Pheromone synthesis. Part 265: Synthesis and stereochemical composition of two pheromonal compounds of the female Korean apricot wasp, Eurytoma maslovskii

Article abstract of DOI:10.1016/j.tet.2020.131410

2,10-Dimethyldodecyl propanoate and 2,8-dimethyldecyl propanoate are two pheromonal compounds secreted by the female Korean apricot wasp, Eurytoma maslovskii. The enantioselective synthesis of all the stereoisomers of both components was conducted; HPLC a

Full text of DOI:10.1016/j.tet.2020.131410

Tetrahedron xxx (xxxx) xxx
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Pheromone synthesis. Part 265: Synthesis and stereochemical
composition of two pheromonal compounds of the female Korean
apricot wasp, Eurytoma maslovskii*
,
Yasutaka Ohkubo a b, Kazuaki Akasaka c, Yui Masuda b, Shunsuke Konishi b,
,
, e, 1
Chang Yeol Yang d, Hirosato Takikawa a *, Kenji Mori a
a Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo,
113-8657, Japan
b Technical Research Institute, R&D Center, T. Hasegawa Co., Ltd., 29-7 Kariyado, Nakahara-ku, Kawasaki, Kanagawa, 211-0022, Japan
c Department of Health and Nutritional Sciences, Shokei Gakuin University, 4-10-1 Yurigaoka, Natori-shi, Miyagi, 981-1295, Japan
d Horticultural and Herbal Crop Environment Division, National Institute of Horticultural and Herbal Science, 100 Nongsaengmyeong-ro, Iseo-myeon,
Wanju-gun, Jeollabuk-do, 55365, South Korea
e Photosensitive Materials Research Center, Toyo Gosei Co., Ltd, 4-2-1 Wakahagi, Inzai-shi, Chiba, 270-1609, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
2,10-Dimethyldodecyl propanoate and 2,8-dimethyldecyl propanoate are two pheromonal compounds
secreted by the female Korean apricot wasp, Eurytoma maslovskii. The enantioselective synthesis of all
the stereoisomers of both components was conducted; HPLC analysis based on the chiral derivatization
method (OhruieAkasaka method) was applied for the clarification of the stereochemical composition of
these two components. The most pheromonally active compound, (2S,10R)-dimethyldodecyl propanoate,
was also the most abundant component in the cuticular extract.
Received 26 June 2020
Received in revised form
10 July 2020
Accepted 13 July 2020
Available online xxx
© 2020 Elsevier Ltd. All rights reserved.
Keywords:
Eurytoma maslovskii
Pheromone
Enantioselective synthesis
OhruieAkasaka method
1. Introduction
of E. maslovskii via GC-MS analysis, various blend combinations of
these components caught no males of E. maslovskii in field tests that
The wasp Eurytoma maslovskii (Hymenoptera: Eurytomidae)
poses a serious threat to Korean apricot orchards. The cuticular
extract of its females was shown to be active as a sex attractant,
and then seven candidate structures, (Z)-15-methyl-7-nonacosene,
(Z)-17-methyl-7-hentriacontene, 3,7-dimethylheptacosane, 3,7,11-
trimethylnonacosane, 8,12-dimethyltriacontane, 8,18-dimethyl-
triacontane, and 3,7,17-trimethylnonacosane, were proposed for
the pheromonal components on the basis of GC-MS analysis in 2016
[2]. The synthesis of all the seven pheromone candidates as ste-
reoisomeric mixtures was previously reported by our group [2].
Even though the first four components (with unknown stereo-
chemistry) were identified as part of the female-specific secretion
were conducted in Korea between April and May in 2016. These
results suggested that these hydrocarbons are not genuine phero-
mone [2]. In 2017, the synthesis of four tri-substituted pyrazines
isolated from E. maslovskii was also reported [3]. Regrettably, these
components also failed to attract male E. maslovskii in field test
(conducted between April and May in 2017) despite showing strong
electroantennogram activity [3]. Thus, in our continued efforts to
clarify the structure of the genuine pheromone(s) of E. maslovskii,
the components 2,10-dimethyldodecyl propanoate (1) and 2,8-
dimethyldecyl propanoate (2) were reported as possible phero-
mone candidates (Fig. 1) [4]. The non-stereoselective and enan-
tioselective synthesis of 1 and 2 enabled us to confirm the
stereochemistryeactivity relationship in these compounds as well
as the total composition of the natural pheromone. The former was
clarified via field bioassay that was executed in Korea [4], whereas
the latter was determined using HPLC analysis based on a chiral
derivatization method, namely the OhruieAkasaka method [5]. In
*
For Part 264, see Ref. [1].
* Corresponding author.
E-mail address: atakikawa@mail.ecc.u-tokyo.ac.jp (H. Takikawa).
Diseased on April 16, 2019. This research had been conducted by K.M.
1
https://doi.org/10.1016/j.tet.2020.131410
0040-4020/© 2020 Elsevier Ltd. All rights reserved.
Please cite this article as: Y. Ohkubo et al., Pheromone synthesis. Part 265: Synthesis and stereochemical composition of two pheromonal
compounds of the female Korean apricot wasp, Eurytoma maslovskii, Tetrahedron, https://doi.org/10.1016/j.tet.2020.131410

2
Y. Ohkubo et al. / Tetrahedron xxx (xxxx) xxx
Scheme 2. Synthesis of 1 and 2.
Fig. 1. Structures of E. maslovskii pheromone candidates.
Reagents: (a) Mg, THF; CuBr, NMP, THF; (b) LDA, MeI, HMPA, THF (c) LiAlH4, THF; (d)
EtCOCl, pyridine, CH2Cl2; (e) aq. NaOH, THF; (f) (COCl)2; (g) 14, n-BuLi, THF; (h)
NaHMDS, MeI, THF.
this paper, synthetic and analytical parts of studies on E. maslovskii
pheromones are described in detail.
performed by treatment with LDA and MeI to give 8 in 72% yield.
Reduction of 8 with LiAlH4 afforded 10 (93%), which was then
esterified to furnish 1 as a mixture of all the possible stereoisomers
(96%). In the same manner, a mixture of all the possible stereo-
isomers of 2 was also synthesized (41% from 3) using ethyl 6-
bromohexanoate (5) instead of 4.
2. Results and discussion
2.1. Synthesis of the pheromone candidates
The synthetic plan toward the candidate compounds 1 and 2
with high enantiomeric purity is shown in Scheme 1. The chiral
center at C10 of 1 and C8 of 2 could be installed starting from
optically active 1-bromo-2-methylbutane (3). The Grignard
Since the MS profiles of the synthesized 1 and 2 were in good
accordance with those of the naturally occurring pheromone can-
didates [4], we commenced with the synthesis of all the possible
stereoisomers of 1 and 2. The chiral starting material (R)-3 was
prepared according to the reported procedure from (R)-2-
methylbutanoic acid [8], whereas (S)-3 is commercially available.
