Synthesis of the four stereoisomers of 2,6-dimethyloctane-1,8-dioic acid, a component of the copulation release pheromone of the cowpea weevil, Callosobruchus maculatus

Article abstract of DOI:10.1271/bbb.69.2401

A diastereomeric mixture and the four stereoisomers of 2,6-dimethyloctane- 1,8-dioic acid (2), a copulation release pheromone of the cowpea weevil, Callosobruchus maculatus, were synthesized. The stereoisomeric purities of the four synthetic isomers of 2

Full text of DOI:10.1271/bbb.69.2401

Biosci. Biotechnol. Biochem., 69 (12), 2401–2408, 2005
Synthesis of the Four Stereoisomers of 2,6-Dimethyloctane-1,8-dioic Acid,
a Component of the Copulation Release Pheromone of the Cowpea Weevil,
Callosobruchus maculatus
Tomonori NAKAI,1 Arata YAJIMA,1 Kazuaki AKASAKA,2 Takayuki KAIHOKU,1
y
1;
Miki OHTAKI,1 Tomoo NUKADA,1 Hiroshi OHRUI,2 and Goro YABUTA
1Department of Fermentation Science, Faculty of Applied Biological Science,
Tokyo University of Agriculture, Sakuragaoka 1-1-1, Setagaya-ku, Tokyo 156-8502, Japan
2Graduate School of Life Science, Tohoku University, Tsutsumidori-Amamiya 1-1, Aoba-ku,
Sendai 981-8555, Japan
Received July 20, 2005; Accepted August 22, 2005
A diastereomeric mixture and the four stereoisomers
of 2,6-dimethyloctane-1,8-dioic acid (2), a copulation
CO H
2
release pheromone of the cowpea weevil, Callosobruchus
maculatus, were synthesized. The stereoisomeric puri-
ties of the four synthetic isomers of 2 were determined
by the HPLC analyses of their bis-2-(2,3-anthracenedi-
carboximide)-1-cyclohexyl esters.
HO C
2
1
2
CO H
2
HO C
2
Key words: copulation release pheromone; cowpea wee-
vil; Callosobruchus maculatus; 2-(2,3-an-
thracenedicarboximide)-1-cyclohexyl ester
Fig. 1. The Structures of Copulation Release Pheromones of Azuki
Bean and Cowpea Weevils.
The cowpea weevil, Callosobruchus maculatus, and
the azuki bean weevil, C. chinensis, are serious cosmo-
politan pests of stored products such as cowpea, azuki,
and-or other pulses. Various studies have been con-
ducted on the pheromones of the azuki bean weevil,
C. chinensis,1–7) and the copulation release pheromone
(electin) was identified as callosobruchusic acid {(E)-
3,7-dimethyl-2-octene-1,8-dioic acid (1)} by Yamamoto
et al. in 1981 (Fig. 1).1) Synthetic studies2–7) and the
biological activities4) of 1 were reported, but the
absolute configuration of the natural product remains
obscure. On the other hand, during the course of pest-
management programs, evidence for the presence of the
sex pheromone of C. maculatus was reported by Rup
and Sharma in 1978.8) The biology associated with
female calling and the production of the pheromone
were reported by Qi and Burkholder in 1982.9) Identi-
fication of the sex pheromones of C. maculatus was
reported by Phillips et al. in 1996.10) Recently, Ohsawa
and his co-workers identified a copulation release
pheromone of C. maculatus from the acidic fraction
of the crude extracts of about 3,000 females (Fig. 1)
(K. Ohsawa, personal communication). The pheromone
induces protrusion of the genital organ with the neutral
fraction of the extracts, which contain some hydro-
carbons. The structure of the pheromone was proposed
to be 2,6-dimethyloctane-1,8-dioic acid (2) on the basis
of the GC–MS spectrum of the corresponding partially
purified methyl esters. Since a pure sample of 2 was
unavailable due to the scarcity of the material, such
physical properties as IR, NMR, and ½ꢀꢀD of the natural
product were unavailable. In order to determine the
absolute configuration of the natural product and clarify
the biological activity-structure relationship, we became
interested in synthesizing the four possible stereoisom-
ers of 2. This paper describes the synthesis of the
diastereomeric mixture and the four stereoisomers of
2,6-dimethyloctane-1,8-dioic acid (2), a copulation
release pheromone of the cowpea weevil, C. maculatus.
