone. The enantiomeric excess of the synthetic
z
pheromone was evaluated to be 88 by GLC separa-
mixture of 3a and 3b in about 70–80
z
reproducible
tion of the enantiomers of 5c in a chiral stationary
phase as previously reported,4) This also elucidated
the absolute conˆguration of this pheromone as
yields by using azeotropically pretreated lead tetraa-
cetate as well as by inverting the order of its addition;
i.e., adding a solution of 2 in benzene to a benzene
solution of lead tetraacetate that had been azeotropi-
cally pretreated with dry toluene. The rationale for
this improvement in the product ratio is not yet clear,
although preventing the gradual decomposition of
lead tetraacetate into lead(IV) oxide by moisture
during the 20-min portionwise-addition period and
(1R,3R) through a direct comparison of the retention
time of the synthetic alcohol (5c) with that of the
alcohol derived from the natural pheromone by
hydrolysis.4) Despite the partial enantiomeric impu-
rity, which was probably due to the original optical
＋
purity of ( )-a-pinene used as the starting material
23
in this synthesis ([
a
]
9
44 (neat, d
＋ ＝
0.86), lit14)
D
W
20
＋
51.69 (neat)), the synthetic pheromone
or the exclusion of acetic acid, which was probably
contained in commercial lead tetraacetate to some
extent, might have been eŠective for the successful
outcome. Treatment of the mixture of 3a and 3b in
methanol with ozone was followed by reductive
workup of the resulting ozonides with sodium
borohydride and then methanolysis of the acetate
ester group with potassium carbonate to give 4 in a
[a
]
D
showed almost the same pheromonal activity as the
natural pheromone.4)
Experimental
IR spectra were measured as ˆlms by a Jasco IR
Report-100 spectrometer. 1H-NMR spectra were
recorded with TMS as an internal standard in CDCl3
by a Varian Gemini 2000 spectrometer (300 MHz) or
a Varian UNITYplus-500 spectrometer (500 MHz).
Optical rotation values were measured with a Horiba
Septa-300 polarimeter, and mass spectra were
one-pot operation and 72
z yield after chromato-
graphic puriˆcation. Triol 4 was then converted into
a mixture of 5a and 5b by treating with trimethyl
orthoformate in the presence of pyridinium
p-tol-
uenesulfonate and subsequent heating of the result-
ing crude product in acetic anhydride.11) The ratio of
5a and 5b was determined to be 1:1.34 by analyzing
obtained with a Jeol JMS-700 spectrometer operated
23
in the EI mode. (
＋
)-
a
-Pinene ([
a
]
＋
44
9
(neat,
d
＝
D

Synthesis of the Sex Pheromone of Pseudococcus cryptus
2629
＝
0.86)) was purchased from Tokyo Kasei Kogyo Co.
Merck silica gel 60 (70–230 mesh) was used for silica
gel column chromatography.
3?
-CH), 3.66 (1H, dd,
J
10.7, 8.0 Hz, 3
?-CH);
HREIMS m z (M＋-H2O): calcd. for C10H18 O2,
W
170.1307; found, 170.1307.
(1S,2R,5S)-2,6,6-Trimethylbicyclo[3.1.1]hept-3-
en-2-yl acetate (3a). A reaction ‰ask was charged
with lead tetraacetate (14.6 g, 33.0 mmol) and dry
toluene (30 ml), and the solvent was removed with a
[(1R,3R)-3-Isopropenyl-2,2-dimethylcyclobutyl]-
methanol (5c). To a stirred solution of 4 (500 mg,
2.66 mmol) and pyridinium
p-toluenesulfonate
(344 mg, 1.33 mmol) in tetrahydrofuran (5.3 ml) was
added trimethyl orthoformate (1.45 ml, 13.3 mmol).
