Organic synthesis in pheromone science

Article abstract of DOI:10.3390/10091023

Examples are given to illustrate the use of chemical and/or enzymatic asymmetric reactions in the synthesis of the new pheromones of the broad-horned flour beetle, flea beetle, currant stem girdler and Colorado potato beetle. The relationships between ste

Full text of DOI:10.3390/10091023

Molecules 2005, 10, 1023-1047
molecules
ISSN 1420-3049
http://www.mdpi.org
Keynote Lecture
Organic Synthesis in Pheromone Science
Kenji Mori
Emeritus Professor, The University of Tokyo, 1-20-6-1309, Mukogaoka, Bunkyo-ku, Tokyo 113-0023,
Japan, Fax: (+81)-3-3816-6889. E-mail: kjk-mori@arion.ocn.ne.jp
Received: 23 April 2005 / Published: 30 September 2005
Abstract: Examples are given to illustrate the use of chemical and/or enzymatic
asymmetric reactions in the synthesis of the new pheromones of the broad-horned flour
beetle, flea beetle, currant stem girdler and Colorado potato beetle. The relationships
between stereochemistry and bioactivity among pheromones are summarized to
emphasize biodiversity as revealed in pheromone perception.
Keywords: Enantioselective synthesis; Lactone; Lipase; Pheromones; Terpenes
Thank you for your kind introduction. I also thank Profs. Tkachev and De Kimpe for their kind
invitation to attend this conference. This is my first visit to Siberia and I really expect to see something
new in Altai mountains after the Conference. May I have the first PowerPoint picture, please…
Figure 1
Organic Synthesis in Pheromone Science
1. Synthesis as Structural Proof
2. Synthesis for Large-Scale Preparation
3. Synthesis to Clarify the Structure-Activity Relationship
Kenji Mori
Emeritus Professor, The University of Tokyo
Consultant, Fuji Flavor Co., Insect Pheromone and
Traps Division
Consultant, RIKEN Research Center for
Allergy and Immunology

Molecules 2005, 10
1024
Today I would like to tell you about these three aspects in organic synthesis related to pheromone
science: No. 1; Synthesis can prove or disprove the proposed structure of a pheromone. No. 2:
Synthesis can provide a substantial amount of a useful pheromone. No. 3: Synthesis can clarify the
structure-activity relationships among pheromones (Figure 1).
Figure 2
Synthesis and Pheromone Activity of Bombykol and Its Isomers
OH
12 10
Bombykol
Activity (Lockstoffeinheit)
µg/mL pet. ether
1
10Z,12Z
10Z,12E
10E,12Z
10E,12E
10–2
10–12
100
The silkworm moth
(Bombyx mori)
10–10
Natural bombykol
A. Butenandt, E. Hecker, M. Hopp, W. Koch, Liebigs Ann. Chem. 1962, 658, 39.
Since the beginning of pheromone chemistry, synthesis has been one of the very important
methodologies. Professor Butenandt isolated and identified bombykol as the female-produced sex
pheromone of the silkworm moth, Bombyx mori (Figure 2). The final stage of his investigation was to
synthesize the four cis/trans isomers of bombykol. Because only the (10E,12Z)-isomer was as active as
the
pheromone
itself,
the
structure
of
bombykol
was
determined
as
(10E,12Z)-10,12-hexadecadien-1-ol.
Figure 3
Examples of Wrong and Correct Structures
Proposed for Pheromones
OH
Gypsy moth
(Lymantria dispar)
O
OAc
Gyptol
Disparlure
(Beroza, 1970)
(Jacobson, 1961)
O
O
OCOEt
American cockroach
(Periplaneta americana)
O
(Jacobson, 1963)
Periplanone-B
(Persoons, 1976)

Molecules 2005, 10
1025
In the past, at the beginning of pheromone research, there were some cases in which incorrect
structures were proposed for pheromones (Figure 3). In 1961 Jacobson claimed gyptol to be the
pheromone of the gypsy moth, and in 1963 he claimed this unusual cyclopropane compound to be the
pheromone of the American cockroach. These two compounds were soon synthesized by others and
the synthetic compounds did not work as pheromones at all. Further studies on these two insects later
enabled Beroza and Persoons to identify disparlure and periplanone B as the true pheromones of gypsy
moth and American cockroach, respectively. Again, synthesis played the major role.
Figure 4
(+)-Acoradiene, Aggregation Pheromone of the
Broad-horned Flour Beetle, Gnatocerus cornutus
Isolation and structure proposal
S. Tebayashi, N. Hirai, T. Suzuki, S. Matsuyama, H. Nakakita, T. Nemoto,
H. Nakanishi J. Stored Prod. Res. 1998, 34, 99.
PCy3
Retrosynthetic analysis
Cl
Cl
Ph
Ru
OH
PCy3
OP
OP
Ring closing
olefin metathesis
OH
A
B
(+)-Acoradiene (1)
O
H
CO2H
[1]
[1]
O
O
H
C
D
(+)-Pulegone (2)
[1] J. Wolinsky, T. Gibson, D. Chan, and H. Wolf, Tetrahedron, 1965, 21, 1247.
S. Kurosawa, M. Bando, and K. Mori, Eur. J. Org. Chem. 2001, 4395.
Now I shall tell you how we have determined the correct stereostructure of the aggregation
pheromone of the broad-horned flour beetle (Figure 4). Isolation and structure proposal of this
pheromone was reported in 1998 by Tebayashi et al. at the University of Tsukuba in Japan.
Figure 5
1H-NMR spectra of (+)-acoradiene
(400 MHz, CDCl3)
13C-NMR spectra of (+)-acoradiene
(100 MHz, CDCl3)
Natural product
Natural product
Synthetic sample
Synthetic sample
(1R,4R,5S)-1
(Proposed structure)

Molecules 2005, 10
1026
The proposed structure, (+)-acoradiene, was unique as the only pheromone with a
spirosesquiterpene structure. We therefore synthesized it in 2001. Ring-closing olefin metathesis
(Β→Α) was the key-step. Because diol A was nicely crystalline, its structure could be determined
beyond doubt by X-ray analysis, conducted by Dr. Bando. When we synthesized (+)-acoradiene, Dr.
Kurosawa carefully compared the NMR spectrum of the synthetic product with that of the pheromone
(Figure 5). Here you can see that the NMR spectra of these two samples are not identical. The
proposed structure, therefore, must be incorrect. We hypothesized that the natural pheromone was one
of the possible isomers of 1, but this hypothesis must be proven. We decided to synthesize a
stereoisomeric mixture of all the possible isomers of 1.
Figure 6
Synthesis 1
1) Br2, AcOH
2) NaOEt, EtOH
(75%, 2 steps)
OH
HO
CO2Et
CO2Et
O
p-TsOH, benzene
O
3) O3, EtOAc
(92%)
(R)-(+)-Pulegone [(R)-2]
(quant.)
O
O
3
4
1) LiAlH4,Et2O
(92%)
OH
DCC, CuCl,
AlCl3, benzene
(95%)
Et2O
(65%)
2) dil. HCl aq.
(86%)
O
5
O
6
NaCN, AcOH,
POCl3, Py.
(82%)
EtOH
(73%)
(30% conversion)
CN
CN
HO
O
71)
8
9
(d.s. = 1:1)
1) J. N. Marx, L. R. Norman, J. Org. Chem., 1975, 40, 1602.
The synthesis of a stereoisomeric mixture of acoradiene started from (R)-(+)-pulegone to give
spiro ketone 11 (Figure 6). Hydrocyanation of 7 furnished cyanohydrin 8, which was dehydrated to
give 9.
Figure 7
Synthesis 2
1) Mg, MeOH
MeMgBr
(98%)
THF
(97%)
2) DIBAL, CH2Cl2
(83%)
CN
CHO
OH
11
9
10
1) Dess-Martin periodinane
CH2Cl2 (88%)
Preparative
Gas Chromatography
2) Ph3PCH3Br, n-BuLi,
THF (82%)
Conditions
column: TC-WAX
temp.: 70 to 230ºC (1.5ºC/min)
carrier gas: N2 (130 kPa)
(76% conversion)
1
Rt (min)
53.5
54.3
54.5
55.1
1H NMR spectrum was identical
with that of the natural product