It also describes HPLC analyses of their bis-2-(2,3-
anthracenedicarboximide)-1-cyclohexyl esters.11–18)
Results and Discussion
Our synthetic plans of 2 are shown in Scheme 1. We
first planned to synthesize a diastereomeric mixture for
the authentic sample of 2. Diacid (2RS,6RS)-2 was
obtained by oxidation of corresponding diol A. Diol A
y
To whom correspondence should be addressed. Fax: +81-3-5477-2622; E-mail: yabta@nodai.ac.jp

2402
T. NAKAI et al.
a
b
HO
HO
CO H
2
OAc
OH
HO C
2
(2RS,6RS)-2
3 (= B)
HO
HO
OH
A
B
4
c
OAc
HO
OH
5 (= A)
CO2H
HO2C
COOR
ROOC
(2S,6R)-2
Bn
R = H: (2RS,6RS)-2
R = Me: (2RS,6RS)-2a
d
e
O
O
N
OP
O
R =
O
C
N
O
Bn
N
O
(2RS,6RS)-2b
O
+
OHC
OP
OH
PPh
3
Scheme 2. Synthesis of (2RS,6RS)-2.
O
O
D
E
(a) KOH, MeOH, rt (97% yield). (b) PtO2, H2, MeOH, rt (74%
yield). (c) Jones reagent, acetone, 0 ꢁC (quant.). (d) CH2N2. ether
(97% yield). (e) (1S,2S)-2-(2,3-anthracenedicarboximide)-1-cyclo-
hexanol, EDC, DMAP, toluene, CH3CN.
F {= (R)-citronellol}
Scheme 1. Retrosynthetic Analyses of (2RS,6RS)- and (2S,6R)-2.
was derived from the known compound B.19) In the
synthesis of optically active 2, the methyl group of C-2
was introduced by diastereoselective Evans alkyla-
tion20,21) of C. The chiral auxiliary group D22,23) con-
nected with known aldehyde E24) by Wittig condensa-
tion. Aldehyde E was prepared from optically active
citronellol (F). Hence we selected citronellol (F) as the
origin of the C-6 chiral center.
Scheme 2 summarizes the synthesis of (2RS,6RS)-2.
The known compound 3,19) derived from geraniol, was
hydrolyzed and subsequent catalytic hydrogenation on
PtO2 gave saturated diol 5 (¼ A). Jones oxidation of 5
gave (2RS,6RS)-2. Since the structure of the natural 2
has been determined by GC–MS analysis of the
corresponding dimethyl ester, the synthetic (2RS,6RS)-
2 was derived to dimethyl ester by treating with
diazomethane to give (2RS,6RS)-2a. The retention time
on GC analysis and the MS spectrum of the synthetic
2a are identical with those of the natural product
(K. Ohsawa, unpublished data). In order to discriminate
the diastereomers, diacid (2RS,6RS)-2 and diester
(2RS,6RS)-2a were subjected to various analyses such
as GC and HPLC with chiral or achiral stationary
phases, but the diastereomers were inseparable. This
problem was solved by the Ohrui–Akasaka method.11–18)
Fig. 2. Chromatogram of (1R,2R)-2Acyclo-O Ester of (2RS,6RS)-2
(2b), Column: Develosil ODS-A-3, Mobile Phase: MeOH, Flow
Rate: 0.8 ml/min, 20 ꢁC.
Namely, the diacid (2RS,6RS)-2 was converted to bis-
(1R,2R)-2-(2,3-anthracenedicarboximide)-1-cyclohexyl
(2Acyclo-O) ester (2b). HPLC analysis of 2b with an
ODS column gave the four peaks (Fig. 2). This means
that it is possible to discriminate the stereochemistry not
only of synthetic but also of natural 2 using this method.
Since the Ohrui–Akasaka method uses not UV but a
fluorescence detector on HPLC analysis, the required
amount of the sample is sufficient at the fmol level.12)
Thus it is a powerful tool for pheromone chemistry,
which often suffers from scarcity of the requisite
pheromones.

Synthesis of the Copulation Release Pheromone of a Cowpea Weevil
2403
Bn
Ref. 24
6’
a, b
O
N
OH
(R)-6 (=F) 97%e.e.
Bn
OHC
OTHP
OTHP
O
(R)-7 (=E)
9 (=C)
O
Bn
c
d
O
N
O
N
CO H
2
OTHP
O
O
O
O
10
11
Bn
e
CO H
2
O
N
HO C
2
PPh
3
O
O
(2S,6R)-2
(S)-8 (=D)
Similarly
CO H
(S)-6
(R)-6
(S)-8
2
+
HO C
2
(2S,6S)-2
(2R,6R)-2
(2R,6S)-2
CO H
(R)-8
(R)-8
2
+
+
HO C
2
CO H
(S)-6
2
HO C
2
Scheme 3. Synthesis of the Four Stereoisomers of 2.
(a) (S)-8, benzene, reflux (b) catalyst, H2, AcOEt (2 steps, 80% yield). (c) NaHMDS, MeI, THF, ꢂ78 ꢁC (84% yield). (d) Jones reagent,
acetone (89% yield). (e) LiOH, H2O2, THF, H2O (96% yield).
Although we succeeded in discriminating the four
isomers of 2 by the Ohrui–Akasaka method, the absolute
configuration of each component remained unidentified.