The resulting solution was stirred for 3 h at room
temperature and then diluted with ether. The ethereal
solution was successively washed with a saturated
aqueous NaHCO3 solution, water and brine, dried
(MgSO4) and concentrated in vacuo to give a color-
less oil, which was then dissolved in acetic anhydride
(5.3 ml). The solution was stirred at re‰ux tempera-
ture for 12 h under a nitrogen atmosphere, cooled
with an ice-water bath, and then diluted with
tetrahydrofuran (10 ml). To the solution was added
dropwise a solution of NaOH (6 g) in water (50 ml)
while cooling with a water bath. The mixture was
stirred for 12 h at room temperature and then
extracted with ether. The ethereal solution was
successively washed with water and brine, dried
(MgSO4) and concentrated in vacuo. The residue was
chromatographed over silica gel (15 g, eluting with
rotary evaporator at 459C in vacuo. The residual
solid was suspended in dry benzene (80 ml) under a
nitrogen atmosphere, and the mixture was allowed to
warm to 659C. To the resulting orange solution was
quickly added a solution of 2 (5.00 g, 36.7 mmol) in
dry benzene (20 ml), and the mixture was stirred at
9
65 C for 40 min. The mixture was cooled to room
temperature and ˆltered through a pad of Celite}.
The ˆltrate was mixed with 1 ml of water and
vigorously shaken for several minutes to destroy the
excess lead tetraacetate, before being dried with a
mixture of MgSO4 and K2CO3. The mixture was
ˆltered through a pad of Celite} and concentrated in
vacuo to give 5.31 g (75
z) of an inseparable mixture
of 3a and 3b, the ratio of which was determined to be
1
1
95:5 by a H-NMR analysis of the mixture. The H-
NMR spectral data for 3a, which, to the best of our
knowledge, have not previously appeared in the
literature, are as follows:
d
: 0.97 (3H, s, 6-CH3), 1.38
pentane-ether, 15:1) to give 360 mg (88z) of 5c,
9
15.4 (c 1.10, chloroform); IR n :
＋ ＝
max cm－
D
2
3
1
(3H, s, 6-CH3), 1.64–1.68 (1H, m), 1.96 (3H, s,
[a
]
＝
2-CH3), 2.19 (1H, br q,
J
6.0 Hz), 2.34–2.43 (2H,
3320 (m, br), 3060 (w), 2940 (s), 2850 (m), 1640 (m),
m), 6.04 (1H, ˆnely split d,
J
＝
8.7 Hz, 3-H), 6.36
1450 (m), 1360 (m), 1015 (m), 1005 (m), 880 (m); 1H-
＝
(1H, dd,
J
8.7, 6.3 Hz, 4-H).
NMR
1.565 (1H, s, OH), 1.567 (1H, q,
1.90 (1H, dt, 10.7, 7.4 Hz, 4-H), 2.02–2.14 (1H,
m, 1-H), 2.39 (1H, br dd,
(1H, dd,
d: 0.84 (3H, s, 2-CH3), 1.24 (3H, s, 2-CH3),
＝
J
10.7 Hz, 4-H),
(S)-2-[(1S,3R)-3-Hydroxymethyl-2,2-dimethylcy-
J
＝
＝
10.7, 7.4 Hz, 3-H), 3.55
clobutyl]-1,2-propanediol (
4
). A solution of this
J
mixture of 3a and 3b (5.31 g, 27.4 mmol) in methanol
J 10.9, 6.5 Hz, OCH), 3.62 (1H, dd, J
＝ ＝
＝
CH),
(100 ml) was treated with ozone for 70 min at
10.9, 8.1 Hz, OCH), 4.56–4.59 (1H, m,
78
9
C. To the solution was added sodium boro-
4.80–4.83 (1H, m,
CH); HREIMS m z (M＋ ):
W
－
＝
hydride (2.58 g, 68.3 mmol) portionwise, the mixture
being stirred at
calcd. for C10H18 O, 154.1358; found, 154.1361. The
enantiomeric excess of 5c was determined to be 88z
－
78
9C for 3 h and then allowed
to gradually warm to room temperature. To the
mixture was then added potassium carbonate (7.55 g,
54.6 mmol), and the mixture was stirred at re‰ux
temperature for 4 h. After being cooled to room
temperature, the mixture was ˆltered, and the ˆlter
cake was washed with chloroform. The combined
ˆltrate and washings were concentrated in vacuo, and
the residue was chromatographed over silica gel
(300 g, eluting with chloroform-methanol, 30:1) to
by a GLC analysis with a chiral stationary phase
(Supelco, Beta dex 120}) as reported in the litera-
ture.4)
[(1R,3R)-3-Isopropenyl-2,2-dimethylcyclobutyl]-
methyl acetate (5a) and [(1R,3R)-3-Isopropenyl-2,2-
dimethylcyclobutyl]methyl formate (5b). A mixture
of 5a and 5b was obtained in the same manner as that
described for the preparation of 5c, except that the
reaction mixture obtained by heating a mixture of 7a
and 7b with acetic anhydride was worked up by dilut-
ing it with ether and then successively washing the
ethereal solution with a saturated aqueous NaHCO3
solution, water and brine. The solution was dried
(MgSO4) and concentrated in vacuo to give an oil.