Molecules 2005, 10
1027
Reduction of 9 with magnesium and methanol gave the saturated nitrile, which was further
reduced with DIBAL to give aldehyde 10 (Figure 7). The remaining two carbons were attached to 10
by Grignard and Wittig reactions, respectively, to give 1 as a stereoisomeric mixture. The mixture
could be separated by preparative GC, and a fraction with a retention time of 54.3 min showed an
NMR spectrum identical with that of the natural product. The pheromone must be a stereoisomer of 1.
But how about the stereochemistry of that isomer?
Figure 8
Comparison of the Characteristic Spectral Data between Natural
Product and Its Diastereoisomers
Table 1. Characteristic 1H NMR data (δ/ppm)
1
7
5
4
13
1R*,4S*,5S*2a) 1R*,4R*,5S*3) 1R*,4S*,5R*4)
natural1)
1R*,4R*,5R*
no
4.61 (d)
4.82 (br.s)
5.31 (m)
4.62 (s)
4.83 (s)
5.32 (m)
4.72 (s)
4.83 (t)
5.33 (br.t)
4.60 (br.s)
4.75 (br.s)
5.25 (m)
13-Ha
13-Hb
7-H
data
available
natural1): [α]D = +37.1 (c = 12, hexane)
1R,4S,5S : [α]D25 = –39.6 (c = 0.3, hexane)2b)
1) S. Tebayashi, N. Hirai, S. Matsuyama, T. Suzuki, H. Nakakita, T. Nemoto, H. Nakanishi,
J. Stored Prod. Res. 1998, 34, 99.
2a) W. Oppolzer, F. Zutterman, K. Bättig, Helv. Chim. Acta, 1983, 66, 522.
2b) D. Solas, J. Wolinsky, J. Org. Chem., 1983, 48, 670.
3) S. Kurosawa, M. Bando, K. Mori, Eur. J. Org. Chem., 2001, 4395.
4) B. Tomita, T. Isono, Y. Hirose, Tetrahedron Lett., 1970, 1371.
At this stage Dr. Tashiro surveyed the literature through SciFinder, and collected the NMR data of
the stereoisomers of acoradiene (Figure 8). This table shows the chemical shift values of the olefinic
protons of the acoradiene stereoisomers. Although the (1R,4R,5R)-isomer was unknown, the data of
other three stereoisomers could be compared with those of the pheromone. The δ-values of the natural
pheromone were in good accord with those of (1R,4S,5S)-isomer. In 1983 Wolinsky had reported the
specific rotation of that isomer to be –39.6, while that of the natural pheromone was +37.1. The natural
pheromone therefore must be (1S,4R,5R)-isomer. This conclusion has to be proven by a synthesis.
Figure 9
Retrosynthetic Analysis
T. Tashiro, S. Kurosawa, K. Mori, Biosci. Biotechnol. Biochem. 2004, 68, 663.
O
O
(1S,4R,5R)-1
A
B
O
O
O
O
O
O
O
CO2Me
O
O
C
E
(S)-(–)-Pulegone [(S)-2]
D
cf. D. Solas, J. Wolinsky, J. Org. Chem., 1983, 48, 670.

Molecules 2005, 10
1028
Figure 9 shows the retrosynthetic analysis of (1S,4R,5R)-acoradiene Our analysis is a slight
modification of Wolinsky’s synthesis of the (1R,4S,5S)-isomer.
Figure 10
Synthesis 3
O
ref. 1)
O
O
O
1) t-BuOK,
DMF, ∆
(3 steps)
O
LDA
O
12 (= E)
(S)-2
HMPA, THF
(77%)
2) CH2N2, Et2O
(70%, 2 steps)
O
ref. 2)
O
O
O
I
15 (= D)
(2 steps)
14
methyl vinyl ketone (13)
1) LiAlH4, THF
(77%)
O
O
O
O
5% HCl aq.
O
CO2Me
CHO
O
THF
(quant.)
2) PCC, AcONa,
MS4A, CH2Cl2
(84%)
16 (= C)
18 (= B)
17
1) J. Wolinsky, H. Wolf, T. Gibson, J. Org. Chem., 1963, 28, 274.
2) J. C. Stowell, B. T. King, H. F. Hauck, Jr., J. Org. Chem., 1983, 48, 5381.
(S)-Pulegone, the starting material, was converted to lactone 12 according to Wolinsky (Figure 10).
The alkylating agent 14 was prepared from methyl vinyl ketone. Alkylation of the lactone 12 with
iodide 14 afforded 15, which was treated with potassium t-butoxide to cleave the lactone ring. The
corresponding methyl ester 16 was reduced with lithium aluminum hydride and the generated alcohol
was oxidized with PCC to furnish aldehyde 17. Treatment of 17 with dilute hydrochloric acid gave 18,
the precursor for aldol cyclization.
Figure 11
Synthesis 4
Ph3PCH3I,
n-BuLi,
1N NaOH aq.
O
O
O
EtOH
(97%)
THF
(96%)
20 (= A)
18
19
overall yield: 23%
[from (S)-pulegone: (S)-2, 13 steps]
1) Na, liq. NH3, THF
[α]D24 = +38.2 (c = 1.39, hexane)
2) AgNO3–SiO2 silica gel
chromatog.
(76%, 2 steps)
natural1): [α]D = +37.1 (c = 12, hexane)
ent-12): [α]D25 = –39.6 (c = 0.3, hexane)
(1S,4R,5R)-1
1) S. Tebayashi, N. Hirai, S. Matsuyama, T. Suzuki, H. Nakakita, T. Nemoto, H. Nakanishi,
J. Stored Prod. Res. 1998, 34, 99.
2) D. Solas, J. Wolinsky, J. Org. Chem., 1983, 48, 670.

Molecules 2005, 10
1029
Treatment of the keto aldehyde 18 with dilute sodium hydroxide provided spiroketone 19, to which
a methylene group was added by Wittig reaction to give 20 (Figure 11). Finally, 1,4-reduction of diene
20 with sodium in liquid ammonia yielded (1S,4R,5R)-acoradiene 1 in 23% overall yield. Its specific
rotation value was in good agreement with that of the pheromone. Then, how about the NMR
spectrum ?
Figure 12
1H-NMR spectra of (+)-acoradiene
(400 MHz, CDCl3)
13C-NMR spectra of (+)-acoradiene
(100 MHz, CDCl3)
Natural product
Natural product
Synthetic sample
Synthetic sample
(1S,4R,5R)-1
[(+)-α-Acoradiene]
As you can see in Figure 12, both proton and carbon NMR spectra of the synthetic product were
identical with those of the natural pheromone In the case of this sesquiterpene pheromone, our
synthesis could finally establish its true structure.
Figure 13
The Aggregation Pheromone of the Flea Beetle, Aphthona flava
6
H
H
2
O
(1R,2S)-1
(6S,7R)-2
H
5
(S)-4
(5S,5aR)-3
(Stereochemistry as proposed by Bartelt)
Isolation: R. J. Bartelt, A. A. Cossé, B. W. Zilkowski, D. Weisleder,
F. A. Momany, J. Chem. Ecol., 2001, 26, 2397.
Synthesis (Racemate): R. J. Bartelt, D. Weisleder, F. A. Momany, Synthesis, 2003, 117.
Synthesis and Stereochemistry: S.Muto, M. Bando, K. Mori, Eur. J. Org. Chem. 2004, 1946.