In order to determine their absolute configurations, we
synthesized the four stereoisomers of 2. Scheme 3
summarizes our stereoselective synthesis of 2. Optically
active (97% e.e.) citronellol (R)-6 (¼ F) was converted
to known aldehyde 7 (¼ E) in the reported manner.24)
Aldehyde 7 was coupled with a chiral auxiliary group
(S)-8 (¼ D)22,23) by Wittig reaction, followed by
catalytic hydrogenation to give 9 (¼ C). In this step,
we initially used Pd/C for the syntheses of (2S,6R)- and
(2R,6S)-2. However, as discussed below, partial race-
mization at C-60 of 9 was observed. In order to avoid this
racemization, we turned to the use of PtO2 as a catalyst
for the synthesis of (2R,6R)- and (2S,6S)-2. The
diastereoselective Evans alkylation20,21) of 9 with methyl
iodide in the presence of NaHMDS as a base gave 10.
Deprotection of the THP group and simultaneous
oxidation of 10 were carried out by Jones oxidation to
give 11. Finally, the chiral auxiliary group of 11 was
removed by LiOOH25) to give (2S,6R)-2. The overall
yield of (2S,6R)-2 was 57% from the known com-
pound 7. Similarly, the other three isomers of 2 were
synthesized.
With the four stereoisomers of 2 in hand, the purities
of each sample were determined by the Ohrui–Akasaka
method. Figure 3 shows the chromatograms of each
sample. The fastest-moving isomer was (2S,6R)-2b, and
the retention times were prolonged as follows:
(2S,6S) < (2R,6R) < (2R,6S). Table 1 shows the chro-
matographic data for the samples. According to the
HPLC analysis data, the diastereoselectivities of Evans
alkylation of C-2 were estimated to be about 93:7
(entry 4) to 97:3 (entry 3). On the other hand, partial
racemization at C-6 of the two samples was observed by
comparison with the enantiomeric purity of the starting
(R)- and (S)-citronellol (6) (entries 1 and 4). The
enantiomeric purity of both the starting (R)- and (S)-
citronellol (6) was 97% e.e., but those of the synthetic
(2S,6R)- and (2R,6S)-2 at C-6 were 94.4 and 88.8%
e.e. respectively. This partial racemization is probably
caused by catalytic hydrogenation of the double bond
with Pd/C as a catalyst. Indeed, this partial racemization
was not observed in entries 2 and 3 (97% e.e. at C-6), in
which we used PtO2 as a catalyst in the hydrogenation
step. In the course of hydrogenation, the related
palladium catalyst-mediated partial racemization was
observed at a branched chain.26) In spite of the
possibility of partial racemization, palladium catalysts

2404
T. NAKAI et al.
Fig. 3. Chromatograms of (1R,2R)-2Acyclo-O Esters of Synthetic 2; 1: (2S,6R), 2: (2S,6S), 3: (2R,6R), 4: (2R,6S), 5: Unknown.
Table 1. Stereoisomeric Purities of the Synthetic 2 Determined by HPLC Analyses of 2b
Peak area ratio (%)a
Retention time
Entry
Sample
(min)b
(2S,6R)
(2S,6S)
(2R,6R)
(2R,6S)
1
2
3
4
(2S,6R)-2b
(2S,6S)-2b
(2R,6R)-2b
(2R,6S)-2b
12.6
14.4
16.9
22.6
91.9
1.0
3.3
5.4
2.8
94.7
ndc
5.3
ndc
ndc
4.3
95.2
0.2
1.5
92.5
1.9
aThe detail of the analytical conditions are described in Experimental.
bThe retention time of the major peak.
cNot detected.
are widely used in synthetic studies. The maintenance of
the stereoisomeric purity of a synthetic product with a
branched-chain after the hydrogenation step by such a
highly sensitive analytical method as the Ohrui–Akasaka
method should be confirmed. Although the stereo-
isomeric purity of some synthetic sample was slightly
diminished, the purity of each sample was estimated to
be >91%. In order to study the enantio-specifity of
pheromone perception, it is known that samples with
>85% optical purity are suitable in most cases.27) Thus
our synthetic samples can be used to study the enantio-
specifity of the pheromone perception of C. maculatus.
Experimental
Optical rotation values were measured on a Jasco
DIP-140. IR spectra were measured using a Shimadzu
IR-470 spectrometer. NMR spectra were recorded with a
1
Jeol JNM-A400 operating at 400 MHz for H spectra
and 100 MHz for 13C NMR spectra. Chemical shifts are
reported as ppm relative to CHCl3 measured from the
solvent resonance (7.24 ppm). Mass spectra were re-
corded with a Shimadzu GCMS-QP 2000A running
in the EI scan mode. Elemental compositions were
analyzed on a J-Science Microcorder JM10. Column
chromatography was carried out using silica gel
(Wakogel C-200).