Although the crude product showed virtually a single
give 3.71 g (72
zation of which from hexane-ethanol aŠorded
colorless prisms, mp 96–97 C (Yanaco MP-J3);
1.12, ethanol); IR
max cm－1: 3350
(vs, br), 2950 (s), 2910 (s), 2860 (m), 1450 (m), 1065
(s), 1030 (s), 1000 (s); 1H-NMR
: 1.10 (3H, s,
-CH3), 1.17 (6H, s, 3-H3, 2 -CH3), 1.59–1.68 (1H,
m, 4 -H), 1.83–2.01 (3H, m, 1 -H, 3 -H, 4 -H), 3.37
(1H, br d, 11.0 Hz, 1-H), 3.57 (1H, br d,
11.0 Hz, 1-H), 3.58 (1H, dd, 10.7, 6.0 Hz,
z) of 4 as a colorless solid, recrystalli-
9
23
＋
＝
[
a
]
5.29
9(c
n
D
d
2?
?
?
1
?
?
?
spot on TLC (Merck silica gel 60 F254), its H-NMR
＝
＝
J
J
spectrum revealed that it was a mixture of 5a and 5b.
J
＝
Repeated chromatography of the mixture over silica

2630
T. NAKAHATA et al.
＝
gel (Merck silica gel 60 (230–400 mesh), pentane-
ether, 100:1) enabled the isolation of small amounts
of pure samples of 5a and 5b together with a large
10.7, 7.6 Hz, 4
?
-H), 2.19 (1H, dddd,
J
10.7, 9.0,
＝
7.6, 6.2 Hz, 1
?-H), 2.39 (1H, dd,
J
10.7, 7.6 Hz,
＝
3
?
-H), 3.01 (2H, s, 2-H2), 3.96 (1H, dd,
J
11.2,
11.2, 6.2 Hz,
-C
1
＝
amount of their mixture. The H-NMR spectral data
9.0 Hz, O–CH), 4.08 (1H, dd,
J
for 5a were identical with the reported data.12,13)
Formate 5b, which had not been reported earlier,
O–CH), 4.57 (1H, s, 3
?-C
＝
CH), 4.81 (1H, s, 3
?
＝
CH), 4.84 (1H, s, 4-H), 4.91 (1H, s, 4-H); 13C-NMR
(125 MHz) : 16.11, 22.48, 22.87, 22.96, 30.92,
39.78, 41.08, 43.59, 48.83, 65.15, 109.45, 114.64,
138.54, 144.99, 171.40; MS m z (relative intensity):
23
＋
showed the following physical properties: [
a
]
d
D
14.1
9
(
c
1.16, chloroform); IR n
max cm－1: 3055 (w),
＝
2940 (s), 2850 (m), 1720 (vs), 1640 (m), 1450 (m),
W
1
1170 (s), 880 (m); H-NMR
d
: 0.83 (3H, s, 2-CH3),
236 (47
z
, M＋ ), 168 (34
), 107 (22 ), 100 (41
), 83 (31 ), 81 (22 ), 69 (100
), 55 (45 ), 41 (38
); HREIMS m z (M＋ ):
z
), 153 (20
), 93 (32
), 68 (44
z
), 136 (37
), 85
), 67
z
),
＝
1.22 (3H, s, 2-CH3), 1.63 (1H, q,
J
10.7 Hz, 4-H),
121 (39
z
z
z
z
＝
＝
10.7,
1.65–1.67 (3H, m, C–CH3), 1.92 (1H, dt,
J
(55
(20
z
z
z
z
z
z
z
7.4 Hz, 4-H), 2.16–2.28 (1H, m, 1-H), 2.14 (br dd,
z
W
＝
＝
J
10.7, 7.4 Hz, 3-H), 4.05 (1H, dd,
J
11.3,
J 11.3, 6.6 Hz,
calcd. for C15H24O2, 236.1776; found, 236.1781. The
1H-NMR and mass spectra of the synthetic phero-
mone matched those of the natural pheromone.