Molecules 2005, 10
1030
The next topic is the aggregation pheromone of the flea beetle, Aphthona flava (Figure 13).
Bartelt et al. at the U.S. Department of Agriculture isolated these himachalene-type sesquiterpenes as
the male-produced sex pheromone of the flea beetle. They proposed the stereochemistry as depicted
here. They also reported a synthesis of the racemic pheromones. We became interested in synthesizing
these enantiomers to confirm the proposed stereochemistry. The results have been published recently.
Our synthetic plan was to use citronellic acid so as to determine the stereochemistry at the
methyl-branching.
Figure 14
Synthesis 1
1) PDC, DMF
OHC
EtO2C
2) EtI, K2CO3
(S)-5
(S)-6
DMF (2 steps 74%)
Takasago, 97%e.e.
1) O3, MeOH
(EtO)2P(O)CH(Me)CO2Et
NaH, THF (96%)
EtO2C
CHO
2) Me2S (72%)
(S)-7
H2, PtO2
EtO2C
EtO2C
CO2Et
CO2Et
EtOAc (quant.)
(S)-8
(S)-9
Citronellal manufactured by Takasago Corporation according to Noyori was our starting material
(Figure 14). Dr. Muto carried out the experimental work. (S)-Citronellal was oxidized and esterified to
give ethyl ester 6. Ozonolysis of 6 afforded aldehyde (S)-7, which was converted to unsaturated ester 8
by Horner-Wadsworth-Emmons reaction. Hydrogenaton of 8 over Adams’ platinum oxide gave
saturated diester 9.
Figure 15
Synthesis 2
EtO2C
t-BuOK
aq. NaOH
EtO2C
CO2Et
MeOH
(85%)
m-xylene
(79%)
O
(S)-9
(S)-10
H
1) LDA, TMSCl, THF
t-BuOK, MeI
TMS
t-BuOH
O
2) MeLi,
O
O
(88%)
O
3) MeONa, MeOH
(44%)
(S)-12
(S)-11
(1R,2S)-1
mp 52.0-53.5 °C
22
[α]D -62 (c 0.51, hexane)

Molecules 2005, 10
1031
Dieckmann condensation of 9 by treatment with postassium t-butoxide gave 10, which was
hydrolyzed and decarboxylated to give (2RS,6S)-2,6-dimethylcycloheptanone 11 (Figure 15). This
dimethyl ketone 11 was further methylated to give 12. Finally (S)-12 was converted to crystalline
(1R,2S)-ketone 1 by Stork modification of the Robinson annelation. This ketone 1 was also reported as
a natural pheromone, but its chiroptical data were not reported.
Figure 16
Synthesis 3
H
O
(1R,2S)-1
THF
(69%)
Ph3PMeBr
[α]D21 -110 (c 0.85, hexane)
[α]D +82 (c 0.09, hexane)*
26
[α]D -10 (c 0.65, hexane)
n-BuLi
[α]D <+10 (c 0.001, hexane)*
H
H
1) HCO2H, MeOH
chloranil
2) AgNO3-SiO2
chromatog.
C6H6
(63%)
(88%)
(5S,5aR)-3
(S)-4
(6S,7R)-2
[α]D23 -12 (c 0.85, hexane)
Natural Product: [α]D +1.6 (c 0.0023, hexane)*
* R. J. Bartelt, A. A. Cosse, B. W. Zilkowski, D. Weisleder, F. A. Momany, J. Chem.Ecol.,
2001, 26, 2397.
We therefore converted (1R, 2S)-1 to three other pheromone components whose specific rotations
had been reported by Bartelt (Figure 16). When we compared the specific rotations of our synthetic
products with the values reported by Bartelt, we were surprised, because our products were
levorotatory, while the natural products had been reported as dextrorotatory.
Figure 17
Synthesis 4
H
9 steps
OHC
O
overall yield 13%
(R)-5
(1S,2R)-1
Takasago, 97%e.e.
[α]D23 +64 (c 0.79, hexane)
H
H
(6R,7S)-2
(R)-4
(5R,5aS)-3
[α]D26 +6.0 (c 0.90, hexane)
α D
[ ] 25 +7.8 (c 0.45, hexane)
[α]D25 +115 (c 0.55, hexane)
These enantiomers are the pheromone components.
Our conclusion is opposite to that of Bartelt et al.

Molecules 2005, 10
1032
We repeated the synthesis by starting from (R)-citronellal (Figure 17). Then, our products were all
dextrorotatory like the natural products. Therefore these enantiomers are the pheromone components,
and our conclusion is opposite to that of Bartelt. Indeed these compounds were active as aggregation
pheromones against flea beetle in Hungary.
Figure 18
X-ray Analysis
14
2
H
1
O
(1R,2S)-(–)-1
We were confident about our stereochemical assignment, because the stereochemistry of
(1R,2S)-ketone was unambiguously determined by X-ray analysis (Figure 18).
Figure 19
Stereochemical Correlation for Assignments of Opposite
Absolute Configurations to (+)-ar-Himachalene
(1) S. Muto, M. Bando, K. Mori, Eur. J. Org. Chem. 2004, 1946.
OHC
(R)-(+)-Citronellal
(R)-(+)-ar-Himachalene
(2) R. C. Pandey, Sukh Dev, Tetrahedron 1968, 24, 3829.
O
(S)-(+)-ar-Himachalene
(S)-(+)-ar-Turmerone
V. K. Honwad, A. S. Rao, Tetrahedron 1965, 21, 2593.
CO2H
(S)-(+)-1
V. Prelog, H. Scherrer
CO2H
CO2H
Helv. Chim. Acta,
1959, 42, 2227.
D. J. Cram, J. Am. Chem. Soc.
(R)-(–)-1 1952, 74, 2137.
(S)-(+)-2