Conclusion
Synthesis of the diastereomeric mixture and the four
stereoisomers of 2 was achieved. The four synthetic
stereoisomers were discriminated from each other by
HPLC analysis of the corresponding bis-(1S,2S)-2-(2,3-
anthracenedicarboximide)-1-cyclohexyl ester. The opti-
cal purities of the synthetic 2 were determined by the
same method. Our synthetic samples were pure enough
to use in the study of the enantio-specifity of the
pheromone perception of C. maculatus. Since the
Ohrui–Akasaka method requires an fmol level sample,
it is a powerful tool for the determination of the absolute
configuration of the natural product. Bioassay of the
synthetic samples and determination of the absolute
configuration of the natural product using this analytical
method are currently under way.
(2E,6E)-2,6-Dimethyl-2,6-octadiene-1,8-diol
(4).
Acetate 3 (50 mg, 0.24 mmol) was dissolved in MeOH
(8 ml), then 2 M KOH (4 ml) was added. The reaction
mixture was stirred for 5 min and then poured into water,
and the aqueous mixture was extracted with ether and the
organic phases were washed with brine and dried over
MgSO4. The solvent was evaporated and the residue was
purified by column chromatography with hexane/EtOAc
(5:1) to give 4 as a colorless oil (39 mg, 97%). IR ꢁmax
(film) cmꢂ1: 3330 (br. s, O–H), 2900 (s, C–H), 1000
(s, C–O), 590 (w). NMR ꢂH (CDCl3): 1.65 (s, 3H, 6-
CH3), 1.67 (s, 3H, 2-CH3), 2.01–2.19 (m, 4H, 4, 5-H),
3.98 (s, 2H, 1-H), 4.14 (d, J ¼ 7:3 Hz, 2H, 8-H), 5.36
(m, 2H, 3, 7-H). Found: C, 70.55%; H, 10.55%. Calcd.
for C10H18O2: C, 70.55%; H, 10.66%.

Synthesis of the Copulation Release Pheromone of a Cowpea Weevil
2405
(2RS,6RS)-2,6-Dimethyloctane-1,8-diol (5). A solu-
tion of 4 (444 mg, 2.60 mmol) in MeOH (8 ml) was
charged with PtO2 (10 mg, 0.05 mmol). The reaction
mixture was stirred vigorously under an atmosphere of
hydrogen for 2 h. The catalyst was removed by filtration
with Celite and rinsed with methanol. The solvent was
evaporated and the residue was purified by column
chromatography with hexane/EtOAc (5:1) to give 5 as a
colorless oil (336 mg, 74%). IR ꢁmax (film) cmꢂ1: 3330
(br. s, O–H), 2900 (s, C–H), 1470 (m, C–H), 1390 (m,
C–H), 1040 (s, C–O), 690 (w). NMR ꢂH (CDCl3): 0.87
(d, J ¼ 6:8 Hz, 3H, 6-CH3), 0.89 (d, J ¼ 6:8 Hz, 3H, 2-
CH3), 1.02–1.41 (m, 6H, 3, 4, 5, 6-H), 1.55–1.63 (m, 3H,
2, 7-H), 3.37–3.51 (m, 2H, 1-H), 3.61–3.72 (m, 2H, 8-
H). Found: C, 69.03%; H, 12.51%. Calcd. for C10H22O2:
C, 68.92%; H, 12.72%.
identical with those of the dimethylester of the natural
product (K. Ohsawa, unpublished data).
Preparations and HPLC analyses of bis-(1R,2R)-2-
(2,3-anthracenedicarboximide)-1-cyclohexyl ester of
2,6-dimethyloctane-1,8-dioic acid (2b). To a solution
of 2,6-dimethyloctane-1,8-dioic acid (2) in MeCN:tolu-
ene (1:1), (1R,2R)-2-(2,3-anthracenedicarboximide)-1-
cyclohexanol (2ACyclo–OH) (10 eq.), 4-N,N-dimethyl-
aminopyridine (DMAP, catalytic amount), and 2-(3-di-
methylaminopropyl)-1-ethylcarbodiimide hydrochloride
(EDC, 30 eq.) were successively added. The mixture
was stirred at 40 ꢁC overnight. An aliquot was then
loaded onto silica gel TLC plate (10 cm length, Silicagel
60 F254, Art ꢂ5744, Merck) and developed with hexane/
EtOAc (4:1, v/v). The target spot detected by fluores-
cence was collected, packed in a Pasteur pipette, and
eluted with EtOAc/EtOH (4:1, v/v). After evaporation
of the solvent with an N2 gas stream, the residue was
dissolved in MeOH and directly used for HPLC analysis.
HPLC analyses: The prepared 2b was separated
on a reverse-phase column (Develosil ODS-A-3, 4.6
mm i.d. ꢃ 150 mm, Nomura Chemical, Aichi, Japan).
Detection was carried out by monitoring the fluores-
cence intensity at 462 nm (excitation at 298 nm). The
separation was performed with MeOH at a flow rate
0.8 ml/min. The column temperature was kept at 20 ꢁC;
tR(2S,6R) = 12.6, tR(2S,6S) = 14.4, tR(2R,6R) = 16.9,
tR(2R,6S) = 22.6.