The Grignard coupling between (S)-3 and 4 gave (S)-6, which was
then hydrolyzed to afford (S)-12. After conversion of (S)-12 into the
corresponding acyl chloride, the product was treated with the
lithium salt of (S)-14 to give (4S,100S)-15 (63%, 4 steps). The dia-
stereoselective methylation of (4S,100S)-15 was successfully ach-
ieved by treatment with NaHMDS and MeI to afford a mixture of
(4S,20S,100S)- and (4S,20R,100S)-17 (96:4). However, this mixture was
easily separated by silica-gel column chromatography to give the
pure (4S,20S,100S)-17 (69%). After reductive cleavage of the chiral
auxiliary (91%), the resulting (2S,10S)-10 was then converted to
(2S,10S)-1 (83%). In the same manner, (2R,10S)-1 was prepared by
using (R)-14 instead of (S)-14. By changing the starting bromide 3
from (S) to (R), (2S,10R)- and (2R,10R)-1 were also prepared. All the
possible stereoisomers of 2 were synthesized uneventfully.
All the synthesized 1 and 2 were then employed for the field
bioassay. By the bioassay, (2S,10R)-1 was shown to be the most
active as the aggregation pheromone, whereas (2S,8R)-2 and
(2S,8S)-2 were the second and third most active compounds,
respectively [4]. All the synthesized intermediate alcohols (10 and
11) were used for analytical studies on the composition of the
natural pheromone (vide infra).
coupling between 3 and
u-bromoester (4 or 5) would be appro-
priate for elongation of carbon chain. Introduction of the chiral
center at C2 of 1 and 2 would be possible by Evans’ method [6],
which is one of the most reliable and widely used method for
conducting diastereoselective a-alkylation. The reductive cleavage
of a chiral auxiliary followed by propanoylation would give the
target compounds 1 and 2.
As shown in Scheme 2, the non-stereoselective synthesis of 1
and 2 was first executed. According to the reported procedure [7],
the Grignard coupling between 3 and ethyl 8-bromooctanoate (4)
was mediated by CuBr to afford 6 (96%). Since diastereoselective
methylation was unnecessary in this series, a-methylation of 6 was
Scheme 1. Synthetic plan.
Please cite this article as: Y. Ohkubo et al., Pheromone synthesis. Part 265: Synthesis and stereochemical composition of two pheromonal
compounds of the female Korean apricot wasp, Eurytoma maslovskii, Tetrahedron, https://doi.org/10.1016/j.tet.2020.131410

Y. Ohkubo et al. / Tetrahedron xxx (xxxx) xxx
3
2.2. Composition of the natural pheromone of E. maslovskii
composition of nat-10/11 was identical to that of the nat-1/2, we
could clarify the total composition of the aggregation pheromone of
E. maslovskii.
As shown in Scheme 3, the natural pheromone, which contained
a mixture of 1 and 2 (nat-1/2), was hydrolyzed to afford the cor-
responding alcohols (nat-10/11) in order to determine its stereo-
chemical composition via the OhruieAkasaka method [5]. The
resulting alcohols were then esterified by treatment with
OhruieAkasaka reagents, namely (1R,2R)- or (1S,2S)-2-(naphtha-
lene-2,3-dicarboximido)cyclohexanecarboxylic acid (19, Reagent I)
and (1R,2R)- or (1S,2S)-2-(anthracene-2,3-dicarboximido)cyclo-
hexanecarboxylic acid (20, Reagent II), in the presence of EDC and
DMAP. Reagents I (19) and II (20) are now commercially available
from Tokyo Chemical Industry Co., Ltd. The prepared
OhruieAkasaka derivatives of nat-10/11, i.e., nat-(1R,2R)-21/22, nat-
(1S,2S)-21/22, nat-(1R,2R)-23/24, and nat-(1S,2S)-23/24, were
analyzed via a 2D-HPLC system [9] (Fig. SI-1). This system is quite
useful for analyzing natural products because it can remove inter-
fering substances, reduce the run time, and improve reliability. In
this system, the first column was used for the purification of the
two desired fatty alcohol derivatives without disturbing their ste-
reochemical compositions. Then, only the desired fractions were
introduced into the second column to enable the separation of the
stereoisomers.
3. Conclusion
The synthesis of all the possible stereoisomers of 2,10-
dimethyldodecyl (1) and 2,8-dimethyldecyl propanoate (2), the
aggregation pheromones of E. maslovskii, was accomplished. This
enabled us to confirm the absolute configurations of the pher-
omonally active compounds via bioassay analysis and to determine
the total composition of the natural pheromone through careful
HPLC analysis based on the OhruieAkasaka method. As the results,
the most pheromonally active compound (2S,10R)-1 was proven to
be the most abundant (64.4%). Interestingly, the second most
abundant component (20.6%) was the third most active compound
(2S,8S)-2, and the component percentage of the second active
compound, (2S,8R)-2, was only 0.3%.
4. Experimental section
4.1. Synthesis of 1 and 2
The most critical issue to overcome, i.e., the scarcity of the
natural sample, was achieved by thoroughly investigating the
appropriate analytical conditions using synth-21e24. Fortunately,
we found that 21, which was prepared from 2,10-dimethyl-1-
dodecanol (10) and Reagent I (19), and 24, which was prepared
from 2,8-dimethyl-1-decanol (11) and Reagent II (20), were suitable
for determining the stereochemical composition of the parent
compounds 10 and 11, respectively (Fig. SI-2.).
As the results, the total composition of nat-10/11 was deter-
mined as follows: i) the ratio of nat-10 to nat-11 was 70.5 to 29.5, ii)
the stereochemical composition of nat-10 was determined as
(2S,10S):(2S,10R):(2R,10S):(2R,10R) ¼ 0.7:91.4:1.6:6.2, and iii) the
stereochemical composition of nat-11 was also determined as
4.1.1. General
All melting points were uncorrected. Melting points were
recorded on a Yazawa Micro Melting Point Apparatus BY-2. Gas
chromatography was performed with an Agilent 6850 GC system
under the following conditions: column: Agilent HP-1, 100%
dimethylpolysiloxane, 30 m length x 0.25 mm i.d., 0.25
mm df;
carrier gas, N2; flow rate, 0.7 mL minꢀ1; temp: 150e300 ꢁC (þ5 ꢁC/
min) for oxazolidinones, 70e300 ꢁC (þ5 ꢁC/min) for other com-
pounds. Optical rotation values were measured with a Jasco P-2300
polarimeter. NMR spectra were recorded by a JEOL JNM ECX-400
spectrometer (400 MHz for 1H and 100 MHz for 13C) and chemi-
cal shifts (d) were reported using residual solvents of CDCl3 as an
internal standard (7.26 ppm for 1H and 77.00 ppm for 13C). Mass
spectra were obtained with an Agilent 5977 MSD coupled with an
Agilent 7890B GC system. High resolution mass spectra were
measured with a JEOL JMS-T100GCV spectrometer operated in the
(2S,8S):(2S,8R):(2R,8S):(2R,8R)
¼
69.9:1.0:11.8:17.3. Since the
FI mode. Kanto Kagaku silica gel 60 N (63e210 mm) was used for
column chromatography. Analytical thin-layer chromatography
was performed using Merck silica gel 60 F254 plates (0.25 mm). All
air- and/or water-sensitive reactions were carried out under N2
atmosphere in dry solvents.