Molecules 2005, 10
1033
Why were two opposite absolute configurations assigned to (+)-ar-himachalene? Now, we have to
solve this question (Figure 19). The specific rotations of our final products were measured as hexane
solutions according to Bartelt. We assigned the (R)-configuration to our (+)-ar-himachalene, because it
was derived from (R)-citronellal. Bartelt assigned the (S)-configuration to (+)-ar-himachalene, because
Pandey and Sukh Dev gave the (S)-configuration to (+)-ar-himachalene by synthesizing it from
(S)-(+)-ar-turmerone. The (S)-Configuration was given to (+)-ar-turmerone by Honwad and Rao on
the basis of their correlation of (+)-ar-turmerone to (S)-(+)-1. Its opposite enantiomer (-)-1 was
previously synthesized by Cram, and the (R)-configuration was assigned to it by Prelog by
homologating (R)-(+)-2 to (R)-(-)-1. Upon seeing such big names as Prelog, Cram and Sukh Dev, I
became cautious, and examined their conversion procedures carefully. Then finally I decided to trace
the experiment reported by Pandey and Sukh Dev. To do so, I had to synthesize optically active
ar-turmerone first, because it was not available in Japan.
Figure 20
Bn
Synthesis of (R)-ar-Turmerone
HN
O
Bn
SOCl2
NaHMDS
O
N
O
CO2H
COCl
n-BuLi, THF
MeI, THF
(85%)
(quant.)
O
3
O
(77%)
1
2
mp 62-64 ºC
[α]D24 = +71.3 (CHCl3)
Bn
LiAlH4
1) TsCl, C5H5N
KOH
OH
N
O
CN
OH
THF
(67%)
2) NaCN, DMSO
(78%)
O
O
HO
(50%)
4
5
6
[α]D23 = +108 (CHCl3)
[α]D24 = –14.6 (CHCl3)
[α]D23 = +4.1 (hexane)
1)
Me
O
O
MeN(OMe)H·HCl
MgBr
CO2H
N
THF
(i-Pr)2NEt, EDC
DMAP, CH2Cl2
(94%)
OMe
2) dil HCl
(88%)
9
7
8
(R)-ar-Turmerone
[α]D22 = –60.6 (CHCl3)
[α]D23 = –43.7 (CHCl3)
[α]D28 = +8.6 (hexane)
Figure 20 shows my synthesis of (R)-ar-turmerone. This experiment was done by me personally
in May-July, this year. Commercially available acid 1 was first converted to the corresponding acyl
chloride 2, which was coupled with (S)-4-benzyl-2-oxazolinone, a chiral auxiliary developed by David
Evans, to give 3. This was methylated with NaHMDS and methyl iodide to afford 4. Reduction of 4
with lithium aluminum hydride gave 5, which was converted to carboxylic acid 7, the so-called Rupe’s
acid, via 6. The acid 7 was derivatized to Weinreb amide 8. Treatment of the amide 8 with 2-methyl-
propenylmagnesium bromide afforded (R)-ar-turmerone of about 98% ee, as determined by GC
analysis on a chiral stationary phase.

Molecules 2005, 10
1034
Figure 21
Enantiomeric Purity of (R)-ar-Turmerone prepared from
Rupe's Acid of Higher mp.
75.02% e.e.
(R)
O
87.51%
Rt: 239.58 min
O
(S)
12.49%
Rt: 240.21 min
Rt (min)
Column: CHIRAMIX®: S. Tamogami, et al. Flavour Fragr. J. 2001, 16, 349.
Figure 21 shows the GC analysis of (R)-ar-turmerone on a CHIRAMIX chiral stationary phase of
Hasegawa Perfume Co. When I used Rupe’s acid of a higher mp as the intermediate, the enantiomeric
excess of the resulting ar-turmerone was 75% ee.
Figure 22
Enantiomeric Purity of (R)-ar-Turmerone prepared from
Rupe's Acid of Lower mp.
: 98.14% e.e.
O
99.07%
Rt: 238.88 min
O
0.93%
Rt: 239.42 min
Column: CHIRAMIX®
When Rupe’s acid with a lower mp was used as the intermediate, the resulting ar-turmerone was of
98% ee (Fig.22). Lower melting or oily Rupe’s acid was enantiomerically purer than the higher
melting material!

Molecules 2005, 10
1035
Figure 23
Conversion of (R)-ar-Turmerone to (R)-ar-Himachalene
1) N2H4
AlCl3, CS2
O
KOH
O
heat
–40 ~ –20ºC 1h
then reflux (46ºC)
4h (40%)
O
HO
OH
(R)-ar-Himachalene
10
11
2) SiO2 chromatog.
(40%)
[30% recovery]
9
[α]D22 = –52.7 (CHCl3)
(R)-(–)-ar-Turmerone
[α]D23 = –2.4 (CHCl3)
cf.) R. C. Pandey, Sukh Dev, Tetrahedron 1968, 24, 3829.
+3.8 (hexane)
Wolff-Kishner
cf.) K. Mori, N. Mizumachi, M. Matsui,
reduction
Agric. Biol. Chem. 1976, 40, 1611.
O
(S)-cis-Verbenol
Pheromone component of
[α]D25 = +56.4 (CHCl3)
Natural product:
[α]D27 = +5.9 (CHCl3)
Ips paraconfusus
OH
[α]D22 = –9.8 (CHCl3)
[α]D23 = +11.4 (MeOH)
[α]D = +2.92 (CHCl3) Sukh Dev
[α]D = –2.2 (hexane) Bartelt
Figure 23 shows the conversion of (R)-ar-turmerone to (R)-ar-himachalene, and clarifies the
reason why Bartelt had made a mistake. The synthetic (R)-ar-turmerone was treated with aluminum
chloride in carbon disulfide, first at a low temperature then at reflux. The initial low temperature was
very important for the success of this cyclization to give 10. Wolff-Kishner reduction of 10 gave
(R)-ar-himachalene 11. Pandey and Sukh Dev measured the specific rotations of both (S)-ar-turmerone
and (S)-ar-himachalene as chloroform solutions, and they were both dextrorotatory. When the specific
rotation of my (R)-ar-himachalene was measured, I immediately found the reason why Bartelt made an
error. It was levoratory in chloroform, but dextrorotatory in hexane. Although Sukh Dev reported that
they used chloroform, Bartelt did not care about the solvent and used hexane, without knowing the fact
that a different solvent may change the sign of rotation. A similar phenomenon was reported by us in
1976. (1S,4S,5S)-cis-Verbenol is a pheromone component of the bark beetle, Ips paraconfusus. At that
time there was confusion. Some people called (S)-cis-verbenol as (+)-cis-verbenol, while others called
it (-)-cis-verbenol. Our study of this compound revealed it to be levorotatory in chloroform, while
dextrorotatory in methanol. The important lesson here in this scheme is the fact that the sign of rotation
may change by using a different solvent. We should be careful about this fact.
Figure 24
(4R,9Z)-9-Octadecen-4-olide, the Female Sex Pheromone
of the Currant Stem Girdler, Janus integer
O
O
n-C8H17
(R)-1
Isolation and Identification
A. A. Cossé, R. J. Bartelt, D. G. James, R. J. Petroski, J. Chem. Ecol.
2001, 27, 1841.
Synthesis and Stereochemistry
D. G. James, R. J. Petroski, A. A. Cossé, B. W. Zilkowski, R. J. Bartelt,
J. Chem. Ecol. 2003, 29, 2189.
Synthesis of Both Enantiomers
C. Shibata, K. Mori, Eur. J. Org. Chem. 2004, 1083.