(2RS,6RS)-2,6-Dimethyloctane-1,8-dioic acid (2). To
a solution of 5 (50 mg, 0.29 mmol) in acetone (4 ml),
Jones reagent was added dropwise until an orange-
brown color persisted. Thereafter, the reaction mixture
was poured into water, the aqueous mixture was
extracted with EtOAc and organic phases were washed
successively with water and brine, and dried over
MgSO4. The solvent was evaporated and the residue
was purified by column chromatography with hexane/
EtOAc (5:1) to give 2 as a colorless oil (70 mg, quant.).
IR ꢁmax (film) cmꢂ1: 3100 (m, O–H), 2930 (s, C–H),
1700 (s, C=O), 1440 (m), 1300 (m), 1240 (s, C–H),
1170 (m), 1130 (w), 1020 (w), 950 (m), 800 (w), 740
(w), 690 (w), 640 (w). NMR ꢂH (CDCl3): 0.95 (d, J ¼
6:8 Hz, 3H, 6-CH3), 1.16 (d, J ¼ 6:8 Hz, 3H, 2-CH3),
1.19–1.47 (m, 5H, 3, 4, 5-H), 1.65 (m, 1H, 3-H), 1.95
(m, 1H, 6-H), 2.11–2.20 (m, 1H, 7-H), 2.26–2.23 (m,
1H, 7-H), 2.46 (m, 1H, 2-H). NMR ꢂC (CDCl3): 16.8
(C-9), 19.7 (C-10), 24.3 (C-4), 29.8 (C-6), 33.4 (C-3),
36.2 (C-5), 39.2 (C-2), 41.3 (C-7), 179.4 (C-8), 182.9
(C-1). Found: C, 59.49%; H, 8.98%. Calcd. for
C10H18O4: C, 59.39%; H, 8.97%.
(4S,60R)-3-[60-Methyl-80-(tetrahydro-2H-pyran-2-yl-
oxy)octanoyl]-4-phenylmethyl-1,3-oxazolidin-2-one (9).
A mixture of (R)-7 (400 mg, 1.87 mmol) and (S)-8
(1.34 g, 2.81 mmol) was dissolved in benzene. The
reaction mixture was refluxed at 60 ꢁC for 4 d and then
the solvent was evaporated. The residue was purified by
column chromatography with hexane/EtOAc (20:1) to
give coupling compound (738 mg). This was dissolved
in AcOEt (50 ml), and the solution was charged with Pd/
C (6 mg, 0.03 mmol). The reaction mixture was stirred
vigorously under an atomosphere of hydrogen for 2 h.
The catalyst was removed by filtration with Celite and
rinsed with methanol. The solvent was evaporated and
the residue was purified by column chromatography
with hexane/EtOAc (10:1) to give (4S,60R)-9 as a
Dimetyl (2RS,6RS)-2,6-dimetyloctanedioate (2a). A
solution of 2 (48 mg, 0.25 mmol) in ether (2 ml) was
treated with CH2N2. After stirring until a yellow color
persisted, the reaction mixture was evaporated to give 2a
(53 mg, 97%). IR ꢁmax (film) cmꢂ1: 2950 (s, C–H), 1740
(s, C=O), 1450 (m), 1385 (m), 1200 (br. m) (1050 (w),
840 (w), 750 (w). NMR ꢂH (CDCl3): 0.89 (d, J ¼
6:8 Hz, 3H, 6-CH3), 1.12 (d, J ¼ 6:8 Hz, 3H, 2-CH3),
1.23–1.41 (m, 4H, 4, 5-H), 1.59 (m, 2H, 3-H), 1.92 (m,
1H, 6-H), 2.09 (dd, J ¼ 6:8, 15.1 Hz, 1H, 7-H), 2.28 (m,
1H, 7-H), 2.41 (sxt, J ¼ 6:8 Hz, 1H, 2-H), 3.64 (s, 3H,
CH3–O), 3.65 (s, 3H, CH3–O). GC–MS analysis;
column: DB-5 (30 m ꢃ 0:25 mm), carrier gas He (1.3
ml/min), 100 ꢁC (2 min) to 220 ꢁC (4 ꢁC/min), tR ¼
14:2, m=z: 199 (M–CH3Oþ), 171, 166, 157, 143, 139,
125, 111, 97, 88, 83, 74, 69, 59, 55 (100), 43, 41. Found:
C, 62.61%; H, 9.52%. Calcd. for C12H22O4: C, 62.58%;
H, 9.63%. The retention time and MS spectrum were
22
colorless oil (716 mg, 80%). ½ꢀꢀD þ48ꢁ (c 0.12,
CHCl3). IR ꢁmax (film) cmꢂ1: 2930 (s, C–H), 1780 (s,
C=O), 1700 (s, C=O), 1460 (s), 1390 (s), 1230 (m, C–
H), 1140 (m), 1030 (m), 900 (m), 870 (m), 810 (m), 750
(m), 700 (m). NMR ꢂH (CDCl3): 0.88 (d, J ¼ 6:8 Hz,
3H, 60-CH3), 1.16–1.83 (m, 15H, 30, 40, 50, 60, 70, 300, 400,
500-H), 2.74 (dd, J ¼ 9:8, 13.7 Hz, 1H, CHH–Ph), 2.91
(m, 2H, 20-H), 3.28 (dd, J ¼ 3:4, 13.7 Hz, 1H, CHH–
Ph), 3.34–3.52, 3.72–3.87 (m, total 4H, 80, 600-H), 4.14
(m, 2H, 5-H), 4.55 (m, 1H, 200-H), 4.62–4.68 (m, 1H, 4-
H), 7.17–7.34 (m, 5H, Ph). Found: C, 69.08%; H,
8.48%; N, 3.39%. Calcd. for C24H35NO5: C, 69.04%; H,
8.45%; N, 3.35%.