4.1.2. Ethyl 10-methyldodecanoate (6)
To a mixture of Mg turnings (2.80 g, 115 mmol) and a piece of I2
in THF (42.0 g), a solution of 3 (14.5 g, 96.0 mmol) in THF (43.5 g)
was added dropwise at 30 ꢁC. After stirring for 3 h, the resulting
Grignard reagent was added dropwise to a solution of 4 (20.1 g,
80.0 mmol) and CuBr (0.29 g, 2.0 mmol) in NMP (31.7 g, 320 mmol)
and THF (71.1 g) at 10 ꢁC. After stirring for 3 h, the reaction mixture
was poured into 20% aq. NH4Cl solution and extracted with hexane.
The organic layer was washed with brine, dried over MgSO4, and
concentrated under reduced pressure. The residue was distilled to
give 6 (18.7 g, 96% yield). bp 108 ꢁC/0.08 kPa; GC tR 23.40 min
(91.5%); 1H NMR (CDCl3, 400 MHz)
d
0.83 (3H, d, J ¼ 6.4 Hz), 0.85
(3H, t, J ¼ 7.6 Hz), 1.05e1.15 (2H, m), 1.21e1.37 (13H, m), 1.25 (3H, t,
J ¼ 7.2 Hz), 1.61 (2H, m), 2.28 (2H, t, J ¼ 7.6 Hz), 4.12 (2H, q,
J ¼ 7.2 Hz); 13C NMR (CDCl3, 100 MHz)
d 11.39, 14.24, 19.20, 24.98,
27.05, 29.14, 29.26, 29.48 (2C), 29.92, 34.38, 34.39, 36.60, 60.12,
173.92; MS (70 eV, EI) m/z 242 (13, Mþ), 213 (17), 199 (26), 157 (40),
143 (11), 115 (10), 101 (66), 97 (16), 89 (14), 88 (100), 83 (18), 73
(14), 70 (17), 69 (15), 57 (16), 55 (17), 43 (13), 41 (12); HRMS calcd
for C15H30O2: 242.2246, found: 242.2239.
Scheme 3. Derivatization of the natural pheromone.
Please cite this article as: Y. Ohkubo et al., Pheromone synthesis. Part 265: Synthesis and stereochemical composition of two pheromonal
compounds of the female Korean apricot wasp, Eurytoma maslovskii, Tetrahedron, https://doi.org/10.1016/j.tet.2020.131410

4
Y. Ohkubo et al. / Tetrahedron xxx (xxxx) xxx
4.1.3. Ethyl 2,10-dimethyldodecanoate (8)
(3H, d, J ¼ 6.4 Hz), 0.85 (3H, t, J ¼ 7.6 Hz), 1.06e1.15 (2H, m),
To
a
solution of LDA, prepared from (i-Pr)2NH (2.42 g,
1.21e1.36 (9H, m), 1.25 (3H, t, J ¼ 7.6 Hz), 1.62 (2H, quint, J ¼ 7.6 Hz),
24.0 mmol) and n-BuLi (1.57 M in hexane; 14.0 mL, 22.0 mmol) in
THF (20.0 mL), a solution of 6 (4.85 g, 20.0 mmol) in THF (10.0 mL)
was added dropwise at ꢀ78 ꢁC. After stirring for 30 min, a solution
of MeI (3.40 g, 24.0 mmol) and HMPA (1.08 g, 6.00 mmol) in THF
(5.0 mL) was added dropwise. After stirring for 1 h, the reaction
mixture was poured into 20% aq. NH4Cl and extracted with hexane.
The organic layer was washed with brine, dried over MgSO4, and
concentrated under reduced pressure. The residue was purified by
silica-gel column chromatography (hexane/EtOAc ¼ 20:1) to give 8
(3.69 g, 72% yield). GC tR 23.67 min (98.2%); 1H NMR (CDCl3,
2.29 (2H, t, J ¼ 7.6 Hz), 4.12 (2H, q, J ¼ 7.6 Hz); 13C NMR (CDCl3,
100 MHz)
d 11.38, 14.25, 19.19, 25.00, 26.89, 29.18, 29.47, 29.60,
34.36, 34.40, 36.53, 60.13, 173.92; MS (70 eV, EI) m/z 187 (11), 186
(15), 169 (20), 151 (16), 139 (11), 129 (29), 95 (25), 83 (11), 71 (54),
70 (100), 69 (13), 57 (18), 55 (21), 43 (31), 41 (15); HRMS calcd for
C13H26O2: 214.1933, found: 214.1934.
4.1.7. Ethyl 2,8-dimethyldecanoate (9)
In the same manner as described for the synthesis of 8, 7 (4.85 g,
20.0 mmol) was converted to 9 (1.00 g, 47% yield). GC tR 19.18 min
(96.3%); 1H NMR (CDCl3, 400 MHz)
d
0.84 (3H, t, J ¼ 6.4 Hz), 0.85
400 MHz)
d
0.84 (3H, d, J ¼ 6.4 Hz), 0.85 (3H, t, J ¼ 7.6 Hz), 1.07e1.15
(2H, m), 1.13 (3H, d, J ¼ 7.2 Hz), 1.23e1.41 (14H, m), 1.25 (3H, t,
(3H, t, J ¼ 7.6 Hz), 1.06e1.15 (2H, m), 1.14 (3H, d, J ¼ 6.8 Hz),
1.23e1.43 (10H, m), 1.25 (3H, t, J ¼ 7.2 Hz), 1.64 (1H, m), 2.41 (1H,
sext, J ¼ 6.8 Hz), 4.13 (2H, q, J ¼ 7.2 Hz); 13C NMR (CDCl3, 100 MHz)
J ¼ 7.2 Hz), 1.66 (1H, m), 2.41 (1H, sext, J ¼ 7.2 Hz), 4.13 (2H, q,
J ¼ 7.2 Hz); 13C NMR (CDCl3, 100 MHz)
d 11.40, 14.27, 17.07, 19.21,
27.06, 27.22, 29.49, 29.53 (2C), 29.92, 33.82, 34.38, 36.61, 39.56,
60.04,176.99; MS (70 eV, EI) m/z 256 (13, Mþ), 213 (10),199 (21),171
(19), 157 (16), 115 (55), 103 (10), 102 (100), 87 (15), 83 (10), 74 (20),
69 (13), 57 (17), 55 (14), 43 (11), 41 (11); HRMS calcd for C16H32O2:
256.2402, found: 256.2397.
d
11.37, 14.25, 17.05, 19.17, 26.91, 27.25, 29.46, 29.85, 33.82, 34.35,
36.52, 39.55, 60.02, 176.94; MS (70 eV, EI) m/z 228 (5, Mþ), 183 (11),
171 (49), 157 (13), 129 (15), 115 (68), 103 (11), 102 (100), 97 (10), 87
(23), 83 (14), 74 (31), 71 (11), 69 (19), 57 (24), 55 (20), 43 (14), 41
(18), 29 (11); HRMS calcd for C14H28O2: 228.2089, found: 228.2108.
