Efficient and stereo-selective syntheses of three stereoisomers of the sex pheromone of the cowpea weevil, Callosobruchus maculatus

Article abstract of DOI:10.1271/bbb.70309

An efficient and stereoselective synthesis of three stereoisomers of the sex pheromone of the cowpea weevil, Callosobruchus maculatus, is reported.

Full text of DOI:10.1271/bbb.70309

Biosci. Biotechnol. Biochem., 71 (11), 2720–2724, 2007
Efficient and Stereo-Selective Syntheses of Three Stereoisomers
of the Sex Pheromone of the Cowpea Weevil,
Callosobruchus maculatus
Arata YAJIMA,y Masamichi YAMAMOTO, Tomoo NUKADA, and Goro YABUTA
Department of Fermentation Science, Faculty of Applied Biological Science, Tokyo University of Agriculture,
1-1-1 Sakuragaoka, Setagaya-ku, Tokyo 156-8502, Japan
Received May 17, 2007; Accepted July 19, 2007; Online Publication, November 7, 2007
[doi:10.1271/bbb.70309]
An efficient and stereoselective synthesis of three
stereoisomers of the sex pheromone of the cowpea
weevil, Callosobruchus maculatus, is reported.
Key words: sex pheromone; cowpea weevil; Calloso-
bruchus maculatus; mild oxidation
The cowpea weevil, Callosobruchus maculatus, is a
serious cosmopolitan pest of stored products such as the
cowpea, azuki and other pulses, and is to be found
throughout the tropics and subtropics.1) The mating
behavior of the weevil has two phases: (i) sex attraction
and (ii) copulation release. The contact copulation
release pheromone of C. maculatus has recently been
identified by Nojima and co-workers as a synergistic
blend of hydrocarons and 2,6-dimethyloctane-1,8-dioic
acid (1) (Fig. 1).2) This pheromone induces the male
Fig. 1. Structures of the Copulation Release Pheromone and Sex
Pheromones of Callosobruchus maculatus.
weevil to extrude its genital organ and to attempt
copulation. We have succeeded in determining the
stereoisomeric composition of the pheromone by using
the 2D-Ohrui-Akasaka method.3,4)
ization of 4 to 2 and 3 has been reported by Fujisawa,9)
so we decided to develop an efficient and stereoselective
procedure for the syntheses of 4, 5 and 6.
Evidence for the presence of a volatile female sex
pheromone in C. maculatus has been reported.5–7)
Phillips and co-workers reported the isolation and
structural determination of the sex pheromones of
female C. maculatus in 1996.8) These sex pheromones
elicit long-range orientation by males, and are five-
branched heptenoic acids [2E (2), 2Z (3), methylene
(4), 3E (5) and 3Z (6)] (Fig. 1). The structures of the
pheromones were determined by comparing the GC–MS
spectra of the natural products with those of synthetic
samples. Scheme 1 summarizes Phillips’ syntheses of 2–
6. They prepared mixtures of the corresponding ethyl
esters, each ester being separated by semipreparative-
scale GC from the mixture. Their procedure is not
suitable for large-scale preparation. In connection to our
studies on the copulation release pheromone of C. mac-
ulatus, we were interested in the stereoselective syn-
thesis of the sex pheromones of C. maculatus. Isomer-
Results and Discussion
Scheme 2 shows our stereoselective syntheses of 4, 5
and 6. The corresponding alcohols were prepared in
different ways. First, the most unstable ꢀ-exo-methylene
derivative was synthesized according to Chong’s proce-
dure.10) Commercially available 3-methyl-3-buten-1-ol
(7) was treated with n-BuLi in the presence of tetra-
methylenediamine (TMEDA), before the resulting dian-
ion was alkylated with n-propyl bromide to give 8 in
a 46% yield. This relatively low yield reflects the
volatility of the product. In our preliminary experiments,
the target acid (4) was very sensitive to acidic or basic
conditions. Partial isomerization to a more stable ꢁꢀ-
unsaturated acid occurred during preparation under such
y
To whom correspondence should be addressed. Fax: +81-3-5477-2622; E-mail: ayaji@nodai.ac.jp

Synthesis of the Sex Pheromone of a Cowpea Weevil
2721
Scheme 1. Phillips’ Synthesis of the Sex Pheromones (2–6).
a
b
COOH
OH
OH
7
8
4
d, e
f, g
f, g
I
COOH
Lit. 13
80%
OR
OH
5
R = H: (E)-10
(E)-12
OH
c
c
R = TBS: (E)-11
COOH
9
OR
OH
d, e
Lit. 14
60%
I
R = H: (Z)-10
(Z)-12
6
R = TBS: (Z)-11
Scheme 2. Syntheses of 4, 5 and 6.