2406
T. NAKAI et al.
(4R,60S)-isomer. In the same manner as described
8.57%; N, 3.18%. Calcd. for C25H37NO5: C, 69.58%;
H, 8.64%; N, 3.25%.
above, (4R,60S)-9 was obtained from 8.70 g of (S)-7
22
(15.2 g, 76%). ½ꢀꢀD ꢂ38:2ꢁ (c 1.10, CHCl3). IR and
1H NMR spectra were indistinguishable from those of
(4S,60R)-isomer. Found: C, 69.04%; H, 8.41%; N,
3.45%. Calcd. for C24H35NO5: C, 69.04%; H, 8.45%;
N, 3.35%.
(4R,20R,60R)-isomer. In the same manner as described
above, (4S,20S,60S)-10 was obtained from 3.3 g of
22
(4R,60R)-9 (2.8 g, 82%). ½ꢀꢀD ꢂ49:1ꢁ (c 1.00, CHCl3).
IR and 1H NMR spectra were indistinguishable from
those of (4S,20S,60R)-isomer. Found: C, 69.63%; H,
8.72%; N, 3.22% Calcd. for C25H37NO5: C, 69.58%; H,
8.64%; N, 3.25%.
(4S,60S)-isomer. In the same manner as described
above, except for using PtO2 as a catalyst in the
hydrogenolysis, (4S,60S)-9 was obtained from 5.27 g of
22
(S)-7 (8.60 g, 68%). ½ꢀꢀD þ33ꢁ (c 0.12, CHCl3). IR
(4R,20R,60S)-isomer. In the same manner as described
above, (4R,20R,60S)-10 was obtained from 270 mg of
1
and H NMR spectra were indistinguishable from those
22
of (4S,60R)-isomer. Found: C, 69.03%; H, 8.39%; N,
3.55%. Calcd. for C24H35NO5: C, 69.04%; H, 8.45%, N,
3.35%.
(4R,60S)-9 (230 mg, 83%). ½ꢀꢀD ꢂ46ꢁ (c 0.50, CHCl3).
IR and 1H NMR spectra were indistinguishable from
those of (4S,20S,60R)-isomer. Found: C, 69.61%; H,
8.68%; N, 3.22%. Calcd. for C25H37NO5: C, 69.58%; H,
8.64%; N, 3.25%.
(4R,60R)-isomer. In the same manner as described
above, (4R,60R)-9 was obtained from 3.0 g of (R)-7
22
(5.4 g, 81%). ½ꢀꢀD ¼ ꢂ34ꢁ (c ¼ 0:22, CHCl3). IR and
(4S,20S,60R)-3-(20,60-Dimethyl-70-carboxyheptanoyl)-
4-phenylmethyl-1,3-oxazolidin-2-one (11). To a solution
of (4S,20S,60R)-10 (79 mg, 0.16 mmol) in acetone (6 ml),
Jones reagent was added dropwise until an orange-
brown colour persisted. Thereafter, the reaction mixture
was poured into water, the aqueous mixture was
extracted with three portions of EtOAc, and the organic
phases were washed successively with water and brine
and dried over MgSO4. The solvent was evaporated and
the residue was purified by column chromatography
with hexane/EtOAc (5:1) to give (4S,20S,60R)-11 as a
1H NMR spectra were indistinguishable from those of
(4S,60R)-isomer. Found: C, 69.05%; H, 8.38%; N,
3.49%. Calcd. for C24H35NO5: C, 69.04%; H, 8.45%;
N, 3.55%.