4.1.4. 2,10-Dimethyl-1-dodecanol (10)
4.1.8. 2,8-Dimethyl-1-decanol (11)
To an ice-cooled suspension of LiAlH4 (380 mg, 10.0 mmol) in
Et2O (10.0 mL), a solution of 8 (2.56 g, 10.0 mmol) in Et2O (10.0 mL)
was added dropwise at 0 ꢁC. After stirring for 1.5 h, water (0.38 g),
15% aq. NaOH (0.38 g) and water (1.14 g) were added dropwise with
vigorous stirring. After adding MgSO4, the resulting mixture was
filtered and the filtrate was concentrated under reduced pressure.
The residue was purified by silica-gel column chromatography
(hexane/EtOAc ¼ 10:1) to give 10 (2.00 g, 93% yield). GC tR
In the same manner as described for the synthesis of 10, 9
(0.80 g, 3.5 mmol) was converted to 11 (0.62 g, 95% yield). GC tR
17.39 min (99.0%); 1H NMR (CDCl3, 400 MHz)
d 0.84 (3H, d,
J ¼ 6.0 Hz), 0.86 (3H, t, J ¼ 7.6 Hz), 0.92 (3H, t, J ¼ 6.4 Hz), 1.07e1.17
(3H, m), 1.21e1.42 (10H, m), 1.48 (1H, br), 1.61 (1H, m), 3.42 (1H, dd,
J ¼ 10.8, 6.8 Hz), 3.50 (1H, dd, J ¼ 10.8, 6.0 Hz); 13C NMR (CDCl3,
100 MHz)
d 11.37, 16.56, 19.19, 27.01, 27.05, 29.46, 29.47, 30.27,
30.28, 33.15, 34.37, 35.75, 36.59, 68.38; MS (70 eV, EI) m/z 139 (22),
111 (12), 98 (15), 97 (48), 85 (24), 84 (20), 83 (82), 71 (62), 70 (100),
69 (58), 57 (91), 56 (37), 55 (54), 43 (40), 41 (32), 29 (11); HRMS
calcd for C12H26O: 186.1984, found: 186.1977.
22.12 min (98.9%); 1H NMR (CDCl3, 400 MHz)
d 0.84 (3H, d,
J ¼ 6.4 Hz), 0.85 (3H, t, J ¼ 7.6 Hz), 0.92 (3H, d, J ¼ 6.8 Hz), 1.06e1.16
(3H, m), 1.21e1.42 (15H, m), 1.60 (1H, m), 3.42 (1H, dd, J ¼ 10.4,
6.4 Hz), 3.51 (1H, dd, J ¼ 10.4, 6.0 Hz); 13C NMR (CDCl3, 100 MHz)
d
11.40, 16.58, 19.21, 26.98, 27.09, 29.49, 29.68, 29.95, 30.00, 33.15,
4.1.9. 2,8-Dimethyldecyl propanoate (2)
34.39, 35.77, 36.63, 68.44; MS (70 eV, EI) m/z 167 (14), 125 (22), 111
(54), 98 (13), 97 (69), 85 (37), 84 (20), 83 (62), 82 (13), 71 (77), 70
(100), 69 (70), 57 (88), 56 (39), 55 (52), 43 (39), 41 (31), 29 (10);
HRMS calcd for C14H30O: 214.2297, found: 214.2280.
In the same manner as described for the synthesis of 1, 11
(250 mg, 1.34 mmol) was converted to 2 (0.31 g, 95% yield). GC tR
22.17 min (98.8%); 1H NMR (CDCl3, 400 MHz)
d 0.84 (3H, d,
J ¼ 6.4 Hz), 0.86 (3H, t, J ¼ 7.6 Hz), 0.92 (3H, d, J ¼ 6.8 Hz), 1.07e1.14
(3H, m), 1.15 (3H, t, J ¼ 7.6 Hz), 1.21e1.38 (10H, m), 1.77 (1H, m), 2.33
(2H, q, J ¼ 7.6 Hz), 3.86 (1H, dd, J ¼ 10.8, 6.8 Hz), 3.95 (1H, dd,
4.1.5. 2,10-Dimethyldodecyl propanoate (1)
To an ice-cooled solution of 10 (643 mg, 3.00 mmol) and pyri-
dine (475 mg, 6.00 mmol) in CH2Cl2 (30.0 mL), propanoyl chloride
(416 mg, 4.50 mmol) was added. After stirring for 1 h, the reaction
mixture was poured into 5% aq. NaHCO3 and extracted with hexane.
The organic layer was washed with brine, dried over MgSO4, and
concentrated under reduced pressure. The residue was purified by
silica-gel column chromatography (hexane/EtOAc ¼ 20:1) and
Kugelrohr distillation to give ( )-1 (775 mg, 96% yield). GC tR
J ¼ 10.8, 6.0 Hz); 13C NMR (CDCl3, 100 MHz)
d 9.18, 11.38, 16.86,
19.19, 26.83, 27.00, 27.63, 29.46, 30.15, 30.16, 32.54, 33.36, 34.37,
36.56, 69.28, 174.61; MS (70 eV, EI) m/z 140 (11), 139 (36), 111 (13),
98 (11), 97 (33), 85 (10), 84 (15), 83 (56), 75 (27), 71 (30), 70 (64), 69
(32), 57 (100), 56 (31), 55 (25), 43 (14), 41 (14), 29 (12); HRMS calcd
for C15H30O2: 242.2246, found: 242.2231.
4.1.10. Ethyl (S)-10-methyldodecanoate [(S)-6]
26.52 min (99.0%); 1H NMR (CDCl3, 400 MHz)
d 0.84 (3H, d,
In the same manner as described for the synthesis of 6, (S)-3
(18.0 g, 119 mmol) was converted to (S)-6 (25.4 g). GC tR 23.30 min
J ¼ 6.4 Hz), 0.85 (3H, t, J ¼ 7.2 Hz), 0.92 (3H, d, J ¼ 6.8 Hz), 1.06e1.18
(3H, m), 1.15 (3H, t, J ¼ 7.6 Hz), 1.21e1.40 (14H, m), 1.77 (1H, m), 2.33
(2H, q, J ¼ 7.6 Hz), 3.86 (1H, dd, J ¼ 10.8, 6.8 Hz), 3.95 (1H, dd,
(96.8%); ½a 2D0
þ5.65 (c ¼ 1.75 in CHCl3); HRMS calcd for C15H30O2:
ꢂ
J ¼ 10.8, 6.0 Hz); 13C NMR (CDCl3, 100 MHz)
d 9.20, 11.39, 16.87,
242.2246, found: 242.2254.