8.8 Hz, OCH), 4.16 (1H, dd,
＝
＝
OCH), 4.56–4.59 (1H, m, CH), 4.81–4.84 (1H, m,
CH), 8.04 (1H, s, CHO); HREIMS m z (M＋ ):
＝
W
calcd. for C11H18O2, 182.1307; found, 182.1307.
Acknowledgments
3-Methyl-3-butenoic acid (
6
). This carboxylic acid
This work was supported, in part, by grant-aid
for scientiˆc research (C) from the Ministry of
Education, Science, Sports and Culture of Japan
(No. 13660103). Financial support given to S. K. by
Nagase Science and Technology Foundation is also
greatly appreciated. We are grateful to Ms. T.
Yamada (Tohoku University) for measuring the mass
spectra. 3-Methyl-3-buten-1-ol was kindly provided
by Kuraray Co.
is a known compound.15) However, to the best of our
knowledge, the preparation of 6 by direct oxidation
of the corresponding homoallylic alcohol with the
Jones reagent has not previously been reported. To a
stirred solution of 3-methyl-3-buten-1-ol (6.00 g,
69.7 mmol) in acetone (200 ml) was added dropwise
the Jones reagent (36.5 ml, 97.5 mmol) at 09C. After
being stirred for 8 h at room temperature, the
mixture was quenched with isopropyl alcohol. The
mixture was diluted with water, and most of the
acetone was evaporated in vacuo. The residue was
extracted with ether, and the ethereal solution was
References
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on citrus. Jpn. J. Appl. Entomol., 40, 25–34 (1996).
2) Arai, T., The presence of sex pheromone of Pseu-
dococcus cryptus Hempel (Homoptera: Pseudoccoci-
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NaHCO3 solution. The combined aqueous layers
were acidiˆed with a 2 aqueous HCl solution to
a saturated aqueous
M
pH 3, and then extracted again with ether. The
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dried (MgSO4) and concentrated in vacuo. The
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,
35, 525–528 (2000).
residue was distilled to give 4.56 g (65
45–47 (4 Torr).
z) of 6, bp
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9
[(1R,3R)-3-Isopropenyl-2,2-dimethylcyclobutyl]-
methyl 3-methyl-3-butenoate ( ). To a stirred solu-
1
tion of 5c (1.20 g, 7.78 mmol) and 6 (1.17 g,
11.2 mmol) in dichloromethane (70 ml) were added
1,3-dicyclohexylcarbodiimide (2.89 g, 14.0 mmol)
and 4-(dimethylamino)pyridine (0.095 g, 0.78 mmol)
at room temperature. After 3 h, the mixture was
diluted with ether, and the ethereal solution was
sex pheromone component of Pseudococcus cryptus
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.
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successively washed with a 0.5
M
aqueous HCl
solution, a saturated aqueous NaHCO3 solution and
brine, dried (MgSO4) and concentrated in vacuo. The
residue was chromatographed over silica gel (50 g,
eluting with pentane-ether, 30:1) to aŠord 1.67 g
21
D
1
＋
＝
(91
(500 MHz)
-CH3), 1.61 (1H, q,
-CCH3), 1.81 (3H, s, 3-CH3), 1.90 (1H, dt,
z
) of 1. [
a
]
18.9
9
(
c
1.17, CHCl3); H-NMR
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d
: 0.81 (3H, s, 2?-CH3), 1.20 (3H, s,
＝
10.7 Hz, 4?-H), 1.66 (3H, s,
2
?
J
＋
-
3
?
J
＝

Synthesis of the Sex Pheromone of Pseudococcus cryptus
2631
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R
,5
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