(a) n-BuLi, TMEDA, n-PrBr, Et2O, ꢀ78 ꢁC to 0 ꢁC (46% yield). (b) Dess-Martin periodinane, CH2Cl2, r.t. then NaClO2, NaH2PO4, 2-methyl-
2-butene, THF, t-BuOH, H2O, 0 ꢁC (52% yield). (c) TBSCl, Et3N, DMAP, CH2Cl2 [92% yield for (E)-11, quant. for (Z)-11]. (d) n-PrMgBr,
PdCl2(dppf), Et2O. (e) TBAF, THF [2 steps, 73% yield for (E)-12, 84% yield for (Z)-12]. (f) Dess-Martin periodinane, CH2Cl2. (g) NaClO2,
NaH2PO4, 2-methyl-2-butene, THF, t-BuOH, H2O, 0 ꢁC (2 steps, 47% yield for 5, 49% yield for 6).
a condition as Jones oxidation. In order to avoid this
isomerization, we chose stepwise mild oxidation of the
alcohol to the corresponding carboxylic acid. However
Dess-Martin oxidation11) of alcohol 8 gave the corre-
sponding aldehyde in a very low yield. Since the
resulting aldehyde was highly volatile and partial
isomerization occurred during isolation process, the
isolation of the aldehyde should be avoided. Finally,
Dess-Martin oxidation of 8 and Pinnick oxidation12) of
the resulting aldehyde in a one-pot reaction gave
desired 4 in a 52% yield without any isomerization.
The ꢀꢂ-unsaturated derivatives were next prepared via
the Negishi stereoselective methylalumination reac-
tion13–15) and Kumada reaction.16) Zirconocene dichlor-
ide-catalyzed methylalumination of commercially avail-
able 4-butyn-1-ol (9) under non-chelation-controlled13)
(at room temperature) or chelation-controlled14) (re-
fluxed in 1,2-dichloroethane) conditions respectively
gave known (E)- and (Z)-10. The resulting hydroxy
group was protected as a t-butyldimethylsilyl (TBS)
ether. Kumada coupling16) of iodides (E)- and (Z)-11
with n-propylmagnesium bromide in the presence of
dichloro[1,10-bis(diphenylphosphinoferrocene)]palladiu-
m(II) [PdCl2(dppf)] as the catalyst, and subsequent
deprotection of the TBS group gave alcohols (E)- and
(Z)-12 in good yields. Stepwise oxidation of these
alcohols by Dess-Martin and Pinnick oxidation gave
desired 5 and 6 (47% and 49% yields in two steps).
Although the isolation of the corresponding aldehydes
succeeded without any isomerization, the aldehydes
were immediately used in the next step without
purification. The overall yields of 4, 5 and 6 from the
commercially available compounds were 24% in two
steps, 25% in six steps and 25% in six steps, respec-
tively. The other isomer could not be detected in the 1H-
and 13C-NMR spectra of the three obtained acids. The
other components of the sex pheromone of C. macula-
tus, ꢁꢀ-unsaturated acids 2 and 3, were prepared by the
method described by Fujisawa from 4.9)
Conclusion
We achieved efficient and stereoselective syntheses of
the components of the sex pheromone of the cowpea
weevil, C. maculatus, 4, 5 and 6. The unstable ꢀ-meth-
ylene or ꢀꢂ-unsaturated acids were prepared without
any isomerizations occurring. The one-pot oxidation
employed in the preparation of 6 would be an efficient
mild oxidation procedure for converting alcohols to
acids. The stereoselective syntheses of 2Z (5),17–19) ꢀ-
methylene (6)9,20–23) and 3Z (6)24,25) have been reported,
but the stereoselective syntheses of 2E (2) and 3E (5)
have not previously been reported. This is therfore
the first example of the stereoselective synthesis of 3E
(5). Our established procedures are suitable for large-
scale preparation of the samples, and provide methods
for the synthesis of derivatives with different carbon
numbers by using various alkyl halides for ꢀ-methylene
or various Grignard reagents for ꢀꢂ-unsaturated acids.