19.21, 26.81, 27.08, 27.65, 29.49, 29.63, 29.83, 29.97, 32.55, 33.36,
34.39, 36.62, 69.30, 174.63; MS (70 eV, EI) m/z 167 (22), 125 (15), 111
(45), 97 (50), 86 (10), 85 (18), 84 (14), 83 (41), 75 (33), 71 (38), 70
(66), 69 (39), 57 (100), 56 (34), 55 (27), 43 (16), 41 (15), 29 (11);
HRMS calcd for C17H34O2: 270.2559, found: 270.2539.
4.1.11. (S)-10-Methyldodecanoic acid [(S)-12]
To a solution of (S)-6 (25.2 g) in THF (120 mL) was added 20% aq.
NaOH (120 g, 0.60 mol). The mixture was heated under reflux for
5 h. After the reaction mixture was cooled to room temperature, the
aqueous layer was separated and washed with Et2O. The aqueous
layer was acidified with 1 M aq. HCl and extracted with Et2O. The
extract was washed with water and brine, dried over MgSO4, and
concentrated under reduced pressure to give (S)-12 (20.8 g). GC tR
4.1.6. Ethyl 8-methyldecanoate (7)
In the same manner as described for the synthesis of 6, 3 (14.5 g,
96.0 mmol) was converted to 7 (16.7 g, 97% yield). bp 62e71 ꢁC/
0.1 kPa; GC tR 18.46 min (98.0%); 1H NMR (CDCl3, 400 MHz)
d
0.84
23.48 min (99.2%); ½a D20
ꢂ
þ6.13 (c ¼ 1.86 in CHCl3); 1H NMR (CDCl3,
Please cite this article as: Y. Ohkubo et al., Pheromone synthesis. Part 265: Synthesis and stereochemical composition of two pheromonal
compounds of the female Korean apricot wasp, Eurytoma maslovskii, Tetrahedron, https://doi.org/10.1016/j.tet.2020.131410

Y. Ohkubo et al. / Tetrahedron xxx (xxxx) xxx
5
400 MHz)
d
0.84 (3H, d, J ¼ 6.4 Hz), 0.85 (3H, t, J ¼ 7.6 Hz), 1.05e1.15
(23), 57 (24); HRMS calcd for
387.2781.
C
24H37NO3: 387.2773, found:
(2H, m), 1.20e1.38 (13H, m), 1.63 (2H, quint, J ¼ 7.6 Hz), 2.35 (2H, t,
J ¼ 7.6 Hz), 10.67 (1H, br); 13C NMR (CDCl3, 100 MHz)
d 11.40, 19.21,
24.67, 27.05, 29.05, 29.24, 29.46, 29.49, 29.92, 33.97, 34.38, 36.60,
179.70; MS (70 eV, EI) m/z 214 (20, Mþ), 185 (63), 171 (39), 167 (59),
159 (13), 158 (13), 157 (22), 149 (73), 140 (24), 129 (98), 125 (37), 116
(26), 115 (44), 111 (31), 109 (12), 107 (11), 101 (32), 99 (21), 98 (23),
97 (66), 96 (57), 95 (14), 93 (10), 87 (25), 85 (37), 84 (17), 83 (82), 81
(16), 73 (81), 71 (47), 70 (24), 69 (71), 67 (11), 60 (52), 57 (100), 56
(34), 55 (71), 43 (57), 42 (10), 41 (56), 29 (20); HRMS calcd for
4.1.14. (2S,10S)-2,10-Dimethyl-1-dodecanol [(2S,10S)-10]
To an ice-cooled suspension of LiAlH4 (490 mg, 12.9 mmol) in
THF (25.0 mL), a solution of (4S,20S,100S)-17 (2.00 g, 5.16 mmol) in
THF (10.0 mL) was added dropwise. After stirring for 16 h, the re-
action mixture was quenched by addition of water (0.49 g) and then
dissolved by addition of 2 M aq. HCl. The resulting mixture was
extracted with Et2O. The organic layer was washed with 5% aq.
NaHCO3 and brine, dried over MgSO4, and concentrated under
reduced pressure. The residue was purified by silica-gel column
chromatography (hexane/EtOAc ¼ 10:1) to give (2S,10S)-10 (1.00 g,
C
13H26O2: 214.1933, found: 214.1938.
4.1.12. (4S,100S)eN-[100-Methyldodecanoyl]-4-benzyl-2-
oxazolidinone [(4S,100S)-15]
91% yield). GC tR 21.99 min (99.4%); ½a D20
ꢀ1.76 (c ¼ 1.81 in CHCl3);
ꢂ
1H NMR (CDCl3, 400 MHz)
d
0.84 (3H, d, J ¼ 6.4 Hz), 0.85 (3H, t,
A solution of (S)-12 (6.90 g) in (COCl)2 (4.08 g, 32.2 mmol) was
stirred for 16 h at room temperature. The reaction mixture was
concentrated under reduced pressure to give the corresponding
acyl chloride (7.68 g). To a cooled solution of (S)-14 (6.28 g,
35.4 mmol) in THF (100 mL), n-BuLi (1.57 M in hexane; 23.6 mL,
37.2 mmol) was added dropwise at ꢀ78 ꢁC. After stirring for 30 min,
a solution of the above-prepared acyl chloride in THF (20.0 mL) was
added dropwise. After removal of cooling-bath, the stirring was
continued for 16 h. The reaction mixture was then poured into 20%
aq. NH4Cl and extracted with Et2O. The organic layer was washed
with 5% aq. NaHCO3 and brine, dried over MgSO4, and concentrated
under reduced pressure. The residue was purified by silica-gel
column chromatography (hexane/EtOAc ¼ 5:1) to give (4S,100S)-
15 (7.80 g, 63% yield in 4 steps from (S)-3). GC tR 27.20 min (95.8%);
J ¼ 7.2 Hz), 0.92 (3H, d, J ¼ 6.8 Hz), 1.06e1.16 (3H, m), 1.21e1.43
(15H, m), 1.60 (1H, m), 3.41 (1H, dd, J ¼ 10.4, 6.4 Hz), 3.51 (1H, dd,
J ¼ 10.4, 5.6 Hz); 13C NMR (CDCl3, 100 MHz)
d 11.39, 16.57, 19.20,
26.98, 27.09, 29.48, 29.68, 29.95, 30.00, 33.14, 34.38, 35.75, 36.62,
68.41; HRMS calcd for C14H30O: 214.2297, found: 214.2282.