Molecules 2005, 10
1036
The third topic of my talk is the synthesis of (4R, 9Z)-9-octadecen-4-olide, the female sex
pheromone of the currant stem girdler, Janus integer (Figure 24). This insect is a pest of red currant in
North America. This lactone 1 was isolated and identified by Bartelt and his co-workers in the USA.
They synthesized the racemate and (R)-isomer in µg quantities, and proposed the stereochemistry of
the pheromone as R.
Figure 25
Synthesis – 11)
OH
1) Lipase AH-S,
TBDPSO
OH
vinyl acetate
(+)-(R)-A
(33%, 96%e.e.)
TBDPSO
r.t., 22 h, 2-3 times
(±)-A
2) SiO2 chromatog.
OAc
O
TBDPSO
(S)-B
(34%)
OH
O
HO
HO
(+)-(R)-A
CO2Me
D
C
O
12 steps, overall yield 1.2 %
96.3%ee, Z:E = 95:5
[α]D27 = +24 (c 0.50, CHCl3)
O
n-C8H17
(R)-1 (36 mg)
1) C. Shibata, K. Mori, Eur. J. Org. Chem. 2004, 1083.
This scheme shows the outline of our recent synthesis, carried out by Ms. Shibata (Figure 25). We
used lipase to achieve kinetic resolution of (±)-A. Subsequently, (+)-A was converted to (R)-1. The
amounts of the enantiomers of 1 secured by this synthesis was only 30-50 mgs. Last year Dr. James at
Washington State University in the USA requested me to synthesize gram quantities of (R)-1 so that he
might be able to carry out a large scale test in the field. I therefore had to develop a new and more
efficient synthesis.
Figure 26
Retrosynthetic Analysis
O
O
O
O
n-C8H17
(4R,9Z)-9-Octadecen-4-olide [(R)-1]
A
n-C8H17
O
O
N
n-C8H17
B
D
2,4,4-Trimethyl-2-oxazoline (C)
OH
AD
OH
n-C8H17
n-C8H17
E
HO
5-Hexen-1-ol (G)
n-C8H17
1-Decyne (F)

Molecules 2005, 10
1037
In Figure 26 you can see my new retrosynthetic analysis. The lactone 1 will be obtained by
semi-hydrogenation of the acetylenic lactone A. Compound A can be synthesized by alkylating C with
epoxide B. Epoxide B is available from glycol D. Diol D can be prepared by asymmetric
dihydroxylation of E. E is to be constructed by combining two commercially available compounds,
1-decyne (F) and 5-hexen-1-ol (G).
Figure 27
Synthesis – 2
n-C8H17C CH
1) TsCl, C5H5N
OH
I
3
2
2) NaI, DMF
(92%)
n-BuLi, THF
(71%)
bp 84–85ºC/40 Torr
1) AD-mix-β®
t-BuOH, H2O
0–5 ºC, 6 h
r.t. overnight
MeC(OMe)3
OH
OH
PPTS
n-C8H17
n-C8H17
(R)-5
mp 50.5–52 ºC
[α]D24 = +7.4 (c 3.2, MeOH)
CH2Cl2
4
2) Recryst'n from
hexane (x 5)
(20%, 94%ee)
Et
N
Et
N N
AD-mix-β® 1000 g
N
= K2Os2O2(OH)4 0.52 g
O
O
(DHQD)2PHAL
OMe
5.52 g
700 g
294 g
(DHQD)2PHAL
K3Fe(CN)6
K2CO3
MeO
N
N
H. C. Kolb, M. S. VanNieuwenhze, K. B. Sharpless, Chem. Rev. 1994, 94, 2483.
Because I have no one working with me in my pheromone synthesis, I executed the synthesis by
myself (Figure 27). Alcohol 2 was converted to iodide 3 via the corresponding tosylate. Alkylation of
octylacetylene with 3 gave enyne 4. This was dihydroxylated by treatment with AD-mix-β® to give
crude diol as a solid. Recrystallization of this solid from hexane gave (R)-5 of 87% ee in 60% yield
based on 4. Due to the low melting point and high solubility of (R)-5, its purification by
recrystallization was difficult. The yield of (R)-5 of 94% ee was only 20% based on 4 after five
repeated recrystallizations.
Figure 28
Synthesis – 3
OMe
K2CO3
O
Br
AcBr
O
OAc
aq. MeOH
(87%, 3 steps)
CH2Cl2
n-C8H17
n-C8H17
(R)-6
(S)-7
H
N
H
*
O
H O
2
N
Co
n-C8H17
t-Bu
O
O
t-Bu
AcO
(R)-8, [α]D22 = +7.93 (Et2O)
t-Bu
t-Bu
(72%)
O
96%ee
(0.7 mol%)
n-C8H17
OH
OH
THF, H2O (0.4 eq)
rt, 3 days
(R)-8
87%ee
(20%)
n-C8H17
(S)-5, (49%ee)
* (R,R)-Salen cobalt catalyst.
M. Tokunaga, J.F. Larrow, F. Kakiuchi, E.N. Jacobsen,
Science 1997, 277, 936.

Molecules 2005, 10
1038
The diol (R)-5 of 87% ee was then converted to epoxide (R)-8 by the method of Sharpless.
Accordingly, (R)-5 was treated with trimethyl orthoacetate and PPTS to give an orthoester. The
resulting orthoacetate (R)-6 quickly reacted with acetyl bromide to furnish acetoxy bromide (S)-7
(Figure 28). This was treated with potassium carbonate in aqueous methanol to give epoxide (R)-8 of
87% ee. I then purified the epoxide by Jacobsen’s hydrolytic kinetic resolution. Treatment of (R)-8 of
87% ee with Jacobsen’s (R,R)-salen cobalt catalyst in the presence of 0.4 equiv. of water in THF
afforded in 72% yield epoxide (R)-8 of 96% ee. Purification of (R)-8 by Jacobsen’s method was far
simpler and more efficient than the recrystallization of diol (R)-5. The enantiomeric purity of (R)-8
could be determined by chiral GC.
Figure 29
GC Analysis of Epoxide 8
Low e.e. Sample: 86.92% e.e.
O
O
n-C8H17
93.46%
n-C8H17
Rt: 254.25 min
6.54%
Rt: 259.37 min
High e.e. Sample: 96.02% e.e.
O
O
n-C8H17
1.99%
Rt: 259.37 min
n-C8H17
98.01%
Rt: 254.23 min
Rt (min)
Column: Octakis-(2,3-di-O-methoxymethyl-6-O-tert-butyldimethylsilyl)-γ-cyclodextrin
The enantiomers of epoxide 8 could be separated by GC employing a γ-cyclodextrin-based column
(Figure 29). Jacobsen’s HKR afforded the epoxide of 96% e.e.
Figure 30
Synthesis – 4
O
*
OH
O
N
O
n-BuLi
n-C8H17
n-C8H17
N
THF
(R)-8
(R)-9
–78ºC – r.t.
O
O
O
O
H2, Lindlar Pd
dil HCl
n-C8H17
THF
60 ºC, 0.5 h
C6H12, -5–0 ºC
(94%)
n-C8H17
(R)-1 (1.50 g)
(R)-10
[α]D23 = +21.7 (c 3.21, CHCl3)
[α]D23 = +24.2 (c 3.20, CHCl3)
(96%e.e.)
14% Overall yield
(11 steps)
*A. I. Meyers, E. D. Mihelich, R. L. Nolen,
J. Org. Chem. 1974, 39, 2783.