Philips has reported that the sex pheromones of

2722
A. YAJIMA et al.
C. maculatus (2–6) elicited long-range orientation by
males, and that acids 3E (5) and 3Z (6) had greater
biological activity than the other isomers.8) Shu et al.
have reported that a blend of the two acids, 3E (5) and
3Z (6), was highly attractive to male C. maculatus.26)
Female-secreted sex pheromones of C. analis27) and
C. subinnotanus28) have also been reported. The sex
pheromone of C. analisi is 2Z (3), and that of C. sub-
innotanus is a mixture of 2E (2) and 2Z (3). Compound
2Z (3) is a common component of the sex pheromone of
C. maculatus, C. analis and C. subinnotanus, and the
ratio of the other components in their sex pheromone
might play a crucial role in species recognition. Detailed
biological studies on the structure-activity relationship
will be carried out with these five synthetic acids.
Dess-Martin periodinane (534 mg, 1.26 mmol) at room
temperature. After stirring for 2 h, to the solution were
successively added THF (4 ml), t-BuOH (1 ml), 2-
methyl-2-buten (426 ml) and H2O (4 ml). The mixture
was then cooled to 0 ꢁC and NaClO2 (284 mg, 3.15
mmol) and NaH2PO4 (188 mg, 1.58 mmol) were added.
The solution was stirred for 2 h, and then poured into
water. The aqueous phase was extracted with ether. The
organic extract was washed with brine, dried with
Na2SO4 and concentrated in vacuo. The residue was
purified by silica gel chromatography, employing 4%
EtOAc/hexane as the eluent, to afford 4 (78 mg, 52% in
two steps). IR ꢃmax (film) cmꢀ1: 3084, 2932, 2869, 2674,
1712, 1650, 1411, 1298, 1220, 1101, 902, 738, 471.
NMR ꢄH (CDCl3): 0.91 (3H, t, J ¼ 7:3 Hz, 7-CH3), 1.32
(2H, sxt, J ¼ 7:3 Hz, 6-CH2), 1.43 (2H, sep, J ¼ 7:3 Hz,
5-CH2), 2.12 (2H, t, J ¼ 7:3 Hz, 4-CH2), 3.08 (2H, s, 2-
CH2), 4.93 (1H, s, C=CHH), 4.96 (1H, s, C=CHH).
NMR ꢄC (CDCl3): 13.9, 22.3, 29.5, 35.5, 41.6, 114.0,
142.0, 177.8. Anal. Found: C, 67.70; H, 9.84%. Calcd.
for C8H14O2: C, 67.57; H, 9.92%.
Experimental
IR spectra were measured with a Shimadzu IR-470
spectrometer. NMR spectra were recorded with a Jeol
1
JNM-A400 instrument operated at 400 MHz for the H-
spectra and at 100 MHz for 13C-NMR spectra. Chemical
shifts are reported as ppm relative to CHCl3 measured
from the solvent resonance (7.26 ppm for 1H- and
77.0 ppm for 13C-NMR). The elemental compositions
were analyzed by a J-Science JM10 MICROCORDER.
Column chromatography was carried out with silica gel
(Wakogel C-200).
(E)-tert-Butyldimethylsilyl 4-iodo-3-methyl-3-butenyl
ether [(E)-11]. To an ice-cooled solution of (E)-10
(810 mg, 308 mmol) in CH2Cl2 (10 ml) were succes-
sively added Et3N (528 ml, 3.8 mmol), a catalytic amount
of DMAP (ca. 10 mg) and TBSCl (735 mg, 409 mmol).