4.1.15. (2S,10S)-2,10-Dimethyldodecyl propanoate [(2S,10S)-1]
In the same manner as described for the synthesis of 1, (2S,10S)-
10 (800 mg, 3.73 mmol) was converted to (2S,10S)-1 (841 mg, 83%
yield). GC tR 26.52 min (99.3%); ½a D20
ꢂ
þ5.23 (c ¼ 1.73 in CHCl3); 1H
NMR (CDCl3, 400 MHz)
d
0.84 (3H, d, J ¼ 6.4 Hz), 0.85 (3H, t,
J ¼ 7.6 Hz), 0.92 (3H, d, J ¼ 6.8 Hz), 1.06e1.18 (3H, m), 1.15 (3H, t,
J ¼ 7.6 Hz), 1.21e1.39 (14H, m), 1.77 (1H, m), 2.33 (2H, q, J ¼ 7.6 Hz),
3.85 (1H, dd, J ¼ 10.8, 7.2 Hz), 3.96 (1H, dd, J ¼ 10.8, 6.0 Hz); 13C
m.p. 44 ꢁC; ½a 2D0
ꢂ
þ41.0 (c ¼ 3.12 in CHCl3); 1H NMR (CDCl3,
400 MHz)
d
0.84 (3H, d, J ¼ 6.4 Hz), 0.85 (3H, t, J ¼ 7.2 Hz), 1.05e1.17
NMR (CDCl3, 100 MHz) d 9.19, 11.38, 16.86, 19.20, 26.81, 27.08, 27.64,
(2H, m), 1.21e1.41 (13H, m), 1.60e1.73 (2H, m), 2.76 (1H, dd,
J ¼ 13.2, 9.6 Hz), 2.85e3.01 (2H, m), 3.30 (1H, dd, J ¼ 13.2, 3.2 Hz),
29.48, 29.62, 29.83, 29.97, 32.54, 33.36, 34.38, 36.61, 69.29, 174.62.
HRMS calcd for C17H34O2: 270.2559, found: 270.2547.
Subsequently, in the same manner, (2R,10S)-, (2S,10R)-, and
(2R,10R)-1 were synthesized. (See SI).
4.15e4.22 (2H, m), 4.67 (1H, m), 7.21 (2H, m), 7.25e7.36 (3H, m); 13
C
NMR (CDCl3, 100 MHz)
d 11.40, 19.21, 24.27, 27.07, 29.13, 29.40,
29.48, 29.52, 29.95, 34.38, 35.53, 36.61, 37.93, 55.15, 66.13, 127.32,
128.94 (2C), 129.41 (2C), 135.33, 153.45, 173.46; MS (70 eV, EI) m/z
373 (8, Mþ), 282 (19), 219 (23),198 (15),197 (100),179 (13),178 (24),
134 (12),123 (18),117 (18),109 (19), 97 (22), 95 (12), 91 (11), 83 (15),
71 (11), 57 (18), 55 (10); HRMS calcd for C23H35NO3: 373.2617,
found: 373.2626.
4.1.16. Ethyl (S)-8-methyldecanoate [(S)-7]
In the same manner as described for the synthesis of 6, (S)-3
(15.0 g, 99.0 mmol) was converted to (S)-7 (21.8 g). GC tR 18.72 min
(96.0%); [
214.1933, found: 214.1949.
a
]20D þ6.82 (c ¼ 1.81 in CHCl3); HRMS calcd for C13H26O2:
4.1.13. (4S,20S,100S)eN-[(20,100-Dimethyldodecanoyl]-4-benzyl-2-
oxazolidinone [(4S,20S,100S)-17]
4.1.17. (S)-8-Methyldecanoic acid [(S)-13]
In the same manner as described for the synthesis of (S)-12, (S)-
7 (21.8 g) was converted to (S)-13 (14.2 g). GC tR 19.21 min (99.4%);
To a cooled solution of (4S,100S)-15 (4.32 g, 11.6 mmol) in THF
(120 mL), NaHMDS (1.0 M in THF; 12.8 mL, 12.8 mmol) was added
dropwise at ꢀ78 ꢁC. Subsequently, MeI (8.20 g, 57.8 mmol) was
added to the mixture. After removal of cooling-bath, the reaction
mixture was stirred for 16 h, poured into 20% aq. NH4Cl, and
extracted with Et2O. The organic layer was washed with brine,
dried over MgSO4, and concentrated under reduced pressure. The
Rf values of the major (20S)- and minor (20R)-isomers were 0.38 and
0.27 (eluent: n-hexane/AcOEt ¼ 5:1), respectively. The residue was
purified by silica-gel column chromatography (hexane/
EtOAc ¼ 10:1) to give (4S,20S,100S)-17 (3.11 g, 69% yield). GC tR
½
a 2D0
ꢂ
þ7.44 (c ¼ 1.78 in CHCl3); 1H NMR (CDCl3, 400 MHz)
d 0.84
(3H, d, J ¼ 6.4 Hz), 0.85 (3H, t, J ¼ 7.2 Hz), 1.08e1.18 (2H, m),
1.21e1.38 (9H, m), 1.64 (2H, quint, J ¼ 7.6 Hz), 2.35 (2H, t, J ¼ 7.6 Hz),
10.69 (1H, br); 13C NMR (CDCl3, 100 MHz)
d 11.39, 19.19, 24.68,
26.86, 29.09, 29.47, 29.57, 33.92, 34.36, 36.52, 179.39; MS (70 eV, EI)
m/z 186 (4, Mþ), 157 (10), 139 (47), 130 (15), 129 (100), 121 (22), 111
(12), 101 (21), 98 (14), 97 (43), 95 (10), 87 (31), 85 (17), 83 (19), 81
(11), 73 (57), 71 (27), 69 (42), 60 (25), 57 (39), 56 (15), 55 (38), 43
(25), 41 (28), 29 (11); HRMS calcd for C11H22O2: 186.1620, found:
186.1630.