Molecules 2005, 10
1039
The epoxide 8 furnished the target lactone as shown in this scheme (Figure 30). Epoxide (R)-8 was
added to the carbanion derived from 2,4,4-trimethyl-2-oxazoline, and the product was treated with
dilute hydrochloric acid to give acetylenic lactone (R)-10. Lindlar hydrogenation of the acetylenic
lactone (R)-10 furnished the target lactone (R)-1 of 96% ee. The overall yield of (R)-1 was 14%
through 11 steps. I prepared 4 g of (R)-1 and sent it to Dr. James. In the next flight season in 2005, he
will carry out a large-scale field bioassay in the USA. When gram quantities of a pheromone are
needed, we have to develop an efficient synthetic route to achieve the goal.
Figure 31
Female Sex Pheromone of the New World
Screwworm Fly, Cochliomyia hominivorax
OAc
OAc
Me(CH2)9
(CH2)12 (CH2)4Me
Me(CH2)13
(CH2)7 (CH2)5Me
A (very active)
B (= 1) (active)
OAc
OAc
Me(CH2)9
Me(CH2)9
(CH2)11 (CH2)5Me
Me(CH2)9
Me(CH2)9
(CH2)10 (CH2)6Me
C
D
OAc
O
(CH2)13 (CH2)3Me
(CH2)13 (CH2)5Me
E
F
Identicication of 16 compounds including A–F by IR and EI-MS:
J. G. Pomonis, L. Hammack, H. Haak, J. Chem. Ecol. 1993, 19, 985.
Synthesis of stereoisomeric mixtures of A–D and F:
A. Furukawa, C. Shibata, K. Mori, Biosci. Biotechnol. Biochem. 2002, 66, 1164.
Synthesis of a stereoisomeric mixture of E and the enantiomers of F:
K. Mori, Biosci. Biotechnol. Biochem. 2003, 67, 2224.
Synthesis and Bioactivity of the stereoisomers of A:
K. Mori, T. Ohtaki, H. Ohrui, D. R. Berkebile, D. A. Carlson, Eur. J. Org. Chem. 2004, 1089.
Let us turn to the next and fourth topic, the female sex pheromone of the new world screwworm
fly, Cochliomyia hominivorax (Figure 31). The screwworm fly is a serious pest to livestock in Central
and South America. Its female-produced sex pheromone was first studied by Pomonis at U.S.
Department of Agriculture in 1993. They isolated 16 pheromone candidates from females, but they
were unable to identify the pheromonally active compounds. In cooperation with Dr. D.A. Carlson at
U.S. Department of Agriculture, I began the cooperative work on this pheromone in 2001. By his
intuition Dr. Carlson chose these six compounds as real pheromone candidates. We synthesized them
as racemic and diastereomeric mixtures, and Dr. Carlson found A and B to be pheromonally active.
Figure 32
Bioassay
OAc
(CH2)12 (CH2)9Me
very active
OAc
(CH2)7 (CH2)13Me
active
Me(CH2)4
Me(CH2)5

Molecules 2005, 10
1040
Because four stereoisomers are possible for A and B, it is necessary to synthesize them in order to
clarify the stereochemistry-pheromone activity relationship. Very recently, I synthesized four
stereoisomers of A. Ohtaki and Ohrui analyzed their enantiomeric purities, and Berkebile and Carlson
found all of them to be pheromonally active. Figure 32 picture shows the bioassay of these pheromone
components The male fly can perceive these pheromone molecules. If a µg quantity of A or B was put
on the surface of the dead body of the fellow male fly, the living male fly reacted, and embraced the
dead body as if it were a living female fly.
Figure 33
Retrosynthetic Analysis of (7S,15R)-1
OAc
Me(CH2)13
(CH2)7 (CH2)5Me
(7S,15R)-1
OTBS
I(CH2)3Me
Me(CH2)13
Me(CH2)13
(CH2)7
Enzymatic Resolution*
OH
(CH2)7
TMS
Me(CH2)11Br
Br(CH2)5OTHP
TMS
OHC
*P. Allevi, P. Ciuffreda, M. Anastasia, Tetrahedron: Asymmetry 1997, 8, 93.
(cf.) K. Mori, et al. Eur. J. Org. Chem. 2004, 1089.
OH
OAc
(CH2)4Me
Me(CH2)9
(CH2)12 (CH2)4Me
Me(CH2)9 (CH2)10
I
Here is our retrosynthetic analysis (Figure 33). In the case of our recent synthesis of this acetate,
we could employ commercially available enantiomers of 1-octyn-3-ol. But in the present case of 1, we
could not depend on commercially available starting materials. Therefore, enzymatic resolution of an
acetylenic intermediate was chosen as the key step.
Figure 34
Synthesis – 1*
1) LiAlH4, Et2O
Me(CH2)11MgBr
Li2CuCl4, THF
OHC
(S)-Citronellal (2)
TsO
2) TsCl, C5H5N
(96%)
(S)-3
Takasago, 97%e.e.
HIO4·2H2O
OsO4, NMO
OH
Me(CH2)13
Me(CH2)13
THF
(quant.)
t-BuOH, Me2CO,
H2O, 3 d., r.t.
OH
(3RS,6R)-5
(R)-4
(94%, 2 steps)
mp 51–53ºC, [α]D22 –0.2 (hexane)
MsCl
THPO(CH2)5MgBr
THF (64%)
(CH2)5OTHP
Me(CH2)13
Me(CH2)13
(R)-6
[α]D22 +1.1 (hexane)
CHO
C5H5N,
CH2Cl2
OH
(6RS,9R)-7
*K. Mori, T. Ohtaki, H. Ohrui, D.R. Berkebile, D.A. Carlson, Biosci. Biotechnol. Biochem.
2004, 68, 1768.

Molecules 2005, 10
1041
Lipase-catalyzed resolution of acetylenic alcohols is a known process as studied by Anastasia. The
key acetylenic alcohol could be prepared from 1-bromododecane, citronellal, 5-tetrahydropyranyloxy-
pentyl bromide and trimethylsilylacetylene. This synthesis (Figure 34) was also carried out by me.
(S)-Citronellal was reduced with lithium aluminum hydride, and the resulting alcohol was tosylated to
give 3. Chain-elongation of 3 with dodecylmagnesium bromide in the presence of dilithium
tetrachlorocuprate under the Schlosser conditions afforded (R)-4. This was dihydroxylated with
osmium tetroxide to give 5 as crystals. Glycol 5 was cleaved with periodic acid to give aldehyde (R)-6.
Further chain-elongation of 6 with tetrahydropyranyloxypentylmagnesium bromide furnished 7, whose
secondary hydroxy group was removed by reduction of the corresponding mesylate.
Figure 35
Synthesis – 2
1) LiAlH4, THF
(CH2)5OTHP
Me(CH2)13
Me(CH2)13
(R)-9
(CH2)8OH
2) TsOH, THF,
EtOH
OMs
(6RS,9R)-8
(39%, 3 steps)
mp 39–40ºC, [α]D20 +0.2 (hexane)
PCC, NaOAc
OH
LiC CTMS
Me(CH2)13
(CH2)7CHO
Me(CH2)13
(CH2)7
THF
(80%)
MS4A, CH2Cl2
(72%)
TMS
(R)-10
[α]D21 +0.1 (hexane)
(3RS,11R)-11
14% overall yield based on 2
Similarly
OH
OHC
Me(CH2)13
(CH2)7
TMS
(R)-2
(3RS,11S)-11
After removal of the THP protective group, crystalline alcohol (R)-9 was obtained (Figure 35).
PCC oxidation of (R)-9 gave aldehyde 10. Addition of lithium trimethylsilylacetylide to 10 gave
acetylenic alcohol 11, the substrate for the enzymatic kinetic resolution. Similarly, its
(3RS,11S)-isomer was synthesized from (R)-citronellal.
Figure 36
Synthesis – 3 (Lipase-catalyzed Asymmetric Acetylation 1)
OH
Lipase PS-D (Amano)
Me(CH2)13
(CH2)7
CH2=CHOAc, (i-Pr)2O
14 days, r.t.; then
SiO2 chromatog.
TMS
(3RS,11R)-11
OAc
OH
K2CO3
Me(CH )
(CH2)7
Me(CH2)13
(CH2)7
↑
(63%)
(71%)
2 13
↑
MeOH
(79%)
TMS
TMS
(3R,11R)-12
[α]D22 +29.8 (hexane)
99.5%e.e. 92.5%e.e.
(3R,11R)-13
mp 38.0–38.5ºC, [α]D22 +4.3 (hexane)
OH
OH
K2CO3
Me(CH2)13
(3S,11R)-11
[α]D22 –1.7 (hexane)
(CH2)7
Me(CH2)13 ↑ (CH2)7 ↑
MeOH
(66%)
98.5%e.e.
98%e.e.
(3S,11R)-13
oil, [α]D22 –4.0 (hexane)