(4S,20S,60R)-3-[20,60-Dimethyl-80-(tetrahydro-2H-pyran-
2-yloxy)octanoyl]-4-phenylmethyl-1,3-oxazolidin-2-one
(10). To a cooled solution of (4S,60R)-9 (300 mg,
0.629 mmol) in THF (5 ml) at ꢂ78 ꢁC, 1 M NaHMDS
(0.69 ml, 0.69 mmol) in THF was added dropwise. After
the reaction mixture was stirred for 30 min at the same
temperature, MeI (120 ml, 1.89 mmol) was added. The
solution was stirred overnight and then the reaction
mixture was poured into water. The aqueous mixture
was extracted with three portions of ether, and the
organic phases were washed successively with water and
brine and dried over Na2SO4. The solvent was evapo-
rated and the residue was purified by column chroma-
tography with hexane/EtOAc (10:1) to give 10 as a
22
colorless oil (60 mg, 89%). ½ꢀꢀD þ55:7ꢁ (c 1.00,
CHCl3). IR ꢁmax (film) cmꢂ1: 3300 (br. m, O–H), 2930
(s, C–H), 1780 (s, C=O), 1700 (s, C=O), 1460 (w) 1390
(s), 1230 (s, C–H), 1100 (w), 1050 (w), 1020 (w), 970
(w), 920 (w), 740 (s), 700 (m). NMR ꢂH (CDCl3): 0.94
(d, J ¼ 6:8 Hz, 3H, 60-CH3), 1.15–1.40 (m, 5H, 30, 40, 50-
H), 1.20 (d, J ¼ 6:8 Hz, 3H, 20-CH3), 1.74 (m, 1H, 30-
H), 1.94 (m, 1H, 60-H), 2.13 (dd, J ¼ 6:8, 15.1 Hz, 1H,
70-H), 2.31 (dd, J ¼ 6:8, 15.1 Hz, 1H, 70-H), 2.74 (dd,
J ¼ 9:6, 13.2 Hz, 1H, CHH–Ph), 3.24 (dd, J ¼ 3:2,
13.2 Hz, 1H, CHH–Ph), 3.69 (sxt, J ¼ 6:8 Hz, 1H, 20-H),
4.08 (m, 2H, 5-H), 4.66 (m, 1H, 4-H), 7.18–7.32 (m, 5H,
Ph). Found: C, 66.49%; H, 7.63%; N, 3.80%. Calcd. for
C20H27NO5: C, 66.46%; H, 7.53%; N, 3.88%.
22
colorless oil (259 mg, 84%). ½ꢀꢀD þ49:9ꢁ (c 1.05,
CHCl3). IR ꢁmax (film) cmꢂ1: 2930 (s, C–H), 1780 (s,
C=O), 1700 (s, C=O), 1460 (m), 1380 (m), 1230 (m, C–
H), 1030 (m), 900 (w), 870 (w), 700 (m), 500 (w). NMR
ꢂH (CDCl3): 0.86 (d, J ¼ 6:8 Hz, 3H, 60-CH3), 1.16–1.83
(m, 15H, 30, 40, 50, 60, 70, 300, 400, 500-H), 1.20 (d, J ¼
6:8 Hz, 3H, 20-CH3), 2.74 (dd, J ¼ 9:6, 13.2 Hz, 1H,
CHH–Ph), 3.25 (dd, J ¼ 3:2, 13.2 Hz, 1H, CHH–Ph),
3.32–3.52, 3.68–3.88 (m, total 5H, 20, 80, 600-H), 4.14 (m,
2H, 5-H), 4.55 (m, 1H, 200-H), 4.66 (m, 1H, 4-H), 7.18–
7.33 (m, 5H, Ph). Found: C, 69.62%; H, 8.73%; N,
3.30%. Calcd. for C25H37NO5: C, 69.58%; H, 8.64%; N,
3.25%.
(4S,20S,60S)-isomer. In the same manner as described
above, (4S,20S,60S)-11 was obtained from 5.5 g of
22
(4S,20S,60S)-10 (4.5 g, 95%). ½ꢀꢀD
þ48ꢁ (c 0.70,
CHCl3). IR and 1H NMR spectra were indistinguishable
from those of (4S,20S,60R)-isomer. Found: C, 66.42%; H,
7.64%; N, 3.85%. Calcd. for C20H27NO5: C, 66.46%; H,
7.53%; N, 3.88%.
(4S,20S,60S)-isomer. In the same manner as described
above, (4R,20R,60R)-10 was obtained from 7.20 g
(4R,20R,60R)-isomer. In the same manner as described
above, (4R,20R,60R)-11 was obtained from 2.7 g of
22
22
(4S,60S)-9 (5.87 g, 80%). ½ꢀꢀD þ46:3ꢁ (c 1.00, CHCl3).
(4R,20R,60R)-10 (2.3 g, 95%). ½ꢀꢀD ꢂ55ꢁ (c 0.30,
IR and 1H NMR spectra were indistinguishable from
those of (4S,20S,60R)-isomer. Found: C, 69.64%; H,
CHCl3). IR and 1H NMR spectra were indistinguishable
from those of (4S,20S,60R)-isomer. Found: C, 66.31%; H,

Synthesis of the Copulation Release Pheromone of a Cowpea Weevil
2407
22
(4R,20R,60R)-11 (1.0 g, 96%). ½ꢀꢀD ꢂ11ꢁ (c 0.30,
7.69%; N, 3.92%. Calcd. for C20H27NO5: C, 66.46%;
H, 7.53%; N, 3.88%.