27.09 min (99.2%); ½a D20
ꢂ
þ63.3 (c ¼ 1.65 in CHCl3); 1H NMR (CDCl3,
4.1.18. (4S,80S)eN-[(80-Methyldecanoyl]-4-benzyl-2-oxazolidinone
[(4S,80S)-16]
400 MHz)
d
0.83 (3H, d, J ¼ 6.4 Hz), 0.85 (3H, t, J ¼ 7.6 Hz), 1.05e1.15
(2H, m), 1.21e1.45 (14H, m), 1.22 (3H, d, J ¼ 6.8 Hz), 1.73 (1H, m),
2.77 (1H, dd, J ¼ 13.2, 9.6 Hz), 3.27 (1H, dd, J ¼ 13.2, 3.2 Hz), 3.70
(1H, sext, J ¼ 6.8 Hz), 4.15e4.22 (2H, m), 4.68 (1H, m), 7.22 (2H, m),
In the same manner as described for the synthesis of (4S,100S)-
15, (S)-13 (6.00 g) was converted to (4S,80S)-16 (8.00 g, 67% yield in
4 steps from (S)-3). GC tR 24.17 min (94.4%); m.p. 56 ꢁC; ½a D20
þ45.2
ꢂ
7.25e7.36 (3H, m); 13C NMR (CDCl3, 100 MHz)
d 11.40, 17.36, 19.21,
27.07, 27.27, 29.48, 29.55, 29.67, 29.93, 33.44, 34.38, 36.60, 37.71,
37.91, 55.36, 65.99, 127.32, 128.92 (2C), 129.44 (2C), 135.35, 153.06,
177.37; MS (70 eV, EI) m/z 387 (6, Mþ), 296 (10), 233 (32), 212 (16),
211 (100), 183 (22), 178 (27), 117 (13), 113 (12), 99 (13), 85 (20), 71
(c ¼ 1.63 in CHCl3); 1H NMR (CDCl3, 400 MHz)
d 0.84 (3H, d,
J ¼ 6.0 Hz), 0.86 (3H, t, J ¼ 7.2 Hz), 1.06e1.17 (2H, m), 1.22e1.43 (9H,
m), 1.60e1.74 (2H, m), 2.77 (1H, dd, J ¼ 13.2, 9.6 Hz), 2.85e3.01 (2H,
m), 3.30 (1H, dd, J ¼ 13.2, 3.2 Hz), 4.14e4.22 (2H, m), 4.68 (1H, m),
Please cite this article as: Y. Ohkubo et al., Pheromone synthesis. Part 265: Synthesis and stereochemical composition of two pheromonal
compounds of the female Korean apricot wasp, Eurytoma maslovskii, Tetrahedron, https://doi.org/10.1016/j.tet.2020.131410

6
Y. Ohkubo et al. / Tetrahedron xxx (xxxx) xxx
7.21 (2H, m), 7.25e7.36 (3H, m); 13C NMR (CDCl3, 100 MHz)
d
11.39,
NaHCO3 solution (3.0 mL). The desired alcohols were extracted
from the aqueous layer twice with hexane/IPE (3:1; 2.0 mL). The
combined organic layer was washed with sat. NaHCO3 solution
(2.0 mL), and the separated aqueous layer was extracted with
hexane/IPE (3:1; 2.0 mL). The combined organic layer was washed
with brine (2.0 mL), and the separated aqueous layer was extracted
with hexane/IPE (3:1; 2.0 mL). Finally, the combined organic layer
was concentrated under reduced pressure. The resultant residue
(containing nat-10/11) was dissolved in toluene/CH3CN (1:1;
1.0 mL), and a 0.5 mL aliquot was esterified by treatment with
(1R,2R)-19 (large excess amount), in the presence of EDC (large
excess amount) and DMAP (cat. amount) at 35 ꢁC for more than 6 h.
After completion of reaction, the reaction mixture was loaded onto
a silica gel TLC plate (0.2 mm, 10 ꢃ 20 cm, Merck art 5554) and
developed with hexane/EtOAc (5:1, v/v). The desired fraction was
collected, packed into the short column, and eluted with EtOH/
EtOAc (1:1, v/v). The eluate was concentrated to ca. 0.1 mL under Ar
stream, and diluted with MeOH (0.05 mL) to furnish the sample
solution of nat-(1R,2R)-21/22. In the same manner, the solution of
nat-(1S,2S)-21/22 was prepared by using (1S,2S)-19. The solutions
of nat-(1R,2R)-23/24 and nat-(1S,2S)-23/24 were also prepared by
condensation with 20 instead of 19.
19.20, 24.28, 26.92, 29.17, 29.47, 29.73, 34.37, 35.54, 36.54, 37.94,
55.15, 66.13, 127.33, 128.94 (2C), 129.41 (2C), 135.33, 153.45, 173.45;
MS (70 eV, EI) m/z 345 (9, Mþ), 254 (29), 219 (26), 178 (23), 170 (13),
169 (100), 151 (44), 134 (15), 117 (22), 116 (11), 109 (14), 95 (52), 91
(15), 83 (14), 81 (17), 69 (12), 57 (17), 55 (13), 43 (12); HRMS calcd
for C21H31NO3: 345.2304, found: 345.2297.
4.1.19. (4S,20S,80S)eN-[(20,80-Dimethyldecanoyl]-4-benzyl-2-
oxazolidinone [(4S,20S,80S)-18]
In the same manner as described for the synthesis of
(4S,20S,100S)-17, (4S,80S)-16 (4.00 g, 11.6 mmol) was converted to
(4S,20S,80S)-18 (3.14 g, 78% yield). The ratio of (20S)- and (20R)-iso-
mers in crude 18 was 96:4. The Rf values of each isomers were 0.47
and 0.33 (eluent: hexane/EtOAc
¼
5:1), respectively. GC tR
24.04 min (99.5%); ½a D20
ꢂ
þ65.3 (c ¼ 1.84 in CHCl3); 1H NMR (CDCl3,
400 MHz)
d
0.83 (3H, d, J ¼ 6.4 Hz), 0.85 (3H, t, J ¼ 7.2 Hz), 1.04e1.15
(2H, m), 1.22e1.44 (10H, m), 1.22 (3H, d, J ¼ 6.8 Hz), 1.73 (1H, m),
2.77 (1H, dd, J ¼ 13.2, 9.6 Hz), 3.27 (1H, dd, J ¼ 13.2, 3.2 Hz), 3.71
(1H, sext, J ¼ 6.8 Hz), 4.14e4.22 (2H, m), 4.68 (1H, m), 7.21 (2H, m),
7.25e7.36 (3H, m); 13C NMR (CDCl3, 100 MHz)
d 11.39, 17.35, 19.19,
26.94, 27.31, 29.46, 30.00, 33.45, 34.36, 36.53, 37.71, 37.92, 55.36,
65.99, 127.32, 128.92 (2C), 129.44 (2C), 135.35, 153.06, 177.37; MS
(70 eV, EI) m/z 359 (7, Mþ), 268 (17), 233 (34), 184 (14), 183 (100),
178 (26), 155 (20), 117 (15), 99 (16), 91 (11), 85 (26), 71 (23), 57 (27),
55 (10); HRMS calcd for C22H33NO3: 359.2460, found: 359.2466.
4.2.2. Stereoisomer separations by 2D-HPLC system
Fig. SI-1 shows the 2D-HPLC system employed for these ana-
lyses. By using this system, stereoisomer separations of the above-
prepared derivatives (21e24) were performed under low column
temperature conditions. Based on our preliminary investigations
on stereoisomer separation employing synth-21e24, 21 and 24
were suitable for determination of their stereochemical composi-
tions of 10 and 11, respectively. (Fig. SI-2).