Molecules 2005, 10
1042
After some preliminary screening experiment, lipase PS-D (Amano) was chosen to achieve
asymmetric acetylation of 11 (Figure 36). Accordingly, lipase PS-D and vinyl acetate were added to a
solution of (3RS,11R)-11 in diisopropyl ether, and the mixture was stirred for 2 weeks at room
temperature. The product was separated by silica gel chromatography to give the acetylated (R)-acetate
12 and non-acetylated (S)-alcohol 11. Treatment of 12 with potassium carbonate in methanol removed
both TMS and acetyl protective groups to give alcohol (3R,11R)-13. Similarly, (3S,11R)-11 yielded
(3S,11R)-13. The stereochemical purity of these alcohols was satisfactory.
Figure 37
Synthesis – 4 (Lipase-catalyzed Asymmetric Acetylation 2)
OH
Me(CH2)13
(CH2)7
↑
↑
Similarly
97.5%e.e. 79%e.e.
OH
(3R,11S)-13
oil, [α]D22 +3.0 (hexane)
OH
Me(CH2)13
(CH2)7
TMS
(3RS,11S)-11
Me(CH2)13 ↑ (CH2)7 ↑
98.5%e.e.
98%e.e.
(3S,11S)-13
mp 37.5–38.0ºC, [α]D25 –4.0 (hexane)
O
O
O
R
S
N
N
C=O
O
O=C
S
R
O
O
Me(CH2)13
(CH2)7
Me(CH2)13
Derivatives of 13 for HPLC analysis
K. Imaizumi, H. Ohrui et al. Anal. Sci. 2003, 19, 1243.
(CH2)7
In the same manner, (3RS,11S)-11 furnished (3R,11S)-13 and (3S,11S)-13 (Fig.37). The
stereochemical purity of these alcohols were determined by the HPLC analysis of these derivatives
prepared by the method of Ohrui.
Figure 38
1) H2, PtO2, EtOAc
r.t., 15 min
2) TBAF, THF
Synthesis – 5
1) TBSCl, imidazole
DMF
OH
OTBS
Me(CH2)13
(CH2)7
(3R,11R)-13
(92%, 2 steps)
(CH2)3Me
Me(CH2)13
(CH2)7
2) n-BuLi, n-BuI
THF, HMPA
(56%, 2 steps)
(7R,15R)-14
OAc
Ac2O, DMAP
OH
(CH2)7 (CH2)5Me
Me(CH2)13
(CH2)7 (CH2)5Me
Me(CH2)13
↑
↑
C5H5N, CH2Cl2
(83%)
(7S,15R)-1
oil, [α]D23 –0.3 (hexane)
98.5%e.e. 91%e.e.
(7S,15R)-15
mp 68–69ºC, [α]D25 +0.2 (hexane)
Overall yield: 3% (17 steps)
based on (S)-citronellal (2)
Similarly
OH
OAc
OH
Me(CH2)13 (CH2)7 (CH2)5Me
(7R,15R)-1
Me(CH2)13 (CH2)7
Me(CH2)13 (CH2)7 (CH2)5Me
↑
↑
oil, [α]D24 +0.1 (hexane)
(3S,11R)-13
98%e.e. 97%e.e.
(7R,15R)-15
mp 50.5–51ºC, [α]D25 –1.5 (hexane)

Molecules 2005, 10
1043
Conversion of acetylenic alcohol 13 to the final product 1 is shown in this scheme (Figure 38).
Chain-elongation of 13 was executed after converting it to the corresponding TBS ether by employing
butyllithium and butyl iodide. The resulting 14 was hydrogenated over Adams’ platinum oxide, and the
TBS protective group was removed to give alcohol 15 as crystals. Its stereochemical purity was also
determined. Finally, acetylation of 15 gave the final product, acetate 1. Similarly, three other isomers
were also synthesized.
Figure 39
Synthesis – 6
OAc
OH
Me(CH2)13 (CH2)7
(3R,11S)-13
OH
Me(CH2)13 (CH2)7 (CH2)5Me
(7S,15S)-1
Me(CH2)13
(CH2)7 (CH2)5Me
↑
↑
oil, [α]D21 –0.2 (hexane)
98%e.e. 83%e.e.
(7S,15S)-15
mp 51–52ºC, [α]D25 +2.2 (hexane)
OAc
OH
OH
Me(CH2)13
(CH2)7 (CH2)5Me
Me(CH2)13 (CH2)7
Me(CH2)13 (CH2)7 (CH2)5Me
↑
↑
(7R,15S)-1
oil, [α]D25 +0.2 (hexane)
(3S,11S)-13
98%e.e. 96%e.e.
(7R,15S)-15
mp 71–72ºC, [α]D25 –0.2 (hexane)
O
O
R
S
N
N
O=C
C=O
O
S
R
O
O
O
Me(CH2)13
(CH2)7
(CH2)5Me
Me(CH2)13
(CH2)7
(CH2)5Me
Derivatives of 15 for HPLC analysis
The stereochemical purity of these alcohols 15 were also determined by the HPLC analysis of
their derivatives (Figure 39). I thus synthesized all the four stereoisomers of the screwworm fly
pheromone, and their bioassay was carried out in the USA. In this particular case, all of the four
stereoisomers showed pheromone activity.
Figure 40
Aggregation Pheromone of the Male Colorado Potato
Beetle, Leptinotarsa decemlineata
OH
OH
O
(Adult)
(Larva)
(S)-1
Isolation and Synthesis:
J. E. Oliver, J. C. Dickens, T. E. Grans,
Tetrahedron Lett., 2002, 43, 2641–2643

Molecules 2005, 10
1044
My fifth and last topic is the male-produced aggregation pheromone of the Colorado potato beetle,
Leptinotarsa decemlineata (Figure 40). This is a pest insect of potatoes in the USA. Its isolation and
synthesis were reported by Oliver at U.S. Department of Agriculture in 2002. They synthesized this
unique monoterpene from (S)-linalool, and established its absolute configuration as S. Dr. Dickens at
U.S. Department of Agriculture requested me to synthesize gram quantities of (S)-1, because their
synthesis provided only mg quantities of it. The problem was how to make S-stereocenter in a simple
manner. We planned to use an enzymatic method. Dr. Tashiro mainly did the experimental work.
Figure 41
Synthesis - 1.
O
Enzymatic Resolution of Epoxide A
O
Lipase
OAc
OH
B
C
vinyl acetate, Et2O
OH
O
A
Table 1 Results of Lipase Catalyzed Resolutions
2,3-Epoxygeraniol 2,3-Epoxynerol
Ac2O
Pyridine
B
C
Time (min)
Lipase Temp. Time (min)
e.e.*
e.e.*
AH
r.t.
70
25
65
25
15
–
24%
50%
59%
72%
42%
–
60
20
50%
46%
60%
74%
26%
–
*Determined by HPLC analysis of B
Conditions
Column : Chiralcel-OD®
Eluent : Hexane / i-PrOH = 200 : 1
Flow rate : 0.25 mL / min
Detection : 210 nm
AK
r.t.
PS
r.t.
120
160
15
PS
0 ºC
r.t.
PS-C
F-AP
r.t.
–
Various lipases were screened to achieve enzymatic kinetic acetylation of 2,3-epoxygeraniol and
2,3-epoxynerol (Figure 41). When used at 0°C, lipase PS was found to be the best.
Figure 42
Synthesis - 2.
1) TBDPSCl, DMAP
Et3N, CH2Cl2
(92%)
1) 60% HClO4 aq., DMF*
0 ºC
OH
OH
O
OH
2) SO3·Py., DMSO
Et3N, CH2Cl2
(77%)
2) K2CO3, MeOH
(85%, 2 steps)
5 (97% ee)
OAc
6
OH
TBAF
OH
O
[α]D25 = +3.83 (c = 0.79, CHCl3)
b.p. 105 ºC (1.2 Torr)
OTBDPS
OH
THF
(65%)
O
(S)-1 (93% ee): Active
7 (93% ee)
similarly
OH
Ac2O
O
O
OH
O
(R)-1 (92% ee): Inactive
Pyridine
(92%)
OH
OAc
5 (95% ee)
10
[α]D24 = –3.44 (c = 1.01, CHCl3)
Mixture of (S)-1 and (R)-1 (1 : 1)
* R.M. Hanson, Tetrahedron Lett., 1984, 25, 3783.
b.p. 112 ºC (2.5 Torr)
Inactive