After stirring for 1 h, the reaction mixture was poured
into water. The aqueous phase was extracted with
CH2Cl2. The organic extract was washed with brine,
dried with Na2SO4 and concentrated in vacuo. The
residue was purified by silica gel chromatography,
employing 1% ether/hexane as the eluent, to afford
(E)-11 (1.14 g, 88%). IR ꢃmax (film) cmꢀ1: 3059, 2951,
2932, 2894, 2858, 2734, 2318, 1617, 1467, 1382, 1254,
1006, 915, 835, 776, 731, 668. NMR ꢄH (CDCl3): 0.04
(6H, s, Si–CH3), 0.88 (9H, s, t-Bu), 1.85 (3H, s, 3-CH3),
2.42 (2H, t, J ¼ 6:8 Hz, 2-CH2), 3.68 (2H, t, J ¼ 6:8 Hz,
1-CH2), 5.93 (1H, s, 2-H). Anal. Found: C, 40.25; H,
7.11%. Calcd. for C11H23IOSi: C, 40.49; H, 7.10%.
3-Methylene-1-heptanol (8). To a solution of TMEDA
(11.0 ml, 72.0 mmol) in dry ether (30 ml) was added
1.58 M n-BuLi (35.0 ml, 55.3 mmol) at 0 ꢁC, and the
mixture was gradually warmed to room temperature and
stirred for 1 h. After cooling to 0 ꢁC, 3-methyl-3-buten-
1-ol (7, 2.81 ml, 28.0 mmol) was added slowly to the
mixture. The mixture was then stirred at room temper-
ature for 6 h to generate a heterogeneous brown
suspension. This slurry was cooled to ꢀ78 ꢁC, and 1-
bromopropane (2.90 ml, 31.9 mmol) was slowly added.
The reaction mixture was allowed to warm to room
temperature and stirred for 3 h. The reaction was
quenched by a sat. NH4Cl solution, and the aqueous
layer was extracted with ether. The organic extract was
dried with MgSO4, and concentrated in vacuo to give a
crude product. This product was purified by column
chromatography, employing 2% EtOAc/hexane as the
(Z)-tert-Butyldimethylsilyl 4-iodo-3-methyl-3-butenyl
ether [(Z)-11]. In the same manner as that just described,
(Z)-11 was obtained from 175 mg of (Z)-10 (274 mg,
quant). IR ꢃmax (film) cmꢀ1: 2952, 2859, 2350, 2327,
1467, 1383, 1254, 1105, 1009, 915, 835, 776, 668. NMR
ꢄH (CDCl3): 0.04 (6H, s, Si–CH3), 0.88 (9H, s, t-Bu),
1.85 (3H, s, 3-CH3), 2.41 (2H, t, J ¼ 6:3 Hz, 2-CH2),
3.68 (2H, t, J ¼ 6:3 Hz, 1-CH2), 5.93 (1H, s, 4-H). Anal.
Found: C, 40.50; H, 6.99%. Calcd. For C11H23IOSi: C,
40.49; H, 7.10%.
eluent, to afford 8 (1.65 g, 46%). IR ꢃmax (film) cmꢀ1
:
3350, 3078, 2930, 2869, 2314, 1787, 1644, 1461, 1378,
1177, 1049, 892, 737; NMR ꢄH (CDCl3): 0.91 (3H, t,
J ¼ 7:3 Hz, 7-CH3), 1.34 (2H, m, 6-CH2), 1.43 (2H, m,
5-CH2), 1.50 (1H, br.s, OH), 2.03 (2H, t, J ¼ 7:3 Hz, 4-
CH2), 2.30 (2H, t, J ¼ 6:3 Hz, 2-CH2), 3.71 (2H, t, J ¼
6:3 Hz, 1-CH2), 4.81 (1H, s, C=CHH), 4.87 (1H, s,
C=CHH). Anal. Found: C, 75.22; H, 12.52%. Calcd. for
C8H16O: C, 74.94; H, 12.58%.
(E)-3-Methyl-3-heptene-1-ol [(E)-12]. A Grignard
reagent was prepared in ether from Mg (108 mg,
4.5 mmol) and a catalytic amount of I2 and 1-bromo-
propane (608 mg, 4.5 mmol). This solution was added to
a solution of (E)-11 (500 mg, 1.5 mmol) and PdCl2(dppf)
(368 mg, 0.45 mmol) in dry ether (10 ml) at room
3-Methylene-heptanoic acid (4). To a stirred solution
of 8 (134 mg, 1.05 mmol) in CH2Cl2 (2 ml) was added

Synthesis of the Sex Pheromone of a Cowpea Weevil
2723
temperature. The reaction mixture was stirred for 12 h
and then poured into water. The aqueous phase was
extracted with ether, and the organic extract was dried
over Na2SO4 and concentrated in vacuo. The crude
residue was dissolved in THF (6 ml). To the solution,
1 M tetrabutylammonium fluoride (TBAF, 3.0 ml, 3.0
mmol) was added, and the mixture was stirred for 2 h at
room temperature. The solvent was then concentrated
in vacuo, and the residue was poured into water. The
aqueous phase was extracted with ether. The organic
extract was washed with brine, dried over Na2SO4 and
concentrated in vacuo. The residue was purified by silica
gel chromatography, employing 10% ether/pentane as
the eluent, to afford (E)-12 (139 mg, 72% in two steps).