4.1.20. (2S,8S)-2,8-Dimethyl-1-decanol [(2S,8S)-11]
In the same manner as described for the synthesis of (2S,10S)-10,
(4S,20S,80S)-18 (800 mg, 2.23 mmol) was converted to (2S,8S)-11
(410 mg, 99% yield). GC tR 17.26 min (98.8%); ½a D20
ꢀ2.16 (c ¼ 1.71 in
ꢂ
The derivatives 21 were used to determine the stereochemical
composition of nat-10. A solution of nat-21/22 (10 mL) was sepa-
CHCl3); 1H NMR (CDCl3, 400 MHz)
d
0.84 (3H, d, J ¼ 6.4 Hz), 0.85
(3H, t, J ¼ 7.2 Hz), 0.92 (3H, d, J ¼ 6.8 Hz), 1.05e1.16 (3H, m),
rated on a Develosil ODS-HG-3 column (Nomura chemicals, 4.6 mm
i.d. x 150 mm) eluted with MeOH/CH3CN (3:7, v/v) at 0.12 mL minꢀ1
and 0 ꢁC (in an ice bath). The desired fractions between 63.0 and
68.0 min, and between 100.0 and 110.0 min were loaded onto the
second columns via a column switching device (PT-8000, Tosoh),
and then separated on the Develosil ODS-HG-3 columns (3.0 mm
i.d. x 250 mm and 3.0 mm i.d. x 150 mm in series) eluted with
MeOH/CH3CN/THF (48:28:24, v/v/v) at 0.12 mL minꢀ1 and ꢀ45 ꢁC
(cooled by Cryocool CC-100 equipped with Cryotrol). Detection was
performed by a fluorescence detector FP-4025 (JASCO, excitation at
262 nm and emission at 380 nm). Pumps used were PU-920
(JASCO) and L2130 (Hitachi), and the autosampler was L-2200
(Hitachi).
1.21e1.42 (10H, m), 1.57 (1H, s), 1.60 (1H, m), 3.42 (1H, m), 3.51 (1H,
m); 13C NMR (CDCl3, 100 MHz)
d
11.40, 16.59, 19.22, 27.02, 27.07,
29.48, 30.29, 33.16, 34.39, 35.78, 36.61, 68.44; HRMS calcd for
12H26O: 186.1984, found: 186.1969.
C
4.1.21. (2S,8S)-2,8-Dimethyldecyl propanoate [(2S,8S)-2]
In the same manner as described for the synthesis of 1, (2S,8S)-
11 (300 mg, 1.61 mmol) was converted to (2S,8S)-2 (368 mg, 94%
yield). GC tR 22.25 min (98.9%); ½a D20
ꢂ
þ6.06 (c ¼ 1.47 in CHCl3); 1H
NMR (CDCl3, 400 MHz)
d
0.84 (3H, d, J ¼ 6.4 Hz), 0.86 (3H, t,
J ¼ 7.6 Hz), 0.92 (3H, d, J ¼ 6.4 Hz), 1.06e1.18 (3H, m), 1.15 (3H, t,
J ¼ 7.6 Hz), 1.21e1.39 (10H, m), 1.77 (1H, m), 2.33 (2H, q, J ¼ 7.6 Hz),
3.85 (1H, dd, J ¼ 10.4, 6.8 Hz), 3.96 (1H, dd, J ¼ 10.4, 6.0 Hz); 13C
The derivatives 24 were used to determine the stereochemical
composition of nat-11. A solution of nat-23/24 (10 mL) was sepa-
NMR (CDCl3, 100 MHz) d 9.20, 11.39, 16.88, 19.21, 26.84, 27.01, 27.65,
29.47, 30.17, 32.55, 33.37, 34.38, 36.57, 69.30,174.64; HRMS calcd for
rated on a Develosil ODS-HG-3 column (4.6 mm i.d. x 150 mm)
eluted with MeOH/CH3CN (3:7, v/v) at 0.12 mL minꢀ1 and 0 ꢁC. The
desired fraction between 104.5 min and 115.0 min was loaded onto
the second columns via a column switching device, and then
separated on the Develosil ODS-HG-3 columns (3.0 mm i.d. x
250 mm and 3.0 mm i.d. x 150 mm in series) eluted with MeOH/
THF (73:27, v/v) at 0.10 mL minꢀ1 and ꢀ40 ꢁC. Detection was per-
formed by fluorescence detector (excitation at 298 nm and emis-
sion at 460 nm).
C
15H30O2: 242.2246, found 242.2254.
Subsequently, in the same manner, (2R,8S)-, (2S,8R)-, and
(2R,8R)-2 were also synthesized. (See SI).
4.2. Composition of the natural pheromone of E. maslovskii
4.2.1. Saponification and derivatization of the naturally occurring
pheromone
The natural pheromone sample collected from 2500 females
(probably containing 10e15 ng of nat-1/2; see Ref. [4]) was dis-
solved in isooctane/2-propanol (1:1; 0.8 mL). A 0.2 mL aliquot was
added to the test tube, followed by 0.1 M KOH (in EtOH; 2.0 mL) and
distilled water (0.2 mL). The test tube was stood at 90 ꢁC for 40 min
without capping. After saponification, the residual solvent was
removed under CO2 gas stream. The residue was dissolved in
hexane/diisopropyl ether (IPE) (3:1; 2.0 mL) and washed with sat.
Although synth-22 gave a single peak at 167 min, synth-21 were
separated into four peaks (Fig. SI-3).
The ratio of nat-10:nat-11 was estimated to be 70.5:29.5, which
was average of data (n ¼ 4) obtained by using nat-(1R,2R)- 21/22
and nat-(1S,2S)-21/22 (Fig. SI-4).
In the separation of nat-(1R,2R)-21, 2nd peak overlapped 3rd
peak because 2nd peak was much larger than 3rd peak, resulting a
single peak. Therefore, the peak area of 2nd peak was the sum of
Please cite this article as: Y. Ohkubo et al., Pheromone synthesis. Part 265: Synthesis and stereochemical composition of two pheromonal
compounds of the female Korean apricot wasp, Eurytoma maslovskii, Tetrahedron, https://doi.org/10.1016/j.tet.2020.131410

Y. Ohkubo et al. / Tetrahedron xxx (xxxx) xxx
7
that of (2S,10R)- and (2R,10R)-21. On the other hand, nat-(1S,2S)-21
gave four peaks and separated into each stereoisomer. Thus, the
stereochemical composition of nat-10 could be determined as
(2S,10R):(2R,10R):(2R,10S):(2S,10S) ¼ 91.4:6.2:1.6:0.7 (Fig. SI-5).
Synth-24 could be separated into three peaks instead of four
(Fig. SI-6). However, it was possible to determine the ratio of four
stereoisomers from the results obtained with both nat-(1R,2R)-24
and nat-(1S,2S)-24. (Fig. SI-7) The stereochemical composition of
nat-11 was (2S,8S):(2R,8R):(2R,8S):(2S,8R) ¼ 69.9:17.3:11.8:1.0.
The complete composition of the pheromone of E. maslovskii
was summarized in Table in Fig. SI-8.
for this work. This work was financially supported in part by JSPS
KAKENHI Grant Number 16K07721.
Appendix A. Supplementary data
Supplementary data to this article can be found online at
https://doi.org/10.1016/j.tet.2020.131410.
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Declaration of competing interest
The authors declare that they have no known competing
financial interests or personal relationships that could have
appeared to influence the work reported in this paper.
Acknowledgments
We would like to dedicate this paper to Mrs. Keiko Mori with our
whole heart. We thank T. Hasegawa Co., Ltd. for generous support
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Please cite this article as: Y. Ohkubo et al., Pheromone synthesis. Part 265: Synthesis and stereochemical composition of two pheromonal
compounds of the female Korean apricot wasp, Eurytoma maslovskii, Tetrahedron, https://doi.org/10.1016/j.tet.2020.131410