Molecules 2005, 10
1045
By repeating the lipase-catalyzed kinetic resolution three times, (2S,3R)-2,3-epoxyneryl acetate (5)
was prepared (Figure 42). Its enantiomeric purity was about 97% ee. Treatment of 5 with 60%
perchloric acid in DMF at 0°C gave (2S,3S)-6 with Walden inversion at C-3. The primary hydroxy
group of 6 was then protected as TBDPS ether, and the secondary hydroxy group was oxidized to give
7. Removal of the TBDPS protective group of 7 afforded the Colorado potato beetle pheromone (S)-1
in gram quantities. Its enantiomeric purity was 93% ee. Similarly, (2R,3S)-10 afforded (R)-1.
Bioassay of these samples in the USA revealed that (S)-1 was active, while a 1:1 mixture of (S)-1 and
(R)-1 was inactive. Thus (R)-1 seems to inhibit the activity of the natural pheromone with
S-configuration.
Figure 43
Relationships between Stereochemistry and Pheromone Activity (1)
Only one enantiomer is bioactive, and
the antipode does not inhibit the action
of the pheromone.
Only one enantiomer is bioactive,
but its antipode inhibits the action of
the pheromone.
A
B
O
O
H
CHO
O
O
O
Japanese beetle
etc.
western
pharaoh's ant
(faranal)
gypsy moth
(disparlure)
pine beetle
etc.
(exo-brevicomin)
Only one enantiomer is bioactive,
but its diastereomer inhibits the action
of the pheromone.
The natural pheromone is a single enantiomer,
but its diastereomer is also equally active.
D
C
O
O
*
OH
*
*
O
O
O
*
O
maritime pine scale
cigarette beetle
(serricornin)
drugstore beetle
(stegobinone) etc.
(natural pheromone)
(unnatural but active)
Diastereomers at the chiral center
with * are inhibitors.
Now let me summarize my pheromone work (Figure 43). By synthesizing and biotesting the
stereoisomers of pheromones, we could clarify the relationship between stereochemistry and
pheromone activity. The relationship is not simple but complicated.
In group A, only one enantiomer is bioactive, and the antipode does not inhibit the action of the
pheromone. This is common to other bioactive molecules.
In group B, only one enantiomer is bioactive, but its antipode inhibits the action of the pheromone.
In the case of the Japanese beetle pheromone, its racemate is inactive.
In group C, only one enantiomer is bioactive, but its diastereomer inhibits the action of the
pheromone. We must prepare diastereomerically pure pheromones.
In group D, the natural pheromone is a single enantiomer, but its diastereomer is also equally
active. The stereochemical recognition at the receptor site seems to be more flexible.
In group E, all the stereoisomers are bioactive (Figure 44). The pheromone receptor must be very
flexible.
In group F, even in the same genus, different species use different enantiomers. Enantiomerism is
employed to avoid mixed marriages.

Molecules 2005, 10
1046
Figure 44
Relationships between Stereochemistry and Pheromone Activity (2)
All the stereoisomers are bioactive.
E
Even in the same genus, different species
use different enantiomers.
F
OH
OH
n-C18H37
(CH2)7
O
Ips paraconfusus Ips calligraphus
[(+)-ipsdienol]
[(–)-ipsdienol]
German cockroach
etc.
(CH2)6Me
(CH2)6Me
O
O
Both the enantiomers are required
for bioactivity.
G
Colotois pennaria
Erannis defoliaria
OH
OH
H Only one enantiomer is as active as the natural
pheromone, but its activity can be enhanced by
the addition of a less active stereoisomer.
Gnathotrichus sulcatus
[(+)-sulcatol]
[(–)-sulcatol]
"The natural pheromone is not
enantiomerically pure!"
CHO
CHO
red flour beetle
(unnatural and less active)
(natural pheromone)
In group G, both the enantiomers are required for bioactivity. To show bioactivity, both the
enantiomers must exist.
In group H, only one enantiomer is as active as the natural pheromone, but its activity can be
enhanced by the addition of a less active stereoisomer. I cannot understand the reason why.
Figure 45
Relationships between Stereochemistry and Pheromone Activity (3)
One enantiomer is active on male insects,
while the other is active on females.
Only the meso-isomer is active.
J
I
O
O
n-C12H25
(CH2)9
n-C12H25
O
O
tsetse fly
(R) male
(S) female
(Glossina pallidipes)
olive fruit fly
[(–)-olean]
[(+)-olean]
"The natural pheromone
is a racemate."
Diversity is the Keyword of Pheromone Response.
In group I, one enantomer is active on male insects, while the other is active on females (Figure
45). In this particular case of olive fruit fly, the female-produced sex pheromone is a racemate.
In group J, only the meso-isomer is active, while the enantiomers are inactive.

Molecules 2005, 10
1047
Figure 46
Summary
H
O
O
n-C8H17
currant stem girdler
broad-horned
flour beetle
flea beetle
OH
OAc
(CH2)7 n-C6H13
OH
O
n-C14H29
screwworm fly
Colorado potato beetle
I have talked on the synthesis of these five new pheromones (Figure 46).
Figure 47
Enantioselective synthesis is possible
by employing:
1. Enantiopure starting materials
2. Chemical asymmetric reactions
3. Enzymatic asymmetric reactions
Criteria for choosing one of them are:
1. Selectivity
2. Efficiency
3. Simplicity
Our goal is to provide useful materials.
Many thanks to my co-workers and my friend
entomologists, and
THANK YOU FOR YOUR ATTENTION!
Enantioselective synthesis is possible by employing (1) enantiopure starting materials, (2)
chemical asymmetric reactions and (3) enzymatic asymmetric reactions (Figure 47). Criteria for
choosing one of them are (1) selectivity, (2) efficiency, and (3) simplicity. Our goal is to provide useful
materials to others. In summary, diversity is the keyword of pheromone response. In the case of chiral
pheromones, we must synthesize and bioassay stereoisomers to know the stereochemistry-bioactivity
relationships. Only after that, we may be able to think about the practical use of pheromones. The
diversity in pheromone response could be clarified only through experimental efforts of chemists and
biologists. I thank all of my co-workers to provide synthetic samples and then to bioassay them.
Thank you for your attention.
© 2005 by MDPI (http://www.mdpi.org). Reproduction is permitted for noncommercial purposes.