IR ꢃmax (film) cmꢀ1: 3339, 2958, 2930, 2870, 1456,
1382, 1183, 1046, 620. NMR ꢄH (CDCl3): 0.90 (3H, t,
J ¼ 7:3 Hz, 7-CH3), 1.37 (2H, sxt, J ¼ 7:3 Hz, 6-CH2),
1.63 (3H, s, 3-CH3), 2.00 (2H, dt, J ¼ 7:3, 7.3 Hz, 5-
CH2), 2.26 (2H, t, J ¼ 5:8 Hz, 2-CH2), 3.65 (2H, t,
J ¼ 5:8, 1-CH2), 5.25 (1H, t, J ¼ 7:3 Hz, 4-H). Anal.
Found: C, 74.81; H, 12.58%. Calcd. for C8H16O: C,
74.94; H, 12.58%.
s, 2-CH2), 5.25 (1H, t, J ¼ 7:3 Hz, 4-H). NMR ꢄC
(CDCl3): 13.8, 16.2, 22.6, 30.1, 44.8, 127.6, 130.2,
178.5. Anal. Found: C, 67.44; H, 9.85%. Calcd. for
C8H14O2: C, 67.57; H, 9.92%.
(Z)-3-Methyl-3-heptenoic acid (6). In the same man-
ner as that just described, 6 was obtained from 33 mg of
(Z)-12 (18 mg, 49% in two steps). IR ꢃmax (film) cmꢀ1
:
2964, 2672, 2353, 1834, 1412, 1300, 1161, 937. NMR
ꢄH (CDCl3): 0.90 (3H, t, J ¼ 7:3 Hz, 7-CH3), 1.37 (2H,
sxt, J ¼ 7:3 Hz, 6-CH2), 1.80 (3H, d, J ¼ 0:2 Hz, 3-
CH3), 1.99 (2H, dt, J ¼ 7:3, 7.3 Hz, 5-CH2), 3.09 (2H, s,
2-CH2), 5.39 (1H, t, J ¼ 6:8 Hz, 4-CH). NMR ꢄC
(CDCl3): 13.8, 22.7, 23.9, 30.2, 37.2, 127.3, 129.7,
178.1. Anal. Found: C, 67.66; H, 10.16%. Calcd. for
C8H14O2: C, 67.57; H, 9.92%.
Acknowledgments
We thank Dr. George N. Mbata (Fort Valley State
University) for suggesting this study. We also thank Mr.
N. Kawanishi and Mr. K. Aoki for their early contribu-
tion with the synthetic study.
(Z)-3-Methyl-3-heptene-1-ol [(Z)-12]. In the same
manner as that just described, (Z)-12 was obtained from
265 mg of (Z)-11 (87 mg, 84% in two steps). IR ꢃmax
(film) cmꢀ1: 3331, 2959, 2928, 2870, 2398, 2300, 1453,
1377, 1044, 1007, 891. NMR ꢄH (CDCl3): 0.90 (3H, t,
J ¼ 7:3 Hz, 7-CH3), 1.35 (2H, sxt, J ¼ 7:3 Hz, 6-CH2),
1.72 (3H, s, 3-CH3), 2.00 (2H, dt, J ¼ 7:3, 7.3 Hz, 5-
CH2), 2.33 (2H, t, J ¼ 6:3 Hz, 2-CH2), 3.66 (2H, t,
J ¼ 6:3 Hz, 1-CH2), 5.34 (1H, t, J ¼ 7:3 Hz, 4-H). Anal.
Found: C, 75.11; H, 12.41%. Calcd. for C8H16O: C,
74.94; H, 12.58%.
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2724
A. YAJIMA et al.
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