CHCl3). Found: C, 59.41%; H, 8.69%. Calcd. for
1
C10H18O4: C, 59.39%; H, 8.97%. IR, H and 13C NMR
spectra were identical to those of (2S,6S)-2.
(4R,20R,60S)-isomer. In the same manner as described
above, (4R,20R,60S)-11 was obtained from 200 mg of
22
(4R,20R,60S)-10 (160 mg, 93%). ½ꢀꢀD ꢂ57:6ꢁ (c 1.10,
(2R,6S)-isomer. In the same manner as described
above, (2R,6S)-2 was obtained from 190 mg of
CHCl3). IR and 1H NMR spectra were indistinguishable
from those of (4S,20S,60R)-isomer. Found: C, 66.49%; H,
7.34%; N, 3.87%. Calcd. for C20H27NO5: C, 66.46%; H,
7.53%; N, 3.88%.
22
(4R,20R,60S)-11 (90 mg, 98%). ½ꢀꢀD ꢂ17:2ꢁ (c 2.02,
CHCl3). Found: C, 59.55%; H, 8.82%. Calcd. for
1
C10H18O4: C, 59.39%; H, 8.97%. IR, H and 13C NMR
spectra were identical to those of (2S,6R)-2.
(2S,6R)-2,6-Dimethyloctane-1,8-dioic acid (2). A so-
lution of (4S,20S,6R)-11 (50 mg, 0.12 mmol) in THF
(2 ml) and water (6 ml) was treated with 30% H2O2
(58 ml, 0.48 mmol) followed by solid LiOH (12 mg,
0.24 mmol). After stirring for 30 min, the reaction was
treated with a solution of aq. Na2SO3 followed by 0.5 N
NaHCO3. Following removal of THF in vacuo on a
rotary evaporator, the residue was diluted with water and
extracted with three portions of CH2Cl2. The aqueous
phase was acidified to pH 1–2 with 5 N HCl and extracted
with three portions of AcOEt. The AcOEt extracts were
combined, and dried with Na2SO4, and the solvent was
evaporated and the residue purified by column chroma-
tography with hexane/EtOAc (1:5) to give (2S,6R)-2 as a
Acknowledgments
We wish to acknowledge valuable discussions on the
natural pheromone and measurement of GC–MS spectra
with Professor K. Ohsawa and Professor S. Yajima
(Tokyo University of Agriculture). We express our
gratitude to Mr. M. Takenaka (Takasago International
Co.) for his kind gift of citronellol.
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colorless oil (28 mg, 96%). ½ꢀꢀD þ20ꢁ (c 0.30, CHCl3).
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1700 (s, C=O), 1440 (m), 1300 (m), 1240 (s, C–H), 1170
(m), 1130 (w), 1020 (w), 950 (m), 800 (w), 740 (w), 690
(w), 640 (w). NMR ꢂH (CDCl3): 0.95 (d, J ¼ 6:8 Hz, 3H,
6-CH3), 1.16 (d, J ¼ 6:8 Hz, 3H, 2-CH3), 1.20–1.44 (m,
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(2S,6S)-isomer. In the same manner as described
above, (2S,6S)-2 was obtained from 2.00 g of
22
(4S,20S,60S)-11 (900 mg, 93%). ½ꢀꢀD þ9:3ꢁ (c 0.41,
CHCl3). IR ꢁmax (film) cmꢂ1: 2930 (s, C–H), 2700 (br.
m, O–H), 1700 (s, C=O), 1440 (m), 1300 (m), 1240 (s,
C–H), 1170 (m), 1130 (w), 1020 (w), 950 (m), 800 (w),
740 (w), 690 (w), 640 (w). NMR ꢂH (CDCl3): 0.95 (d,
J ¼ 6:8 Hz, 3H, 6-CH3), 1.16 (d, J ¼ 6:8 Hz, 3H, 2-
CH3), 1.33–1.44 (m, 3H, 5, 6-H), 1.64 (m, 2H, 4-H),
1.95 (m, 2H, 3-H), 2.17 (dd, J ¼ 6:8, 15.1 Hz, 1H, 7-H),
2.29 (dd, J ¼ 6:8, 15.1 Hz, 1H, 7-H), 2.46 (sxt, J ¼
6:8 Hz, 1H, 2-H). NMR ꢂC (CDCl3): 16.8 (C-9), 19.8
(C-10), 24.3 (C-4), 29.8 (C-6), 36.1, 36.1 (C-3,5), 39.1
(C-2), 41.3 (C-7), 179.4 (C-8), 183.0 (C-1). Found: C,
59.44%; H, 8.84%. Calcd. for C10H18O4: C, 59.39%;
H, 8.97%.
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above, (2R,6R)-2 was obtained from 2.2 g of
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